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Photoperiod and temperature effects on the growth and development of rice (Oryza sativa L.) Azmi, Abdul Razzaque 1969

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PHOTOPERIOD AND TEMPERATURE EFFECTS ON THE GROWTH AND DEVELOPMENT OF RICE (ORYZA SATIVA L.) by ABDUL RAZZAQUE AZMI Sc. ( H o n s ) , U n i v e r s i t y o f Dacca, P a k i s t a n , 1954 M . S c , U n i v e r s i t y o f Dacca, P a k i s t a n , 1955 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n t h e Department o f P l a n t S c i e n c e We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA June 1969 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the r e q u i r e m e n t s f o r an advanced degree -at the U n i v e r s i t y o f B r i t i s h Columbia, I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and Study. I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada i i i Supervisor: Professor Douglas P. Ormrod ABSTRACT The objective of t h i s study was to determine how the r i c e plant responds to combinations of temperature and photoperiod. Both temperature and photoperiod are import-ant f o r normal completion of the l i f e c ycle, but there has been l i t t l e study of t h e i r combined e f f e c t s i n r i c e . Controlled temperature and photoperiod experiments were conducted i n growth cabinets using 4 temperatures; 35/18, 35/26.5, 35/35 and 40.5/18°C day/night. There were 4 photoperiods of 8, 10, 12 and 14 hours. Light was provided by cool white fluorescent tubes. The day temp-erature periods corresponded to the photoperiods. Four v a r i e t i e s were selected: Kangni-27 and Dokribasmati from Dokri, Pakistan; Caloro from C a l i f o r n i a , U.S.A.; and Bluebonnet-50 from Texas, U.S.A. Growth c h a r a c t e r i s t i c s , net photosynthesis rates, and flowering were measured and chlorophyll a and b, carotenoid, carbohydrate and ash concentrations were determined. The e f f e c t of photoperiod on flowering was most pronounced at 35/26.5. The delays i n flowering at 14 hours f o r t h i s temperature were 30, 30, 21 and 63 days i n Kangni, Caloro, Dokri and Bluebonnet compared to the optimum, photoperiod which varied among v a r i e t i e s . The delays observed at 35/18 were 23, 14, 6 and 2 days. i v A t 35/26.5 a l l v a r i e t i e s showed a s i g n i f i c a n t p h o t o p e r i o d i c e f f e c t on f l o w e r i n g , but a t 35/18, D o k r i and Bluebonnet d i d not show a s i g n i f i c a n t p h o t o p e r i o d i c e f f e c t . 35/35 was most u n s a t i s f a c t o r y f o r f l o w e r i n g . A s i m i l a r but l e s s s e r i o u s e f f e c t was found a t 40.5/18. F i n a l d r y m a t t e r p r o d u c t i o n was h i g h a t 35/35 and 40.5/18; an i n c r e a s e o f 3 t o 8 g per pot was noted a t t h e s e t e m p e r a t u r e s compared w i t h 35/26.5 and 35/18. There was an i n c r e a s e o f about 5 g p e r pot a t m a t u r i t y f o r each i n c r e a s e o f 2 hours i n p h o t o p e r i o d . P a n i c l e c h a r a c t e r i s t i c s were g e n e r a l l y u n a f f e c t e d by t e m p e r a t u r e , but t h e r e were some p h o t o p e r i o d e f f e c t s . A t t h e 12-hour p h o t o p e r i o d p a n i c l e s o f a l l v a r i e t i e s were 2 t o 4 cm l o n g e r t h a n a t o t h e r p h o t o p e r i o d s and a t 10-and 12-hour p h o t o p e r i o d s t h e r e were 10 t o 32 more s p i k e l e t s p e r p a n i c l e t h a n a t 8 and 14 h o u r s . S t e r i l i t y was v e r y h i g h a t 35/35 (95%) and 40.5/18 ( 6 9 % ) . Average s t e r i l i t y a t 35/18 and 35/26.5 was about 36%. There was 8 t o 24% l e s s s t e r i l i t y a t 10- and 12-hour p h o t o p e r i o d compared w i t h 8 o r 14 h o u r s . H u n d r e d - g r a i n w e i g h t was u n a f f e c t e d by p h o t o p e r i o d o r t e m p e r a t u r e . H i g h numbers o f t i l l e r s were c o n s i s t e n t l y o b s e r v e d a t 40.5/18 and 35/18 and low numbers a t 35/35. The d i f f e r e n c e s v a r i e d w i t h t h e stage o f growth. P l a n t s a t 14-hour p h o t o p e r i o d had c o n s i s t e n t l y more t i l l e r s t h a n V t h o s e a t o t h e r p h o t o p e r i o d s . Kangni and D o k r i had h i g h e r numbers o f t i l l e r s t h a n C a l o r o and Bluebonnet. L e a f development was f a s t e s t a t 40.5/18 and t h e 12-hour p h o t o p e r i o d . T h i s was e s p e c i a l l y so a t 6 and 8 weeks. Kangni and D o k r i had f a s t e r development t h a n C a l o r o and Bluebonnet. P l a n t h e i g h t was 2 t o 5 cm g r e a t e r a t 2 weeks a t 35/26.5 and 35/35 but a t 4, 6 and 8 weeks, p l a n t h e i g h t was g r e a t e r a t 35/18. The s h o r t e s t p l a n t s were obser v e d a t 40.5/18. The r a t e o f net p h o t o s y n t h e s i s on a l e a f b l a d e w e i g h t b a s i s was h i g h e s t a t 2 weeks i n a l l v a r i e t i e s a t a l l p h o t o p e r i o d s and t e m p e r a t u r e s . The r a t e g e n e r a l l y d e c l i n e d w i t h t h e a g i n g o f p l a n t s . The g r e a t e s t d e c l i n e a t 8 weeks, compared t o 2 weeks, was 71% i n D o k r i and l e a s t was 65% i n Bluebonnet. E x c e p t a t 2 weeks, t h e h i g h e s t r a t e o f p h o t o s y n t h e s i s was a t 40.5/18 but a t 6 and 8 weeks t h e r e were a l s o h i g h r a t e s a t 35/35. The r a t e was c o n s i s t e n t l y h i g h e r i n p l a n t s growing i n the 8-hour p h o t o p e r i o d . The r a t e was h i g h e r i n t h e 8-hour p h o t o p e r i o d compared t o t h e 14-hour by 28 and 25% a t 6 and 8 weeks r e s p e c t i v e l y . Both C a l o r o and Bluebonnet had h i g h e r n e t p h o t o s y n t h e t i c r a t e s t h a n Kangni and D o k r i . I n a l l v a r i e t i e s c h l o r o p h y l l and c a r o t e n o i d c o n t e n t d e c l i n e d w i t h age. Both c h l o r o p h y l l and c a r o t e n o i d were h i g h a t 40.5/18 a t a l l s t a g e s . C h l o r o p h y l l v i c o n c e n t r a t i o n was a l s o high at 35/18 at 2, 4 and 6 weeks. A d e f i n i t e c o r r e l a t i o n between c h l o r o p h y l l content and photosynthesis was not shown, but there was a s i g n i f i c a n t c o r r e l a t i o n between c h l o r o p h y l l and f r e s h weight at a l l temperatures and photoperiods except at 2 weeks. T o t a l water s o l u b l e carbohydrate and t o t a l ash content d i d not show d e f i n i t e trends according t o stages of growth. No r e l a t i o n s h i p could be shown between f l o r a l i n i t i a t i o n and combined carbohydrate and ash content. TABLE OF CONTENTS Page INTRODUCTION 1 LITERATURE REVIEW 5 P h o t o p e r i o d i s m 5 Types o f P h o t o p e r i o d i c Responses 5 E f f e c t o f Short-Day 8 E f f e c t o f Long-Day 9 I n d i f f e r e n t R e a c t i o n 11 V a r i e t a l C l a s s i f i c a t i o n 11 Developmental Phases 12 Development o f P r i m o r d i a 15 N a t u r a l D a y l e n g t h 16 E c o l o g i c a l A d a p t a b i l i t y 16 Number o f Leaves 18 Components o f Y i e l d 19 Temperature 21 E f f e c t o f Temperature D u r i n g R i p e n i n g P e r i o d 2 5 S o i l C o n d i t i o n s and M i n e r a l N u t r i t i o n 26 Mechanism o f P h o t o p e r i o d C o n t r o l 2 7 C a r b o h y d r a t e s 2 9 P h o t o s y n t h e s i s 32 Growth Stages and P h o t o s y n t h e s i s 32 Le a f M a t u r i t y 33 M o r p h o l o g i c a l Changes and P h o t o s y n t h e s i s 34 V a r i e t a l D i f f e r e n c e s 34 v i i i D i u r n a l and S e a s o n a l F l u c t u a t i o n s 35 E n v i r o n m e n t a l F a c t o r s 36 P h o t o s y n t h e s i s and Dry M a t t e r P r o d u c t i o n 46 C h l o r o p h y l l and C a r o t e n o i d s 49 C h l o r o p h y l l and C a r o t e n o i d Content 49 E f f e c t o f D a y l e n g t h , L i g h t I n t e n s i t y and Temperature 51 C h l o r o p h y l l and P h o t o s y n t h e s i s 54 D r y - M a t t e r P r o d u c t i o n and C h l o r o p h y l l 55 M i n e r a l N u t r i t i o n and S o i l C o n d i t i o n s 56 MATERIALS AND METHODS 5 8 V a r i e t i e s 58 Growth C a b i n e t s 60 P h o t o p e r i o d and Temperature. 6 0 C u l t u r a l P r a c t i c e s 61 L e a f Number and T i l l e r s ' 6 2 F l o w e r i n g 6 3 P h o t o s y n t h e s i s 6 4 Pigment A n a l y s i s 68 T o t a l S o l u b l e C a r b o h y d r a t e s 70 T o t a l Ash 7 0 S t a t i s t i c a l A n a l y s i s 70 RESULTS 71 G e n e r a l O b s e r v a t i o n s 71 F l o w e r i n g 71 Y i e l d D e t e r m i n i n g C h a r a c t e r s 79 i x Development 9 3 Photosynthesis 9 8 Net Photosynthesis at D i f f e r e n t Stages 9 8 Net A s s i m i l a t i o n Rate 104 Dry Weight 110 T o t a l C h l o r o p h y l l 115 Carotenoids 12 0 C h l o r o p h y l l and Net Photosynthesis 124 T o t a l C h l o r o p h y l l and T o t a l Fresh Weight 124 T o t a l Soluble Carbohydrates 124 T o t a l Soluble Carbohydrates and T o t a l Ash 128 DISCUSSION 134 SUMMARY AND CONCLUSION 161 BIBLIOGRAPHY 164 X LIST OF TABLES T a b l e Page 1 Some c h a r a c t e r i s t i c f e a t u r e s o f v a r i e t i e s used i n t h e e x p e r i m e n t s 59 2 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on number o f days from s o a k i n g t o h e a d i n g i n 4 v a r i e t i e s o f r i c e 7 8 3 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on d r y m a t t e r (g) produced p e r pot (3 p l a n t s ) by 4 v a r i e t i e s o f r i c e a t t h e f i n a l h a r v e s t 80 4 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on t h e number o f p a n i c l e s p e r pot i n 4 v a r i e t i e s o f r i c e 82 5 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on t h e l e n g t h o f p a n i c l e (cm) i n 4 v a r i e t i e s o f r i c e 83 6 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on t h e number o f s p i k e l e t s p e r p a n i c l e i n 4 v a r i e t i e s o f r i c e 84 7 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on p e r c e n t s t e r i l i t y i n 4 v a r i e t i e s o f r i c e 86 8 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on 1 0 0 - g r a i n w e i g h t (g) i n 4 v a r i e t i e s o f r i c e 87 9 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on t h e number o f t i l l e r s p e r p l a n t a t 3 weeks i n 4 v a r i e t i e s o f r i c e 89 I x i T a b l e Page 10 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on the number o f t i l l e r s p e r p l a n t a t 5 weeks i n 4 v a r i e t i e s o f r i c e 90 11 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on t h e number o f t i l l e r s per p l a n t a t 7 weeks i n 4 v a r i e t i e s o f r i c e 91 12 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on the number o f t i l l e r s p e r p l a n t a t 9 weeks i n 4 v a r i e t i e s o f r i c e 92 13 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on the number o f l e a v e s on the main culm i n 4 v a r i e t i e s o f r i c e a t 3 weeks 94 14 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on the number o f l e a v e s on t h e main culm i n 4 v a r i e t i e s o f r i c e a t 5 weeks 95 15 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on t h e number o f l e a v e s on t h e main culm i n 4 v a r i e t i e s o f r i c e a t 7 weeks 96 16 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on the number o f l e a v e s on t h e amin culm i n 4 v a r i e t i e s o f r i c e a t 9 weeks 97 17 The e f f e c t o f p h o t o p e r i o d and t e m p e r a t u r e on the p l a n t h e i g h t (cm) a t 2 weeks i n 4 v a r i e t i e s o f r i c e 99 x i i 18 The e f f e c t o f p h o t o p e r i o d and temperature on the p l a n t h e i g h t (cm) a t 4 weeks i n 4 v a r i e t i e s o f r i c e 100 19 The e f f e c t o f p h o t o p e r i o d and te m p e r a t u r e on t h e p l a n t h e i g h t (cm) a t 6 weeks i n 4 v a r i e t i e s o f r i c e 101 20 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on t h e p l a n t h e i g h t (cm) a t 8 weeks i n 4 v a r i e t i e s o f r i c e 102 21 C o r r e l a t i o n c o e f f i c i e n t ( r ) v a l u e s between mg C 0 2 p e r gram f r e s h l e a f b l a d e weight per hour and mg CC^ p e r square d e c i m e t e r l e a f s u r f a c e p e r hour 103 2 2 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on ne t p h o t o s y n t h e s i s a t 2 weeks i n 4 v a r i e t i e s o f r i c e (mg CO2 per g f r e s h l e a f b l a d e w e i g h t p e r hour) 105 23 The e f f e c t o f p h o t o p e r i o d and te m p e r a t u r e on net p h o t o s y n t h e s i s a t 4 weeks i n 4 v a r i e t i e s o f r i c e (mg CO^ per g f r e s h l e a f b l a d e w e i g h t p e r hour 106 24 The e f f e c t o f p h o t o p e r i o d and tem p e r a t u r e on ne t p h o t o s y n t h e s i s a t 6 weeks i n 4 v a r i e t i e s o f r i c e (mg C0 2 p e r g f r e s h l e a f b l a d e w e i g h t p e r hour 107 x i i i 25 The e f f e c t of photoperiod and temperature on net photosynthesis at 8 weeks i n 4 v a r i e t i e s of r i c e (mg CC^ per g f r e s h l e a f blade weight per hour) 108 26 The e f f e c t of photoperiod and temperature on the net a s s i m i l a t i o n r a t e i n 4 v a r i e t i e s of r i c e (g of dry weight produced per day per dm2) 109 27 The e f f e c t of photoperiod and temperature on the dry weight (g per pot) at 2 weeks of 4 v a r i e t i e s of r i c e 111 28 The e f f e c t of photoperiod and temperature on the dry weight (g per pot) at 4 weeks of 4 v a r i e t i e s of r i c e 112 2 9 The e f f e c t of photoperiod and temperature on the dry weight (g per pot) at 6 weeks of 4 v a r i e t i e s of r i c e 113 3 0 The e f f e c t of photoperiod and temperature on the dry weight (g per pot) at 8 weeks of 4 v a r i e t i e s of r i c e 114 31 The e f f e c t of photoperiod and temperature on the c h l o r o p h y l l content (mg per g f r e s h weight) at 2 weeks i n 4 v a r i e t i e s of r i c e 116 32 The e f f e c t of photoperiod and temperature on the c h l o r o p h y l l content (mg per g f r e s h weight) at 4 weeks i n 4 v a r i e t i e s of r i c e 117 x i v 3 3 The e f f e c t of photoperiod and temperature on the c h l o r o p h y l l content (mg per g f r e s h weight) at 6 weeks i n 4 v a r i e t i e s of r i c e 118 34 The e f f e c t of photoperiod and temperature on the c h l o r o p h y l l content (mg per g f r e s h weight) at 8 weeks i n 4 v a r i e t i e s of r i c e 119 35 The e f f e c t of photoperiod and temperature on the carotenoid content (mg carotenoid per l i t e r ) at 2 weeks i n 4 v a r i e t i e s of r i c e 121 3 6 The e f f e c t of photoperiod and temperature on the carotenoid content (mg carotenoid per l i t e r ) at 4 and 8 weeks i n 4 v a r i e t i e s of r i c e 122 3 7 The e f f e c t of photoperiod and temperature on the carotenoid content (mg carotenoid per l i t e r ) at 6 weeks i n 4 v a r i e t i e s of r i c e 123 38 The values of c o r r e l a t i o n c o e f f i c i e n t s ( r ) between net photosynthesis and t o t a l c h l o r o p h y l l (mg per g f r e s h weight) at 2, 4, 6 and 8 weeks i n 4 v a r i e t i e s of r i c e 125 39 The values f o r c o r r e l a t i o n c o e f f i c i e n t s ( r ) between net photosynthesis and c h l o r o p h y l l a (mg per g f r e s h weight) at 2, 4, 6 and 8 weeks i n 4 v a r i e t i e s of r i c e 126 40 The values f o r c o r r e l a t i o n c o e f f i c i e n t s ( r ) between t o t a l c h l o r o p h y l l and t o t a l f r e s h weight average of 4 v a r i e t i e s of r i c e 12 7 X V Hi The e f f e c t of photoperiod and temperature on the carbohydrate content (mg per g dry weight) at 4 weeks i n 4 v a r i e t i e s of r i c e 129 42 The e f f e c t of photoperiod and temperature on the carbohydrate content (mg per g dry weight) at 8 weeks i n 4 v a r i e t i e s of r i c e 130 43 The e f f e c t of photoperiod and temperature on the carbohydrate plus ash (mg per g dry weight) at 4 weeks i n 4 v a r i e t i e s of r i c e 131 44 The e f f e c t of photoperiod and temperature on the carbohydrate plus ash (mg per g dry weight) at 8 weeks i n 4 v a r i e t i e s of r i c e 132 x v i LIST OF FIGURES Figure Page 1 The controlled environment chamber i n use for net CO^ exchange studies with r i c e . The plants are sealed i n the glass chamber and an a i r stream i s passed continuously through the infrared analyzer. Lights are mounted on the Dexion frame. A r e f l e c t i v e surface i s placed around the outside of the glass chamber. 65 2a A general view of the r i c e plants i n the growth cabinets at 8 weeks afte r transplanting 14-hour photoperiod. 0, 35/18 and N, 35/26.5°C 72 2b A general view of the r i c e plants i n the growth cabinets at 8 weeks af t e r transplanting 14-hour photoperiod. M, 35/35 and P, 40.5/18°C 73 3a Variety Kangni at 2 5 days. Top 14-hour and bottom 8-hour photoperiod. 1. 35/35, 2. 35/26.5, 3. 35/18, 4. 40.5/18 day/night temperature. 74 3b Variety Caloro at 25 days. Top 14-hour and bottom 8-hour photoperiod. 1. 35/35, 2. 35/26.5, 3. 35/18, 4. 40.5/18 day/night temperature. 75 3c Variety Dokri. at 25 days. Top 14-hour and bottom 8-hour photoperiod. 1. 35/35, 2. 35/26.5, 3. 35/18, 4. 40.5/18 day/nigut temperature 76 3d Variety Bluebonnet at 25 days* Top 14-hour and bottom 8-hour photoperiod. 1. 35/35, 2. 35/26.5, 3. 35/18, 4. 40.5/18 day/night temperature 77 ACKNOWLEDGEMENTS Simple words o f acknowledgement w i l l not do j u s t i c e t o a l l t h e h e l p t h a t I r e c e i v e d from P r o f e s s o r D. P. Ormrod. He has not o n l y been a g u i d e , an a d v i s o r but a t t i m e s a c o u n s e l l o r a l s o . I g r a t e f u l l y acknow-l e d g e i t . I am a l s o t h a n k f u l t o him f o r s u g g e s t i n g t h e problem so p e r t i n e n t t o my c o u n t r y and a l s o f o r p r o v i d i n g t h e f a c i l i t i e s . I am a l s o t h a n k f u l t o my committee members Dr. V. C. B r i n k ( C h a i r m a n ) , Department o f P l a n t S c i e n c e ; Dr. D. J . Wort, P r o f e s s o r , Department o f Botany; , Dr. A. J . Renney, P r o f e s s o r and Dr. G. W. E a t o n , A s s o c i a t e P r o f e s s o r , Department o f P l a n t S c i e n c e ; and Dr. J . de V r i e s , Department o f S o i l S c i e n c e , f o r t a k i n g c o n t i n u e d i n t e r e s t i n my work. I am e s p e c i a l l y t h a n k f u l t o Dr. G. W. Eaton f o r h e l p i n g me w i t h S t a t i s t i c s and computer programming. I am a l s o t h a n k f u l t o t h e chairman o f t h e P a k i s t a n Atomic Energy Commission f o r s e l e c t i n g me and A.I.D. Government o f Canada f o r p r o v i d i n g t h e Colombo P l a n S c h o l a r s h i p . T e c h n i c a l h e l p from Mr. A s h l e y H e r a t h i s g r a t e f u l l y acknowledged. INTRODUCTION About one quarter of the world's c e r e a l production i s r i c e and over h a l f of t h i s i s grown i n the t r o p i c s . Compared to wheat, only h a l f the acreage i s devoted to r i c e ; but, because r i c e i s high y i e l d i n g the t o t a l r i c e production almost equals t o t a l world wheat production. Even though r i c e i s high y i e l d i n g , f u r t h e r increases i n y i e l d are p o s s i b l e , p a r t i c u l a r l y i n the t r o p i c a l v a r i e t i e s . Rice i s g e n e r a l l y considered to be a t r o p i c a l crop but the range of c l i m a t i c v a r i a t i o n i t can t o l e r a t e i s probably wider than that of any other crop; thus, i t i s grown as f a r north as Korea and Czechoslovakia (49°N) and as f a r south as 35° i n A u s t r a l i a . I t i s grown at an a l t i t u d e of 4,000 f t . i n Peru, 6,000 f t . i n the P h i l i p p i n e s , and 10,000 f t . i n I n d i a (Mickus, 1959; Mooma and Vergara, 1963). Although r i c e can grow i n v a r i e d c l i m a t i c c o n d i t i o n s the y i e l d s d i f f e r widely. The y i e l d d i f f e r e n c e s appear to be somewhat r e l a t e d to l a t i t u d e because (1) the y i e l d of r i c e i n the t r o p i c s i s g e n e r a l l y low (2) the y i e l d of r i c e p r o g r e s s i v e l y increases w i t h the l a t i t u d e a t t a i n i n g maximum value beyond 30° N and S (3) the highest y i e l d s i n temperate regions are higher than i n the t r o p i c s . Thus f o r c o u n t r i e s such as Japan, A u s t r a l i a , the United S t a t e s , and the Mediterranean c o u n t r i e s y i e l d s of 4 to 6 tons/hectare are u s u a l , whereas i n c o u n t r i e s , such as I n d i a , P a k i s t a n , Thailand, and the P h i l i p p i n e s , the n a t i o n a l average y i e l d s seldom exceed 2 tons/hectare (Jackson, 1966). 2 The higher y i e l d s i n temperate regions can p a r t l y be explained by b e t t e r water c o n t r o l , land p r e p a r a t i o n , weed and pest c o n t r o l , and other c u l t u r a l p r a c t i c e s . I t i s a l s o due to the use of v a r i e t i e s which respond to high r a t e s of f e r t i l i z e r (Jackson, 1966). Many consider t h i s to be the main reason f o r higher y i e l d s . I t has been suggested that the areas l o c a t e d i n higher l a t i t u d e s are subject to more hours of sunshine than s i m i l a r areas i n the t r o p i c s . Lower temperatures cause a slower development of r i c e i n temperate regions than i n t r o p i c a l regions thereby lengthening the v e g e t a t i v e p e r i o d . The e f f e c t of l i g h t can be c l a s s i f i e d i n t o two broad c a t e g o r i e s : 1. photo-energy processes and 2. photo-stimulus processes. Photosynthesis belongs i n the f i r s t group; stem e l o n g a t i o n , l e a f expansion, pigment formation and f l o w e r i n g belong to the second (Best, 1962). Photosynthesis has long been the subject of i n t e n s i v e study and a l a r g e body of l i t e r a t u r e has accumulated. I t i s c l e a r t h a t r a t e of photosynthesis i s not only a f f e c t e d by such f a c t o r s as l i g h t i n t e n s i t y , temperature, and CC^ c o n c e n t r a t i o n , but a l s o by species and growth-stage. The e f f e c t of l i g h t i n t e n s i t y on r a t e of photosynthesis i s w e l l understood but the e f f e c t of l i g h t d u r a t i o n on subsequent photosynthesis has not r e c e i v e d the same a t t e n t i o n . This has a l s o been the case w i t h e f f e c t of temperature on photosynthesis. In most studi e s p l a n t s were 3 grown at one temperature and then subjected to d i f f e r e n t temperatures f o r the purpose of studying photosynthesis. Studies l i k e these have been of great value i n understanding the p h y s i o l o g i c a l response of p l a n t s to sudden change i n environment but f a i l to take i n t o c o n s i d e r a t i o n the adaptation of a pla n t to a long term change i n environment. Flowering, i n photoperiodic s e n s i t i v e v a r i e t i e s , depends upon d u r a t i o n of darkness. Onset of f l o w e r i n g too e a r l y or too l a t e i n the l i f e of p l a n t s can cause severe r e d u c t i o n i n y i e l d . Flowering i n r i c e has r e c e i v e d a t t e n t i o n , but i t s i n t e r a c t i o n with temperature has only r e c e n t l y been c r i t i c a l l y s t u d i e d . P h o t o - s t i m u l a t i o n of pigment formation i s important from the poin t of view of photosynthesis. Attempts t o c o r r e l a t e photosynthesis w i t h c h l o r o p h y l l content have not been t o t a l l y s u c c e s s f u l , nor has dry matter production been c o r r e l a t e d w i t h c h l o r o p h y l l content. There have been many t h e o r i e s e x p l a i n i n g the process of f l o w e r i n g i n p l a n t s , but none so f a r i s capable of e x p l a i n i n g a l l the f a c t s . "And i f anybody were asked to name a phenomenon of p l a n t l i f e where the gap between morphology and physiology i s the widest, he would c e r t a i n l y i n d i c a t e f l o w e r i n g " (Chailakhyan, 1968). No statement can more a p p r o p r i a t e l y describe the motive f o r the present study than t h i s passage from the foreword by Nuttonson (1965). "Many d i f f e r e n t c l imates and 4 s o i l s o f t e n enforce d i f f e r e n t types of e x t e r n a l a d a p t a b i l i t y of a given v a r i e t y . Because of i t s s i g n i f i c a n c e i n r e l a t i o n to genetic and agronomic problems, an understanding of the growth-development p o t e n t i a l i t i e s of a p l a n t v a r i e t y against the background of s p e c i f i c environments i s extremely important." 5 LITERATURE REVIEW Photoperdodism In 19 2 0 Garner and A l l a r d c l e a r l y demonstrated f o r the f i r s t time the importance of day length i n f l o w e r i n g . I t was then almost 18 years before Hamner and Bonner (193 8) discovered that the dark period was the c r i t i c a l part of the photoperiodic c y c l e . Parker et a l . (1946) worked out the a c t i o n spectrum f o r the photoperiodic c o n t r o l of f l o r a l i n i t i a t i o n i n short day p l a n t s i n 1946 and 13 years l a t e r B u t l e r et a l . (1959) i s o l a t e d the pigment system i n v o l v e d . The f i r s t p hotoperiodic study i n r i c e i s c r e d i t e d to Mihara (192 3) who demonstrated that p l a n t s grown under i n t e r r u p t e d l i g h t flowered one month e a r l i e r than c o n t r o l p l a n t s . Yoshi (1927, 1929) demonstrated f o r the f i r s t time the d i f f e r e n c e s i n photoperiodic s e n s i t i v i t y of d i f f e r e n t r i c e v a r i e t i e s . The l i t e r a t u r e on photoperiodism i n r i c e and r e l a t e d t o p i c s i s exhaustive, and not a l l of i t r e a d i l y a v a i l a b l e . For e a r l i e r work there are e x c e l l e n t reviews p a r t i c u l a r l y by Moringa (1954) Best (1959) and more r e c e n t l y by Katayama (1963). Types of Photoperiodic Response Rice i s g e n e r a l l y considered a short day p l a n t ( S a l i s b u r y , 1963). In h i s c l a s s i f i c a t i o n of the r e a c t i o n of the p l a n t to photoperiod and temperature, r i c e i s placed under 6 two c a t e g o r i e s : 1. short day p l a n t promoted by high temperature and 2. day n e u t r a l p l a n t promoted by high temperature. This c l a s s i f i c a t i o n may i n c l u d e most of the r i c e v a r i e t i e s , but there have been many ways used to designate s e n s i t i v i t y of r i c e v a r i e t i e s to photoperiods. Vergara (1965) has t r i e d to c l a r i f y some of the very confusing l i t e r a t u r e . He c l a s s i f i e s "photoperiodic n o n - s e n s i t i v e " v a r i e t i e s as those i n which the delay i n f l o w e r i n g due t o adverse photoperiods i s not more than 10 days. The other v a r i e t i e s were considered as s e n s i t i v e and were f u r t h e r subdivided i n t o s t r o n g l y and weakly photoperiodic. Unfortunately no c r i t e r i a f o r such d i v i s i o n were given. An e a r l i e r report from the same i n s t i t u t e (Anon., 1963) described the f o l l o w i n g c r i t e r i a f o r the c l a s s i f i c a t i o n of photoperiodic response of r i c e v a r i e t i e s : 1. the maximum r a t e of change from vege t a t i v e t o reproductive growth p o s s i b l e w i t h increase i n day-length, 2. the b a s i c growth d u r a t i o n , 3. Maximum change i n growth du r a t i o n p o s s i b l e . V a r i e t i e s t h a t are g e n e r a l l y considered non-seasonal f a l l between 2 0 and 3 0 days i n maximum r a t e of change. Katayama (1964a) simply c l a s s i f i e d r i c e v a r i e t i e s i n t o s e n s i t i v e and i n s e n s i t i v e . Those s t r a i n s which d i d not show any change i n growing period were considered i n s e n s i t i v e and the r e s t s e n s i t i v e . He recognized the complexity of the problem and assumed three components of paramount importance i n determining the photoperiodic 7 s e n s i t i v i t y : 1. p l a n t age, 2. c r i t i c a l day length and 3. a c c e l e r a t i o n degree i n short day treatment. Best (196 0) studied the whole range of photoperiods between 0 and 2 4 hours. He p l o t t e d the time from sowing t o f l o r a l i n i t i a t i o n on the ordinate against the photoperiod used on the a b s c i s s a . The slope of the response curve so obtained gave the s e n s i t i v i t y of r i c e v a r i e t i e s to v a r y i n g photoperiod. He concluded from a la r g e number of response curves t h a t at l e a s t i n r i c e the response i s q u a n t i t a t i v e r a t h e r than q u a l i t a t i v e i n nature. He found the optimum photoperiod to range from 8% hours to 13 hours, 11 hours being the most common one. Chandraratna (19 54, 1955, 19 64) stu d i e d response by means of response curves. He f i t t e d the second 2 degree polynomial of the form y = a + bx + cx . where y = germination to heading i n t e r v a l i n days x = photoperiod i n hours a, b and c = constants This r e l a t i o n s h i p was v a l i d only when photoperiods of 8 to 13 hours were used and d i d not hold under the f u l l range of photoperiods. According to t h i s r e l a t i o n s h i p the minimum value f o r germination-heading i n t e r v a l i s obtained when ^ = b + 2cx = 0 which i s termed minimum heading d u r a t i o n . The value of x under such c o n d i t i o n s i s -b/2c. x under such c o n d i t i o n i s the optimum photoperiod. S u b s t i t u t i n g 2 -b/2c i n place of x i n y = a + bx +cx , the value y = a 2 -b /4c i s obtained which i s the minimum f l o w e r i n g d u r a t i o n . Roberts and Carpenter (196 2) disagreed with Chandraratna 8 and argued that even i f small photoperiod i n t e r v a l s are taken the data cannot be f i t t e d to a simple equation. Norin 20, CP-231, M i l f o r 6 ( 2 ) , and many other v a r i e t i e s f o l l o w a s t r a i g h t l i n e equation r a t h e r than a second degree polynomial (Vergara, Puranabhavung and L i l i s , 1965). E f f e c t of Short-Day Photoperiodic response i n r i c e i s q u a n t i t a t i v e (Best, 1959, I960; Chandraratna, 1954, 1964). Under very short photoperiods i t takes longer t o flower but as the photoperiod increases the number of days to f l o w e r i n g g r a d u a l l y decreases t i l l i t reaches the optimum value. Further increase i n photoperiod p r o g r e s s i v e l y delays f l o w e r i n g (Chandraratna, 1954; Best,1960; Ormrod et a l . , 1960; Anon., 1963; E n y i , 196 3a; Vergara, Puranabhavung and L i l i s , 1965; Vergara and L i l i s , 1967- and Roberts and Carpenter, 1962). Evidence f o r the q u a l i t a t i v e nature of the short day response i s not c o n c l u s i v e because i n many cases the experiments were terminated too e a r l y . Thus, Vergara and L i l i s (1967) d i d not get any f l o w e r i n g under long day co n d i t i o n s (14 hours) i n CH-10 and BPI-76 f o r 200 days. S i m i l a r r e s u l t s were reported by Vergara, Puranabhavung and L i l i s (1965) and Ormrod et a l . (1960). The longest periods f o r which the experiment was continued was i n the research of Roberts and Carpenter (1962). A f t e r 348 days they found that v a r i e t i e s Lead 35 and Radin china 4 d i d not flower i n a 14 hour photoperiod but when removed to a 10% 9 hour p h o t o p e r i o d a t t h e end o f t h e experiment b o t h v a r i e t i e s f l o w e r e d w i t h i n 32 days. T h i s s u g g e s t s a q u a l i t a t i v e r e s p o n s e . Dore (1959) and V e r g a r a and L i l i s (1967) c l a i m e d a q u a l i t a t i v e r e s ponse i n BPI-76, GEB-24 and H e e n a t i 897 6. On t h e o t h e r hand, Asakuma and Kaneda (1967) w o r k i n g w i t h 10 s e n s i t i v e s t r a i n s i n c l u d i n g Zuiho t h e most s e n s i t i v e Japanese s t r a i n , c o u l d get f l o w e r i n g i n a l l s t r a i n s under c o n t i n u o u s i l l u m i n a t i o n . E f f e c t o f Long-Day Most e v i d e n c e s u g g e s t s t h a t r i c e i s a s h o r t day p l a n t but t h e r e have been a few r e p o r t s i n d i c a t i n g t h a t i n some v a r i e t i e s o f r i c e f l o w e r i n g i s hastened by l o n g days. Gangulee (1955) found v a r i e t y Karang sarang t o be promoted by l o n g days. M i s r a (1955, 1956 and 1960a) w o r k i n g w i t h o t h e r v a r i e t i e s came t o a s i m i l a r c o n c l u s i o n . V e r g a r a and L i l i s (1967) c r i t i c i z e d t h e c o n c l u s i o n drawn. They r e s t u d i e d most o f the v a r i e t i e s used by t h e o t h e r workers and c o u l d not f i n d any l o n g day e f f e c t . They c o n c l u d e d t h a t the l o n g day e f f e c t o b s e r v e d was due t o t h e f a c t t h a t o n l y two photo-p e r i o d s were used and as t h e s h o r t p h o t o p e r i o d used was s u b o p t i m a l p l a n t s f l o w e r e d e a r l i e r i n l o n g e r p h o t o p e r i o d . I t i s i n t e r e s t i n g t o note t h a t f o r v a r i e t i e s CH-10 and T136, V e r g a r a and L i l i s (1967) found 10-hour p h o t o p e r i o d t o be optimum and t h e two v a r i e t i e s f l o w e r e d i n 76 and 66 days r e s p e c t i v e l y . M i s r a (1960a) f o r t u i t o u s l y d i d , i n c l u d e a 10-hour p h o t o p e r i o d i n h i s s t u d i e s . I n h i s experiment 10 CH-10 and T136 flowered i n 102 and 99 days r e s p e c t i v e l y . D i f f e r e n c e s of 26 and 3 3 days from the f i g u r e s of Vergara and L i l i s (1967) w i l l have to be explained before any c o n c l u s i o n can be drawn. C l a s s i f i c a t i o n of q u a n t i t a t i v e response i n t o short or long day poses a problem, e s p e c i a l l y i n r i c e where temperature and other f a c t o r s exert an e f f e c t separate from the p hotoperiodic e f f e c t . The a n a l y s i s of the response curves of Best (1960) Chandraratna (1954, 1963) Ormrod et a l . (196 0) and Vergara, Puranabhavung and L i l i s (196 5) shows some i n t e r e s t i n g f e a t u r e s . V a r i e t y Japan I shows most r a p i d f l o w e r i n g at 15 hours and slower f l o w e r i n g at sh o r t e r and longer photoperiods with such a response i t should not be c l a s s i f i e d as short-day v a r i e t y . Tainan, BB.5 and CP.2 31 (Vergara, Puranabhavung and L i l i s , 1965) a l s o do not q u a l i f y f o r a short day category. The v a r i a t i o n i n optimum photoperiod i s a l s o s u r p r i s i n g . Thus, Best found the optimum photoperiod to be 9 to 14% hours i n a 1959 re p o r t and 8% to 13 hours i n a 1960 r e p o r t . Vergara st a t e d that the optimum ranges from 8 to 14 hours i n a 1965 re p o r t and 8 to 13 hours i n a 19 67 r e p o r t . M i l f o r 6(2) flowered e a r l i e s t under 24 hour photoperiod. The optimum photoperiod c a l c u l a t e d from the data of Chandraratna (1954) and.Ormrod et a l . (1960) was 10 to 12% hours and 12 t o 15 hours r e s p e c t i v e l y . 11 I n d i f f e r e n t Reaction Vergara (1965) proposed that a d i f f e r e n c e of 9 or 10 days i n response to d i f f e r e n t photoperiods should not be considered as s i g n i f i c a n t . He proposed the term "photoperiod-n o n s e n s i t i v e " f o r v a r i e t i e s showing such a response. Vergara and L i l i s (1967), Vergara, Puranabhavung and L i l i s (1965), Misra (1956, 1960a), Velasco and Dela Fuente (1958) and L Lantican and Parker (1961) found many v a r i e t i e s which could be considered i n d i f f e r e n t to photoperiod. Katayama (1964a) made an extensive survey of the genus Oryza (47 2 s t r a i n s and 25 s p e c i e s ) . He used the c r i t e r i a t h a t a p l a n t whose heading date i s a c c e l e r a t e d by more than 20 days by short day t r e a t -ment i n comparison w i t h c o n t r o l i s s e n s i t i v e and a pl a n t whose heading date i s ac c e l e r a t e d by l e s s than 10 days i s i n s e n s i t i v e . He found t h a t i n r i c e 28.3% of the s t r a i n s were i n s e n s i t i v e . V a r i e t a l C l a s s i f i c a t i o n Yoshi (1927) was the f i r s t to examine the v a r i e t a l d i f f e r e n c e s i n r i c e . S a l i s b u r y (1963) c l a s s i f i e d r i c e i n t o two c a t e g o r i e s : 1. short day promoted by high temperature and 2. day n e u t r a l promoted by high temperature. Wada (1942) made the f o l l o w i n g c l a s s i f i c a t i o n : 1. h i g h l y s e n s i t i v e to temperature and s l i g h t l y s e n s i t i v e . t o photoperiod, 2. s l i g h t l y s e n s i t i v e to temperature and h i g h l y s e n s i t i v e to photoperiod, 3. h i g h l y s e n s i t i v e to both. V a r i e t i e s have been c l a s s i f i e d according t o response to daylength , according to growth d u r a t i o n , and according t o season of p l a n t i n g . The confusion 12 and the ambiguity that has been created has been pointed out by Vergara (1965). He suggests t h a t f o r p h y s i o l o g i c a l s t u d i e s standard method of t e s t i n g f o r s e n s i t i v i t y should be e s t a b l i s h e d . Lantican and Parker (1961) c l a s s i f i e d a v a r i e t y as s e n s i t i v e when the maximum range i n i t s sowing-heading per i o d exceeded 23 days. Velasco and Dela Fuente (1958) considered a v a r i e t y weakly photoperiodic i f the d i f f e r e n c e i n the age at f l o w e r i n g between short day and long day t r e a t -ment was l e s s than 30 days and s t r o n g l y photoperiodic i f the d i f f e r e n c e was more than 30 days. They a l s o gave the c l a s s i f i c a t i o n based on growth d u r a t i o n . V a r i e t i e s t a k i n g l e s s than 110 days to mature were considered very e a r l y , 111 to 130 e a r l y , 131 to 150 medium l a t e , and greater than 150 l a t e . A comparable c l a s s i f i c a t i o n by Nuttonson (1965) con-s i d e r s growth d u r a t i o n of 102 to 107 very e a r l y , 111 to 118 e a r l y , 126 to 132 midseason and 155 to 164 as l a t e . Developmental Phases Vergara, Puranabhavung and L i l i s (1965) d i v i d e d the growth d u r a t i o n i n t o three phases: 1. vegeta t i v e growth, 2. reproductive growth and 3. r i p e n i n g . He f u r t h e r subdivided the ve g e t a t i v e growth phase i n t o two: 1. bas i c v e g e t a t i v e phase and 2. photoperiod s e n s i t i v e phase. K a k i z a k i (1938) as quoted by Noguchi and Kamata (1959) defined b a s i c v e g e t a t i v e phase as "that part of veget a t i v e growth which f o l l o w s germination of seeds and cannot be e l i m i n a t e d by environmental c o n d i t i o n s . " The bas i c v e g e t a t i v e 13 phase i s thus the minimum growth required before a plant can become receptive to photoperiodic induction. The photoperiod sensitive phase, also c a l l e d eliminable phase (Vergara, Puranabhuvung and L i l i s , 1965) i s the duration between minimum and maximum possible growth. The reproductive and ripening phases are considered to be constant at a l l photoperiods. It takes about 35 days from the s t a r t of photoperiod treatment to flowering hence basic vegetative phase can be obtained by subtracting 35 days from the minimum number of days from sowing to flowering. Best (19 59) gave the range f o r the basic vegetative phase as 14 to 7 3 days depending upon variety. Vergara, Puranabhavung and L i l i s (1965) found t h i s to be 10 to 70 days and concluded that basic vegetative phase was longer i n v a r i e t i e s less affected by photoperiod whereas v a r i e t i e s sensitive to photoperiod had the longest photoperiod sensitive phase. Noguchi and Kamata (1959) were able to induce flowering i n Nor i n No. 11 at the 5 leaf stage. They concluded that the basic vegetative phase of Norin No. 11 i s the duration from germination to development of fourth l e a f . Nagai (196 3) found that the r i c e embryo has 3 leaf primordia and that i t i s impossible for the r i c e plant to flower with only two leaves unless panicle i n i t i a t i o n can occur during embryo formation. If i t were possible to have panicle i n i t i a t i o n at germination then 4 to 5 leaves would be the minimum necessary. Noguchi and Kamata (1959) were able to get i n i t i a t i o n 14 i n Norin No. 11 at the time of germination according to these c r i t e r i a . Flowering not only depends on the application of the r i g h t photoperiod at the r i g h t time but also depends on the number of cycles given. A certain basic number of cycles i s necessary which decreases with the aging of the plant. The number of cycles needed also depends upon the *jlength of the e f f e c t i v e photoperiod. Katayama (1964a) found 5 days of 12% hour photo-period to be s u f f i c i e n t f o r C8436 and C8437 but even 25 cycles were not s u f f i c i e n t f o r v a r i e t i e s C8448 and W1064. Kyoto Asahi required nine, 14-hour, s i x , 13-hour and only three, 12-hour photoperiod cycles to flower. Vergara et a l . (1966) and Noguchi et a l . (1965) found si m i l a r r e s u l t s . The number of cycles required depended on the age of the plant (Suge, 1968; Asakuma and Kaneda, 1967). Thus 6 cycles were required at 8 l e a f stage 5 at 11 and only one cycle was s u f f i c i e n t at 14 le a f stage i n Zuhio (Suge, 1968). Misra (1960a) found somewhat d i f f e r e n t r e s u l t s . He found that treatment of 7 day old seedling with short days f o r 3, 4, 5 and 6 weeks progressively delayed flowering i n early and late winter v a r i e t i e s ^ S i r c a r and Sen (1953) found effectiveness of photoinduction to be proportional to the number of photoinductive cycles. Mishra and Misro (1961) found si m i l a r r e s u l t s . 15 Katayama (1964a) d i v i d e d the r i c e v a r i e t i e s i n t o f i v e groups depending on t h e i r r e a c t i o n to aging: 1. Pla n t s t h a t d i d not show any aging e f f e c t . 2. Pla n t s f o r which maximum s e n s i t i v i t y was reached at 55 days then remained unaffected. 3. P l a n t s f o r which photoperiod s e n s i t i v i t y reached a plateau at the age of 7 0 days. 4. Pla n t s f o r which s e n s i t i v i t y reached a plateau at the age of 85 days. 5. P l a n t s f o r which s e n s i t i v i t y reached a plateau at the age of 100 days. Development of Primordia Once flower i n i t i a t i o n takes p l a c e , subsequent development i s unaffected by change i n photoperiod according to Oka et a l . (1952). Oka (1958) and Katayama (1963, 1964a) found 3 0 days to be the i n t e r v a l between i n i t i a t i o n and heading under s u i t a b l e temperatures. Vergara, Puranabhavung and L i l i s (19 65) considered reproductive and r i p e n i n g phases to be constant. Chandraratna (1954), Noguchi et a l . (1965) and Vergara et al. (1966) found d i f f e r e n c e s i n number of days between i n i t i a t i o n and f l o w e r i n g . Chandraratna (1954) found s i g n i f i c a n t d i f f e r e n c e s i n the subsequent development of flower primordia i n the v a r i e t y Kohumawi B - l l . The number of days from i n i t i a t i o n to f l o w e r i n g was 2 3.8, 31.6 and 36.8 i n 10, 12 and 13 hour photoperiod r e s p e c t i v e l y . Best (19 59) b e l i e v e d that there may or may not be any 16 d i f f e r e n c e s depending on the v a r i e t y s t u d i e d . N a t u r a l Day Length Many of the e a r l i e r s t u d i e s were performed simply by v a r y i n g the date of sowing. The range of photoperiod obtained depends on the l a t i t u d e of the l o c a t i o n . Near the t r o p i c s there i s very l i t t l e v a r i a t i o n i n photoperiod but i n temperate regions photoperiod can be extended but temperature i n t e r a c t i o n becomes more pronounced which may lead t o m i s i n t e r p r e t a t i o n . Thus, S i r c a r and Sen (1953) studied the w inter paddy R u p s a i l by sowing on 21st September and 2 5th February. They a t t r i b u t e d the d i f f e r e n c e s i n flower-ing to decreasing temperature i n the f i r s t case and i n c r e a s i n g temperature i n the other case, but there was a concomitant decreasing and i n c r e a s i n g photoperiod. Oka et a l . (1952) i n a comprehensive three year study concluded t h a t the r e d u c t i o n i n growth period w i t h l a t e r p l a n t i n g i n sp r i n g i s due to r i s e i n temperature and i n autumn due to shortening of day l e n g t h . Gangulee (1955), Sen and M i t r a (1958), Oka (1958) Lantican and Parker (19 61), and Venkataraman (1964) made s i m i l a r s t u d i e s . Dore (1959) studied Siam 29, an i n d i c a v a r i e t y and found t h a t at Malaca when sown i n June i t flowered i n 329 days compared to 161 days when sown i n September though the day length v a r i e d by only 14 minutes. E c o l o g i c a l A d a p t a b i l i t y Low temperatures during short photoperiods c h a r a c t e r i z e temperate reg i o n s . Coupled w i t h shorter growing 17 pe r i o d t h i s c l e a r l y produces a r e s t r i c t i o n on photoperiod s e n s i t i v e v a r i e t i e s . On the other hand i n the t r o p i c s low temperature i s never a problem whereas photoperiod s e n s i t i v i t y imparts a d i s t i n c t advantage i n r e g u l a t i n g growth. Oka et a l . (195 2) and Oka (19 58) found that northern p a r t s of Japan, China and the e q u a t o r i a l zone showed no s e n s i t i v e v a r i e t i e s . Both s e n s i t i v e and n o n s e n s i t i v e v a r i e t i e s were found between 38° to 15° north or south. In the northern l a t i t u d e they a l s o found that the lower the l a t i t u d e the higher the s e n s i t i v i t y . In northern temperate regions the r i c e crop season i s short and the days are long; t h e r e f o r e , only v a r i e t i e s i n s e n s i t i v e to daylength can grow while i n the t r o p i c s , the range of annual change of daylength becomes smaller so higher s e n s i t i v i t y i s necessary. Dore (1959) found a response to annual change of 14 minutes i n photoperiod. Velasco and Dela Fuente (1958) found t h a t 80% of the r i c e v a r i e t i e s o r i g i n a t i n g between 20°N and S were s t r o n g l y p h o t o s e n s i t i v e whereas,50% of those o r i g i n a t i n g beyond 21°N and S were s t r o n g l y s e n s i t i v e v a r i e t i e s . By f a r the most comprehensive study was done by Katayama (1964b). He used 285 s t r a i n s of Oryza belonging to 2 c u l t i v a t e d and 13 w i l d species. He found t h a t : 1. C r i t i c a l daylength of c u l t i v a t e d as w e l l as w i l d s t r a i n s i s s i g n i f i c a n t l y c o r r e l a t e d w i t h the l a t i t u d e of t h e i r n a t i v e l o c a t i o n . 18 2. C o r r e l a t i o n observed by 0 . s a t i v a and 0.glaberrima i s very s i m i l a r . 3. C o r r e l a t i o n s f o r c u l t i v a t e d r i c e are s i m i l a r to that found f o r w i l d species. 4. The adaptation to n a t u r a l photoperiod has played a most e s s e n t i a l r o l e i n the existence of c u l t i v a t e d and w i l d species. A r t i f i c i a l s e l e c t i o n of c u l t i v a t e d species f o r various agronomic c h a r a c t e r i s t i c s was c a r r i e d out independently of the photoperiodic response of the genotype. He found that the c r i t i c a l day length of c u l t i v a t e d and w i l d s t r a i n changes by 2.563 and 3.548 minutes res p e c t -i v e l y f o r each degree s h i f t i n l a t i t u d e . Number of Leaves Vergara e_t a l . (1966) found a p a r a l l e l i s m between photoperiod e f f e c t and number of leaves developed on the main culm. At the optimum photoperiod the number of leaves at f l o w e r i n g was 9. At 13 hour photoperiod the f l o w e r i n g was delayed by 29 days and the number of leaves at f l o w e r i n g was 19. Under i n c r e a s i n g photoperiod the ve g e t a t i v e phase was probably prolonged. Temperature had a pronounced e f f e c t on l e a f emergence. Thus, under 12 hour photoperiod number of leaves formed were 15 and 13 at 28 and 30°C r e s p e c t i v e l y (Vergara et a l . 1966). The v a r i a t i o n i n l e a f number i s more pronounced i n s e n s i t i v e v a r i e t i e s . I n s e n s i t i v e v a r i e t i e s do I 19 not show such a v a r i a t i o n (Inouye, 1965 ; Anon., 1963 ; Noguchi, 1959, 1960; Noguchi and Kamata, 1959, 1965; Noguchi et a l . , 1965). The l a t t e r workers a l s o found t h a t good n u t r i t i o n a l c o n d i t i o n s and high temperature allowed f l o w e r i n g at the l e a s t number of leaves followed by good n u t r i t i o n a l c o n d i t i o n and low temperature, low n u t r i t i o n a l c o n d i t i o n s and high temperature, and low n u t r i t i o n a l c o n d i t i o n s and low temperature. Enyi (19 6 3a) d i d not f i n d any p a r a l l e l i s m w i t h respect t o l e a f development and f l o w e r i n g response i n the v a r i e t y Sida Cero which flowered at 9th l e a f stage i n 5, 7 and 9-hour photoperiod but at 10 and 14-hour photo-period the number of leaves were 10 and 12 r e s p e c t i v e l y though no f l o w e r i n g occurred i n 14 hour photoperiod. Components of Y i e l d 1. P l a n t height and number of t i l l e r s E nyi (1963a) found v a r i a b l e e f f e c t s of photoperiod on number of t i l l e r s but at 10 weeks a 14-hour photoperiod had greater number of t i l l e r s than 5, 7, 9 or 12-hour photoperiod. A s i m i l a r trend was shown f o r p l a n t height. Coolhaas and Wormer (1953) d i d not f i n d any d i f f e r e n c e i n t i l l e r i n g but found v a r i a b l e e f f e c t s on height i n the v a r i e t y Kameji ( n o n s e n s i t i v e ) . P l a n t s were t a l l e r i n 18-hour photo-p e r i o d than 12-hour, but the trend was reversed i n v a r i e t y T j i n a ( s e n s i t i v e v a r i e t y ) . Vergara, L i l i s and Tanaka (1965) found no change i n length i n Tainan 3 but i n Podiwi-A-8 and Chung-Lin-Chun there was increase i n height w i t h 20 i n c r e a s i n g photoperiod. Vergara and L i l i s (1966) found fewer t i l l e r s w i t h i n c r e a s i n g number of photoinductive c y c l e s . S i r c a r and Sen (1953) found mean pl a n t height of 26.23 cm i n September sown and 47.8 5 cm i n February sown p l a n t s and the r e s p e c t i v e number of t i l l e r s was 3.2 and 8.5. Mi s r a (1954a) found continuous short day exposure r e s u l t s i n fewer t i l l e r s compared w i t h a few c y c l e s of short day photoperiod. 2. Number and length of p a n i c l e s Misra (1954a,b, 1955, 1956) studied the e f f e c t of photoperiod on p a n i c l e formation. Both the number of p a n i c l e s formed and length of p a n i c l e were reduced i n a short photoperiod (10 hours) and i n a long photoperiod (24 hours) but the length of p a n i c l e was unaffected (Venkataraman, 1964). Greatest ear length occurred i n 1st J u l y to 1st August p l a n t i n g s . Subsequent p l a n t i n g s had reduced ear le n g t h . Vergara and L i l i s (1966) studied the e f f e c t of number of c y c l e s on 25 day o l d BPI-76 p l a n t s and found t h a t the number of p a n i c l e s increased w i t h i n c r e a s i n g c y c l e s up t o 22 c y c l e s whereas the length of p a n i c l e decreased wi t h i n c r e a s i n g c y c l e s . Enyi (1963a) found maximum p a n i c l e length i n a photoperiod of 9 hours. Increase or decrease i n photoperiod decreased the p a n i c l e l e n g t h . 3. Number of s p i k e l e t s per p a n i c l e , s t e r i l i t y and g r a i n  weight Vergara and L i l i s (1966) found more s p i k e l e t s and increased s t e r i l i t y w i t h i n c r e a s i n g photoperiod c y c l e s . 21 Grain weight on the other hand decreased a f t e r 18 c y c l e s . Enyi (1963a) found p a n i c l e weight t o be higher i n 9-and 12-hour photoperiods compared to 7-or 14-hours. Misra (19 54b) found that p l a n t s i n 8-and 10-hour photoperiod had s i g n i f i c a n t l y fewer s p i k e l e t s and g r a i n per p a n i c l e but higher s t e r i l i t y than p l a n t s i n 24-hour photoperiod. Grain weight was higher i n p l a n t s grown i n short day. S i m i l a r trends were presented i n other papers by Misra (1955, 1956). Misra (1960b, 1962) found s t e r i l i t y i n r i c e to be dependent on v a r i e t y used but per cent s t e r i l i t y i n general was higher i n short days i n e a r l y v a r i e t i e s than i n l a t e . Short photoperiods i n general brought about a greater degree of s t e r i l i t y and long photoperiods a l e s s e r degree of s t e r i l i t y . Causes of s t e r i l i t y have not been studied i n r i c e . Recently, Moss and Heslop-Harrison (1968) showed th a t i n maize p o l l e n s t e r i l i t y increases w i t h short day treatment and there i s a tendency to sex r e v e r s a l . The e f f e c t i s purely photo-p e r i o d i c as the e f f e c t can be reversed by night i n t e r r u p t i o n by low i n t e n s i t y l i g h t . Nagai (1963) found high s t e r i l i t y i n r i c e i n short photoperiods but d i d not mention p o l l e n s t e r i l i t y although under high and low temperatures he found the cause of s t e r i l i t y t o be reduced percentage of normally developed p o l l e n g r a i n s . Temperature One of the most important f a c t o r s t h a t modify the photoperiodic response of p l a n t s i s temperature. The extreme 22 case i s found i n p l a n t s l i k e P h a r b i t i s which f l o w e r i n continuous l i g h t when given 16 hours of 5°C treatment or i n 8 hours photoperiod at 25°C. Lolium f a i l s t o f l o w e r even i n i n d u c t i v e photoperiod i f kept at 10°C. I t i s g e n e r a l l y b e l i e v e d that low temperature may s u b s t i t u t e f o r dark and high temperature f o r l i g h t periods (Best, 1959). E a r l i e r s t u d i e s i n r i c e were made by using d i f f e r e n t dates of p l a n t i n g . R e s u l t s thus obtained made a valuable c o n t r i b u t i o n t o understanding of temperature e f f e c t on various aspects of r i c e physiology but they lacked the p r e c i s i o n r e q u i r e d i n separating the temperature e f f e c t from photo-p e r i o d i c e f f e c t . A measure of c o n t r o l was obtained by using the greenhouse. S i r c a r and Sen (1953), Oka et a l . (1952), Manuel and Velasco (1957), Noguchi (1959), Noguchi and Kamata (1959), Oka (1958), Asakuma and Iwashita (1961), Venkataraman (1964), Cho (1963), Sasamura (1965), and Naqvi and Hamid (1965) used t h i s technique to study the e f f e c t of temperature and photoperiod. Flowering d u r a t i o n , l e a f emergence and y i e l d components were s t u d i e d . With the advent of growth cabinets more r i g i d manipulation of temperature was p o s s i b l e . Thus, Noguchi (1960) and Noguchi and Kamata (1965) found that both i n Norin No. 11 and Iburiwase f l o w e r i n g occurred i n 3 9 days at 30°C but 76 and 81 days r e s p e c t i v e l y at 20°C. When p l a n t s were t r a n s f e r r e d from high t o low temperature the f l o w e r i n g was delayed and v i c e versa. The r a t e of l e a f emergence was higher i n high 23 temperature. Noguchi (1960) and Noguchi and Kamata (1965) considered 15°C as the lowest l i m i t where f l o r a l i n i t i a t i o n can occur. Matsushima et al_. (1964, a and b) studied the combined e f f e c t s of a i r temperature and water temperature at d i f f e r e n t stages of growth. At e a r l y stages of p l a n t growth only water temperature had the e f f e c t i r r e s p e c t i v e of a i r temperature ( a i r temperature used was 16, 21, 31 and 36°C). Water temperature of 31°C had the most favourable e f f e c t on y i e l d followed by 21°C while 16°C had the most unfavourable e f f e c t . At a l a t e r stage a i r temperature a l s o became important and a combination of 31°C a i r and 21°C water temperature was most b e n e f i c i a l . The importance of water temperature at e a r l y stages was due to the f a c t t h a t the shoot apex of r i c e p l a n t s stays below or near the water surface. Number of t i l l e r s , p l a n t h e i g h t , number of leaves on the main culm, and sowing to heading i n t e r v a l were a l l a f f e c t e d by water temperature at the e a r l y stage. Grain y i e l d , number of s p i k e l e t s per p a n i c l e and per cent of ripened g r a i n was best i n 31°C water temperature. In a 12-hour photoperiod Vergara, Puranabhavung and L i l i s (1965) found a l l 16 v a r i e t i e s studied flowered e a r l i e r i n 3 0°C constant temperature than 2 5°C constant temperature. Highly photoperiod s e n s i t i v e v a r i e t i e s a l s o tended to be h i g h l y s e n s i t i v e t o temperature. F l u c t u a t i n g 24 day temperature (20 to 40 C) and constant nig h t temperature of 21°C proved best. Depending on v a r i e t y a r e d u c t i o n i n f l o w e r i n g time of 5 to 44 days was obtained. Nagai (1963) used three temperatures 21, 25 and 30°C and found maximum shortening of time t o f l o w e r i n g at 30°C. He studi e d f o r the f i r s t time the e f f e c t of d i u r n a l temperature f l u c t u a t i o n s under c o n t r o l l e d c o n d i t i o n s , the regime used was A. 25°C constant, B. 25° day and 20°C n i g h t , C. 30° day and 20°C night and 12 hour photoperiod. In two Japanese v a r i e t i e s FS5 and NR25, f l o w e r i n g occurred l a s t i n A then B and e a r l i e s t i n C; i n NR18, f l o w e r i n g occurred e a r l i e s t i n C and l a s t i n B; and i n Tetep, e a r l i e s t i n A and l a s t i n C. The only study found i n which a range of temperatures and photoperiods was used, was that of Roberts and Carpenter (1965). They used the temperature range of 35/25, 35/30, 40/30 and 35/35°C day and night and photoperiod of 8%, 10% and 11% hours. They found one v a r i e t y Kogbati 3 t o t a l l y i n s e n s i t i v e to temperature and photoperiod. Taichu 65, which i s considered to be photoperiod i n s e n s i t i v e i n the f i e l d , proved to be s e n s i t i v e at 35/20°C. U n l i k e other workers they b e l i e v e d t h a t higher temperatures cause delay i n f l o w e r i n g . At lower temperatures f l o w e r i n g occurred e a r l i e s t i n 8% hour photo-per i o d but at higher temperatures the tendency was t o flower e a r l i e r at 10% hours. Temperatures of 35/35°C day and night proved d e l e t e r i o u s i n every case except Kogbati 3. 25 Ormrod and Bunter (1961) and Herath and Ormrod (1965) studied the cold tolerance of r i c e v a r i e t i e s . Caloro and Bluebonnet were found to be the most low temperature tolerant v a r i e t i e s and 16°C was found to be minimum tolerated by them. Ef f e c t of Temperature During Ripening Period Delay i n heading, lower grain y i e l d due to fewer panicles per h i l l , fewer spikelets per panicle, lesser weight per 1000 kernels and lower percent mature grains, lower l e a f area index and accumulation of carbohydrates i n l e a f sheath and culm i s the c h a r a c t e r i s t i c of r i c e plant growing i n regions with cool climates. Rice plants •growing i n regions with warmer climate have opposite c h a r a c t e r i s t i c s (Kudo e_t a l . , 1966). Nagato et a l . (1961, 1966) and Nagato and Ebata (1965) studied the e f f e c t of high temperatures during the ripening period and found that high temperature accelerated the kernel development so much that the grain remained u n f i l l e d at 30°C. 100-grain weight was less and white-ridge and milky-white kernel increased. Best (1959) summarized the temperature e f f e c t thus: " I n i t i a t i o n was i n general accelerated e s p e c i a l l y at 27-29°C. A delay i n i n i t i a t i o n at lower temperature or higher temperature was often very marked. The temp-erature optimum tended to be higher i n long photoperiods and lower i n short photoperiods. Low temperature markedly retarded inflorescence development below 22 to 25°C, the panicle often f a i l e d to emerge. The temperature which accelerated inflorescence development most appeared to be of the order of 35 to 37°C.:; Katayama (1963) found the retarding e f f e c t of low night temperature remarkably stronger i n l a t e strains than i n early ones. On the other hand, the accelerating e f f e c t of high night temperature was stronger i n the early strains than the late ones. S o i l Conditions and Mineral Nutrit i o n Water logged conditions have been shown by Enyi (1963b) to hasten flowering compared to upland conditions. Both i n upland and lowland r i c e , a water logged condition f o r 4 weeks beginning 4 weeks a f t e r transplanting was best. Continuous i r r i g a t i o n with a high water l e v e l during early stages of growth depressed growth (Best, 1959). High P and K and low N were b e n e f i c i a l f o r early flowering (Enyi, 1963b). S p l i t application s i g n i f i c a n t l y reduced the number of days to flowering. Noguchi (1959) did not f i n d any e f f e c t of N, P or K but plots with N had more leaves at the time of flowering. S i m i l a r l y N, P, and K had no e f f e c t at low temperatures. Phosphorous accelerated heading and nitrogen alone delayed i t (Noguchi, 1959). Flowering took place i n 68, 69, 69, 71 and 67 days i n f e r t i l i z e r combinations of NPK, NPO, NOK, 000 and OPK respectively (0 represents zero l e v e l ) (Noguchi, 1959). In another experiment Noguchi and Kamata 27 (1959) obtained the figures for the above combination of f e r t i l i z e r s of 43, 44, 46, 44 and 43 days respectively. In the f i r s t study 0.5 gm each of the N, P, and K was used i n 2 l i t e r of s o i l and i n the second experiment 1 gm each of N, P, and K was used i n 3 l i t e r s of s o i l i n d i c a t i n g that either f e r t i l i z e r quantity or s o i l volume or both play a r o l e i n flowering. Perhaps s o i l volume i s more important as Pantastico (1961) found that 400 to 1,600 kg of ammonium sulphate per hectare had the same e f f e c t . Late applications of nitrogen delayed flowering but l a t e application of phosphate s l i g h t l y hastened i t (Pantastico, 1961). Noguchi et a l . (1965) studied the in t e r a c t i o n of photoperiod and n i t r a t e status and found that nitrogen d e f i c i e n t plants flowered e a r l i e r i n short days but under natural daylengths flowering was delayed i n both nitrogen d e f i c i e n t and nitrogen excess treatments. In 000 treatments flowering was delayed i n short days and prevented i n natural daylengths. Mechanism of Photoperiod Control Chailakhyan (1968) has recently reviewed i n d e t a i l the mechanism and theories explaining the flowering process. Searle (1965) i n a s i m i l a r a r t i c l e reviewed the biochemical aspect of flowering. Yoshida et a l . (1967) found a change i n nucleotide r a t i o i n m-RNA alone when induction has taken place. They have discussed other a r t i c l e s concerning the nucleic acid metabolism i n 28 p h o t o p e r i o d i c a l l y induced p l a n t s . They b e l i e v e that the f o l l o w i n g sequence occurs 1. Photoperiodic derepression of s p e c i f i c gene DNA ^ t r a n s c r i p t i o n to m-RNA > synthesis of enzyme p r o t e i n d i r e c t e d by RNA £ synthesis of f l o r a l stimulus with the a i d of an enzyme. They c a l l e d the m-RNA messenger RNA f o r f l o r a l stimulus enzyme (FS-RNA). The p o s s i b i l i t y that m-RNA may i t s e l f be the f l o r a l stimulus i s h i n t e d . There have not been many attempts to study the mechanism of f l o w e r i n g using r i c e as t e s t m a t e r i a l . Sen 14 (1964) fed CC>2 i n an attempt to determine the compound or compounds r e s p o n s i b l e f o r f l o w e r i n g ; he found no q u a l i t a t i v e change i n induced and non-induced p l a n t s . Induced p l a n t s always had la r g e q u a n t i t i e s of l a b e l e d compounds both i n leaves and shoot apices. He suggested th a t shoot apices may be the s i t e of synthesis of f l o r a l s t i m ulus. Inouye (196 5) found i n h i b i t i o n by 2 - t h i o u r a c i l and r e v e r s a l of i n h i b i t i o n by u r a c i l . M i t r a and Sen (1966) used i n h i b i t i o n of n u c l e i c a c i d synthesis and p r o t e i n synthesis to determine i f f l o w e r i n g i s i n h i b i t e d . Use of chloramphenicol, actinomycin D, p o r f i r o m y c i n , DNase and RNase, pepsin and t r y p s i n i n h i b i t e d f l o w e r i n g i n d i c a t i n g the involvement of n u c l e i c acids and p r o t e i n i n flower formation. Inouye (196 5) used Norin No. 15, a v a r i e t y t o t a l l y i n s e n s i t i v e to photoperiod, hence i t cannot be sa i d whether f l o r a l stimulus was blocked or the develop-mental process i t s e l f was i n h i b i t e d . Suge and Osada 29 (1967 a,b) studied the synthesis and t r a n s l o c a t i o n of f l o r a l stimulus and found that d e f o l i a t i o n of leaves immediately a f t e r i n d u c t i v e c y c l e i n h i b t e d f l o w e r i n g . The t r a n s l o c a t i o n of the stimulus was a l s o found to be temperature dependent, slower at 16°C than at 2 5°C. They a l s o found i n h i b i t i o n by 2 - t h i o u r a c i l and p a r t i a l r e v e r s a l by u r a c i l but i n h i b i t i o n induced by 8-azaguanine was n e a r l y completely reversed by guanine at any time during short day treatment. Suge (1968) found a s i g n i f i c a n t decrease i n growth i n h i b i t o r s i n methanol e x t r a c t of f r e s h p l a n t decreasing w i t h advancement of age or with short day treatment. Kurasava et a l . (1955) reported increase i n t o t a l carbohydrate, s t a r c h and sucrose both i n stem and l e a f sheath up t o 10 days a f t e r f l o w e r i n g . Murayama et a l . (195 5) reported a gradual increase i n c o n c e n t r a t i o n of s t a r c h i n l e a f sheath from the t i l l e r i n g stage to heading. Hasegawa and Nighikawa (19 57) found high sucrose content i n l e a f blade and l e a f sheath during v e g e t a t i v e growth, and a decrease i n sucrose content at f l o w e r i n g . Carbohydrates Grainger (1938, 1948, 1964) studied the r e l a t i o n s h i p between carbohydrate metabolism and f l o w e r i n g . In h i s 1964 r e p o r t he presents a d e t a i l e d study using 35 s t r a i n s belonging to 17 d i f f e r e n t species and came to the c o n c l u s i o n t h a t flower i n i t i a t i o n occurs i n no case unless a s u f f i c i e n t number of l e a f i n i t i a l s have developed and 30 a s u f f i c i e n t l y high value of the combined percent of t o t a l carbohydrate and ash occurs i n the shoot. Though amount of ash was important the carbohydrate was always the major partner. Tsybulko (1965) claimed almost the same response independently though Grainger's 19 3 8 work has been acknowledged. Another i n t e r e s t i n g f a c t i s brought by the study of Tsybulko (1962) who found that i n long day p l a n t s most of the t r a n s l o c a t i o n and accumulation occurs i n day time while i n short day p l a n t s most of t r a n s l o c a t i o n and accumulation occurs at n i g h t . Any s h i f t i n photoperiod upsets the p e r i o d of t r a n s l o c a t i o n thus a f f e c t i n g f l o w e r i n g . Sadik (1967) and Sadik and Ozbun (1968) found the accumulation of s t a r c h i n induced apices. Chemical a n a l y s i s revealed both s t a r c h and s o l u b l e carbohydrates to be higher i n induced p l a n t s . On suppressing the f l o w e r i n g a decrease i n carbohydrate l e v e l was n o t i c e d . Trione (1966) found high l e v e l s of carbohydrates i n wheat at the time of f l o w e r i n g . Yoshida and Ahn (196 8) studied the accumulation process of carbohydrates i n four v a r i e t i e s of r i c e though o b j e c t i v e of t h e i r study was not f l o w e r i n g . An a n a l y s i s of data i n d i c a t e s that i n each of the 4 v a r i e t i e s t e s t e d t o t a l carbohydrates reached optimum value at the time of f l o w e r i n g . This was true whether the experiment was conducted i n dry or wet season. Bowden et a l . (1968) d i d not f i n d any change i n carbohydrate content r i g h t up to anthesis i n orchard grass. Temperature and Carbohydrate Smith (1968) studied two temperature regimes: 18.5 day 10°C night and 29.5 day 21°C night and found g e n e r a l l y higher carbohydrates i n pla n t at low temperature. At high temperature no fr u c t o s a n accumulated whereas at low temperature very high accumulation of fructosans was found. Younger and Nudge (1968) studied the e f f e c t of temperature on three v a r i e t i e s of Poa and found highest c o n c e n t r a t i o n at two lowest temperatures (.16/7 and 18/13°C day/night) but both dry weight and numbers of shoots were highest i n two high temperatures (27/21, 27/16°C day/night). Even decreasing the s o i l temperature increased the carbohydrate content (Nowakowski et a l . , 1965). Alberda (1957) concluded that carbohydrate content was i n v e r s e l y r e l a t e d to night temperature and found d e f i n i t e c o r r e l a t i o n between the y i e l d i n dry weight of r o o t s , stubble and leaves and the amount of s o l u b l e carbohydrate i n these p a r t s . Auda et a l . (1966) found i n c r e a s i n g carbohydrate concen t r a t i o n w i t h i n c r e a s i n g l i g h t i n t e n s i t i e s , longer photoperiods and low temperatures. Eagles (1967) found higher water and a l c o h o l s o l u b l e carbohydrates at 5 and 10°C compared to 20 and 30°C. 32 PHOTOSYNTHESIS Crop y i e l d , whether i t i s i n the form of g r a i n , straw, or f r u i t represents i n the f i n a l a n a l y s i s the balance between photosynthesis and r e s p i r a t i o n . This balance can be a f f e c t e d by many f a c t o r s both g e n e t i c a l and environmental. The environmental f a c t o r s that a f f e c t the balance most are l i g h t , temperature and carbon d i o x i d e . The economic importance of photosynthesis i s i n i t s c o n t r i b u t i o n to the p l a n t parts used f o r food. In r i c e photosynthesis o c c u r r i n g from 10 days before heading to 30 days a f t e r heading c o n t r i b u t e s most to the developing g r a i n (Tanaka et a l . , 1966). Murata (196!+) c a l l s t h i s t h e " y i e l d production p e r i o d " , but the importance of photosynthesis i n e a r l i e r stages cannot be neglected as growth i t s e l f a f f e c t s photosynthesis. The r e l a t i o n s h i p photosynthesis > growth can b e t t e r be represented as photosynthesis ' growth (Sweet and Wareing, 1966). Growth Stages and Photosynthesis The stage at which photosynthesis i s measured i s very important, because i t has been shown i n r i c e that the photosynthetic r a t e at e a r l y stages i s very low but g r a d u a l l y increases to a peak, and then slowly d e c l i n e s (Tanaka et a l . , 1966; Tanaka and Yamaguchi, 1968; Takeda, 1961; Yamada, 1963; Murata, 1961). The r a t e shows i t s maximum at the stage when most a c t i v e t i l l e r i n g takes place 33 (Murata, 1961; Yamada, 1963). Tanaka et a l . (1966) found t h i s to be at the p a n i c l e i n i t i a t i o n stage. Yamada (196 3) found that the post peak photosynthetic depression i s greater i n l a t e v a r i e t i e s than i n e a r l y v a r i e t i e s . The depression c o i n c i d e s w i t h the mid-season depression of growth found i n these v a r i e t i e s . Some increase i n the photosynthetic a c t i v i t y was noted i n the r i p e n i n g stage i n the l a t e v a r i e t i e s (Murata, 1961; Yamada, 1963). Murata (1961) on the b a s i s of measurements of photosynthetic a c t i v i t y at d i f f e r e n t stages d i v i d e d v a r i e t i e s i n t o the f o l l o w i n g groups: 1. The v a r i e t i e s that maintain a r e l a t i v e l y high l e v e l of photosynthesis throughout the e n t i r e p eriod of growth. 2. The v a r i e t i e s that show a r e l a t i v e l y low l e v e l of photosynthetic a c t i v i t y throughout the whole growth p e r i o d . 3. The v a r i e t i e s whose photosynthetic a c t i v i t y i s high i n the e a r l y stage of growth but d e c l i n e s sharply i n the l a t e r stages. 4. The v a r i e t i e s whose photosynthetic a c t i v i t y though not very high i n the e a r l y stages of growth stays on a r e l a t i v e l y high l e v e l i n the l a t e r p e r i o d . Leaf M a t u r i t y Photosynthetic a b i l i t y of the r i c e l e a f i s low i n unexpanded stage, g r a d u a l l y increases as the l e a f expands 34 and reaches maximum i n the f u l l y expanded mature l e a f (2nd or 3rd l e a f from t o p ) . Thereafter the photosynthetic a c t i v i t y d e c l i n e s w i t h the aging of the l e a f and i n very o l d leaves assumes a negative value. The f l a g l e a f when f u l l y expanded has the highest photosynthetic a c t i v i t y (Murata, 1961j A k i t a et a l . , 1968; Tanaka et a l . , 1966). S i m i l a r trends have been shown i n other crop p l a n t s by Treharne et a l . (1968) and Forsyth and H a l l (1965). Morphological Changes and Photosynthesis Matsushima et a l . (1964) studied the e f f e c t of some morphological features on the r a t e of photosynthesis and found no d i f f e r e n c e under s u f f i c i e n t l i g h t between angle of incidence of l i g h t and photosynthesis, there was a s l i g h t lowering when l i g h t was p a r a l l e l t o l e a f blade. There was no d i f f e r e n c e i n r a t e of photosynthesis between obverse and reverse of l e a f blade. Curved l e a f blades had lower e f f i c i e n c y than s t r a i g h t l e a f blades. I f l e a f area i s equal p l a n t s w i t h short and more numerous leaves have higher photosynthetic e f f i c i e n c y than p l a n t s w i t h other types of leaves. Murata (1961) found a r e l a t i o n -ship between p l a n t h e i g h t , l e a f t hickness and photosynthetic a c t i v i t y . V a r i e t a l D i f f e r e n c e s E a r l y v a r i e t i e s g e n e r a l l y have the highest maximum population photosynthetic c a p a c i t y followed by medium and l a t e v a r i e t i e s i n t h a t order; the d u r a t i o n of 35 photosynthesis however i s longer i n l a t e v a r i e t i e s . The photosynthetic c a p a c i t y curve assumes a pyramidal shape wit h time i n e a r l y , p l a t e a u - l i k e i n l a t e and h y b r i d shape i n medium v a r i e t i e s (Murata, 1961; Osada and Murata, 1965a, 1965b; Hayashi, 1966, 1968; and Tanaka et a l . , 1966). D i u r n a l and Seasonal F l u c t u a t i o n s Murata and Iyama (1963a) studied the d i u r n a l f l u c t u a t i o n s i n photosynthesis i n I t a l i a n rye grass, orchard grass, l a d i n o c l o v e r , common vetch, b a r l e y and rye and found no f l u c t u a t i o n during the day. A s l i g h t f l u c t u a t i o n observed i n some cases was due to f l u c t u a t i o n i n CC^ con c e n t r a t i o n . Iyama et a l . (1964) i n 9 forage species studied d i d not f i n d any f l u c t u a t i o n during the day and i n some species photosynthetic r a t e was constant f o r 24 hour p e r i o d . Tanaka et_ a l . (1966) found a c l e a r cut d i f f e r e n c e i n rat e of photosynthesis i n v a r i e t i e s Peta and 81-B25 reaching peak at about noon. Ikenaga et a l . (1968) found seasonal v a r i a t i o n i n net a s s i m i l a t i o n r a t e s which was p a r a l l e l to the s o l a r r a d i a t i o n . He found an upward trend from l a t e A p r i l to l a t e May, a d i p i n June, however, the upward trend again continued i n J u l y reaching a peak i n l a t e J u l y , a f t e r which i t dropped r a p i d l y . Bamberg et a l . (1967) working with stone pine found a d e f i n i t e decrease i n photosynthetic c a p a c i t y throughout the winter even i n p l a n t s grown i n greenhouses. Gaastra (1962) reported s i m i l a r f l u c t u a t i o n s i n r i c e . 36 Environmental Factors  L i g h t L i g h t i s one of the most important environmental f a c t o r s governing photosynthesis. One of the reasons given f o r low production i n the t r o p i c s i s a l a c k of s o l a r r a d i a t i o n due to cloudy periods and short days. Murata (1961) found s a t u r a t i o n l i g h t i n t e n s i t y to range from 45 Klux to 60 Klux i n the v a r i e t i e s of r i c e which he stu d i e d . At 10 Klux photosynthetic r a t e compared t o r a t e at s a t u r a t i o n l i g h t i n t e n s i t y was 36% i n Norin No. 29 but 5 8% i n Zuiho and Bluerose i n d i c a t i n g v a r i e t a l d i f f e r e n c e s . The compensation values ranged between 500-1,000 lux (Yamada, 1963). Takeda (1961) a l s o obtained t h i s same f i g u r e i n p l a n t s 3 weeks a f t e r t r a n s p l a n t i n g under community c o n d i t i o n s but u n l i k e detached leaves the photosynthesis s a t u r a t i o n point completely disappeared even under f u l l s u n l i g h t c o n d i t i o n s (100 Klux) at about the p a n i c l e formation stage. Ormrod (1961) working w i t h Caloro d i d not get s a t u r a t i o n point even at 8,000 foo t candle (85, Klux) i n 3% and 5 week o l d p l a n t s . The compensation poi n t v a r i e d w i t h temperature; at 40°F (4°C) i t was 15 0 f o o t candles, (1.6 Klux) at 60°F (15.5°C) 400, (4.2 Klux) and at 80°F (26.5°C) 1400 f o o t candles (14.8 K l u x ) . The values f o r net a s s i m i l a t i o n r a t e increase w i t h l i g h t i n t e n s i t y r i g h t up to f u l l s u n l i g h t . The 37 higher the net a s s i m i l a t i o n at f u l l s u n l i g h t the steeper the decrease i n net a s s i m i l a t i o n r a t e w i t h decrease i n l i g h t i n t e n s i t y (Hayashi, 1968). A k i t a et a l . (1968) worked w i t h i n d i v i d u a l leaves from p l a n t s of d i f f e r e n t age and derived an equation which describes the r e l a t i o n -ship of photosynthesis to l i g h t i n t e n s i t y at high l i g h t i n t e n s i t i e s , that i s above 10 Klux. Murata et a l . (196 8) d e r i v e d an equation to c a l c u l a t e the e f f i c i e n c y of s o l a r energy conversion to dry matter i n r i c e . Tanaka et a l . (1966) found that s a t u r a t i o n l i g h t i n t e n s i t y was l e s s f o r lower, than upper leaves. They a l s o found t h a t second to f o u r t h leaves account f o r most of the l e a f area of the population hence they can be taken as r e p r e s e n t i n g the trend of the population a c c o r d i n g l y , they found a s a t u r a t i o n l i g h t i n t e n s i t y of 5 0 Klux and a -2 -1 maximum c a p a c i t y of about 17 mg CC^/dm /hr . Ormrod (1964) reported a compensation l i g h t i n t e n s i t y of 3000 foot candles (31.8 Klux) f o r bean and even at 12,000 foot candles (127 K l u x ) s a t u r a t i o n p o i n t was not reached. The species t h a t have the highest r a t e of photosynthesis a l s o have a higher l i g h t s a t u r a t i o n p o i n t (corn sorghum and sugar cane) than the ones wi t h lower r a t e of photosynthesis (Gaastra, 1959; Moss, 1967). Moss (1967) gave the example of a s e r i e s of 4 s p e c i e s , corn, sunflower, tobacco and dogwood. Tobacco i s r e p r e s e n t a t i v e of a l a r g e m a j o r i t y of crop p l a n t s w i t h r a t e s of 38 photosynthesis 1/3 to 1/2 that of corn and reach the s a t u r a t i o n point at about 1/3 f u l l s u n l i g h t . D i f f e r e n c e s between species as lar g e as t h i s cannot be explained on the ba s i s of l i g h t i n t e r c e p t i n g a b i l i t y , t hat i s , c h l o r o p h y l l content and l e a f t h i c k n e s s . At low l i g h t i n t e n s i t y the r e l a t i o n between photosynthesis and l i g h t i n t e n s i t y i s l i n e a r . With f u r t h e r increase i n l i g h t i n t e n s i t y photosynthesis increases 4 l e s s r a p i d l y u n t i l f i n a l l y at about 10 x 10 ergs - 1 - 2 sec cm complete l i g h t s a t u r a t i o n i s reached. CC^ conc e n t r a t i o n s t r o n g l y a f f e c t s the r a t e of s a t u r a t i o n ; at s a t u r a t i o n l i g h t and CC^ concentration temperature a f f e c t s photosynthesis i n d i c a t i n g photochemical, d i f f u s i o n and biochemical processes t o be l i m i t i n g i n f i r s t , second and t h i r d case (Gaastra, 1959, 1962). Although the e f f e c t of l i g h t i n t e n s i t y has been the subject of many c r i t i c a l s t u d i e s , the e f f e c t of l i g h t d u r a t i o n has not been studied very c r i t i c a l l y . El-Sharkaway et a l . (1965) and Elmore et a l . (1967) reported 50 to 80% increase i n photosynthesis i n cotton grown i n summer compared t o tha t grown i n winter i n g l a s s houses, w i t h n a t u r a l photoperiod. Bamberg e_t al_, (1967) studied the e f f e c t of n a t u r a l , 12 and 8 hour photoperiod and found no d i f f e r e n c e i n stone pine. The absence of photoperiod e f f e c t may be due to temperature e f f e c t as the v a r i e t y i s adapted to low temperature (maximum recorded temperature 39 was about 12°C). Hesketh (1968) studied photosynthesis under d i f f e r e n t l i g h t and temperature c o n d i t i o n s but because the l i g h t p e r i o d was 16 hours i n each case the s p e c i f i c l i g h t p e r i o d e f f e c t could not be determined. Temperature The e f f e c t of temperature on photosynthesis has long been the subject of i n t e n s i v e study. The e a r l i e s t paper quoted by Rabinowitch (1956) i s that of Boussaugault which was published i n 1874. Rabinowitch (1956) has reviewed the s t a t e of knowledge up to 19 5 4. Since then many more st u d i e s have been made embodying new ideas and concepts, but e s s e n t i a l l y confirming the e a r l i e r f i n d i n g s . Photosynthesis combines sequences of photo-chemical, p h y s i c a l and biochemical processes. Although the d i r e c t e f f e c t of temperature on photosynthesis concerns only the biochemical aspects temperature i s i n d i r e c t l y i n v o l v e d i n a l l three processes and a c c o r d i n g l y the shape of the temperature curve w i l l vary according to the co n d i t i o n s i n which the experiment i s performed. Both l i g h t i n t e n s i t y and CO^ supply w i l l have e f f e c t s on the curve. The f o l l o w i n g c o n d i t i o n s can be obtained and w i l l have the e f f e c t s noted as explained. 1. When there i s weak l i g h t and adequate CO^ supply the o v e r a l l r a t e of photosynthesis i s p r a c t i c a l l y equal to that of primary photochemical r e a c t i o n . 40 2. When the supply of CO^ i s low, the temperature c o e f f i c i e n t may be e s s e n t i a l l y t h a t of supply processes and the Q^g may be 1.2 t o 1.3. 3. When the l i g h t and CC^ concentrations are not l i m i t i n g , the e f f i c i e n c y w i l l be determined by non-photochemical processes and the Q ^ Q may reach or exceed 2. The work of Emerson and Green (19 34) and more r e c e n t l y of Gaastra (1965) and Ormrod et a l . (1968) and the comprehensive work of Chmora and Oya (1967) confirm the above view. With atmospheric C0 2 and using short periods Murata (1961) d i d not f i n d any d i f f e r e n c e i n r a t e s of photosynthesis between 2 0 and 3 3°C. The Q^g was found to be a constant 1.1 between 18 and 30°C. The r a t e decreased below 2 0°C and very sharply above 40°C. Yamada (1963) found a longer range i n Norin 3 6 and Rikuu 132. Between 18°C t o 35°C there was no d i f f e r e n c e and Q^g was I . This r e l a t i o n s h i p was v a l i d at a l l seasons and growth stages. Ormrod (1961) d i d not f i n d s i m i l a r r e s u l t s at 1000 foot candles (10.6 Klux) photosynthesis increased from 40° to 60°F (4.4 to 15.5°C) but d e c l i n e d to the compensation poi n t at 80°F (26.5°C). At 3000 and 6000 foot candles (31.8 and 63.6 Klux) photosynthesis was higher at 80°F (26.5°C)compared to 40°F (4.4°C) but s t i l l 41 lower than 60°F (15.5°C) which i s contrary to the f i n d i n g s of Murata (1961) and Yamada (1963). Murata and Iyama (1968) and Murata et a l . (1965) stud i e d the e f f e c t of temperature on photosynthesis on l a r g e number of forage crops between the temperatures of 0 to 140oC. Depending upon the response they c l a s s i f i e d the species studied i n t o 6 groups. Group I , I I and I I I were c h a r a c t e r i z e d by low optimum temperatures f o r photo-synthesis (16-20°C). Group I I I had the broadest plateau f o r temperature optimum followed by group I I and I . Group I contained common vetch , group I I b a r l e y , naked b a r l e y , wheat, r y e , I t a l i a n rye grass, p e r e n n i a l rye grass and group I I I orchard grass, l a d i n o c l o v e r and a l f a l f a . Group I to I I I belonged t o so c a l l e d Northern type p l a n t s . Group IV to VI showed a high temperature optimum f o r photosynthesis (20-40°C). Those belonging to IV and VI had a broad plateau f o r temperature optimum. Group IV contained sudan grass, d a l l i s grass, new sergo maize group V bahia grass, bermuda grass and rhodes grass and group VI barnyard grass. El-Sharkawy and Hesketh (1964) studied c o t t o n , sorghum, sunflower and Thespesia; Ormrod et a l . (196 8) 12 v a r i e t i e s of b a r l e y ; Eagles (1967), Lolium perenne Wilson (1966), rape, sunflower and maize; and Forsyth and H a l l (1965), lowbush blueberry. In a l l these cases a c h a r a c t e r i s t i c s i n g l e peaked temperature response curve 42 was obtained. The d i f f e r e n c e s i n peaks and p o s i t i o n of optima are obvious. These data can a l l be f i t t e d i n t o one of the s i x c a t e g o r i e s of c l a s s i f i c a t i o n of the Murata et a l . (1965) P h o t o r e s p i r a t i o n One of the problems inherent i n a l l these s t u d i e s i s the e f f e c t of temperature on r e s p i r a t i o n simultaneously w i t h the e f f e c t on photosynthesis. I t has been the p r a c t i c e to assume that r e s p i r a t i o n i n l i g h t i s not d i f f e r e n t from th a t i n dark thus tr u e photosynthesis was obtained by adding the values of C0 2 evolved i n the dark to CO^ taken up i n l i g h t . F o r r e s t e r et_ a l . (1966a, 1966b) and Tregunna et a l . (1961, 1964, 1966) have shown that dark r e s p i r a t i o n i s d i f f e r e n t from r e s p i r a t i o n i n l i g h t ( p h o t o r e s p i r a t i o n ) and p h o t o r e s p i r a t i o n may be higher by s e v e r a l orders of magnitude compared to dark r e s p i r a t i o n . Moss (1966) and Decker (1954) found s i m i l a r evidence. Z e l i t c h (1966) while studying the e f f e c t of g l y c o l a t e oxidase i n h i b i t i o n on photosynthesis found t h a t i n c r e a s i n g temperature g r e a t l y increases the compensation point i n tobacco i n d i c a t i n g greater r e s p i r a t i o n i n l i g h t . Moss (196 8) has confirmed part of Z e l i t c h ! s r e s u l t s . I f c o r r e c t i o n s f o r p h o t o r e s p i r a t i o n of the magnitude given i n Z e l i t c h ' s paper are a p p l i e d then Q ^ Q f o r photosynthesis becomes 2 i n tobacco between 25 and 3 5°C i n c o n t r a s t to an a c t u a l value of 0.86, without the c o r r e c t i o n s . 43 To avoid problems of r e s p i r a t i o n a s s o c i a t e d w i t h i n t a c t p l a n t s Baldry et a l . (1966) studied the temperature e f f e c t on photosynthesis i n i s o l a t e d c h l o r o p l a s t s . They found i n pea c h l o r o p l a s t s a Q^g f o r photosynthesis as high as 9 between the temperature 0 to 6°C reaching the lowest f i g u r e of 1.28 between 25-30°C. Chernov et a l . (1967) using spinach and pea c h l o r o p l a s t s found decreases i n photosynthesis at high temperatures. The high temperatures of 40 and 45°C were too high t o make any v a l i d comparisons. T a r c h e v s k i i (1964) studied the biochemical aspects of photosynthesis and found t h a t as the temperature increased from 15 to 45°C organic phosphates decreased from 25.8 to 3.2,glycine decreased from 10.1 to 0.2 on the other hand there was a tremendous increase i n alanin e from 1.1 t o 57.0. (Figures f o r concentration are i n per cent r a d i o a c t i v i t y i n an aqueous a l c o h o l f r a c t i o n . ) Thermo Adaptation Murata and Iyama (1963b) found the d i f f e r e n c e s i n summer and winter grown p e r e n n i a l ryegrass and orchard grass, w i n t e r grown seedlings being more r e s i s t a n t to low temperature and l e s s to high temperature. Murata e_t a l . (1965) grew the p l a n t s f o r 10 days at 25, 20 and 15°C before measuring photosynthesis and could not f i n d any change. Ten days was perhaps too short a per i o d f o r any adaptive measures to take e f f e c t . Treharne et a l . (1968) found t h a t orchard grass grows at 21°C and measured at 44 29°C had higher photosynthetic r a t e than at 21°C while p l a n t s grown at 2 9°C and measured at 21°C had lower r a t e s of photosynthesis. Hesketh (1968) studied the e f f e c t s of l i g h t and temperature during p l a n t growth on subsequent l e a f a s s i m i l a t i o n , he found no e f f e c t of temperature of growth on l e a f photosynthesis at 3 0°C i n T r i t i c u m  aestivum, Phaseolus v u l g a r i s , and Amaranthus p a l m e r i , but i n Zea mays, Helianthus annuus and Gossypium hersutum photosynthesis was a f f e c t e d by season and temperature of growth. COg Concentration The e f f e c t of CO2 has been demonstrated by Emerson and Green (1934), Gaastra (1959, 1965), Murata (1961), Yamada (1963) and Chmora and Oya (1967). T h e i r f i n d i n g s are e s s e n t i a l l y the same and are best demonstrated by the work of Chmora and Oya (1967). The e f f e c t of l i g h t i n t e n s i t y increases w i t h the increase i n CO2 conce n t r a t i o n and increases the e f f e c t of temperature. M i n e r a l N u t r i t i o n and S o i l Conditions Iyama and Murata (1961) and Murata et a l . (1966) stud i e d the e f f e c t of s o i l water on various crop species and found a v a r y i n g r e l a t i o n s h i p between s o i l water and photosynthesis; i n r i c e a s o i l water l e v e l below 55% of the f i e l d c a p a c i t y decreased photosynthesis. They c l a s s i f i e d r i c e as very weak as regards r e s i s t a n c e t o s o i l water s t r e s s . 45 In maize Sestak and V a c l a v i k (1965) found a c o r r e l a t i o n between s o i l water, photosynthesis and c h l o r o p h y l l content. At.30% s o i l water photosynthesis was badly a f f e c t e d but i t was maximum at 60% at e a r l y stages and at 90% at l a t e r stages. Nitrogen seems to be one element that has been studi e d i n d e t a i l (Takeda, 1961; Murata, 1961; Osada and Murata, 1965a, 1965b; and tanaka and Yamaguchi, 1968). The a p p l i c a t i o n of n i t r o g e n brought about a considerable increase i n photosynthesis regardless of the time of a p p l i c a t i o n , but the e f f e c t decreases as the time of a p p l i c a t i o n i s advanced. In general responsive v a r i e t i e s have shown greater increase i n photosynthesis than non responsive v a r i e t i e s . E a r l y maturing v a r i e t i e s tended to have higher photosynthetic a c t i v i t y than l a t e maturing v a r i e t i e s . Takeda (1961, Murata (1961) and Osada and Murata (1965b) found a s i g n i f i c a n t c o r r e l a t i o n between n i t r o g e n content of the l e a f and photosynthetic a c t i v i t y of the p l a n t . As n i t r o g e n content increased the photosynthetic a c t i v i t y i n creased. Fujiwara and Tsutsumi (1962) stud i e d the e f f e c t of microelement d e f i c i e n c y on the r a t e s of photosynthesis, and the lowest photosynthesis was obtained i n Mn d e f i c i e n t p l a n t s followed by Zn, Fe and Cu. 46 Photosynthesis and Dry Matter Production To the p r a c t i c a l a g r i c u l t u r i s t y i e l d i n g c a p a c i t y of a v a r i e t y i s more important than a l l the d i f f e r e n t processes which go i n t o the production. As a l l the dry matter comes from the process of photosynthesis attempts have been made from time to time to determine the r e l a t i o n -ship between photosynthesis and various other characters of the p l a n t . Takeda (1961), Murata (1961), Yamada (1963) and Osada and Murata (1965a, 1965b) studied the various aspects of dry matter production. Takeda (1961) developed a formula which r e l a t e s photosynthesis and dry matter production. Under favourable c o n d i t i o n s dry matter production i s determined mainly by photosynthetic a c t i v i t y ; under unfavourable c o n d i t i o n s i t i s determined by r e s p i r a t i o n . In e a r l y stages dry matter production i s determined mainly by l e a f area index but w i t h advancement of age dry matter production became sma l l e r . As the l e a f area index increases mutual shading becomes pronounced and f i e l d photosynthetic a b i l i t y a t t a i n s a p l a t e a u . On the other hand, r e s p i r a t i o n increases w i t h the increase i n weight thus the r e l a t i o n between dry matter production and t o t a l l e a f area becomes curved. Yamada (196 3) assumed that dry matter production has a simple r e l a t i o n s h i p to t o t a l photosynthetic production of a p l a n t population per u n i t f i e l d area and t o t a l r e s p i r a t i o n of the p l a n t population. 47 From h i s work he concluded that i n e a r l y stages dry matter production depends on l e a f area. The r e s p i r a t i o n component becomes dominant i n the l a t t e r part of the growth p e r i o d . Conditions which are favourable f o r dry matter production i n the e a r l y p e r i o d are not always b e n e f i c i a l f o r dry matter production i n the l a t t e r part of the growth p e r i o d . The f i n d i n g s are s i m i l a r to those of Takeda (1961), Murata (1961) i n v e s t i g a t e d i n d e t a i l a l l the d i f f e r e n t f a c t o r s mentioned above and t h e i r c o n t r i b u t i o n i n dry matter production. He used the concept of net a s s i m i l a t i o n r a t e (N.A.R.) as has Tanaka et a l . (1966). In place of W Murata (19 61) c a l c u l a t e d NAR from t h i s formula W9 - W, l o g e A 9 - l o g e A, N A R = ' _ 1 x 1 _ ± t2 r i A2 A l where and W2 and A^ and are the p l a n t weight and l e a f area at time t ^ and r e s p e c t i v e l y . This i s a l s o the i n d i r e c t way of e s t i m a t i n g true photosynthesis. Radford (1967) has cautioned t h a t the formula i s v a l i d only when the r e l a t i o n s h i p between the t o t a l dry weight and l e a f area i s l i n e a r between t ^ and t 2 -Tanaka and Yamaguchi (19 68) studied the growth e f f i c i e n c y of r i c e p l a n t s , that i s , the r e l a t i o n s h i p between dry weight and r e s p i r a t i o n . The e f f i c i e n c y was about 60% at a very e a r l y stage f o r seedlings growing i n the dark but at the b o o t i n g - f l o w e r i n g stage i t went down to 40.8, at f l o w e r i n g - m i l k stage to 36.1 and at milk stage-harvest 48 26.6%. The f i g u r e s were lower i n the case of a high l e v e l of n i t r o g e n . In a l l cases mentioned above except NAR the r e s p i r a t o r y component i s taken as that of dark r e s p i r a t i o n . We know now tha t i t i s not true because i n many p l a n t s r e s p i r a t i o n i n the l i g h t may be zero while i n others i t may be s e v e r a l times higher hence i n a l l the above formulae a c o r r e c t i o n w i l l have t o be made f o r p h o t o r e s p i r a t i o n . 49 CHLOROPHYLL AND CAROTENOIDS The high c h l o r o p h y l l content of h i g h l y productive p l a n t i s considered by Anderson (1967) t o be concomitant of an e f f i c i e n t canopy f o r r a d i a t i o n i n t e r c e p t i o n r a t h e r than a necessary c o n d i t i o n f o r high production i n i t s e l f . This c o n c l u s i o n was drawn from t h e o r e t i c a l c o n s i d e r a t i o n s of the v a r i a b l e s i n v o l v e d . Gabrielsen (1948), a f t e r studying the r e l a t i o n s h i p between photosynthesis and c h l o r o p h y l l content, considered c h l o r o p h y l l as a "weak l i g h t f a c t o r " because i t has greatest e f f e c t on r a t e of photo-synthesis i n weak l i g h t i n t e n s i t i e s . C h l o r o p h y l l and Carotenoid Content C h l o r o p h y l l c o n c e n t r a t i o n vary so much not only between species but w i t h i n species that any u n q u a l i f i e d f i g u r e may not be meaningful. N u t r i e n t s t a t u s , stage of development and environmental f a c t o r s a l l a f f e c t the c h l o r o p h y l l content. Goto et al_. (195 2a) and Katayama and Shida (1956, 1961) reported the c h l o r o p h y l l content i n r i c e . Goto et a l . (1952a) found the range of 4.88 mg per gram f r e s h weight to 1.12 mg, depending upon the stage of development. Nitrogen top d r e s s i n g always increased t h i s q u a n t i t i y . The carotenoid content on mg per gram f r e s h weight b a s i s v a r i e d from 1.49 to 0.59 (Goto ejt a l . , 195 2b). Katayama and Shida (1956, 1961) using chromato-graphic techniques studied 95 s t r a i n s i n c l u d i n g 14 lowland, 50 7 upland, 18 s p e c i a l r i c e , 8 p o l y p l o i d s , 32 c h l o r o p h y l l anomalies, 11 f o r e i g n and 5 w i l d species. They found g e n e r a l l y low pigment content i n e a r l y r i p e n i n g v a r i e t i e s . C h l o r o p h y l l a was g e n e r a l l y higher i n lowland r i c e and c h l o r o p h y l l b i n upland, p l o i d y d i d not have any e f f e c t on pigment content and f o r e i g n s t r a i n s g e n e r a l l y had low pigment content. The anomalous s t r a i n s d i d not show much d i f f e r e n c e . Gautam (1962) reported on c h l o r o p h y l l content i n wheat; S m i l l i e and Krotkov (19 61) i n pea; Gej (1966) i n bean, white mustard, buck wheat and sunflower; Radunz (1966) i n Antirrhinum ma j u s ; Shulgin e_t a l . (1962) and Oelke and Andrew (1966) i n corn; and Wada (1968) i n tobacco. One t h i n g t h a t i s c l e a r from these i n v e s t i g a t i o n s i s t h a t c h l o r o p h y l l content v a r i e s w i t h the development of the p l a n t . The p l a n t s t a r t s w i t h low content, g r a d u a l l y b u i l d s up, then d e c l i n e s again. The content a l s o v a r i e s w i t h l e a f p o s i t i o n and the season. Sestak and Catsky (1967) have summarized the f i n d i n g s of various workers concerning c h l o r o p h y l l content. F a l u d i - D a n i e l et a l . (1968) studied the r a t i o of c h l o r o p h y l l a t o c h l o r o p h y l l b and found d i f f e r e n t r a t i o s under d i f f e r e n t l i g h t i n t e n s i t i e s . The t a b u l a t e d f i n d i n g s of other workers i n d i c a t e s that whereas, i n normal p l a n t s the r a t i o may vary from 1.4 ( i n maize) to 4.1 ( i n tomato) } the r a t i o i n mutants v a r i e s from 1.2 ( i n maize) to 2 3.8 51 ( i n b a r l e y ) . According to F a l u d i - D a n i e l et a l . (1968) the absence of c h l o r o p h y l l b i s not accompanied by l e t h a l i t y , but p l a n t s with no or extremely low b content e x h i b i t a reduced growth r a t e , bear fewer seeds, and have abnormal carbohydrate metabolism. E f f e c t of Daylength L i g h t I n t e n s i t y and Temperature The increase i n c h l o r o p h y l l and carotenoid content a f t e r f l o r a l i n d u c t i o n both i n short and long day p l a n t s i s not because these pigments are i n v o l v e d i n the mechanism of f l o w e r i n g but i s due to the general increase i n the t o t a l a c t i v i t y of the p l a n t (Chailakhyan and Bavrina, 1957). They studied the e f f e c t of short day (10 hours) and long day (16-18 hours) on the short day p l a n t s : m i l l e t , p e r i l l a and soybean; the long day p l a n t s : o a t s , rudbeckia and wheat; and the intermediate p l a n t s , tomato and bean. They found t h a t i n short day p l a n t s , i n short day both c h l o r o p h y l l and carotenoid content were higher than when grown i n long day, while i n long day p l a n t s pigment content was higher i n long day compared to short day. S u r p r i s i n g l y , i n tomato the pigment content was higher i n short day and i n bean i n long day. Tomato acts l i k e a short day p l a n t , i n that i t flowers 2 to 4 days e a r l i e r i n short days and bean acts l i k e a long day p l a n t , i n that i t flowers 2 to 3 days e a r l i e r i n long day, which may e x p l a i n the photo-p e r i o d i c e f f e c t on these species. Friend (1961), working 52 w i t h Marquis wheat, found a s i m i l a r long day response. Wolf (1964) used Seneca wheat v a r i e t y and sma l l e r photo-pe r i o d i n t e r v a l s . The r e s u l t s were s i m i l a r but u n l i k e Friend's optimum of 24-hour photoperiod they found maximum c h l o r o p h y l l content at 20-hour photoperiod. Another v a r i a t i o n from Friend's r e s u l t s was a greater r a t i o of c h l o r o p h y l l a to c h l o r o p h y l l b i n photoperiods s h o r t e r than 8 hours. Bavrina (1966) studied the e f f e c t of daylength on the s t a b i l i t y of the c h l o r o p h y l l - p r o t e i n - l i p i d complex and found that long day pl a n t s had a more s t a b l e complex i n long day compared to short day and the reverse was true i n short day p l a n t s : day-neutral p l a n t s behaved as i f they were e i t h e r short-day or long-day p l a n t s . He concluded that c o n d i t i o n s favourable f o r blooming lead to strengthening of the bond of c h l o r o p h y l l to l i p o p r o t e i n . I t seems that c h l o r o p h y l l a i s l e s s f i r m l y bound than c h l o r o p h y l l b as under unfavourable c o n d i t i o n s more a i s e x t r a c t a b l e by pe t r o l i u m ether than b. The p o s s i b i l i t y t h a t c h l o r o p h y l l synthesis i s under the c o n t r o l of the phytochrome system has been stu d i e d by many workers, e s p e c i a l l y the e f f e c t of red, f a r - r e d l i g h t ( P r i c e and K l e i n , 1961; Mitrakos, 1961; Withrow et a l . , 1956). Recently Kasperbauer and H i a t t (1966) working wi t h two i s o g e n i c l i n e s of tobacco found that at the end of the photoperiodic treatment a f i v e minute 53 exposure to red l i g h t increased the c h l o r o p h y l l content compared to 5 minutes exposure t o f a r - r e d ; a f a r - r e d exposure followed by 5 minutes of red r e s t o r e d the balance. They warned th a t i n growth chambers having separate c o n t r o l f o r f l u o r e s c e n t and incandescent l i g h t e r r o r can be introduced should one ki n d of lamp shut o f f before the other. With i n c r e a s i n g l i g h t i n t e n s i t y the concentration of c h l o r o p h y l l increases ( F a l u d i - D a n i e l et a l . , 1968). D i u r n a l f l u c t u a t i o n s i n c h l o r o p h y l l content have been observed by many workers. Bukatsch and Rudolph (196 3) confirmed t h i s f i n d i n g but found that i t i s very c l e a r l y shown i n young growing leaves but disappears as the l e a f becomes o l d . McWilliam and Naylor (1967) studied the i n t e r -a c t i o n of temperature and l i g h t i n the synthesis of c h l o r o -p h y l l and found t h a t i n corn at low temperature c h l o r o p h y l l content was l e s s than at high temperature. The e f f e c t of low temperature became severe with the i n c r e a s i n g l i g h t i n t e n s i t y . They considered the photobleaching to be due to r e d u c t i o n i n r a t e of p r o t o - c h l o r o p h y l l i d e s y n t h e s i s . In wheat, Friend (1961) d i d not f i n d such a temperature e f f e c t . 20°C constant or 2 0°C day and 10°C nigh t had the same e f f e c t i n d i c a t i n g that low temperature has no e f f e c t i n wheat which one should expect as wheat i s a temperate crop and corn t r o p i c a l . Barley s e e d l i n g s , when cooled 54 to 3 C, had increased c h l o r o p h y l l and carotenoid synthesis (Godnev and Shabel ?Skaya,(1964). Treharne et a l . (1968) di d not f i n d any change i n c h l o r o p h y l l content i n two s t r a i n s but i n the t h i r d s t r a i n c h l o r o p h y l l was 2 5% higher at 29/21°C day and night temperature compared to 21/13°C day and night temperature. C h l o r o p h y l l and Photosynthesis Because c h l o r o p h y l l i s the primary receptor of l i g h t energy i t seems l o g i c a l to expect some r e l a t i o n s h i p between c h l o r o p h y l l content and photosynthesis. Attempts have been made from time to time to show t h i s r e l a t i o n s h i p but w i t h c o n f l i c t i n g r e s u l t s . The f i r s t c r i t i c a l study was tha t of Gabrielsen (1948), who not only r e c a l c u l a t e d and r e i n t e r p r e t e d the work of e a r l i e r i n v e s t i g a t o r s but performed h i s own experiments w i t h 10 species of Populus, Ulmus, Sambacus, A t r i p l e x and T r i t i c u m . His co n c l u s i o n was th a t the c o r r e l a t i o n i s v a l i d only i n weak l i g h t . Gaastra (1962) agreed w i t h the f i n d i n g s . In r i c e , Murata (1961) found a high c o r r e l a t i o n between c h l o r o p h y l l content and photosynthesis but he concluded t h a t the c o r r e l a t i o n was apparent r a t h e r than r e a l as under high l i g h t i n t e n s i t y the l i g h t r e a c t i o n could not be l i m i t i n g . Yamada (196 3) found a s i m i l a r c o r r e l a t i o n . In both cases there was a p a r a l l e l c o r r e l a t i o n between p r o t e i n N content and photosynthesis. I t was not resolved i n these s t u d i e s whether increase i n p r o t e i n N was due to 55 an increase i n c h l o r o p h y l l or increase i n c h l o r o p h y l l was , due to an increase i n n i t r o g e n ; Treharne et a l . (196 8) i n orchard grass, and Wada (196 8) i n tobacco found a p a r a l l e l between photosynthesis and c h l o r o p h y l l content. Sestak and Catsky (1962), Sestak (1963, 1966), Sestak and V a c l a v i k (1965) and Sestak and Catsky (1967) studied the r e l a t i o n s h i p i n some d e t a i l i n tobacco, fodder cabbage, sugar beet and maize. They claimed a p o s i t i v e c o r r e l a t i o n between photosynthesis and c h l o r o p h y l l content. They b e l i e v e d t h a t the f a i l u r e of others to f i n d a c o r r e l a t i o n between c h l o r o p h y l l content and photosynthesis was due to f a i l u r e i n choosing s u i t a b l e c o n d i t i o n s , f a i l u r e t o take i n t o c o n s i d e r a t i o n ontogenetic age of the leaves or using extreme l e a f types (mutants or p l a n t s c u l t i v a t e d under abnormal n u t r i t i v e c o n d i d t i o n s ) . They conclude t h a t the l i n e a r expression i s l i m i t e d by the inherent p r o p e r t i e s of the p l a n t as w e l l as by the s e l e c t i o n of experimental procedure. Depending upon c o n d i t i o n s of experiment they 2 found that at c h l o r o p h y l l concentrations of 0.5 to 2.5 mg dm, apparent photosynthesis became zero. He c a l l e d t h i s c o n c e n t r a t i o n the " c h l o r o p h y l l compensation p o i n t " . Dry Matter Production and C h l o r o p h y l l Brougham (1960) stud i e d s e v e r a l v a r i e t i e s of dicotyledons and monocotyledons and found a h i g h l y 56 s i g n i f i c a n t c o r r e l a t i o n ( r = 0.912) between maximum growth ra t e s and amount of c h l o r o p h y l l per u n i t area of land. Oelke and Andrew (1966) on the other hand d i d not f i n d any c o r r e l a t i o n between c h l o r o p h y l l content and ethanol s o l u b l e sugars, crude p r o t e i n , dry weight and ear weight. J a k r l o v a (1967) found i n a meadow community a c o r r e l a t i o n between c h l o r o p h y l l content and dry matter production. P i l a t (1967) found s i m i l a r c o r r e l a t i o n s i n four out of f i v e species t h a t he stu d i e d . Bray (1960) compared various pl a n t communites and found a c o r r e l a t i o n between c h l o r o p h y l l and t h e i r p r o d u c t i v i t y . M i n e r a l N u t r i t i o n and S o i l Conditions Both i r o n and manganese d e f i c i e n c y depress c h l o r o p h y l l formation; manganese excess has a s i m i l a r e f f e c t . Agarwala et a l . (1964), P r i c e and C a r e l l (1964) b e l i e v e t h a t there i s an absolute requirement f o r Fe f o r c h l o r o p h y l l s y n t h e s i s . From t h e i r experiments they concluded that i r o n r e q u i r e d f o r growth i s associated w i t h s i t e s that are d i f f e r e n t from ones that are re q u i r e d f o r c h l o r o p h y l l s y n t h e s i s . Benedict et a l . (1964) found i n t e r a c t i o n between sources of i r o n and photoperiod. In long day i n soybeans both FeNH^SO^^ and FeNTA ( f e r r i c n i t r i t e t r i a c e t a t e ) were e q u a l l y e f f e c t i v e but i n short day i n the presence of FeNH^SO^^ c h l o r o p h y l l c o n c e n t r a t i o n was l e s s than i n FeNTA. Fujiwara and Tsutsumi (1962) studied the e f f e c t of microelement d e f i c i e n c y and found greatest depression i n 57 c h l o r o p h y l l content i n Fe d e f i c i e n t p l a n t s followed by Zn, Mn and Cu, but the greatest depression i n photosynthesis was found i n Zn d e f i c i e n t p l a n t s , followed by Mn,Cu and Fe. 58 MATERIAL AND METHODS Varieti e s Four v a r i e t i e s of r i c e (Oryza sativa L.) were used; three belonged to subspecies i n d i c a and one to subspecies japonica. The choice of v a r i e t i e s was a r b i t r a r y , but the four v a r i e t i e s are grown i n two broad geographical and three cl i m a t i c regions. Vari e t i e s Kangni-27 (Kangni) and Dokribasmati (Dokri) are grown i n southern Pakistan between lat i t u d e 24°-30°N and are indica type, they mature early and are believed to be photoperiod non-sensitive. Bluebonnet-50 (Bluebonnet) which i s another indica type variety i s mainly grown i n Southern United States, between 28° and 36°N. It i s a midseason variety and matures from 137 to 149 days a f t e r seeding. Being of recent o r i g i n (1950) there i s not much published work on t h i s v a r i e t y . Caloro was the only japonica type included i n t h i s study. It i s grown mainly i n C a l i f o r n i a between 36° - 40°N. It i s a midseason variety and i s photoperiod s e n s i t i v e . The two v a r i e t i e s , Kangni and Dokri were obtained through the courtesy of the Rice Botanist, Rice Research Station, Dokri, Pakistan. Bluebonnet and Caloro were obtained through the courtesy of the Research Agronomists, Rice Research Station, Beaumont, Texas, and Rice Research Station, Biggs, C a l i f o r n i a , respectively. Some of the c h a r a c t e r i s t i c s of the v a r i e t i e s used are given i n Table 1. TABLE 1 Some Charac t e r i s t i c Features of Variet i e s Used i n the Experiments Varieties Characters Kangni Caloro Dokri Bluebonnet Subspecies indica japonica indica indica Photoperiodic s e n s i t i v i t y non-sensitive sensitive non-sensitive non-sensitive No. of days to flower 97 A 106 J' M 97 N 85 A 114 J 140B No. of days to maturity 120 A 155 D 105 A 137 H Length of ear head, cm23.6A 22* — — No. of spikelet per panicle 150 A — • -- 133 B % s t e r i l i t y 13. 9 A 14. 2 B 2 8.9A 22.8 B 100-grain weight, g 2.44A 2.8 J M 2.95 1 2.01 A 2.5 J R 2.68 A = A.J. Miah, personal communication J = T.H. Johnston, personal communication M = J . J . Mastenbroeck, personal communication H = Agriculture Handbook No. 289 U.S.D.A. 1966 D = L.L. Davis (1950) B = E.E. Boerema and D.J. McDonald (1965) N = M.'Y. Nuttonson (1965) 60 Growth Cabinets The growth cabinets used were the same as described by Ormrod (1962) wi t h s l i g h t m o d i f i c a t i o n . Each growth room contained four growth cabinets and each cabinet had an independent exhaust fan located i n the center j u s t above the l i g h t tubes. The cone type heaters were replaced by 750-watts A l l s t a t e car heaters (Simpsons-Sears L t d . ) . The cabinet height was extended to 5 f e e t 8 inches. Twelve l i f e l i n e S y l v a n i a F40CW RFL tubes were used as the l i g h t sources. In a d d i t i o n s i x 25-watt incandescent lamps were d i s t r i b u t e d along the center of the cabinet. The l i g h t i n t e n s i t y as measured wi t h Gossen Tri-Lux Foot Candle Meter (P. Gossen and Co. GMBH Ercangen West Germany) was 1400 foot candles (14.8 Klux) at the surface of the pot. The l i g h t i n t e n s i t y at p l a n t l e v e l increased as the p l a n t increased i n height. Where low night temperatures were used, the same time switch operated both the l i g h t s and temperature c o n t r o l s . In the case of high night temperatures, separate time switches were used to operate l i g h t s and heaters. Photoperiod and Temperature Photoperiods s e l e c t e d were 8, 10, 12 and 14 hours. I t i s c l e a r from the l i t e r a t u r e that t h i s range encompasses the optimum photoperiod i n most cases, and a l s o provides a s h o r t e r than optimum (8 hours) and a longer than optimum photoperiod (14 hours). The l i g h t used was f u l l i n t e n s i t y 61 i r r e s p e c t i v e of photoperiod. There i s a c e r t a i n amount of controversy as to s p e c i f i c , and n o n - s p e c i f i c e f f e c t of photoperiod. As characters have been included i n the present study which are s p e c i f i c a l l y a f f e c t e d by l i g h t i n t e n s i t y (growth and photosynthesis) i t was thought advisable to use f u l l l i g h t i n t e n s i t y r a t h e r than i n d u c t i v e l i g h t i n t e n s i t y . Temperatures s e l e c t e d were 35/18, 35/26.5, 35/35 and 40.5/18°C day/night. C u l t u r a l P r a c t i c e s Seeds v i s u a l l y s e l e c t e d f o r u n i f o r m i t y of s i z e were soaked i n 1 per cent v/v commercial bleach s o l u t i o n (Perfex) f o r 16 hours i n P e t r i dishes. A f t e r the completion of t h i s treatment the seeds were thoroughly washed i n running tap water. Seeds thus t r e a t e d and washed were allowed to germinate i n p e t r i dishes at 35/26.5°C day and nigh t temperature and 12-hour photoperiod. At one week a f t e r soaking, s e e d l i n g height v a r i e d from 2 to 4 cm depending upon v a r i e t y . The s h o r t e s t seedlings were of Bluebonnet and t a l l e s t of Kangni 27. Six uniform seedlings were t r a n s p l a n t e d i n t o each 6 - l i t e r p l a s t i c pot c o n t a i n i n g 4.7 kg of steam-treated garden s o i l . Immediately a f t e r t r a n s p l a n t i n g , the pots were t r a n s f e r r e d t o growth cabinets maintained at the des i r e d temperatures and photoperiods. Each treatment had three r e p l i c a t e s , and w i t h i n each cabinet the pots were completely 62 randomized. At the end of each week the pots were r o t a t e d to minimize the e f f e c t of the s l i g h t temperature, and l i g h t gradient w i t h i n each cabinet. The r o t a t i o n was c a r r i e d out so that at the end of the 4th week the i n i t i a l completely randomized p o s i t i o n was obtained. The same procedure was followed f o r the next 4 weeks. The r o t a t i o n continued up to the time of heading a f t e r which i t was stopped due to d i f f i c u l t y i n moving the pots. The pots were kept saturated w i t h water but unflooded up t o the end of the f o u r t h week a f t e r which a l l pots were flooded w i t h tap water, and kept flooded u n t i l harvest. In winter the tap water was mixed with hot water to b r i n g the water temperature t o about 16°C. At the end of 3 weeks p l a n t s i n each pot were thinned to 4 and at the end of 5 weeks one more p l a n t was taken out. This l e f t the 3 most uniform p l a n t s i n each pot f o r f u r t h e r study. Leaf Number and T i l l e r s The number of leaves developed were observed at 2, 3, 5, 7 and 9 week i n t e r v a l s . At each observation date the l a s t developed l e a f was marked by a s p l i t - r u b b e r band cut from rubber tu b i n g . This helped i n keeping the record of l e a f number f o r subsequent counting. The number of t i l l e r s developed was a l s o counted. 63 Flowering The date of emergence of the p a n i c l e from the l e a f sheath was taken as the date of f l o w e r i n g ; i n each pot only the main shoot of each of the p l a n t s was observed. The number of days t o f l o w e r i n g was c a l c u l a t e d as the average f o r the 3 pl a n t s of the number of days from soaking to f l o w e r i n g . P a n i c l e s from each pot were harvested at maturity. The length of the p a n i c l e was measured from the base of the c i l i a t e r i n g ( j u n c t i o n of peduncle and i n f l o r e s c e n c e ) t o the highest seed. The t o t a l number of p a n i c l e s per pot was a l s o recorded. For each p a n i c l e the number of s p i k e l e t s was counted and the average f o r a l l p a n i c l e s i n a pot was c a l c u l a t e d . S i m i l a r l y the number of f i l l e d s p i k e l e t s was a l s o recorded. Percent s t e r i l i t y was c a l c u l a t e d from the f o l l o w i n g r e l a t i o n s h i p a ^+^1-1 •+„ _ -,nn [""total number of f i l l e d s p i k e l e t s " ! , n n -5 s t e r i l i t y = 100 - , , , r- E n—v-rr x 100 J [_ t o t a l number of s p i k e l e t s J 10 0-grain weight was taken f o r s e v e r a l l o t s of seeds and average recorded. In some cases the t o t a l number of seeds was l e s s than 100. In such case 100-grain.weight was c a l c u l a t e d from the weight of a v a i l a b l e number of seeds. A f t e r removal of the p a n i c l e the straw was d r i e d i n a forced d r a f t oven at 80°C f o r 7 days and dry weight i n grams recorded. 64 Photosynthesis A separate s e r i e s of experiments were e s t a b l i s h e d t o measure photosynthesis and other c h a r a c t e r i s t i c s of the r i c e v a r i e t i e s used. The temperature and photoperiods were the same as was the technique of growing the p l a n t s but i n t h i s case the 6 seedlings were t r a n s p l a n t e d i n t o 1 - l i t e r p l a s t i c pots c o n t a i n i n g 1 kg of steam-treated garden s o i l . Observations were taken at 2, 4, 6 and 8 week i n t e r v a l s . As the sampling was d e s t r u c t i v e each cabinet contained 48 pots f o r 4 harvest dates 4 v a r i e t i e s and 3 r e p l i c a t e s . The pots were arranged completely randomly and were r o t a t e d a f t e r one week, then at a l t e r n a t e weeks. A f t e r each harvest the remaining pots were rerandomized to u t i l i z e the space created due to removal of 12 pots. Before the measurement of photosynthesis, dry, and dead leaves were removed from each pot, and one pl a n t was randomly removed f o r c h l o r o p h y l l and carotenoid determination. Photosynthesis was measured i n a Blue M Vapor-Temp c o n t r o l l e d R e l a t i v e Humidity Chamber (Model VP-400 AT, Blue M E l e c t r i c Co., Blue I s l a n d , 111., 60406)(Figure 1). The arrangement of the system and the i n f r a r e d gas analyzer was the same as described by Ormrod and Woolley (1966). Photosynthesis measurements were taken at the day temperature i n which p l a n t s were growing. R e l a t i v e humidity was maintained at 76% ( w i t h i n the accuracy of the wet and dry 65 Figure 1. The c o n t r o l l e d environment chamber i n use f o r net exchange st u d i e s w i t h r i c e . The p l a n t s are sealed i n the g l a s s chamber and an a i r stream i s passed continuously through the i n t r a r e d analyzer. L i g h t s are mounted on the Dexion frame. A r e f l e c t i v e surface i s placed around the outside of the glas s chamber. 66 bulb thermometers). Photosynthesis was allowed to proceed w i t h i n the range of 30 ppm C0 2 above and 30 ppm C0 2 below the ambient C0 2 c o n c e n t r a t i o n . The l i g h t i n t e n s i t y was maintained by means of a bank of 6 S y l v a n i a very high output c o o l white f l u o r e s c e n t tubes g i v i n g a l i g h t i n t e n s i t y of 3,8 00 foot candles (40.3 Klux) at the upper surface of the gla s s p l a n t chamber and 800 foot candles (8.5 Klux) at the base. To avoid e r r o r due to p o s s i b l e d i u r n a l v a r i a t i o n i n photosynthesis w i t h i n the v a r i e t y i t s e l f the sequence of v a r i e t i e s used f o r photosynthesis measurements was kept constant thus Kangni was always used f i r s t f ollowed by C a l o r o . i n the morning period and Dokri followed by Bluebonnet i n the afternoon. For each r e p l i c a t e d u p l i c a t e measurements were taken except when p l a n t s from s h o r t e r photoperiods and young p l a n t s w i t h slow C0 2 exchange r a t e s d i d not allo w d u p l i c a t e measurements to be taken because of i n s u f f i c i e n t time. In such cases only one measurement was taken. A f t e r completion of the whole set of measurements p l a n t s were harvested at ground l e v e l and t h e i r t o t a l f r e s h weights and sheath and l e a f weights i n grams were recorded. P l a n t height i n cm was measured f o r each of the 5 p l a n t s from the base of the sheath t o the highest juncture of the lamina and sheath. This measurement a c t u a l l y gave the height of the sheath r a t h e r than stem, as the stem i n 67 r i c e does not s t a r t developing u n t i l j u s t p r i o r to f l o r a l i n i t i a t i o n . The bulked p l a n t m a t e r i a l was d r i e d i n a forced d r a f t oven at 80°C f o r 7 days and dry weight recorded. E a r l i e r attempts to measure l e a f blade area proved f u t i l e as leaves of Dokri and Bluebonnet r o l l e d before they could be imprinted on O z a l i d paper. Midway i n the experiment an a i r flow planimeter (Paten I n d u s t r i e s PTY L t d . , 1 Dashwood Road, Beaumont, S. Hust.) was i n s t a l l e d so l e a f blade area was a l s o measured i n the remaining experiments. A computer programme was w r i t t e n f o r the various v a r i a b l e s measured. I t c a l c u l a t e d the net photosynthesis per pot i n mg CO^ per hour a l s o mg CC^ per gram dry weight, per gram f r e s h weight, and per gram f r e s h weight l e a f blade per hour. When area was a v a i l a b l e CC^ uptake was a l s o c a l c u l a t e d i n mg CC^ per square decimeter l e a f blade area per hour. C o n t r i b u t i o n of CO^ by root and s o i l was a l s o measured. A f t e r h a r v e s t i n g the p l a n t the pot was placed i n the chamber, CO2 from the chamber was absorbed i n A s c a r i t e t o b r i n g the CC^ c o n c e n t r a t i o n t o 30 ppm below the ambient, a f t e r which the system was c l o s e d . C o n t r i b u t i o n of l e a f sheath was a l s o measured a f t e r removing the l e a f blades. S u r p r i s i n g l y there was no measurable CC^ e v o l u t i o n from the pots. This may be due t o waterlogged c o n d i t i o n s . S i m i l a r l y there was no measurable C0_ uptake by the l e a f 68 sheath; so the c o r r e c t i o n f o r these f a c t o r s was deemed unnecessary. Net a s s i m i l a t i o n r a t e (NAR) was c a l c u l a t e d from the formula given by Murata (1961) W ' - W, l o g e A 9 - l o g e A, NAR = 1 _ 1 x ^ — s i T2 T l A 2 A l where , W2 , A^ and are the pl a n t weight and l e a f area at time t ^ and t2» As area f o r a l l 4 harvests and a l l 4 temperatures was a v a i l a b l e only f o r 8 and 12 hour photo-p e r i o d . NAR i s reported f o r these two photoperiods only. Pigment A n a l y s i s C h l o r o p h y l l a, c h l o r o p h y l l b and t o t a l carotenoids were determined on one p l a n t removed randomly at the time of photosynthesis measurement. A l l the leaves were cut from the pl a n t at the juncture of sheath and lamina and the leaves thus obtained were cut i n t o small pieces and weighed. The cut pieces were ground i n a c h i l l e d mortar i n the presence of sand and a small amount of CaCOg. Cold 80% acetone was added to f a c i l i t a t e g r i n d i n g . F i n a l l y pigments were taken up i n t o c o l d 80% acetone and decanted i n t o a c e n t r i f u g e tube. This procedure was repeated u n t i l no c o l o u r was l e f t i n the mortar. The e x t r a c t was c e n t r i f u g e d f o r 5 minutes at 2000 r.p.m., wi t h the supernatant decanted c a r e f u l l y i n t o a 150 ml volumetric f l a s k and made up to volume wi t h c o l d 80% acetone. 69 O p t i c a l d e n s i t y was measured at 663, 645 and 440.5 ml i n a Beckman DU Spectrophotometer. In the case of very dense s o l u t i o n s f u r t h e r d i l u t i o n s were made. C h l o r o p h y l l a and b were determined by using the s p e c i f i c absorption c o e f f i c i e n t s of McKinney (1940) and the formula of Maclachalan and Z a l i k (196 3) Ca - ( 1 2 - 3 D 6 6 3 - 0.86D 6 t | 5)V d x 1000 x W (19.3D C I | [- - 3.6D c c o)V _ 645 663 d x 1000 x W where C = con c e n t r a t i o n i n mg/g f r e s h weight a = c h l o r o p h y l l a b = c h l o r o p h y l l b D = o p t i c a l d e n s i t y at wave length i n d i c a t e d d = length of l i g h t path i n cm V = f i n a l volume of e x t r a c t i n ml W = f r e s h weight of l e a f m a t e r i a l used i n g The con c e n t r a t i o n of carotenoids was determined by the equation given by Von Wettstein (1957) Cc = 4.695D 4 I + Q 5 - 0 . 268C (a + b) where C =. con c e n t r a t i o n of carotenoids i n mg per l i t e r . 70 T o t a l Soluble Carbohydrates About 3 00 to 5 00 mg of oven d r i e d sample ground to pass 40 mesh was suspended i n 300 ml of d i s t i l l e d water i n a round bottom f l a s k and r e f l u x e d f o r 2 hours. The e x t r a c t was f i l t e r e d and the residue washed wi t h hot d i s t i l l e d water i n t o a 5 00 ml volumetric f l a s k and made to volume wi t h d i s t i l l e d water. T o t a l s o l u b l e carbohydrate was determined by the s u l p h u r i c a c i d o r c i n o l method as given by M i l l e r et al_. (1960) using glucose as standard. T o t a l Ash T o t a l ash was determined by the method of Jackson (1964) at 550°C. Ashing was continued overnight. Repeated ashing and c o o l i n g d i d not show any change i n weight so samples were ashed overnight only. S t a t i s t i c a l A n a l y s i s S t a t i s t i c a l analyses were performed on the b a s i s of 4 x 4 x 4 x 3 (temperatures, photoperiod, v a r i e t y and r e p l i c a t e ) f a c t o r i a l experiments arranged i n a completely randomized design. S i g n i f i c a n t d i f f e r e n c e s between means were deter-mined using Duncan's new m u l t i p l e range t e s t . Unless other-wise noted the 1% s i g n i f i c a n c e l e v e l was used. I f s i g n i f i c a n t second order i n t e r a c t i o n s (T x P x V) were found, the data showing them are presented, otherwise, data i n d i c a t i n g s i g n i f i c a n t f i r s t order i n t e r a c t i o n s are given. Main e f f e c t s are a l s o presented i n the t a b l e s . 71 RESULTS General Observations A general view of the r i c e plants i n the growth cabinets i s shown i n Figure 2a and 2b (14 hour photo-period photographed at 8 weeks). The general e f f e c t of temperature was e a s i l y noted. At 35/35 day and night temperature, Caloro was severely affected, and showed symptoms of ch l o r o s i s , and death of emerging leaves. Bluebonnet showed sim i l a r symptoms, but to a lesser extent. The death of lower leaves and yellowing of f o l i a g e was prominent i n a l l v a r i e t i e s at 35/35 and 35/26.5 temperature regimes, whereas at 35/18 and 40.5/18 temperatures leaves were a darker green colour and the lower leaves did not s t a r t senescing u n t i l l ate i n the growing period. Differences i n growth and development were apparent between a l l the v a r i e t i e s i n the 4 temperatures and 8 and 14 hour photoperiods (Figures 3a, 3b, 3c, 3d). Flowering The number of days from soaking to flowering i s given i n Table 2. Because a l l the v a r i e t i e s flowered i n a l l photoperiods only at 35/18 and 35/26.5 s t a t i s t i c a l analysis was only performed on data from these two temperatures. For the r e s t , the standard error i s reported. 72 gure 2a. A general view of the r i c e p l a n t s i n the growth cabinets at 8 weeks a f t e r t r a n s p l a n t i n g 14-hour photoperiod. 0, 35/18 and N, 35/26.5°C. Figure 2b. A general view of the r i c e p l a n t s i n the growth cabinets at 8 weeks a f t e r t r a n s p l a n t i n g 14-hour photoperiod. M, 35/35 and P, 40.5/18°C. V a r i e t y C a l o r o a t 2 5 days. Top l U - h o u r and bottom 8-hour p h o t o o e r i o d . 1. 35/35 2. 3 5 / ? 3. 35/18 4. un.5/18 d a y / n i g h t temperature F i g . 3 c . V a r i e t y D o k r i a t 2 5 d a y s . Top 1 4 - h o u r and b o t t o m 8-hour p h o t o p e r i o d . 1 . 3 5 / 3 5 2 . 35/21" . f 3. 35/18 4. 40.5/18 d a y / n i g h t t e m p e r a t u r e . F i g . 3d. V a r i e t y Bluebonnet a t 2 5 days. Top l n - h o u r and bottom 8-hour p h o t o p e r i o d . 1. 35/35 2. 3 5/26.5 3. 35/18 4. 40.5/18 d a y / n i g h t t e m p e r a t u r e . 78 TABLE 2 The E f f e c t of Photoperiod and Temperature on Number of Days from Soaking to Heading i n 4 V a r i e t i e s of Rice Temperature Photo- V a r i e t i e s °C period Kangni Caloro Dokri Bluebonnet hr 35/18 8 8 8.3b* 132 .2a 9 3.7ab 172.7a 10 89 .4b 100 .5b 90.3ab 163.4ab 12 89 .4b 80 .2ef 82.4bc 151.5c 14 111.4a 94 .Ibc 88.4abc 153.Obc 35/26.5 8 80.6b 83 . 4ce 85.4bc 119.6d 10 80 .2b 67 •2g 78.4c 101.6e 12 83.3b 69 • Ofg 85.6bc 109.7de 14 113.0a 97 .3b 99. 0a 164.3ab 35/35 8 10 12 14 112.8(1.8) 107 (1.1) 86.6(2.7) 128.5(0.7) 106.8(5.2) 114 (9) 103.8(7.3) 40.5/18 10 12 14 78.5(3 . 6) 112 . 6(17.6) 97.4(2.9) 158 (3 .6) 92.2(4.1) 105 (1.2)96.4(10.7) 144.3(5.1) 98 . 8(3 .7) 83 .2(9 . 2)100 . 8(3 . 6) 126.6(1.1) Temperature oc# 35/18 111.3a 35/26.5 35/35 40.5/18 94.8b 109.8(13.7) 107.8(21.9) Photoperiod hr# 8 107.0b 10 96.3c 12 93 .9c 14 115.0a V a r i e t i e s ^ Kangni 91.9b Caloro 90.5b Dokri 87.9b Bluebonnet 142,0a * Means i n the same column sharing the same l e t t e r d i d not d i f f e r s i g n i f i c a n t l y according to Duncan's New M u l t i p l e Range Test at the 1% l e v e l . Unless otherwise noted the 1% l e v e l was used i n a l l s t a t i s t i c a l analyses. + Standard e r r o r i n brackets # Main e f f e c t s f o r temperature, photoperiod and v a r i e t i e s . Means i n the same row•sharing the same l e t t e r d i d not d i f f e r s i g n i f i c a n t l y . 79 35/35 proved t o be the most d e l e t e r i o u s f o r f l o w e r -i n g . At t h i s temperature a l l v a r i e t i e s f a i l e d to flower w i t h i n the d u r a t i o n of the experiment (2 00 days) at 8-hour photoperiod and, except f o r D o k r i , v a r i e t i e s d i d not flower at 14-hour photoperiod. Caloro was most s e n s i t i v e and f a i l e d to flower at a l l photoperiods. S i m i l a r l y at 40.5/18 a l l v a r i e t i e s f a i l e d to flower i n a 14-hour photoperiod. In both these temperature regimes even where f l o w e r i n g took p l a c e , the s p i k e l e t s were malformed and c h l o r o t i c i n most cases. Of the two temperatures 35/18 and 35/26.5, f l o w e r i n g was delayed at 35/18 at 8-, 10- and 12-hour photoperiods. The l e a s t a f f e c t e d v a r i e t y was Kangni; although f l o w e r i n g was delayed at 14-hour photoperiod. Caloro flowered l a s t at 8 hour photoperiod at 35/18 but i t flowered e a r l i e s t at 35/26.5 at 10-hour photoperiod. In Bluebonnet, f l o w e r i n g was delayed at temperature 35/18 i n a l l photoperiods but the e f f e c t decreased with i n c r e a s i n g photoperiod. At 35/2 6.5 both very short and very long photoperiods delayed f l o w e r i n g . Y i e l d Determining Characters  Dry Weight Greatest dry weight accumulation occurred at 14-hour photoperiod followed by 12-, 10- and 8-hour photo-periods (Table 3). At temperatures of 35/35 and 40.5/18 dry matter production was s i g n i f i c a n t l y higher than at 80 TABLE 3 The E f f e c t of Photoperiod and Temperature on Dry Matter (g) Produced Per Pot (3 P l a n t s ) by 4 V a r i e t i e s of Rice at the F i n a l Harvest Temperature Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/18 35/26.5 35/35 40.5/18 32.0c 35 . 0c 55.2a 41.6b 28 . l b 16 .4c 9. Id 33.7a 27.7c 34.6b 56. 0a 33 .7b 29.2a 20.7b 14.9c 28.8a o, Temperature C 35/18 35/26.5 35/35 40.5/18 29.3b 26.7b 33.8a 34.5a Photoperiod hr 8 23.7d 10 28.4c 12 33 . l b 14 39. 0a V a r i e t i e s Kangni Caloro Dokri 40.0a 21.8b 38.0a Bluebonnet 2 3.4b For footnotes see Table 2 81 35/18 and 35/25.5. Both Kangni and Dokri produced highest dry matter at 35/35 whereas Caloro and Bluebonnet produced lowest dry matter at that temperature. Kangni and Dokri produced s i g n i f i c a n t l y greater dry matter than Caloro and Bluebonnet. Number of P a n i c l e s Per Pot There was no d i f f e r e n c e i n number of p a n i c l e s at 3 5/18 and 35/26.5 (Table 4). The number of p a n i c l e s produced by p l a n t s which d i d head at 35/35 and 40.5/18 seemed a l s o t o be n o n - s i g n i f i c a n t . The e f f e c t of photoperiod was a l s o not pronounced. The 14-hour photoperiod r e s u l t e d i n s i g n i f i c a n t l y more p a n i c l e s than the 12-hour. Kangni, Caloro, and Dokri had a s i g n i f i c a n t l y l a r g e r number of p a n i c l e s than Bluebonnet. Bluebonnet was unaffected by 2 temperatures and 4 photoperiods. P a n i c l e Length There was no e f f e c t of temperature on length of p a n i c l e s (Table 5). Optimum photoperiod f o r length of p a n i c l e was 12-hours followed by 14 hours. Dokri had the longest p a n i c l e and Caloro s h o r t e s t . For Kangni the photoperiod f o s t e r i n g maximum length was 12 hours, f o r Caloro 10, 12, and 14 hours, f o r Dokri 8, 12, and 14 hours, and f o r Bluebonnet 12 hours. Number of S p i k e l e t s Per P a n i c l e Temperature d i d not a f f e c t the number of s p i k e l e t s (Table 6). S i g n i f i c a n t l y higher numbers of s p i k e l e t s were 82 TABLE 4 The E f f e c t of Photoperiod and Temperature on the Number of P a n i c l e s Per Pot i n 4 V a r i e t i e s of Rice Photo- V a r i e t i e s ^ Temperature pe r i o d Kangni Caloro Dokri Bluebonnet oc hr 35/18 8 15.3a 10.6ab 8.0ab 7.0a 10 9.3ab 8.0ab 14.6a 7.3a 12 8.3b 9.0ab 8.0ab 6.0a 14 12.0ab 13.3a 13.6ab 6.3a 35/26.5 8 12.3ab 5.6b 13.3ab 6.3a 10 9.6ab 10.6ab 8.6ab 5.6a 12 8.3b 8.0ab 7.6b 6.0a 14 15.6a 8.0ab 14.3ab 6.0a Temperature °C 35/18 35/26.5 35/35 40.5/18 9.8a 9.1a 8.7(5.5) 10.6(6.5) Photoperiod hr 8 10 12 14 9.8ab 9.2ab 7.6b 11.1a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 11.3a 9.1a 11.0a 6.3b For footnotes see Table 2. 83 TABLE 5 The E f f e c t of Photoperiod and Temperature on the Length of P a n i c l e (cm) i n 4 V a r i e t i e s of Rice V a r i e t i e s Photoperiod Kangni Caloro Dokri Bluebonnet hr 8 20.4b 15-3b 26.5a 20.1b 10 20.4b 17.9a 25 .0b 21.9b 12 23.5a 17.9a 28.1a 27 . 0a 14 22.2ab 19 .2a 27.0ab 21.2b Temperature °C 35/18 35/26.5 35/35 40.5/18 22.3a 22.0a 21.4(5.2) 20.3(4.3) Photoperiod hr 8 10 12 14 20.6c 21.3bc 24.1a 22 .4b V a r i e t y Kangni Caloro Dokri Bluebonnet 21.6b 17.6c 26.7a 22.6b For footnotes see Table 2 84 TABLE 6 The E f f e c t of Photoperiod and Temperature on the Number of S p i k e l e t s Per P a n i c l e i n 4 V a r i e t i e s of Rice Photoperiod hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 8 44.2b 40 ,6a 61.4a 54.6c 10 64.3ab 61.6a 52.7a 96.0b 12 6 5.3 ab 59 . 8a 77.1a 129.3a 14 74.5a 60 .6a 57.8a 40.6c Temperature °C 35/18 35/26.5 35/35 40.5/18 64.7a 65.3a 53.9(30.9) 65.8(22.2 Photoperiod hr 8 10 12 14 50.2c 68.6ab 82.9a 58.4bc V a r i e t y Kangni Caloro Dokri Bluebonnet 62.lab 5 5.6b 62.3ab 80.1a For footnotes see Table 2 85 found at a 12-hour photoperiod compared to 8- and 14-hour photoperiods. Bluebonnet had the highest number of s p i k e l e t s per p a n i c l e but was not s i g n i f i c a n t l y d i f f e r e n t from Kangni and D o k r i . Number of s p i k e l e t s was not a f f e c t e d by photoperiod i n Caloro and Dokri whereas i n Bluebonnet, 12-hour had the highest number of s p i k e l e t s . In Kangni the l a r g e s t number of s p i k e l e t s was i n 14-hour but t h i s was not s i g n i f i c a n t l y d i f f e r e n t from 10- and 12-hour photo-periods . S t e r i l i t y Temperature regimes of 35/18 and 35/26.5 d i d not s i g n i f i c a n t l y d i f f e r i n t h e i r a f f e c t on s t e r i l i t y (Table 7). Highest s t e r i l i t y was found i n p l a n t s at 35/35 followed by 40.5/18 p l a n t s i n both these temperatures were c h a r a c t e r i z e d by high s t e r i l i t y i n a l l photoperiods and i n many cases there was 100% s t e r i l i t y . There was an e f f e c t of photo-p e r i o d ; p l a n t growing i n both long and short photoperiods having greater s t e r i l i t y . Bluebonnet had greater s t e r i l i t y than Kangni, Caloro or D o k r i . At 35/18 the e f f e c t of short photoperiod on s t e r i l i t y was l e s s i n Kangni, Caloro and D o k r i . In Bluebonnet at 8-hour photoperiod there was s i g n i f i c a n t l y more s t e r i l i t y at 35/18 than at 35/26.5 100-Grain Weight 100-grain weight was not s i g n i f i c a n t l y a f f e c t e d by temperature at 35/18 or 35/26.5 (Table 8). 35/35 and 86 TABLE 7 The E f f e c t of Photoperiod and Temperature on Percent S t e r i l i t y i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C pe r i o d hr 35/18 8 16.3bcd* 9. 5c 28.8bc 90. 5a 10 16.6bcd 19.8bc 51.2a 45 .9c 12 18.5bcd 21.5bc 20.2c 68.6b 14 26.6abc 18.1bc 57.4a 87.1a 35/26.5 8 29.3ab 30.4ab 46.0a 48.2c 10 6. 2d 21.9bc 15.9c 37.8c 12 10.4cd 32.5ab 18.8c 45.8c 14 36.7a U5.8a 43.lab 85 .0a Temperature °C 35/18 35/26.5 35/35 40.5/18 37.3a 34.6a 95.3(9.2) 68.7(27.7) Photoperiod hr 8 10 12 14 37.4b 26.9c 29.5c 50.0a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 20.1c 24.9c 35.2b 63.6a * S i g n i f i c a n t at 5% l e v e l . For footnotes see Table 2. 87 TABLE 8 The E f f e c t of Photoperiod and Temperature on 100-Grain Weight (g) i n 4 Var i e t i e s of Rice Photoperiod hr Kangni Var i e t i e s Caloro Dokri Bluebonnet 8 10 12 14 2 .2a 2 .3a 2.3a 2.1a 2.3b 2.6a 2.2b 2.8a 1.9a 2.1a 2.2a 2 . l a 1.9b 2.2a 2.1a 1.6c Temperature C 35/18 2.1a 35/26.5 35/35 40.5/18 2.2a 1.8(0.23) 1.91(0.63) Photoperiod hr 8 2.1b 10 2.3a 12 2.2ab 14 2.2ab Vari e t i e s Kangni 2 .3b Caloro 2.5a Dokri 2.0bc Bluebonnet 1.9c For footnotes see Table 2 88 40.5/18 gave low 100-grain weight values. Highest grain weight was at 10-hour photoperiod, although the weight was not s i g n i f i c a n t l y d i f f e r e n t from 12- and 14-hour photoperiods. There was no difference between 8-, 12-, and 14-hour photoperiods. Caloro had the highest grain weight followed by Kangni and Dokri. Dokri and Bluebonnet did not d i f f e r s i g n i f i c a n t l y . Both Kangni and Dokri were unaffected by photoperiod while Caloro had lower values at 8- and 12-hour photoperiods. Bluebonnet had the smallest kernels at 14-hour photoperiod followed by 8-hour. The 10- and 12-hour photoperiods did not d i f f e r s i g n i f i c a n t l y . Number of T i l l e r s At a l l stages of growth (3, 5, 7 and 9 weeks, Tables 9, 10, 11, and 12) number of t i l l e r s were highest at 35/18 and 40.5/18 and lowest at 35/35. The number of t i l l e r s was highest at 14-hour photoperiod at a l l stages of growth. At 3 and 5 weeks, 8-, 10- and 12-hour photo-periods were almost i d e n t i c a l but at 7 and 9 weeks there were s i g n i f i c a n t l y more t i l l e r s at the 8-hour photoperiod than at 10- or 12-hour photoperiod. Kangni and Dokri had s i g n i f i c a n t l y more t i l l e r s than Caloro or Bluebonnet. In Kangni the highest number of t i l l e r s was at 40.5/18 and 14-hour photoperiod. In Caloro at 3 weeks the highest number of t i l l e r s was at 35/18 and 14-hour photoperiod but at 5, 7 and 9 weeks there was no difference between 35/18 and 40.5/18 temperatures. In 89 TABLE 9 The E f f e c t of Photoperiod and Temperature on the Number of T i l l e r s Per P l a n t at 3 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature °C Photo-p e r i o d hr Kangni Caloro Dokri Bluebonnet 35/18 8 1.4defg l.Of l.Of 1.0c 10 1.7de 1.3def 1.5cde . 1.0c 12 1.6de 1.4def 1.7bcd 1.0c 14 3.1b 3.1a 2.8a 2.1a 35/26.5 8 1.4defg l.Of l . l e f 1.0c 10 1.5def 1.5cde 2.0b 1.0c 12 1.8d 1.3def 1.9bc 1.0c 14 2.5c 2.5b 3.0a 1.8ab 35/35 8 l.Og l.Of l.Of 1.0c 10 l.Og l.Of 1.2ef 1.0c 12 1.2efg 1. 6cd 1.3def 1.0c 14 2.7bc 2.0c 2 .6a 1.3b 40.5/18 8 1.8d l.Of l.Oef 1.0c 10 l . l f g l.Of 1.2ef 1.0c 12 l.Og l . l e f 1.5cde 1.0c 14 3.7a 2.6b 2.9a 2.2a Temperature °C 35/18 35/26.5 35/35 40.5/18 1.7a 1.6a 1.4b 1.6a Photoperiod hr 8 10 12 14 1.1c 1.2b 1.3b 2.6a V a r i e t y Kangni Caloro Dokri Bluebonnet 1.8a 1.5b 1.7a 1.2c For footnotes see Table 2. 90 TABLE 10 The E f f e c t of Photoperiod and Temperature on the Number of T i l l e r s Per Pla n t at 5 Weeks i n 4 V a r i e t i e s of Rice Temperature Photo-°C period hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/18 8 4.8bc 3.4bcd 2.6c 2.0bcd 10 3.Odefg 3 .Ocd 3.3c 2.1bcd 12 2.3fg 3 .Ocd 2.8c 2.lbcd 14 6 .0b 5. 8a 6.3a 3. 3ab 35/26 .5 8 2.8defg 2.6cd 2.5c 1.8bcd 10 3.9cde 3. Ocd 3. 6bc 2.8abcd 12 4.2cd 4.0bc 5. Oab 3.2abc 14 2.8defg 2.3de 2.4c 2.4abc 35/35 8 3.1defg l.Oe 2.9c 1.2d 10 1.9g l.Oe 3 .0c 1.6cd 12 2.3efg 2.5cd 3. 0c 2.lbcd 14 • 3.8cdef 2 .6cd .6. 3a 2.2bcd 40 .5/18 8 4.6bc 3. 6bcd 3.4c 2.Obcd 10 2.8defg 2 .9cd 2 .5c 2.4abcd 12 2.5efg 2.6cd 3.2c 2.5abed 14 8 . 0a 4.8ab 5 . 9a 3.9a Temperature °C 35/18 35/26 .5 35/35 40.5/18 3 . 5a 3.1b 2 .5c 3. 6a Photoperiod hr 8 10 12 14 2 .8b 2.7b 3.0b 4.3a V a r i e t i e s Kangni Caloro Dokri Bluebonm 3.7a 3.0b 3.7a 2.3c For footnotes see Table 2. 91 TABLE 11 The E f f e c t of Photoperiod. and Temperature on the Number of T i l l e r s Per Pla n t at 7 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C per i o d hr 35/18 8 6.2b 3.6b 3 . l c 2.5bcd 10 3.1e 2.9bc 3 . 3c 2.4bcde 12 2.5e 2.8bc 2.8c 2.Obcde 14 6.1b 6 .0a 6.2ab 4.0a 35/26.5 8 4.8cd 3.1bc 3.8c 2.6abcd 10 2.8e 2.8bc 2.5c 1.8cde 12 2.8e 1.8cd 3.0c 2.4bcde 14 3.9de 3.9b 5.6b 3.4ab 35/35 8 2 .6e l.Od 3 .2c l . l e 10 2.5e l.Od 3.3c 2.6abcd 12 2.4e l.Od 3.1c 2.5bcd 14 2.6e l.Od 7.3a 1. 3de 40.5/18 8 5. 6bc 3.8b 3 . 5c 2.2bcde 10 2.9e 3. Obc 3.2c 2.8abcd 12 2.8e 2 .5bc 3.4c 2.9abc 14 8.4a 5.2a 6. 9ab 4.0a Temperature °C 35/18 35/26.5 35/35 40.5/18 3.7a 3 .2b 2.4c 3.9a Photoperiod hr 8 10 12 14 3.3b 2.7c 2.5c 4.7a V a r i e t i e s . Kangni Caloro Dokri Bluebonm 3. 9a 2 .8b 4.0a 2.5b For footnotes see Table 2. 92 TABLE 12 The E f f e c t of Photoperiod and Temperature on the Number of T i l l e r s Per P l a n t at 9 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C per i o d hr 35/18 8 5. 9bc 3.6bc 3.5bde 2.4abc 10 3.1efg 2.8cd 3.3bde 2.4abc 12 2.8fg 2.8cd 2. 9de 2.0bc 14 5.lbcd 4.8ab 6. 6a 3. 9a 35/26.5 8 4.5cde 2.lcde 4.Obde 2.6ab 10 2.9fg 2.3cde 2.4e 1.8bc 12 2.9fg 1.5de 2.8de 2.0bc 14 4.3def 3. 6bc 4.3bd 3. l a b 35/35 8 2.8fg l.Oe 4.6b 1.1c 10 l.Oh l.Oe l.Oe 1.0c 12 2.5g l.Oe 3.2bde 1.8c 14 3. l e f g l.Oe 6 . 5a 1.4c 40.5/18 8 6 . l b 3.4bc 3.5bde 2.2bc 10 2.9fg 2 .9cd 3.3bde 2 .9ab 12 3.0fg 3 .Ocd 3.4bde 2.9ab 14 8 . l a 5 . l a 6. 6a 3.9a Temperature °C 35/18 35/26.5 35/35 40.5/18 3.6a 2.9b 2.1c 3. 9a Photoperiod hr 8 10 12 14 3.3b 2.3c 2.5c 4.5a V a r i e t i e s Kangni Caloro Dokri Bluebom 3. 8a 2.6b 3.9a 2.3b For footnotes see Table 2. 93 Dokri at 3 and 5 weeks the t i l l e r number was high at a l l temperatures and 14-hour photoperiod. At 7 and 9 weeks plants at 35/26.5 had the lowest number of t i l l e r s . Bluebonnet did not show a clearcut temperature or photoperiod e f f e c t , except at 3 weeks when the number of t i l l e r s was high at 35/18, 35/26.5, 40.5/18 and 14-hour photoperiod. Development  Leaf Development Irrespective of age, leaf development was fast e s t at 12-hour photoperiod (3, 5, 7 and 9 weeks, Table 13, 14, 15 and 16). At 7 and 9 weeks le a f development at 8-, 10-and 14-hour did not d i f f e r s i g n i f i c a n t l y . Leaf development was fastest at 40.5/18 and slowest at 35/18 at a l l i n t e r v a l s . Kangni and Dokri had fa s t e r development of leaves compared to Caloro and Bluebonnet. Bluebonnet had more leaves at 7 and 9 weeks than Caloro. In Kangni leaf numbers were greatest at 35/35 at a l l stages. In Caloro more leaves were present i n 12-hour photoperiod at 35/26.5, 35/35 and 40.5/18 than 35/18. The largest numbers of leaves were obtained consistently only at 40.5/18. Dokri showed more le a f development both at 35/35 and 40.5/18. The least responsive variety i n le a f development was Bluebonnet. Plant Height At a l l stages of growth plants were s i g n i f i c a n t l y shorter at 40.5/18 except at 8 weeks when 35/35 and 40.5/18 94 TABLE 13 The E f f e c t of Photoperiod and Temperature on the Number of Leaves on the Main Culm i n 4 V a r i e t i e s of Rice at 3 Weeks V a r i e t i e s Temperature °C Photo-period hr Kangni Caloro Dokri Bluebonnet 35/18 8 5 . 8de 5. 6e 5 . Oe 4.5f 10 6.lcde 6.2bcde 6. Ocd 5 .Odef 12 6.lcde 6 .Ode 6. Ocd 5.2bcde 14 5 . 9de 6.lcde 6 . Ocd 5.7abc 35/26.5 8 6.4abc 6.lcde 6. Ocd 5.1def 10 6 .7ab 6 . 6bc 6 .7ab 5.4abcde 12 6.6abc 6 . 8ab 6.4abc 5 . 9a 14 5. 5e 5. Of 6 .Ocd 5.6abcd 35/35 8 6.7ab 5 .9de 6. Ocd 5.6abcd 10 7.0a 5 . 6e 7.0a 5 . 8ab 12 7 ,0a 6 . 8ab 6.3bcd 5.7abc 14 6.Ocde 6. Ode 6 . Ocd 5.lcde 40 .5/13 8 6.Ocde 6 . Ode 5.7d 4.9ef 10 6.3bcd 6.4bcd 6.2bcd 5.6abed 12 7 .0a 7.3a 6 . 9a 6 . 0a 14 6.Ocde 6 .Ode 6 . Ocd 5.9a Temperature °C 35/18 35/26 .5 35/35 40.5/18 5.7b 6 . l a 6.2a 6 . l a Photoperiod hr 8 10 12 14 5.7c 6.2b 6.4a 5 . 8c V a r i e t i e s Kangni Caloro Dokri Bluebonnet 6. 3a 6 . 2b 6.1b 5.5c For footnotes see Table 2. 95 TABLE 14 The E f f e c t of Photoperiod and Temperature on the Number of Leaves on the Main Culm i n H V a r i e t i e s of Rice at 5 Weeks V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C per i o d hr 35/18 8 9 .4ef 8. 0c 7.8e 7.1f 10 8 . I f 8. 5bc 8 . Ode 7. 4ef 12 8 .Of 8 . 2bc 8.lcde 7.8cdef 14 8 .4ef 8. 6bc 8. 8bc 8.5abc 35/26.5 8 9 . 5bc 9.0b 9 .0b 8.Obcde 10 8.6def 8.8b. 8.7bcd 7.8cdef 12 8.5def 9.0b 8.6bcd 8.Obcde 14 8.5def 8. 6bc 9.0b 8.5abc 35/35 8 10.3a 5. 9e 9.8b 8 . 9a 10 9. 8ab 5.6e 10.0a 9 . 0a 12 9.lbcde 8 . 5bc 8.6bcd 8.5abc 14 9.3bcd 6.3d 9.0b 8.3abcd 40.5/18 8 8.9cde 8 .9b 8.5bcd 7.5def 10 8.Of 9 .0b 9.0b 8.lbcde 12 9.2bcd 11.0a 9. 3ab 9 . 0a 14 8.9cde 9 .0b 9.0b 8. 6ab Temperature °C 35/18 35/26.5 35/35 40.5/18 8 .1c 8.6b 8.5b 8.9a Photoperiod hr 8 10 12 14 8 . 5cb 8.4c 8 .7a 8. 6ab V a r i e t i e s Kangni Caloro Dokri Bluebonnei 8 .8a 8.3b 8 . 8a 8.2b For footnotes see Table 2. 96 TABLE 15 The E f f e c t of Photoperiod and Temperature on the Number of Leaves on the Main Culm i n 4 V a r i e t i e s of Rice at 7 Weeks V a r i e t i e s Temperature oc Photo-per i o d hr Kangni Caloro Dokri Bluebonnet 35/18 8 10.lde 10.0c 9.7f 9 . Oe 10 9. 9e 10.2c lO.Oef 9 . 6de 12 10.lde 10.6c 10,3cdef 9.9cde 14 10.2de 10.4c 10.3cdef 10.2abcd 35/26.5 8 11.2cd 10.7c 11.labcde 9.8cde 10 10.3de 11.1c 10.7bcdef 10.lbcd 12 10.9cde 10.6c ll.Oabcde. . 10.4abcd 14 10.5de 10.6c 10.ldef 10.2abcd 35/35 8 12.8a 5.9d 12 . l a 10.9abc 10 12.3ab 5.6d 12 . l a 11. 2a 12 11.8abc 11.0c 11.5ab 11.lab 14 10.4de 6.3d 11.2abcd 10.lbcd 40 .5/18 8 10.3de 11. 0c 11.Oabcde 10.Ocde 10 10.4de 12.0b 11.3abc 10.9abc 12 11.6bc 13 , 0a 12.0a 11.2ab 14 10.5de l l . l b c 11.Oabcde 10.6abc Temperature °C 35/18 35/26.5 35/35 40.5/18 10. 0c 10.6b 10.4b 11.1a Photoperiod hr 8 10 12 14 10.3b 10.5b 11.1a 10.2b V a r i e t i e s Kangni Caloro Dokri Bluebonnet 10.8a 10.0c 11.0a 10.3b For footnotes see Table 2. 97 TABLE 16 The E f f e c t of Photoperiod and Temperature on the Number of Leaves on the Main Culm i n 4 V a r i e t i e s of Rice at 9 Weeks V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C per i o d hr 35/18 8 11.2e 11.4de 11. 3d 10.5a 10 11. l e 13.Obcd 12.Ocd 12.Oab 12 12.2cde 12.2cde 12.led 12.lab 14 11. l e 12.lcde 12.Ocd 12.Oab 35/26 .5 8 13.Obcd 12.2cde 13.0bc 11.5ab 10 12.Ocde 12.Ocde 12.Ocd 12.0a 12 12.6bcde 11. l e 13.0bc 12.8a 14 12.lcde 12.lcde 12.Ocd 11.9ab 35/35 8 15.5a 5.9g 14.6a 12.9a 10 15.5a 5.0g 15 .0a 12 .9a 12 13.5bc 8 .4f 13.9ab 12.8a 14 12.3cde 9. I f 13.1bc 11.6ab 40.5/18 8 11. 2e 13.2bc 12.4bcd 11.7ab 10 11.6de 14.0ab 13.2bc 13.2a 12 13.9b 15.0a 15.0a 13.1a 14 12.6bcde 13.3bc 12.9bcd 12.5a Temperature °C 35/18 35/26.5 35/35 40.5/18 11.8c 12 .2b 12.Obc 13.1a Photoperiod hr 8 10 12 14 12.0b 12.3b 12.7a 12 .0b V a r i e t i e s Kangni Caloro Dokri Blueboni 12 .6b 11.2d 13 ,0a 12 .2b For footnotes see Table 2. 98 were not s i g n i f i c a n t l y d i f f e r e n t (2, 4, 6, and 8 weeks, Table 17, 18, 19 and 20). Generally p l a n t s were t a l l e r at 35/18 followed by 35/26.5 and 35/35. Pla n t s were sh o r t e s t at 8-hour photoperiod and t a l l e s t at 14-hour photoperiod. The pl a n t height g e n e r a l l y decreased with decreasing photoperiods. At two weeks a l l v a r i e t i e s had maximum height at 35/35. Generally p l a n t height was greater i n high night temperature regimes. At 4 weeks s i m i l a r trends continued but high values were a l s o recorded at 35/18 at 6 weeks except f o r Kangni. The trend i n maximum pla n t height s h i f t e d t o 35/18. Caloro showed low values at 35/35. At 8 weeks highest values were recorded at 35/18 i n a l l photoperiods and i n a l l v a r i e t i e s . Throughout the growth stages low values were recorded at 40.5/18 f o r a l l v a r i e t i e s . Photosynthesis C o r r e l a t i o n Between Weight and Area Bases Complete data on CO2 a s s i m i l a t i o n on an area b a s i s were a v a i l a b l e only f o r 8- and 12-hour photoperiods. A r e g r e s s i o n a n a l y s i s was th e r e f o r e conducted to see i f there was a s i g n i f i c a n t c o r r e l a t i o n between CO2 a s s i m i l a t i o n based on f r e s h weight and based on area. There was a h i g h l y s i g n i f i c a n t c o r r e l a t i o n between the two methods (Table 21), t h e r e f o r e , a l l the r e s u l t s reported are on a weight b a s i s . Net Photosynthesis at D i f f e r e n t Stages The r a t e s of net photosynthesis measured at the day temperature of the growing temperature f o r 2 , 4 , 6 and 99 TABLE 17 The E f f e c t of Photoperiod and Temperature on the o Plan t Height (cm) at 2 Weeks i n 4 V a r i e t i e s of Rice Temperature oc Photo-per i o d hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/18 8 11.5hi 11.6fg 9.1g 8.8de 10 12.Ohi 14.7d 11.8def 10.2de 12 14.0fg 12.6ef 13.8bcd 12.5bc 14 17.2bcd 19.lab 15.5ab 12.5bc 35/26.5 8 15.2ef 15.9cd 13.6bcd 10.2de 10 16.7cde 16.led 12.8cde 13.2ab 12 18.0bc 20.7a 16.9a 14.4ab 14 18.Obc 16.3cd 14.4bc 13.Oab 35/35 8 15.8def 15. Id 12.4cde 10.3de 10 19.1b 20.2a 14.2bc 14.4ab 12 21.7a 18.Obc 16.6a 14.8a 14 14. 5f 14.3de 12.3cde 10.6cd 40.5/18 8 12.5gh 12.3efg 10.2fg 10.lde 10 11.6hi 12.7ef 10.9efg 8 . 9de 12 10.6hi 10.5g 12.8cde 8. 3e 14 1 0 . I i 10. 6g 9.5g 8. 5e Temperature °C 35/18 35/26.5 35/35 40.5/18 12 .9b 15.3a 15.3a 10.6c Photoperiod hr 8 10 12 14 12 .2c 13.7b 14.8a 13.5b V a r i e t i e s Kangni Caloro Dokri Bluebonnet 14.9a 15.0a 12 .9b 11.3c For footnotes see Table 2. 100 TABLE 18 The E f f e c t of Photoperiod and Temperature on the Pl a n t Height (cm) at 4 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature °c Photo-per i o d hr Kangni Caloro Dokri Bluebonnet 35/18 8 22.6ef 24.lcde 21.6cdef 17.4bc 10 20.3f 20 .3f 20.0efg 16.5bcd 12 25.5de 24.6bcde 26.lab 19.5ab 14 27.9bcd 31.1a 2 6.lab 19.7ab 35/26.5 8 15.2g 15.9g 13.6h 10. 2e 10 27.lbcd 22.6def 22.7bcde 17.5bc 12 29.4bc 2 8.0ab 25.Oabc 17,4bc 14 32.8a 27.1bc 26.6a 21.0a 35/35 8 15. 8g 15.lg 12 .4h 10.3e 10 26.3cd 21.5ef 24.3abc 16.8bcd 12 24.8de 21.7ef 22.5cde 16.6bcd 14 31.lab 25.6bcd 23.7abcd 20.lab 40.5/18 8 20 .Of 21.2ef 17.3g 14.3cd 10 19.3f 19.3f 18.8fg 13. 6d 12 21.Oef 22 .8def 18.9fg 14.led 14 22 .Oef 22.6def 20.4defg 14.3cd Temperature °C 35/18 35/26 .5 35/35 40.5/18 22.7a 22 .0a 20.5b 18 .7c Photoperiod hr 8 10 12 14 16. 7d 20.4c 22 . 3b 24.5a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 23.8a 22.7b 21.3c 16.2d For footnotes see Table 2. 101 TABLE 19 The E f f e c t of Photoperiod and Temperature on the Pla n t Height (cm) at 6 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C per i o d hr 35/18 8 2 9.7bcde 32.6ab 29.8ab 21.7bcdef 10 32.2abc 29. Ocde 29.6abc 23.8abcd 12 31.6abc 33 . 8a 29.Oabcd 25.7a 14 29.7bcde 31.7abc 27.2bcde 22.9abcd 35/26.5 8 28.9cdef 29.7bcde 23.5fg 22.3abcde 10 31.Oabcd 25.4fg 28.Obcde 21.2cdef 12 3 3.5a 31.3abcd 28.8abcd 22.6abcd 14 32.9ab 28.0def 31.5a 24.3abc 35/35 8 27.5ef 23.9g 22.3g 20.8cdef 10 31.6abc 23.4g 25.5defg 18.9efg 12 29.8bcde 23.4g 27.lbcde 20.6def 14 31.7abc 28. 3cdef 28.9abcd 25.0ab 40.5/18 8 25.9f 28. 8cdef 24.9efg 16.6g 10 27.9def 27.8def 24.9efg 18.5fg 12 26.4ef 26.2efg 26 .2cdef 20.7def 14 26.Of 27.8def 25.9def 18.5fg Temperature °C 35/18 ,35/26 .5 35/35 40.5/18 28 .8a 27.7b 25.5b 24.6c Photoperiod hr 8 10 12 14 25 .6b 26 .2b 27.3a 27.5a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 29.8a 28.2b 27.1c 21. 5d For footnotes see Table 2. 102 TABLE 20 The E f f e c t of Photoperiod and Temperature on the Pl a n t Height (cm) at 8 Weeks i n 4 V a r i e t i e s of Rice Temperature Photo- Kangni Caloro Dokri Bluebonnet oc period hr 35/18 8 31.9ab 35.4a 31.8a 24.6abcd 10 3 2.6ab 35. 3a 29.6abc 25.2abcd 12 33 .0a 35.4a 30.5ab 27.7a 14 2 9.9ab 32.2abc 28.9abc 24.Oabcd 35/26.5 8 2 9.7ab 3 0.4bcd 25.4cd 22,7abcde 10 31.8ab 31.1abcd 28.4abcd 2 3.3abcde • 12 31.9ab 34.4ab 31.5ab 23.3abcde 14 32.5ab 28.3cde 30.6ab 26.Oab 35/35 8 27.8b 24.1ef 23.7d 20.5de 10 31.5ab 25.1ef 28.labcd 23.lbcde 12 29.3ab 21.5f 25.2cd 19. l e 14 32.Oab 27.Ode 28.Oabcd 25.5abc 40.5/18 8 27.7b 24.4ef 2 7.1bcd 20. 4e 10 27.8b 27.Ode 25.5cd 24.2abcd 12 27.2b 27.7de 27.lbcd 23. Obcde 14 28.0b 27.7de 27.Obcd 21.05cde Temperature °C 35/18 35/26.5 35/35 40.5/18 30.5a 28.8b 25.7c 25.8c Photoperiod hr 8 10 12 14 26.7b 2 8.1a 28.0a 28.0a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 30. 3a 29.2b 28.0c 23 .4d For footnotes see Table 2. 103 TABLE 21 C o r r e l a t i o n C o e f f i c i e n t ( r ) Values between mg CO2 Per Gram Fresh Leaf Blade Weight Per Hour and mg CO2 Per Square Decimeter Leaf Surface Per Hour Photoperiod 8 hr 12 hr Temperature oc 2 wk+ 4 wk 6 wk 8 wk 2 wk 4 wk 6 wk 8 wk 35/18 0. 956 0 .764 0 .957 0. 956 0. 942 0. 900 0. 965 0 .960 35/26.5 0 . 917 0 .917 0 .927 0. 655* 0 . 962 0. 877 0. 943 0 .799 35/35 0. 954 0 .953 0 .740 0. 746 0. 920 0 . 878 0. 878 0 .851 40.5/18 0. 967 0 .923 0 .731 0. 965 0. 715 0. 893 0. 883 0 .983 Weeks a f t e r t r a n s p l a n t i n g . * S i g n i f i c a n t at the 5% l e v e l . A l l other values s i g n i f i c a n t at the 1% l e v e l . 104 8 weeks are given i n Tables 22, 23, 24 and 25. Highest photosynthetic rate at 2 weeks was i n plants grown at 35/18 and lowest i n those grown at 35/26.5 but at 4, 6 and 8 weeks highest rates were recorded at 40.5/18 and 35/35 plants. Plants at 35/26.5 generally had lowest rates except at 8 weeks when they were s i g n i f i c a n t l y better than 35/18. The highest rate at a l l stages was recorded at the 8-hour photoperiod; 10- and 12-hour photoperiods sharing the highest values at 4 and 6 weeks. Net photosynthetic rate was generally low at a l l stages at 14-hour photoperiod. Kangni generally had the slowest rate of net photosynthesis with Caloro and Bluebonnet having the highest values, Dokri occupying an intermediate p o s i t i o n . Except at two weeks Caloro generally showed a higher rate of photosynthesis at 35/35. Least v a r i a t i o n at 2 weeks was shown by Dokri. Out of 16 treatment combinations Dokri had high rates i n 13. At 6 and 8 weeks Bluebonnet showed highest rates at 35/35 at 10- and 8-hour photoperiod respectively. Kangni and Dokri generally had higher rates at 35/18 and 40.5/18 temperature regimes. Net Assimilation Rate At 4 weeks net assimilation rate (NAR) was high at 35/18 and 40.5A8 temperature treatments and low at 35/35 (Table 26). Photoperiod had no e f f e c t on NAR. Bluebonnet had lowest NAR. At 6 weeks there were no v a r i e t a l differences 105 TABLE 2 2 The E f f e c t of Photoperiod and Temperature on Net Photosynthesis at 2 Weeks i n 4 V a r i e t i e s of Rice (mg C0 2 Per g Fresh Leaf Blade Weight Per Hour) V a r i e t i e s Temperature °C Photo-per i o d hr Kangni Caloro Dokri Bluebonnet 35/18 8 29.0ab 34.2b 3 3. 3a 35.3ab 10 25.Oabc 35 .4b 27.5abcd 32.3abc 12 27.4ab 30.4bc 28.Oabcd 29.Obc 14 31. 3a 31.9bc 29.6abc 29.9bc 35/26.5 8 30.5a 44.2a 30.4a 32.3abc 10 15. Oe 18 .9e 21.8d 21.3cde 12 19.2cde 25.4de 22 .6cd 27.9cd 14 26.7ab 2 3.8de 27.2abcd 21.2de 35/35 8 26.8ab 37 .4b 31.0a 37.2a 10 16.7de 21.4de 22.4cd 22.2de 12 17.lde 33 . l b 2 3.8bcd 26.4cd 14 29.7ab 32.2bc 29.7abc 27.5cd HO.5/18 8 25.7abc 21.9de 32 .0a 30.9abc 10 22.8bcd 26.Ocd 2 7.3abcd 19 .4e 12 30 .6a 30.5bc 27.7abcd 3 0.8abc 14 31.0a 31.1bc 29.9ab 30.8abc Temperature °C 35/18 30 . 6a 35/26.5 25 .5c 35/35 27.2b 40.5/18 28.0b Photoperiod hr 8 32 .0a 10 23.5d 12 26 .9c 14 29.0b V a r i e t i e s Kangni Caloro Dokri Bluebonnet 25.3c 29.9a 27 . 8b 2 8.4ab For footnotes see Table 2. 106 TABLE 23 The E f f e c t of Photoperiod and Temperature on Net Photosynthesis at 4 Weeks i n 4 Variet i e s of Rice (mg C0 2 Per g Fresh Leaf Blade Weight Per Hour) Temperature °C Photo-period hr Kangni Varieties Caloro Dokri Bluebonnet 35/18 8 17.9bcd 17.8bcdef 22.7a 18.7bcdef 10 22.1a 23.7a 20.6ab 23.9a 12 18.2abcd 16.3defg 16.4bcde 17.0bcdef 14 10.Of 9.7i 9.0g 14. Of 35/26.5 8 12.9ef 15.4efgh 15.6cde 14.8ef 10 9.9f 21.5abc 13.6defg 16.7cdef 12 14.2def 14.2fghi 18.3abcd 16.0def 14 10.9f 12.7ghi 11.5efg 14. Of 35/35 8 14.9cdef 21.3abc 15.Ode 20.3abcd 10 11.5f 19.9abcde 9.7fg 21.2abc 12 16.4bcde 17.5cdef 16.7bcd 18 . 8bcdef 14 14.3def 17.7cdef 16.4bcde 14.9ef 40.5/18 8 20.3ab 17,5cdef 23.0a 19.4abcde 10 19.2abc 2 2.6ab 20.4abc 21.9ab 12 20.Oab 2 0.7abcd 19.9abc 21.2abc 14 11.7ef 11.3hi 14.2def 14. I f Temperature °C 35/18 35/26.5 35/35 40.5/18 17.4b 14.5c 16.7b 18.6a Photoperiod hr 8 10 12 14 18.0a 18.7a 17.6a 12.9b Varieti e s Kangni Caloro Dokri Bluebonnet 15.3c 17.5ab 16.4b 17.9a For footnotes see Table 2. 107 TABLE 24 The E f f e c t of Photoperiod and Temperature on Net Photosynthesis at 6 Weeks i n 4 V a r i e t i e s of Rice (mg CO^ Per g Fresh Leaf Blade Weight Per Hour) V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet oc p e r i o d hr 35/18 8 12.Oab 14.9b 15.3a 15.7b 10 12.2ab 12.7bcd 14.lab 14.5bcde 12 9.6bcde 10.4cdef 10.6bcdef 12.4def 14 5 .9e 7.3f 7.9efg 8.5g 35/26 .5 8 9.5bcde 12.4bcde 10.4bcdef 8.5g 10 7.3de 15.7b 5.5g 8.2g 12 6.8e 8.9ef 8.9efg 11.2fg 14 6 .7e 10.4cdef 7.4fg l O . l f g 35/35 8 10.labcd 15.0b 12.8abcd 13.6cde 10 11.5abc 19.9a 9.7cdef 21.2a 12 8.8bcde 12.Obcde 9.2def 12.6def 14 8.2cde 15.0b 11.4bcde 11.7defg 40.5/18 8 13.7a 14.0bc 15.8a 17.7b 10 12.5ab 14.6b 16.0a 17.0bc 12 11.6abc 12.4bcde 12.9abc 15.0bcd 14 9.4bcde 9.3def 10.7bcdef lO.Ofg Temperature °C 35/18 35/26.5 35/35 40.5/18 11.5b 9 . 3c 12.7a 13. 3a Photoperiod hr 8 10 12 14 13 . 2a 13.3a 10.8b 9.4c V a r i e t i e s Kangni Caloro Dokri Bluebonnet 9.8c 12.8a 11.2b 13.0a For footnotes see Table 2. 108 TABLE 25 The E f f e c t of Photoperiod and Temperature on Net Photosynthesis at 8 Weeks i n 4 V a r i e t i e s of Rice (mg CO^ Per g Fresh Leaf Blade Weight Per Hour) Temperature °C Photo-period hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/18 8 7.2abc 8.5cdefg 6 .5bc 11.2bcd 10 8.5abc 6.0g 5 . 3c 4.7f 12 6.9bc 7. 5efg 7.3b 7.8def 14 5.5c 6.4fg 5. 3c 6.5ef 35/26.5 8 9 .6ab 10.4cde 8.8ab 10.2bcd 10 6 .4bc 9.4cdef 7 .4bc 10.5bcd 12 8.5abc 7.7efg 7.4bc 9. 9cd 14 6.3bc 10.lcde 8.5abc 8.lcde 35/35 8 8.9abc 11.led 11.0a 17.3a 10 5 . 8c 14.5ab 6 . 9bc 7.9cdef 12 8.3abc 14.7a 9. Oab 9. 9cd 14 7.9abc 8.2defg 9.4abc 8.lcde 40.5/18 8 7.8abc 11.5bcd 7.8abc 13 .4b 10 10 .4a 11.9abc 9 .8ab 13.4b 12 7 .4bc 9.3cdef 8.Oabc 11.4bc 14 6.7bc 8.2defg 7.3bc 8.6cde Temperature °C 35/18 35/26.5 35/35 40.5/18 7.0c 8.7b 9. 9a 9. 6a Photoperiod hr 8 10 12 14 10.11a 8 .7b 8 ,8b 7 .6c V a r i e t i e s Kangni Caloro Dokri Bluebonnet 7.7b 9.7a 7.9b 9 . 9a For footnotes see Table 2. 109 TABLE 2 6 The E f f e c t of Photoperiod and Temperature on the Net A s s i m i l a t i o n Rate i n 4 V a r i e t i e s of Rice (g of dry weight produced per day per dm2) 4th Week" Temperature °C 35/18 0.044a 35/26.5 0.032b 35/35 0 .027c 40.5/18 0.041a Photoperiod hr 8 0.035a 12 0.037a V a r i e t i e s Kangni 0.038a Caloro 0.041a 6th Week Dokri 0.036a Bluebonnet 0.029b Temperature °C 35/18 0.029ab 35/26.5 0.024b 35/35 0.026ab 40.5/18 0.030a Photoperiod hr 8 0.026a 12 0.029a V a r i e t i e s Kangni 0.027a Caloro 0.02 8a 8th Week Dokri 0.028a Bluebonnet 0.026a Temperature °C 35/18 0.018a 35/26.5 0.023a 35/35 0.017a 40.5/18 0.024a Photoperiod hr 8 0.020a 12 0.021a V a r i e t i e s Kangni 0.024ab Caloro 0.017bc Dokri 0.025a Bluebonnet 0.015c * S i g n i f i c a n t at 1% l e v e l f o r 4 week data and at 5% l e v e l f o r 6 and 8 week data. For footnotes see Table 2. 110 and there was no photoperiodic e f f e c t . The temperature e f f e c t was a l s o not pronounced at 6 weeks. Only the NAR at 4-0.5/18 was s i g n i f i c a n t l y higher than at 35/26 . 5 . At 8 weeks, temperatures and photoperiods were not s i g n i f i c a n t l y d i f f e r e n t ; Dokri and Kangni had higher NAR than Bluebonnet and Caloro. Dry Weight At 2 weeks dry matter accumulation was higher at 35/26.5 and 35/35 followed by 35/18 and 40.5/18 (Table 27). Subsequently highest weight was recorded at 35/18 at a l l stages. At 4 weeks (Table 28) 35/26.5 was b e t t e r than 3 5/35 which was b e t t e r than 40.5/18. At 6 weeks there was no d i f f e r e n c e between the three temperatures (Table 29). At 8 weeks 40.5/18 was b e t t e r than 35/26.5 which was b e t t e r than 35/35 (Table 30).' At a l l stages of growth dry matter was highest at 14-hour photoperiod followed by 12, 10 and 8 hours. At 8 weeks, 8- and 10-hour photoperiods were not s i g n i f i c a n t l y d i f f e r e n t . Kangni produced highest dry matter at a l l stages followed by D o k r i , Caloro and Bluebonnet. At no stage of growth d i d Caloro and Bluebonnet record highest values at 40.5/18 but at 8 weeks both Dokri and Kangni had highest values at 40.5/18 at 12- and 14-hour photoperiods. At 6 and 8 weeks Caloro and Bluebonnet d i d not have high values at 35/26.5 and 35/35 except f o r Bluebonnet at 3 5/35, 14 hours. I l l TABLE 2 7 The E f f e c t of Photoperiod and Temperature on the Dry Weight (g per pot) at 2 Weeks of 4 V a r i e t i e s of Rice Temperature °C Photo-per i o d hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/18 8 0.22f 0.16f 0.15d 0.14f 10 0.29ef 0.20ef 0.2 5bc 0.20cdef 12 0.41d 0.2 8de 0.34b 0.2 8bcd 14 0.70ab 0.49a • 0.45a 0.44a 35/26.5 8 0.2.6ef 0.20ef 0.2 5bc 0.14f 10 0.40d 0.25def 0.28bc 0.30bc 12 0 .58c 0.47ab 0.54a 0.43a 14 0.74a 0.39bc 0.44a 0.36ab 35/35 8 0.28ef 0.22ef 0.22cd 0.20cdef 10 0.64bc 0.46ab 0.2 8bc 0.28bcde 12 0.78a 0.40abc 0.52a 0.46a 14 0.56c 0.34cd 0 .47a 0.26bcde 40.5/18 8 0.20f 0.16f 0.15d 0.14f 10 0.33de 0 .25def 0.2 3cd 0.18def 12 0.24f 0 .20ef 0.32bc 0.18ef 14 0.43d 0.27de 0.27bc 0.27bcde Temperature °C 35/18 35/26 .5 35/35 40.5/18 0.32b 0. 38a 0 .40a 0.24c Photoperiod hr 8 10 12 14 0.19d 0. 30c 0 .40b 0.43a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 0.44a 0.30c 0.32b 0.27d For footnotes see Table 2. 112 TABLE 2 8 The E f f e c t of Photoperiod and Temperature on the Dry Weight (g per pot) at 4 Weeks of 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C p e r i o d hr 35/18 8 0. 96g 0 .88cde 0 .76hi 0 .67cd 10 1. 18fg 0 .91cde 1 ,18efgh 0 • 87cd 12 2. 16cd 1 .48b 1 . 84ab 1 .04bc 14 2. 8 3ab 2 • 75a 2 .08a 1 .48a 35/26 .5 8 1. 07fg 0 .76de 0 .91fghi 0 .72cd 10 1. 47ef 0 .77de 1 .19efgh 0 . 80cd 12 2 . 13cd 1 . 24bc 1 .31defg 0 . 66cd 14 3. 02a 1 .36b 2 .12a 1 .57a 35/35 8 1. 03fg 0 .52e 0 .86ghi 0 .51d 10 1. 24fg 0 .77de 1 . 36cdef 0 . 8 3cd 12 1. 74de 0 .85cde 1 . 58bcde 0 .95bcd 14 2 , 46bc 1 .53b 1 .7 3abcd 1 . 3 8ab 40.5/18 8 0. 94g 0 . 75de 0 ,58i 0 .50d 10 1. 06fg 0 .84cde 0 .88ghi 0 .50d 12 1. 32efg 1 .13bcd 1 .07fgh 0 .75cd 14 1. 73de 1 . 39b 1 .7 6abc 1 . 06bc Temperature °C 35/18 35/26.5 35/35 40 .5/18 1. 44a 1 .32b 1 .21c 1 .02d Photoperiod hr 8 10 12 14 0. 78d 0 .99c 1 .33b 1 . 89a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 1. 65a 1 .12c 1 .3b 0 .89d For footnotes see Table 2. 113 TABLE 29 The E f f e c t of Photoperiod and Temperature on the Dry Weight (g per pot) at 6 Weeks of 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet oc period hr 35/18 8 2 .58ef 2 .lOcde 1 .99gh 1. 67def 10 3 .79cd 2 . 80bc 3 .lObcdef 1. 8 5cde 12 4 . 85ab 3 .70b 3 .38abcd 3. 43a 14 5 . 05ab 4 .70a 3 .62abc 2. 61abc 35/26.5 8 2 .04f 1 .38efg 1 ,82gh 1. 35ef 10 2 .27f 1 .37efg 2 .2 7fgh 1. 37ef 12 4 .44bc 2 .61c 2 .5 9defg 1. 67def 14 5 .57a 2 . 03cdef 3 . 86ab 2. 40bcd 35/35 8 2 .12f 1 • 06g 1 .66h 1. 12ef 10 2 .47f 1 • 21fg 2 .37efgh 1. 24ef 12 3 .77cd 1 .42defg 3 .16bcdef 1. 44ef • 14 5 .57a 2 . 31cd 4 .14a 3. 02ab 40.5/18 8 2 .25f 2 .14cde 1 .9 3gh 0 . 88f 10 3 .40de 2 .38c 2 • Olgh 1. 37ef 12 3 .40de 2 .66c 2 . 92cdef 2. 43bcd 14 4 .44bc 2 . 92bc 3 . 2 3bcde 1. 44ef Temperature °C 35/18 35/26.5 35/35 40. 5/18 3 • 22a 2 .44b 2 .38b 2 . 49b Photoperiod hr 8 10 12 14. 1 .76d 2 .21c 2 .99b 3 . 56a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 3 . 6a 2 . 31c 2 .75b 1. 83d For footnotes see Table 2. 114 TABLE 3 0 The E f f e c t of Photoperiod and Temperature on the Dry Weight (g per pot) at 8 Weeks of 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet oc pe r i o d hr 35/18 8 4 .12bcd 3 .12bcdef 3 . 76bcdef 2 .7lcde 10 5 .19b 3 .38bcde 3 . 67bcdef 2 .66cde 12 7 .82a 6 .05a 5 .51a 5 .30a 14 8 .05a 6 .92a 5 .91a 3 . 59bc 35/26.5 8 - 3 .58cd 2 •22efg 2 .98ef 1 . 66e 10 3 .74bcd 2 . 37defg 3 . 87bcdef 1 . 88de 12 6 .88a 4 .34b 4 . 7 8abc 2 .42cde 14 7 . 28a 2 .04efg 5 ,13ab 3 .43bcd 35/35 8 3 .28d 1 • 37g 2 .49f 1 . 39e 10 3 .79bcd 1 .60fg 3 .Oldef 2 .29cde 12 4 . 95bc 1 • 41g 4 . 95abc 1 .61e 14 6 .99a 2 . 66cdefg 5 .43a 4 . 25ab 40.5/18 8 4 .41bcd 2 . 89bcdefg 4 .34abcde 2 .34cde 10 4 .2 8bcd 2 . 50cdefg 3 .41cdef 2 .35cde 12 7 .19a 3 . 99bc 5 . 35a 3 .50bc 14 6 . 86a 3 .9 0bcd 5 . 82a 3 .55bc Temperature °C 35/18 35/26.5 35/35 40 .5/18 4 . 86a 3 .66c • 3 .22d 4 .17b Photoperiod hr 8 10 12 14 2 .92c 3 .13c 4 .76b 5 .11a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 5 .53a 3 .17c 4 .40b 2 . 81d For footnotes see Table 2. 115 T o t a l C h l o r o p h y l l At a l l stages of growth c h l o r o p h y l l concentration was was high at 40.5/18, but not s i g n i f i c a n t l y d i f f e r e n t from 35/18, at 2 and 4 weeks (Tables 31, 32, 33 and 34). Second highest c o n c e n t r a t i o n was g e n e r a l l y at 35/35 at a l l stages. * This was not s i g n i f i c a n t l y d i f f e r e n t from 35/26.5 at 2, 4 and 8 weeks and from 35/18 at 6 and 8 weeks. Generally c h l o r o p h y l l concentration was higher at 8- and 14-hour photoperiods followed by 10-hour. Twelve hour g e n e r a l l y had lower concentrations. Caloro had high concentrations at a l l stages and Kangni had low concentrations. Bluebonnet and Dokri had high and low concentrations at d i f f e r e n t stages. At 2 weeks there was no e f f e c t of temperature on c h l o r o p h y l l concentrations at 10- and 14-hour photoperiods. Kangni and Bluebonnet had s i g n i f i c a n t l y higher concentrations at 35/18 and 40.5/18. Caloro and Dokri showed lowest concentrations at 35/35. Again at 4 weeks there was no e f f e c t of temperature on the c h l o r o p h y l l concentrations at 14-hour photoperiod but at 10 hours 35/18 and 40.5/18 were s i g n i f i c a n t l y d i f f e r e n t from 35/35 and 35/26.5. At 6 weeks both Kangni and Bluebonnet showed high c h l o r o p h y l l concentrations at 35/18 and 40.5/18 i n almost a l l photoperiods. Dokri and Caloro had fewer high values and g e n e r a l l y they were i n short or long photoperiods. Dokri had lowest values i n a l l photoperiods at 35/26.5 and 35/35. 116 TABLE 31 The E f f e c t of Photoperiod and Temperature on the C h l o r o p h y l l Content (mg per g f r e s h weight) at 2 Weeks i n 4 V a r i e t i e s of Rice Photoperiod hr Temperature 8 10 12 14 °C 35/18 4.2 9a 3.77a 4.35b 4.31a 35/26.5 3 .20b 3.80a 3 .95c 4.27a 35/35 3 . 03b 3.62a 3 . 87c 4.10a 40.5/18 3 .93a 3 .89a 4. 80a 4.24a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 35/18 4.03a 4.46a 3 .95b 4.27a 35/26.5 3.45b 4.3 3ab 3.62bc 3.83b 35/35 3.41b 4.05b 3 .52c 3.64b 40.5/18 4.01a 4.27ab 4. 36a 4.24a Temperature °C 35/18 35/26.5 35/35 40.5/18 4.18a 3.81b 3 .66b 4.22a Photoperiod hr 8 10 12 14 3.61b 3.77b 4.24a 4.23a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 3.73c 4.28a 3 . 86bc 3.99b For footnotes see Table 2. 117 TABLE 3 2 The E f f e c t of Photoperiod and Temperature on the C h l o r o p h y l l Content ( mg per g f r e s h weight) at 4 Weeks i n 4 V a r i e t i e s of Rice Photoperiod hr Temperature 8 10 12 14 °c 35/18 4.12a 4.03a 3 .10b 3 .49a 35/26.5 3 .28b 3 . 21b 3.22b 3.47a 35/35 3 .23b 3.04b 3.04b 3.74a 40.5/18 3.87a 3.94a 3 .89a 3.71a Temperature °C 35/18 35/26 . 5 35/35 40.5/18 3 .68a 3.29b 3.26b 3 . 85a Photoperiod hr 8 10 12 14 3.62a 3.55a 3.31b 3 .60a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 3.29b 3.65a 3.66a 3.49ab For footnotes see Table 2. 118 TABLE 3 3 The E f f e c t of Photoperiod and Temperature on the C h l o r o p h y l l Content (mg per g f r e s h weight) at 6 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C period hr 35/18 8 10 12 14 3.24ab 3.53a 2.83bc 3.0 8ab 4.06a 3.09def 3.27bcdef 3.66abc 3.59bc 3.77ab 3.21cde 3.62bc 3.2 6abcd 2.91cde 3.36abcd 3.60a 35/26.5 8 10 12 14 2.12d 1.95d 2.35cd 2.43cd 2.86ef 3.62abcd 2.84f 3.20cdef 2.42f 2 .56f 2.51f 2 .66f 2 .47e 2.95cde 2.84de 2.83de 35/35 8 10 12 14 2.24d 2 . 2 Id 2.47cd 2 .26d 3.38bcdef 2.92ef 3.17cdef 3.32bcdef 2 .55f 2 .84def 2.38f 2.80ef 2.99bcde 3.2 3abcd 2.98cde 2.90cde 40.5/18 8 10 12 14 3.18ab 3 .49a 3.05ab 3.0 8ab 3.80ab 3.34bcdef 3.40bcde 3.66abc 4.17a 3.69abc 3.60bc 3.62bc 3.54a 3.59a 3.43abc 3 .60a Temperature °C 35/18 3.38b 35/26.5 2 .66c 35/35 2.79b 40.5/18 3 .52a Photoperiod hr 8 3.12a 10 3.11a 12 2 .98b 14 3 .15a V a r i e t i e s Kangni 2 .72c Caloro 3.35a Dokri 3.13b Bluebonnet 3.16b For footnotes see Table 2. 119 TABLE 34 The E f f e c t of Photoperiod and Temperature on the C h l o r o p h y l l Content (mg per g f r e s h weight) at 8 Weeks i n 4 V a r i e t i e s of Rice Temperature °C 8 Photoperiod hr 10 12 14 35/18 2.94ab 2.78a 3 .17a 2.2 8b 35/26.5 2 .46c 2.55b 2.21b 2.22b 35/35 2.65bc 2.31b 2 .24b 2 .33b 40.5/18 3.12a 2.81a 2.89a 2.06a Temperature °C 35/18 35/26.5 35/35 40.5/18 2 .79b 2.29b 2 . 38b 2.97a Photoperiod hr 8 10 12 14 2 .79a 2 .54b 2.63ab 2 .47b V a r i e t i e s Kangni Caloro Dokri Bluebonnet 2 .33b 2.87a 2.44b 2.80a For footnotes see Table 2. 120 Carotenoids Carotenoid concentration f o r 2 and 6 weeks i s given i n Tables 3 5 and 3 6 and f o r 4- and 8 weeks i n Table 37. Carotenoid c o n c e n t r a t i o n at two weeks was highest at 40.5/18 followed by 35/18 (Table 35). Lowest concen t r a t i o n was at 8-hour photoperiod followed by 10, 12 and 14 hours. Caloro had the highest concentration followed by Dokri and Bluebonnet. In a l l v a r i e t i e s , 40.5/18 and 14-hour photoperiod g e n e r a l l y r e s u l t e d i n the highest carotenoid l e v e l s . Lowest concentrations were i n d i f f e r e n t treatments f o r d i f f e r e n t v a r i e t i e s : thus i n Kangni, at 35/26.5 and 35/35, 8 and 10 hours; and i n Caloro at 35/26.5, 35/35, 8 hours and at 40.5/18, 12 hours. At 4 weeks there was no d i f f e r e n c e among temperatures (Table 36). Pl a n t at 8- and 10-hour ' photoperiods had high concentrations but there was no s i g n i f i c a n t d i f f e r e n c e from p l a n t s at 10, 12 and 14 hours. Caloro and Bluebonnet had s i g n i f i c a n t l y higher concentrations than Kangni. At 6 weeks 40.5/18 p l a n t s had higher concentrations of carotenoids followed by 35/18 p l a n t s (Table 37). There was no d i f f e r e n c e between 35/26.5 and 35/35. Pla n t s i n 10- and 14-hour photoperiods had s i g n i f i c a n t l y higher c o n c e n t r a t i o n than those i n 12-hour photoperiod. At 8 weeks the temperature e f f e c t was s i m i l a r t o that at 6 weeks but 8-hour photoperiod p l a n t s had s i g n i f i c a n t l y higher c o n c e n t r a t i o n than those at other 121 TABLE 3 5 The E f f e c t of Photoperiod and Temperature on the Carotenoid Content (mg Carotenoid per l i t e r ) at 2 Weeks i n 4 V a r i e t i e s of Rice Temperature Photo-°C per i o d hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/18 8 0.439cde 0.502cd 0.366e , 0.421ef 10 0.419de 0.520cd 0.463bc 0.463cdef 12 0.502bc 0.494cd 0.462bc 0.518c 14 0.420de 0.624a • 0.561a 0.624b 35/26.5 8 0.385ef 0.415ef 0.396cde 0.344gh 10 0.346f 0.500cd 0.411cde 0.502cd 12 0.425de 0.599ab 0.439bcd 0.460cdef 14 0.419de 0.530bcd 0.396cde 0.405fg 35/35 8 0.345f 0.354f 0.359e 0.282h 10 0.344f 0.460de 0.384de 0.479cde 12 0.474bcd 0.534bcd 0.492b 0.489cde 14 0.426de 0.539bc 0.394cde 0.438def 40.5/18 8 0.401de 0.625a 0.443bcd 0.474cdef 10 0.424de 0.531bcd 0.442bcd 0.466cdef 12 0.518b 0.404ef 0.444bcd 0.525c 14 0.704a 0.621a 0.601a 0.713a Temperature °C 35/18 35/26.5 35/35 40.5/18 0.487b 0.436c 0.424c 0.521a Photoperiod hr 8 10 12 14 0.409d 0.447c 0.486b 0.526a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 0.437c 0.516a 0.441cb 0.475b For footnotes see Table 2. 122 TABLE 36 The E f f e c t of Photoperiod and Temperature on the Carotenoid Content (mg Carotenoid per l i t e r ) at 4 and 8 Weeks i n 4 V a r i e t i e s of Rice 4 Weeks Temperature C Photoperiod hr V a r i e t i e s 35/18 0.441a 0.447a Kangni 0.404b 35/26.5 0.417a 10 0.441ab Caloro 0.453a 35/35 0.417a 12 0.402b Dokri 0 .423ab 40.5/18 0.452a 14 0 .438b Bluebonnet 0.466a Temperature C Photoperiod hr V a r i e t i e s 35/18 0.335b 0.354a Kangni 0.291c 8 Weeks 35/26.5 0.290c 10 0.322b Caloro 0.377a 35/35 0.313c 12 0.311b Dokri 0.296c 40.5/18 0.376a 14 0.326b Bluebonnet 0.351b For footnotes see Table 2. 123 TABLE 37 The E f f e c t of Photoperiod and Temperature on the Carotenoid Content (mg Carotenoid per l i t e r ) at 6 Weeks i n 4- V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C per i o d hr 35/18 8 0.362abc 0.444ab 0.385bc 0.3 8 5ab 10 0.386ab 0.386ab 0.382bc 0.361ab 12 0.303abc 0.411ab 0.352bc 0.396ab 14 0.287abc 0.451ab 0.445b 0.412ab 35/26.5 8 0.261bc 0.345b 0.312c 0.319b 10 0.248c 0.436ab 0.320bc 0.425ab 12 0.271abc 0.343b 0.312c 0.361ab 14 0.315abc 0.388ab 0.311c 0.343ab 35/35 8 0.2 5 9bc 0.407ab 0.302c 0.363ab 10 0.304abc 0.385ab 0.384bc 0.427ab 12 0.316abc 0.373b 0.315bc 0.38 5ab 14 0.2 89abc 0.425ab 0.301c 0.331ab 40.5/18 8 0.3 78abc 0.470ab 0.566a 0.404ab 10 0.387ab 0.378b 0.404bc 0.453a 12 0.370abc 0.339b 0.400bc 0.407ab 14 0.397a 0.514a 0.444b 0.454a Temperature °C 35/18 35/26.5 35/35 40.5/18 0.384b 0.349c 0.348c 0.423a Photoperiod hr 8 10 12 14 0.372ab 0.396a 0.353b 0 .382a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 0.321c 0.423a 0.371b 0.389b For footnotes see Table 2. 124 photoperiods (Table 26). Caloro had s i g n i f i c a n t l y higher c o n c e n t r a t i o n followed by Bluebonnet, Dokri and Kangni had s i m i l a r c o n centrations. C h l o r o p h y l l and Net Photosynthesis C o r r e l a t i o n s between net photosynthesis and t o t a l c h l o r o p h y l l are given i n Table 3 8 and net photosynthesis and c h l o r o p h y l l a are given i n Table 39. Some c o r r e l a t i o n was obtained but i t was not uniform throughout a l l treatments. T o t a l c h l o r o p h y l l d i d not show any c o r r e l a t i o n w i t h net photosynthesis at 14-hour photoperiod at a l l stages of growth. At 10-hour photoperiod p l a n t s , there was s i g n i f i c a n t c o r r e l a t i o n i n a l l stages of growth but the c o r r e l a t i o n c o e f f i c i e n t s at 2 and 8 weeks were low. C o r r e l a t i o n w i t h c h l o r o p h y l l a showed almost s i m i l a r trends 'excepting t h a t at.4 and 6 weeks there was a s i g n i f i c a n t c o r r e l a t i o n at 14-hour photoperiod p l a n t s . T o t a l C h l o r o p h y l l and T o t a l Fresh Weight Generally h i g h l y s i g n i f i c a n t c o r r e l a t i o n s were obtained f o r t o t a l c h l o r o p h y l l and f r e s h weight (Table 40). In 8-hour photoperiod p l a n t s at 35/18 and 40.5/18 and i n 10-hour photoperiod p l a n t s at 35/26.5 the c o r r e l a t i o n was not s i g n i f i c a n t at 2 weeks. T o t a l Soluble Carbohydrates Both at 4 and 8 weeks the concentration of t o t a l water s o l u b l e carbohydrates was higher i n p l a n t s at 35/35 125 TABLE 3 8 The Values f o r C o r r e l a t i o n C o e f f i c i e n t s ( r ) between Net Photosynthesis and T o t a l C h l o r o p h y l l (mg per g f r e s h weight) at 2, 4, 6 and 8 Weeks i n 4 V a r i e t i e s of Rice Weeks a f t e r t r a n s p l a n t i n g Photoperiod hr 2 4 6 8 8 0 .1612 0.72 9 9** 0.7485** 0 .3834** 10 0 . 3523'- 0.7836** 0.7 343** 0 . 3332* 12 0 .632 3** 0.2159 0.7425** 0 .047 0 14 0 .0131 0.1100 0.2028 0 .1734 ** S i g n i f i c a n t at 1% l e v e l . * S i g n i f i c a n t at 5% l e v e l . 126 TABLE 39 The Values f o r C o r r e l a t i o n C o e f f i c i e n t s ( r ) between Net Photosynthesis and C h l o r o p h y l l a (mg per g f r e s h weight) at 2, 4, 6 and 8 Weeks i n 4 V a r i e t i e s of Rice Weeks a f t e r t r a n s p l a n t i n g Photoperiod hr 2 4 6 8 8 0 .1698 0.6987** 0.7555** 0 .3942** 10 0 .4907** 0.7722** 0.7173** 0 .3 540* 12 0 .6237** 0.2790 0.8571** 0 .0874 14 -0 .2400 0.3176* 0.449 5** 0 .1718 ** S i g n i f i c a n t at 1% l e v e l . * S i g n i f i c a n t at 5% l e v e l . 127 TABLE 40 The Values f o r C o r r e l a t i o n C o e f f i c i e n t s ( r ) between T o t a l C h l o r o p h y l l and T o t a l Fresh Weight Average of 4 V a r i e t i e s of Rice Weeks a f t e r t r a n s p l a n t i n g Temperature Photo- 2 4 6 8 °C per i o d hr 35/18 8 0, ,0453 n s 0. , 8432 0. .9293 0. .7809 10 0. .9608 0, .9625 0, .9889 0, .6667* 12 0. ,9232 0 . ,6157* 0. ,5 915* 0, ,7235 14 0 , .9653 0, .6687* 0, .6496 0, .8044 35/26.5 8 0, .9887 0 , 8329 0, .8593 0 , .8571 10 -0, .1760 n s 0, ,8042 0, ,6543* 0, ,8407 12 0, ,9190 0, .9899 0, .9592 0, .9284 14 0 . 8483 0. .7078 0. .9870 0, .9575 35/35 8 0, ,6803* 0. .9057 0, . 8450 0, .6995* 10 0, .8737 0, .7624 0, .8583 0, . 8649 12 0. .9658 0, .9406 0 , 9759 0, .9711 14 0 . ,9784 0. ,9862 0, , 8822 0. .9252 40.5/18 8 0 , 5128 n S 0. .9030 0, ,9508 0, .8228 10 0 , .9052 0, ,9706 0, .9878 0, ,6818* 12 0 , .9707 0, .7942 0. .9082 0, .8921 14 0 . ,9217 0. ,6721* 0, ,7880 0. .9264 Not s i g n i f i c a n t . * S i g n i f i c a n t at 5% l e v e l , others s i g n i f i c a n t at 1% l e v e l . 128 than at 35/26.5 (Tables 41 and 42). At 4 weeks carbo-hydrate c o n c e n t r a t i o n was highest at 12-hour photoperiod and lowest at 14 hours. At 8 weeks p l a n t s at both 12 and 14 hours had high concentrations followed by 10 and 8 hours. At 4 weeks Bluebonnet had a s i g n i f i c a n t l y higher c o n c e n t r a t i o n than d i d the other v a r i e t i e s . At 8 weeks Dokri a l s o had a high c o n c e n t r a t i o n . At 4 weeks Kangni had higher concentrations at intermediate photoperiods. Somewhat s i m i l a r r e s u l t s were obtained f o r Bluebonnet. Caloro had high concentrations at 35/26.5 at 8-, 10-and 12-hour photoperiod and at 35/35, 12 hours. Dokri showed l i t t l e e f f e c t of temperature. At 8 weeks a l l v a r i e t i e s except Caloro had lower c o n c e n t r a t i o n at 8-hour photoperiod. At 12- and 14-hour photoperiods at t h i s stage concentrations were g e n e r a l l y high. T o t a l Soluble Carbohydrates and T o t a l Ash There was no e f f e c t of temperature at 4 weeks but at 8 weeks combined carbohydrate and ash content was higher i n p l a n t s at 35/35 (Tables 43 and 44). At 4 weeks, combined contents at 10 and 12 hours were higher than at 8 hours. P l a n t s at 14 hours had the lowest content. At 8 weeks p l a n t s at 12 hours had s i g n i f i c a n t l y higher content than at 8 and 10 hours. There was no v a r i e t a l d i f f e r e n c e s at any stage. At 4 weeks both Kangni and Caloro showed highest contents at 10 hours and Bluebonnet at 12 hours. Dokri had high c o n c e n t r a t i o n at 8, 10 and 12 hours. At 129 TABLE 41 The E f f e c t of Photoperiod and Temperature on the Carbohydrate Content (mg per g dry weight) at 4 Weeks i n 4 V a r i e t i e s of Rice Temperature oc Photo-per i o d hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/26.5 8 49.8cd 65,7ab 63.8abc 73.1c 10 46.3cd 83 . 8a 47.6bc 31.2d 12 69.4bc 93 . 3a 71.3ab 103.3b 14 40.8cd 32.9cd 32 .6c 64.2c 35/35 8 65.4bc 43.Obc 88.2a 57.5cd 10 89.7b 30.7cd 95 .2a 106.1b 12 126.5a 71.2ab 88 . 3a 139.3a 14 26.Od 10. 5d 42.5bc 49.4cd Temperature °C 35/26 . 5 35/35 59.8b 70. 6a Photoperiod hr 8 10 12 14 62 .2b .66.3b 95. 0a 37 .4c V a r i e t i e s Kangni Caloro Dokri Bluebonnet 63 . l b 53.5b 66 .2b 78.0a For footnotes see Table 2. 130 TABLE 42 The E f f e c t of Photoperiod and Temperature on the Carbohydrate Content (mg per g dry weight) at 8 Weeks i n 4 V a r i e t i e s of Rice Temperature °C Photo-period hr Kangni V a r i e t i e s Caloro Dokri Bluebonnet 35/26.5 8 7 .8c 13 .5d 22 .6e 32 .9b 10 104. Oab 37.7bcd 101.4bc 29.3b 12 87 .2b 29.Ocd 62 .2d 112.9a 14 123.3a 74.4a 78.2cd 111.4a 35/35 8 11.2c 63.7ab 69 .4d 30.6b 10 22 . 2c 20 . 5d 120.5ab 40.8b 12 131.3a 53.8abc 143.8a 100.9a 14 110.lab 59.7abc 106.5bc 97 ,4a Temperature °C 35/26.5 35/35 64.2b 73.9a Photoperiod hr 8 10 12 14 31.5c 59.6b 90.1a 95 . l a V a r i e t i e s Kangni Caloro Dokri Bluebonnet 74 .6b 44.1c 88.1a 95.1a For footnotes see Table 2. 131 TABLE 43 The E f f e c t of Photoperiod and Temperature on the Carbohydrate Plus Ash (mg per g dry weight) at 4 Weeks i n 4 V a r i e t i e s of Rice Photoperiod V a r i e t i e s hr Kangni Caloro Dokri Bluebonnet 8 246.4b 238.9b 282.7a 256.1b 10 297.5a 290.7a 290.8a 277.Oab 12 271.Oab 268.lab 252.1a 316.6a 14 199.6c 202.8c 205.5b 215.1c Temperature °C 35/26.5 35/35 253.4a 260.59a Photoperiod hr 8 10 12 14 256.Ob 289.0a 276 .9a 205 .8c V a r i e t i e s Kangni Caloro Dokri Bluebonnet 253.6a 250.1a 257.8a 266.2a For footnotes see Table 2. 132 TABLE 44 The E f f e c t of Photoperiod and Temperature on the Carbohydrate Plus Ash (mg per g dry weight) at 8 Weeks i n 4 V a r i e t i e s of Rice V a r i e t i e s Temperature Photo- Kangni Caloro Dokri Bluebonnet °C period hr 35/26.5 8 149.8d* 155.4e 165.8e 173.8cd 10 247.0a 199.2cd 229.2bc 162.7d 12 206.4bc 166.Ode 183.Ode 270.6a 11 236.2ab 205.3c 201.2cd 227 b 35/35 8 181.Ocd 258.3ab 228.8bc 205.Obc 10 169.7d 200 .9cd 262.6ab 175.5cd 12 221.9ab 268.1a 265.8a 265.6a 14 224.4ab 225.2bc 221.3c 213.9b Temperature °C 35/26.5 35/35 198.7b 224.3a Photoperiod hr 8 10 12 14 189.8c 205.9b 230.9a 219.3ab V a r i e t i e s Kangni Caloro Dokri Bluebonnet 204.6a 209.8a 219.7a 211.8a * S i g n i f i c a n t at 5% l e v e l . 133 8 weeks both Caloro and Dokri had highest contents at 35/35 and lowest contents at 35/26.5, 8 hours. Bluebonnet had a high c o n c e n t r a t i o n at 12 hour photoperiod. P l a n t s i n 8-hour photoperiod g e n e r a l l y had lower c o n c e n t r a t i o n . 134 DISCUSSION As r e c e n t l y as 1965 Roberts and Carpenter noted \ the l a c k of proper s t u d i e s on the i n t e r a c t i o n of temperature w i t h photoperiod. They themselves only studied the e f f e c t s of temperature and photoperiod on f l o w e r i n g . Perhaps the e a r l i e s t study comparable to the present experiments was that of Nagai (1963). He included not only f l o w e r i n g but l e a f development and some y i e l d determining c h a r a c t e r s . The present work takes such s t u d i e s a step f u r t h e r , by i n c l u d i n g range of d i u r n a l l y f l u c t u a t i n g temperatures. The range of photoperiods includes at l e a s t one photoperiod below and one above the optimum range. The e f f e c t of photoperiod on photosynthesis i n r i c e has re c e i v e d scant a t t e n t i o n i n e a r l i e r work and the e f f e c t of photoperiod i n t e r a c t i o n w i t h temperature has not been studied at a l l . The present study includes the e f f e c t of temperature and photoperiod not only on f l o w e r i n g and y i e l d determining characters but a l s o on net photo-s y n t h e s i s , pigments and carbohydrates. Flowering Vergara and L i l i s (1966) proposed a c r i t e r i o n whereby a v a r i e t y was considered photoperiod s e n s i t i v e i f the d i f f e r e n c e i n days t o f l o w e r i n g between optimum and maximum (long photoperiod) was greater than 10 days. Lantican and Parker (1961) considered 23 days as appropriate and Velasco and Dela Fuente (1958) considered 30 days as the appropriate d i f f e r e n c e . A l l these c r i t e r i a seem to be u n r e a l i s t i c and lead t o confusion. As the response i s q u a n t i t a t i v e , a s t r i n g e n t s t a t i s t i c a l t e s t should be a p p l i e d t o data on days to f l o w e r i n g . To avoid f a l s e c l a s s i f i c a t i o n of a v a r i e t y as photoperiod s e n s i t i v e , the high s i g n i f i c a n c e l e v e l of 1% should be used and i f a v a r i e t y shows a s i g n i f i c a n t d i f f e r e n c e between the optimum and longer photoperiods i t w i l l be c l a s s i f i e d as photoperiod-s e n s i t i v e i r r e s p e c t i v e of whether the d i f f e r e n c e i s 9 days or 30 days. In the present d i s c u s s i o n the s t a t i s t i c a l c r i t e r i o n w i l l be used. The longest photoperiod used i n the present study was 14 hours which i n the a v a i l a b l e l i t e r a t u r e i s considered long enough to show long-day photoperiodic e f f e c t s . However, i t seems from the data obtained that a longer photoperiod would have been d e s i r a b l e . Abbasi (1965) considered both Kangni and Dokri as photoperiod n o n - s e n s i t i v e but the present r e s u l t s tend to disprove h i s c o n c l u s i o n s . Dokri d i d not show an e f f e c t of photoperiod at 35/18 where the delay i n f l o w e r i n g at longest photoperiod compared to optimum was only 6 days and n o n s i g n i f i c a n t . At 35/26.5 Dokri was photoperiod s e n s i t i v e . The d i f f e r e n c e between longest photoperiod and optimum was 21 days and s i g n i f i c a n t . There was a l s o a 136 s h i f t i n optimum from 10 hours at 35/26.5 to 12 hours at 35/18. Kangni was a sensitive variety both at 35/18 and 35/26.5. In the f i r s t case the difference was 23 days to flowering and i n the second 33 days, lower night temperature apparently acted to remove the e f f e c t of long photoperiods on these two v a r i e t i e s or that high night temperatures strengthened the eff e c t of long photoperiods. The data f o r 35/35 and 40.5/18 were incomplete but the same trend was apparent. The trend was s i m i l a r i n Caloro and Bluebonnet. Bluebonnet did not show any photoperiodic s e n s i t i v i t y at 35/18. Caloro showed s e n s i t i v i t y both at 35/18 and 35/26.5. The e f f e c t of night temperature was more pronounced, thus i n Bluebonnet the delay at 35/18 was only 2 days between optimum and longest photoperiod but was 63 days at 35/26.5. The respective figures for Caloro werem and 30 days, again in d i c a t i n g the importance of temperature. An in t e r e s t i n g trend was shown by Caloro and Bluebonnet at 35/18. As the photoperiod decreased from 12 to 8 hours the number of days to flowering increased. In Caloro the delay was 52 days and i n Bluebonnet 21 days. This delay was not shown by the other two v a r i e t i e s . This means that low night temperature i n short photoperiods apparently delays flowering i n Caloro and Bluebonnet. , 137 Caloro and Bluebonnet grow i n regions where nig h t s are c h a r a c t e r i z e d by low temperatures. In v a r i e t i e s adapted t o such c o n d i t i o n s the presence of a reproductive system geared t o low temperature provides a d i s t i n c t advan-tage . The delay i n f l o w e r i n g at shorter photoperiods i s due t o longer exposure to low temperatures. A s i m i l a r e f f e c t was found by Nagai (196 3) though the low temperature used by him (20°C) was higher than i n the present study (18.3°C). Katayama (19 64b) found a d i s t i n c t ecotype from Cherrapunji (1,313m above sea l e v e l ) . He argued that because of low growing season temperature, the genotypes were adapted to low temperature r a t h e r than t o daylength. Perhaps a s i m i l a r s i t u a t i o n e x i s t s i n Caloro and Bluebonnet. The s i t u a t i o n d i f f e r s i n Caloro and Bluebonnet, i n that these v a r i e t i e s have not l o s t s e n s i t i v i t y t o daylength. Bluebonnet which i s considered as photoperiod s e n s i t i v e d i d not show any s e n s i t i v i t y to photoperiod at the 35/18 temperature but d i d at 35/26 . 5 . In •the present study the s h o r t e s t d u r a t i o n to f l o w e r i n g recorded was at 10-hour photoperiod and 35/26.5 which was more than the 80 days reported by Vergara, Puranabhavung and L i l i s (1965) and l e s s than the 114 days given by Johnston* and the 140 days reported by Boerema and McDonald (1965). Vergara, Puranabhavung and L i l i s (1965) a l s o reported d i f f e r e n t times from those found i n the present study. * T. H. Johnston, personal communication. 138 The v a r i a t i o n i n times reported i n the l i t e r a t u r e may be due to d i f f e r e n t f i e l d c l i m a t i c c o n d i t i o n s . Both b a s i c v e g e t a t i v e phase (bvp) and photoperiod s e n s i t i v e phase (psp) v a r i e d g r e a t l y . Thus at 35/18 bvp of Bluebonnet was 116 days and psp 21 days whereas corresponding values f o r 35/26.5 were 66 and 63 days, which i s i n sharp c o n t r a s t to those reported by Vergara, Puranabhavung and L i l i s (1965) (45 and 37 days). Caloro showed photoperiodic s e n s i t i v i t y both at 35/18 and 35/26.5. Delay i n f l o w e r i n g was about 14 days at 35/18 and 30 days at 35/26.5 the f l o w e r i n g i n 67 days at 10-hour photoperiod and 6 9 days at 12 hours noted i n the present experiments are the sho r t e s t d u r a t i o n reported f o r the v a r i e t y . I t was shor t e r than the 7 8 days reported f o r 12-hour photoperiod by Ormrod et a l . (1960), 106 days under f i e l d c o n d i t i o n s by Mastenbroek* and 87 t o 107 days reported by Nuttonson (1965) f o r d i f f e r e n t l o c a t i o n s and sowing dates. In both Caloro and Bluebonnet f l o w e r i n g was delayed when the mean temperature was low. In Biggs, C a l i f o r n i a , between 1940 and 1961 the mean temperature never exceeded 26.5°C which i s lower than the 30.8 used i n the present study. This may e x p l a i n f l o w e r i n g i n 67 days i n the present study and i n 106 days as reported f o r C a l i f o r n i a by Mastenbroek*. * J . J . Mastenbroek, personal communication. 139 The bvp f o r Caloro was 45 and 32 days at 35/18 and 35/26.5 respectively. Corresponding values for psp were 52 and 30 days. This means that at low temperature the basic vegetative phase (bvp) i s extended but the photoperiod sensitive phase i s reduced. The reverse was true for high temperature which suggests that i n cases where flowering f a i l e d at 4 0.5/18 the reason was perhaps not the f a i l u r e of f l o r a l induction but f a i l u r e of the subsequent development of f l o r a l primordia. The developmental abnormalities of the infloresence so prevalent at 40.5/18 lend support to t h i s hypothesis. A sim i l a r e r r a t i c flowering response was reported by Roberts and Carpenter (1965) at 40/30°C regimes. Flowering response by a l l v a r i e t i e s at 35/35 and 40.5/18 was e r r a t i c . Some v a r i e t i e s were more sensitive than others thus Caloro f a i l e d to flower i n any photoperiod at 35/35 whereas Dokri flowered i n a l l photoperiods except 8 hours. Moderate or generally high values f o r other growth characters l i k e dry-matter production, pigment concentrations and net photosynthesis rates at 40.5/18 and 35/35 indicate that normal physiological processes had not been disrupted and that, i t was the flowering process i t s e l f which had been affected. Out of 9 v a r i e t i e s studied by Roberts and Carpenter (1965) only one flowered at 35/35°C and at 40/30 only a few v a r i e t i e s flowered. They considered high mo n i g h t temperature to delay f l o w e r i n g which may be contrary to present f i n d i n g s f o r which f l o w e r i n g i n a l l v a r i e t i e s was e a r l i e r at 35/26.5 than 35/18. Dry Matter The dry matter production by p l a n t s i n the present experiment was n o n - s p e c i f i c (Best, 1959), increased dry matter production o c c u r r i n g with i n c r e a s i n g photoperiod. As f u l l i n t e n s i t y of l i g h t was used to increase the photoperiod, such increase i n dry matter i s expected to be due to increased d u r a t i o n of photosynthesis. The r e s u l t s do not agree with those found by Enyi (1963a). He d i d not f i n d any change i n dry weights at 9-, 12- and 14-hour photoperiods which i s s u r p r i s i n g because he used a n a t u r a l daylength up to 12 hours. The e f f e c t of temperature seems to be as s o c i a t e d with the geographical l o c a t i o n of v a r i e t i e s . Kangni and Dokri are grown i n regions where high night and high day temperatures are not uncommon. On the other hand, low night temperatures do not occur during the growing p e r i o d . Consequently, these two v a r i e t i e s recorded the highest dry, matter at 35/35. High day temperature perhaps compensated f o r low nigh t temperature so the second highest y i e l d was recorded at 40.5/18. Caloro and Bluebonnet produced higher dry matter at low night temperature. A nigh t temperature of 26.5°C i s perhaps unusual i n the reg i o n where they grow and 35°C i s very u n l i k e l y to occur. This i s revealed i n 141 dry matter production. Compared to highest y i e l d , i n Caloro the r e d u c t i o n at 35/26.5 was 51% and at 35/35, 72%. For Bluebonnet the corresponding values were 29 and 49%. These are very s t r i k i n g r e d u c t i o n i n y i e l d at high night temperature. H i k o - I c h i (1958) i n a study of 160 v a r i e t i e s came to the c o n c l u s i o n that i n d i c a types are more adaptive than japonica types i n performing v e g e t a t i v e growth under high temperatures. This agrees w i t h the present i n v e s t i g a t i o n s because Kangni and Dokri are i n d i c a types, Caloro i s a japonica type and Bluebonnet a s u b - i n d i c a type. Number and Length of P a n i c l e s The number of p a n i c l e s was unaffected by temp-erature and g e n e r a l l y not by photoperiod except at 14 hours i n which numbers were s i g n i f i c a n t l y higher than at 12 hours. Somewhat s i m i l a r r e s u l t s were reported by Enyi (196 3a) i n d i c a t i n g that there i s no s p e c i f i c photoperiodic response as f a r as number of p a n i c l e s i s concerned. Misra (1955) reported a s l i g h t increase i n p a n i c l e numbers under long day treatment but he used only 2 photoperiods. On the other hand, the r e s u l t s of Vergara and L i l i s (1966) give the impression that s p e c i f i c photoperiodic responses are present. P l a n t s given fewer photoinducting c y c l e s i n long day treatment had fewer p a n i c l e s . As p l a n t s were brought back to non-inductive long day i t seems l o g i c a l 142 to assume th a t the smaller number of p a n i c l e s was not due to s p e c i f i c photoperiod e f f e c t but due to f a i l u r e of subsequent t i l l e r s to head under non-inductive c o n d i t i o n s . In r i c e the i n d u c t i o n i s not t r a n s l o c a t e d to t i l l e r s . This has been demonstrated by Vergara and L i l i s (1966), Manuel and Velasco (1957) and others. As the c o n d i t i o n s of the experiments of other authors were q u i t e d i f f e r e n t from the present experiments (except E n y i , 1963a) a v a l i d comparison i s not p o s s i b l e . I t seems reasonable to conclude from the work of Misra (1954b), Enyi (1953a) and the present work that there i s l i t t l e e f f e c t of photoperiod on number of p a n i c l e s . P a n i c l e length was unaffected by temperatures though there were some increases i n p a n i c l e length at 12-hour photoperiod. A d e f i n i t e photoperiodic e f f e c t was t h e r e f o r e not always apparent. S i m i l a r conclusions were drawn by Misra (1954b, 1955), Enyi (1963a) and Vergara and L i l i s (1966). Venkataraman (1964) a l s o d i d not f i n d a s p e c i f i c increase i n p a n i c l e length but he obtained longest p a n i c l e s i n a J u l y p l a n t i n g and s h o r t e r p a n i c l e s i n subsequent p l a n t i n g s . Number of S p i k e l e t Per P a n i c l e , S t e r i l i t y and 100-Grain  Weight The number of s p i k e l e t s was unaffected by temperature. Photoperiod response seemed to be c h a r a c t e r i s t i c of a v a r i e t y r a t h e r than of any o v e r a l l e f f e c t of 143 photoperiod. Both Caloro and Dokri d i d not show any e f f e c t of photoperiod on the number of s p i k e l e t s . Kangni had fewer s p i k e l e t s i n s h o r t e r photoperiods whereas Bluebonnet showed the decrease both i n short and long photoperiods. Perhaps v a r i a b i l i t y i n the responses of v a r i e t i e s to d i f f e r e n t environmental c o n d i t i o n s has r e s u l t e d i n the d i v e r s i t y i n f i n d i n g s of d i f f e r e n t researchers. Thus Vergara and L i l i s (1966) found increases i n the number of s p i k e l e t s w i t h i n c r e a s i n g short day c y c l e s i n d i c a t i n g p hotoperiodic e f f e c t . In the present study Bluebonnet showed t h i s type of response. Misra (1954b, 1955, 1956) on the other hand found fewer s p i k e l e t s at shorter photoperiods, a response resembling that of Kangni i n the present study. According to Vergara and L i l i s (1966) mean 100-g r a i n weight decreases w i t h shortening photoperiod. Misra (1954b) reported a s l i g h t increase i n 100-grain weight at short photoperiods but i n a l a t e r study ( M i s r a , 1956) he found an increase at long photoperiods. In the present study the v a r i e t a l d i f f e r e n c e s are c l e a r . I t seems reason-able to assume that the number of s p i k e l e t s per p a n i c l e and 100-grain weight i s l a r g e l y determined by f a c t o r s or combination of f a c t o r s other than temperature and photo-pe r i o d . S t e r i l i t y as high as 95.3% at 35/35 and 68.7% at 40.5/18 (Caloro) i n d i c a t e s the d r a s t i c e f f e c t of 144 temperature. Both these temperatures were not d e l e t e r i o u s to v e g e t a t i v e growth. As a matter of f a c t Kangni and Dokri produced highest dry matter at 35/35. A b o r t i v e p a n i c l e s , improperly developed s p i k e l e t s and f a i l u r e of i n f l o r e s c e n c e s to extrude from the l e a f sheath were common i n these two temperature regimes i n d i c a t i n g a s p e c i f i c e f f e c t on reproductive s t r u c t u r e s . I t seems that both high n i g h t temperature, 35°C and high'day temperature, 40.5°C are abnormal f o r reproduction. Nagai (196 3) found high p o l l e n s t e r i l i t y i n low and high temperatures which may be one of the reasons f o r the high s t e r i l i t y observed. Misra's (1960b, 1962) contention that s t e r i l i t y depends upon v a r i e t y i s supported by the present study. Under s i m i l a r c o n d i t i o n s at lower temperatures Bluebonnet had highest s t e r i l i t y and Kangni and Caloro lowest. Misra (1954b, 1960b, 1962) found high s t e r i l i t y i n short photoperiods a s i t u a t i o n found i n the present study only i n Bluebonnet, 8 hour 35/18, and i n D o k r i , 8 hour 35/26.5, but, i n these v a r i e t i e s there was high s t e r i l i t y i n long photoperiods. In almost a l l v a r i e t i e s , i n both temperatures (35/18, 35/26.5) highest s t e r i l i t y values were found i n 14-hour photoperiod. In a recent study Moss and Heslop-Harrison (196 8) found reduced p o l l e n f e r t i l i t y i n maize grown i n short (8 hour) compared to long (18 hour) photoperiod. P o l l e n s t e r i l i t y was considered to be photoperiodic as 145 night i n t e r r u p t i o n by l i g h t removed the e f f e c t of short photoperiod. I t seems u n l i k e l y t h a t short days u n i v e r s a l l y induce p o l l e n s t e r i l i t y i n short day p l a n t s at l e a s t the present study does not support the i d e a . Number of T i l l e r s There were obvious v a r i e t a l d i f f e r e n c e s i n t i l l e r number with both Kangni and Dokri producing more t i l l e r s than Caloro and Bluebonnet. For a l l v a r i e t i e s the number of t i l l e r s was maximum at 14 hours a . f i n d i n g s i m i l a r t o Enyi (1963a) and Vergara and L i l i s (1966). Coolhaas and Wormer (1953) d i d not f i n d any d i f f e r e n c e s between 12 and 18-hour photoperiods. I t i s not c l e a r whether the 12-hour photoperiod they chose was optimum f o r f l o w e r i n g . I f so i t i n d i c a t e s no e f f e c t of longer photoperiods on t i l l e r number, which i s contrary t o the present f i n d i n g s . P l a n t s i n 35/18 and 40.5/18 had the l a r g e s t number of t i l l e r s and 35/35 s m a l l e s t . An examination of temperature regimes r e v e a l s that t i l l e r i n g was unaffected by day temperature and t h a t low night temperature promoted t i l l e r i n g . Thus t i l l e r i n g was highest at 18°C night temperature followed by 26.5 and lowest at 35. This observation coupled w i t h the f a c t that t i l l e r i n g was high at 14-hour photoperiod i n d i c a t e s that t i l l e r i n g i n some way i s dependent upon a v a i l a b l e carbohydrates which are present i n greater amounts due to longer period of 146 photosynthesis or slower r e s p i r a t i o n i n low night temperatures. This idea f i n d support i n the observations by Sato (1965), Tajima (196 5) and Ormrod and Bunter (1961). Sato (1965) found h i g h ' t i l l e r i n g of r i c e at 27/17°C day/ night temperature and found that low temperature treatment always had higher carbohydrates. S i m i l a r l y Tajima (1965) found r e s p i r a t i o n i n r i c e p l a n t s to be 3 times l e s s at 2 0°C than at 35°C. Ormrod and Bunter (1961) found s i m i l a r r e d u c t i o n i n r e s p i r a t i o n i n r i c e with decreased temperature. Rapid u t i l i z a t i o n of carbohydrates during a c t i v e growth has a l s o been reproted by Brown and Blaser (1965) i n orchardgrass and fescue. The observation by Matsushima et a l . (1964b) tha t the number of t i l l e r s i s l i t t l e a f f e c t e d by a i r temperature and more a f f e c t e d by water temperature does not r e f u t e the present f i n d i n g as water temperature was the same as a i r temperature i n the present experiments. They found t h a t low day temperature with low water temperature e f f e c t i v e l y reduced the number of t i l l e r s which means that low day temperatures may no-t be conducive to t i l l e r i n g . Leaf Development Fastest l e a f development was found at the 12-hour photoperiod. There was a l s o an e f f e c t of temperature. At 40.5/18 l e a f development was g e n e r a l l y f a s t e r than at other temperatures. V a r i e t a l d i f f e r e n c e s were a l s o noted. Both Kangni and Dokri showed no adverse e f f e c t s of 35/35, 147 a behaviour c o n s i s t e n t w i t h the behaviour shown f o r many other growth c h a r a c t e r s . P a r a l l e l i s m between l e a f development and photo-p e r i o d e f f e c t on f l o w e r i n g has been found by many workers. Thus Vergara e_t a l . (1966) found a c l o s e p a r a l l e l i s m between e f f e c t of photoperiod on f l o w e r i n g and r a t e of l e a f development. In the present study i n most cases, e a r l i e s t f l o w e r i n g and most r a p i d l e a f development was found i n 12-hour photoperiod followed by 10 hours. 8 and 14-hour photoperiods shared both delayed f l o w e r i n g and slower l e a f development. At the time of f l o w e r i n g , i n 12-hour photoperiods, Kangni had 12 leaves both a t 35/18 and 35/26.5, Caloro had 12 and 11, Dokri 12 and 13 and Bluebonnet 19 and 18. Both Caloro and Bluebonnet showed a decrease i n l e a f number at high n i g h t temperature. Vergara, Puranabhavung and L i l i s (1965) found that temperature s e n s i t i v e v a r i e t i e s have a decreased number of leaves at high temperature and non-s e n s i t i v e v a r i e t i e s have a s l i g h t increase i n l e a f number at high temperature a f i n d i n g s i m i l a r t o that i n the present experiments. Rate of l e a f development was f a s t e s t at e a r l y stages but d e c l i n e d l a t e r , thus i t was about 2.3 leaves per week up to 3 weeks but 1.0 l e a f per week between the s i x t h and seventh week. The h a l f r a t e was thus reached before the seventh l e a f stage which d i f f e r s from tenth l e a f stage reported by Nagai (1963). 148 Pl a n t Height At 2 weeks p l a n t height was greater at 35/26.5 and 35/35 but i n subsequent stages pl a n t height was greater at 35/18. At e a r l y stages when the photosynthetic apparatus i s not yet f u l l y developed p l a n t growth depends upon the e f f i c i e n c y of endosperm u t i l i z a t i o n and t h i s i s f a s t e s t i n high temperatures. Thus Sato (196 5) found p l a n t heights of 13.0, 1.4 and 15.9 cm at 23 and 17°C constant and glasshouse c o n d i t i o n and r a t e of endosperm consumption of 56.1, 6.2 and 69.7% r e s p e c t i v e l y . In the present study p l a n t s had to be grown i n i t i a l l y f o r one week at 35/26.5°C temperature as pla n t height at 35/18 and 40.5/18 was so short t h a t t r a n s p l a n t i n g was d i f f i c u l t . There was no apparent s p e c i f i c e f f e c t of photo-p e r i o d . Generally p l a n t height was higher at longer photo-periods which i s s i m i l a r to the f i n d i n g s of Enyi (1963a), Coolhaas and Wormer (1953) and Vergara, L i l i s and Tanaka (1965). These i n v e s t i g a t o r s found d i f f e r e n t responses depending upon v a r i e t y used, thus i t seems tha t p l a n t height i s p r i m a r i l y a c h a r a c t e r i s t i c of a v a r i e t y which may or may not i n t e r a c t w i t h environment. In the present study at 40.5/18 the e f f e c t of photoperiod was almost non-e x i s t e n t i n a l l v a r i e t i e s at a l l stages of growth which means that temperature and not photoperiod was of o v e r r i d i n g importance i n t h i s case. 149 The data a l s o i n d i c a t e that photoperiod or temperature do not so much a f f e c t the height as the r a t e of attainment of height and the f i n a l height depends upon the v a r i e t y . At 2 weeks the height was greatest at 35/26.5 and 35/35. At 4 and 6 weeks p l a n t s at long photoperiod and 35/18 a l s o were t a l l e r but at 8 weeks the d i f f e r e n c e s i n many cases had disappeared. Photosynthesis Maximum ra t e s of photosynthesis were achieved i n the f i r s t 2 weeks a f t e r t r a n s p l a n t i n g . At 2 weeks a f t e r t r a n s p l a n t i n g there were about 4 f u l l y developed leaves and apparently a l l were i n a high s t a t e of metabolic a c t i v i t y (Tanaka et al_. 1966). With the growth of the pl a n t the lower leaves reach 7 a d e c l i n e i n photosynthetic a c t i v i t y but s t i l l c o n t r i b u t e to weight. That the age of l e a f i s important i n photosynthesis has been pointed out by Murata (1961), Tanaka et a l . (1966) and A k i t a et a l . (1968). The maximum d e c l i n e i n photosynthetic a c t i v i t y i n the present experiments was at 35/18 where at 8 weeks only 22% of the 2 week value was recorded. A drop to 34 to 36% of the 2 week value was recorded f o r the other three temperatures. As the greatest dry weight accumulation was at 35/18 i t seems that not only aging but a l s o mutual shading (due to l a r g e l e a f area) was r e s p o n s i b l e f o r the greater d e c l i n e observed at 35/18. Large l e a f area seems to be a more probable cause because senescence was always slower i n low nigh t temperatures. 150 T o t a l photosynthesis on a per pot basi s showed a d i f f e r e n t t r e n d ; the peak of photosynthesis was not reached u n t i l the s i x t h week. This was true i n a l l temperatures, photoperiods and v a r i e t i e s . The d e c l i n e i n photosynthesis from the s i x t h to the eighth week was a l s o slow and i n some cases there was no change. The peak of a s s i m i l a t i o n i n the present experiment occurred about the same time as the maximum t i l l e r i n g stage. This i s s i m i l a r t o the f i n d i n g of Murata (1961) and Yamada (1963). Tanaka et a l . (196 6) found the peak at the p a n i c l e i n i t i a t i o n stage which may p o s s i b l y have been due to v a r i e t a l d i f f e r -ences . Another i n t e r e s t i n g feature of the present i n v e s t i g a t i o n was th a t high r a t e s of net photosynthesis per gram f r e s h weight of l e a f blade but lower t o t a l CC^ a s s i m i l a t i o n per pot were obtained at 35/3 5 and 40.5/18. S i m i l a r l y highest values of net photosynthetic r a t e were recorded i n p l a n t s grown at 8-hour photoperiod at a l l stages of growth but these p l a n t s had low values f o r t o t a l C0 2 a s s i m i l a t i o n . Adverse photoperiods or temperatures perhaps i n i t i a t e an adaptive mechanism. Shorter d u r a t i o n of photosynthesis or higher r e s p i r a t i o n r a t e s can only be compensated f o r by higher photosynthetic r a t e s . E f f e c t i v e removal of the products of photosynthesis i n long ni g h t s or by r e s p i r a t i o n i n high temperatures may create the d e f i c i e n c y of substrate thereby i n c r e a s i n g the photosynthetic r a t e . 151 In short day p l a n t s i t has been shown th a t most of the carbohydrates i s t r a n s l o c a t e d i n the dark (Tsybulko, 1962). I f t h i s i s a l s o t r u e i n r i c e one would expect greater t r a n s l o c a t i o n i n s h o r t e r days. Increased t o t a l CC^ a s s i m i l a t i o n must be due to l a r g e l e a f area which may be brought about by f a s t l e a f development, broader and longer leaves and more t i l l e r i n g . On the b a s i s of r a t e of photosynthesis a l l the v a r i e t i e s studied f a l l i n t o the t h i r d category (high photosynthesis r a t e s at e a r l y stages) of Murata's (1961) c l a s s i f i c a t i o n but on the b a s i s of t o t a l CO2 a s s i m i l a t e d the v a r i e t i e s come under the f o u r t h category (slow photosynthesis r a t e s at e a r l y s tages). Both Caloro and Bluebonnet have been c l a s s i f i e d as mid-season v a r i e t i e s and Kangni and Dokri as e a r l y . Bluebonnet and Caloro both had higher r a t e s of net photosynthesis throughout a l l the growth stages but when t o t a l C0 2 a s s i m i l a t i o n i s considered both Kangni and Dokri had high values which confirms the f i n d i n g of Murata (1961), Osada and Murata (1965b), Hayashi (1968) and other workers who found t h a t e a r l y v a r i e t i e s g e n e r a l l y have highest maximum population photosynthesis followed by mid-season and l a t e v a r i e t i e s . The e f f e c t of photoperiod on photosynthesis i s c l e a r . Eight-hour photoperiod p l a n t s at a l l stages had high values and as the photoperiod increased the r a t e decreased, thus 10 hours had comparable values to 8 hours only at 4 and 6 weeks, to 12 hour at 4 weeks and f o r 14- hour there were no comparable values. The d i f f e r e n c e between 8 and 14 hours became greater with age. At 2 weeks at 8-hour photoperiod photosynthetic r a t e was 9% higher but at 8 weeks i t was 2 5% higher than the r a t e at 14 hours. There does not seem to have been much a t t e n t i o n paid to the e f f e c t of photoperiod on the r a t e of photo-s y n t h e s i s . El-Sharkawy et a l . (1965 ) and Elmore ejt a l . (1967) d i d f i n d a 50 to 80% increase i n photosynthesis i n cotton grown i n summer compared to that grown i n winter i n the glasshouse. Because no s p e c i f i c c o n t r o l s were a p p l i e d to d e l i n e a t e photoperiods or temperatures i t cannot be s a i d w i t h c e r t a i n t y whether the e f f e c t s observed were photoperiodic or due to temperature or to both. Cotton i s a short day p l a n t w i t h no temperature e f f e c t on photoperiodic response and had there been a photoperiodic e f f e c t one would expect -the p l a n t s to have higher photosynthetic r a t e i n w i n t e r , according to the present study. Hesketh (1968) showed th a t p l a n t s grown under f l u o r e s c e n t l i g h t demonstrated a c l o s e c o r r e l a t i o n between photosynthesis and t r a n s p i r a t i o n . Because p l a n t s were t e s t e d under i d e n t i c a l c o n d i t i o n s of temperature and humidity i n the present study a change i n t r a n s p i r a t i o n r a t e cannot e x p l a i n the d i f f e r e n c e s observed i n net photosynthetic r a t e s . 153 The only known work i n which c o n t r o l l e d photo-periods were used i s that of Bamberg et a l . (1967) and they d i d not f i n d an e f f e c t of photoperiod. The p l a n t used was stone pine which seems to be a f f e c t e d more by temperature than by photopeiod. The temperature recorded during the course of t h e i r experiments never rose above 12°C. The e f f e c t of temperature on photosynthesis i s i n t e r e s t i n g . Three treatments of 4 had the same day temperature (35) and photosynthesis was measured at that temperature. P l a n t s i n the 4th treatment were grown at high day temperature (40.5) w i t h night temperature of 18 s i m i l a r to 35/18 and measured at 40.5. According to published l i t e r a t u r e lowest values were to be expected at 40.5 as Murata (1961) reported a very sharp drop i n photosynthetic r a t e above 40°C and Yamada (196 3) a drop at 35°C but i n the present study g e n e r a l l y higher values were recorded at 40.5. Photosynthetic r a t e s recorded here are i n no case lower than those reported by many r i c e workers so i t cannot be argued that present study was performed on the d e c l i n i n g slope of a temperature response curve. Both growing c o n d i t i o n s w i t h very high day temperature (40.5) and high nig h t temperature (35) favoured high photo-s y n t h e t i c r a t e e s p e c i a l l y at 6 and 8 weeks a f i n d i n g q u i t e i n c o n t r a s t t o that of Ormrod (1961) who found the optimum at 15/6°C which i s lower than lowest nig h t temperature used 154 i n the present study. The discrepancy i s c l e a r l y a r e s u l t of d i f f e r e n t growing c o n d i t i o n s f o r the p l a n t s t e s t e d . Murata et a l . (1965) d i d not f i n d any change i n r a t e of photosynthesis i n some forage species grown f o r 10 days at 25, 20 and 15°C though thermo-adaptation was ( found by Murata and Iyama (19 6 3b) and Treharne et a l . (1968). Thermo-adaptation appears to have played a strong r o l e i n the present experiments. NAR and Dry Weight Tanaka et al_. (1966) supported the argument that l e a f area index (LAI) i s more important f o r dry matter production than net a s s i m i l a t i o n r a t e (NAR) by quoting various a u t h o r i t i e s . D i f f e r e n c e s i n NAR between v a r i e t i e s and species do occur but d i f f e r e n c e s i n dry weight are not considered t o be due t o NAR. Murata (1961) made a comprehensive study of p l a n t growth and found t h a t dry matter production depends on LAI but only at a very e a r l y stage and only i n cases where the s o l a r r a d i a t i o n l e v e l i s not low. NAR i n c o n t r a s t i s not a f f e c t e d very g r e a t l y by the d i f f e r e n c e s between v a r i e t i e s or c u l t u r a l methods at e a r l y stages, according t o Murata (1961). With increase of l e a f area NAR shows increased v a r i a t i o n due to v a r i e t i e s and c u l t u r a l methods. When LAI exceeds a c e r t a i n value NAR begins t o exert a dominant i n f l u e n c e . The present study supports the work of Murata (1961) i n some respects and th a t of Tanaka et a l . (1966) 155 i n o thers. An examination of the data on NAR, dry weight production and net photosynthetic rates shows that there was not much d i f f e r e n c e i n NAR between v a r i e t i e s except f o r Bluebonnet which had s l i g h t l y lower NAR, a f i n d i n g s i m i l a r t o Murata (1961). Kangni had s l i g h t l y lower values f o r photosynthesis but higher values f o r NAR, Blue-bonnet had higher values f o r photosynthesis but lower values f o r NAR. V a r i e t i e s w i t h high NAR had high dry matter production. Kangni produced highest dry matter whereas Bluebonnet was lowest which supports the argument of Murata (1961). To have a low net photosynthetic r a t e but higher NAR i n d i c a t e s a low dark r e s p i r a t i o n r a t e . I t would be i n t e r e s t i n g to see i f there are d i f f e r e n c e s i n dark r e s p i r a t i o n between the two v a r i e t i e s . Dokri had s i m i l a r patterns t o Kangni and Caloro to Bluebonnet. There was no e f f e c t of growing p l a n t s at 8- and 12-hour photoperiod on NAR, a f i n d i n g s i m i l a r t o Murata (1961), but at a l l stages s i g n i f i c a n t l y higher dry matter was produced at 12 hours than 8 hours. S i m i l a r l y there was no d i f f e r e n c e between 35/18 and 40.5/18 i n NAR but dry matter production was s i g n i f i c a n t l y higher at 35/18, which i n d i c a t e s the importance of l e a f area r a t h e r than NAR, a f i n d i n g i n agreement wi t h Tanaka et a l . (1966). Pigments The highest and lowest t o t a l c h l o r o p h y l l concentrations v a r i e d w i t h v a r i e t y and treatments. A value 156 as high as 4.89 mg/g f r e s h weight i n Caloro at 2 weeks and as low as 1.7 6 i n Dokri at 8 weeks was recorded which i s s i m i l a r t o the 4.88 mg and 1.12 mg/g f r e s h weight concentrations reported by Goto (1952a). Kangni g e n e r a l l y had lower c o n c e n t r a t i o n and at 8 weeks both Kangni and Dokri had s i g n i f i c a n t l y lower concentration than Caloro and Bluebonnet, confirming the f i n d i n g s of Katayama and Shida (1956, 1961) that e a r l y r i p e n i n g v a r i e t i e s have lower pigment content. Caloro had high t o t a l c h l o r o p h y l l c o n c e n t r a t i o n at a l l stages. Whether t h i s i n d i c a t e s that japonica v a r i e t i e s i n general have higher c o n c e n t r a t i o n can only be confirmed when more v a r i e t i e s have been t e s t e d . A comparable p a t t e r n of carotenoid c o n c e n t r a t i o n was found i n Caloro. The e f f e c t of photoperiod during p l a n t growth on c h l o r o p h y l l and carotenoids was not c l e a r enough to support the c o n c l u s i o n drawn by Chailakhyan and Bavrina (195 7) that i n short day p l a n t s growing i n short days both c h l o r o p h y l l and carotenoid concentration are higher. S i m i l a r l y concentrations are claimed to be higher i n long day p l a n t s i n long day. F r i e n d (1961) wi t h Marquis Wheat and Wolf (1964) with Seneca wheat have demonstrated t h i s long day e f f e c t . Withrow et a l . (1956), M i t r i k o s (1961), P r i c e and K l e i n (1961) and -Kasperbauer and H i a t t (1966) have demonstrated the s t i m u l a t o r y a c t i o n of red l i g h t on 157 c h l o r o p h y l l synthesis and i t s r e v e r s a l by f a r - r e d l i g h t . Considering the evidence i t seems c l e a r t h a t c h l o r o p h y l l synthesis i s under the i n f l u e n c e of phytochrome. F a i l u r e to f i n d an e f f e c t of photoperiod i n the present study i s d i f f i c u l t t o e x p l a i n . A strong underlying e f f e c t of temp-erature i s c l e a r but an examination of photoperiod w i t h i n a temperature and v a r i e t y a l s o f a i l e d t o r e v e a l any e f f e c t of photoperiod. The e f f e c t of temperature was c l e a r at a l l stages. The c o n c e n t r a t i o n of c h l o r o p h y l l and carotenoids was higher at 40.5/18, s i m i l a r l y high values were found up t o 6 weeks at 35/18. C h l o r o p h y l l concentration was never high at 35/ 26.5 and 35/35 but carotenoids g e n e r a l l y d i d not show such a trend i n d i c a t i n g that they are not so much a f f e c t e d by temperature. A comparison w i t h other species does not seem to be j u s t i f i e d as each species probably r e a c t s to environment i n i t s own way. Thus, McWilliam and Naylor (1967) found lower c o n c e n t r a t i o n of c h l o r o p h y l l i n corn at low temperature (16°C day temperature). Friend (1961) d i d not f i n d any e f f e c t of low n i g h t temperature i n wheat. Treharne et a l . (1968) found greater concentration at 29/21°C a than at 21/13°C i n orchardgrass. In the present study there was a d e f i n i t e e f f e c t of low night temperature. 158 C h l o r o p h y l l and Photosynthesis C o r r e l a t i o n of t o t a l c h l o r o p h y l l or c h l o r o p h y l l a c o n c e n t r a t i o n with photosynthesis was low though h i g h l y s i g n i f i c a n t i n many cases. The value of the c o r r e l a t i o n c o e f f i c i e n t never exceeded 0.86 which agrees with f i n d i n g s of G a b r i e l s e n (1948) and Gaastra (1962). Chances of f i n d i n g a meaningful c o r r e l a t i o n w i l l perhaps depend on the c o n d i t i o n of growth, time of a n a l y s i s and whether the whole p l a n t or an i n d i v i d u a l l e a f i s analysed. At 8-hour photoperiod s i g n i f i c a n t c o r r e l a t i o n s were found only at 4, 6 and 8 weeks at 10 hours at a l l stages and at 14-hour photoperiod there was no c o r r e l a t i o n . The c o r r e l a t i o n w i l l thus depend on the c o n d i t i o n one has chosen; t h i s may be the reason why Murata (1961) and Yamada (196 3) found a high c o r r e l a t i o n between c h l o r o p h y l l and photosynthesis. Sestak (1963, 1966) and Sestak and Catsky (1962, 1967) always found a p o s i t i v e c o r r e l a t i o n between photo-synthesis and c h l o r o p h y l l content. They b e l i e v e t h a t f a i l u r e of others to f i n d a c o r r e l a t i o n was due to f a i l u r e i n choosing s u i t a b l e c o n d i t i o n s , f a i l u r e to take i n t o c o n s i d e r a t i o n ontogenetic age of the leaves or use of extreme l e a f c o n d i t i o n s , t h a t i s , c h l o r o t i c or senescing leaves. Whether c o r r e l a t i o n with leaves r a t h e r than w i t h p l a n t s r e f l e c t s the t r u e r e l a t i o n s h i p can only be determined 159 when a comparative study has been made on l e a f and pl a n t bases. The f a i l u r e to f i n d meaningful c o r r e l a t i o n s i n the present study may be due t o the f a c t that whole p l a n t s were used. C h l o r o p h y l l and Fresh Weight Highly s i g n i f i c a n t c o r r e l a t i o n s were found between c h l o r o p h y l l content ( t o t a l per pot) and f r e s h weight produced. There were a few n o n - s i g n i f i c a n t values at 2 weeks at 8-hour photoperiod and i t seems that p l a n t s i n these treatments were s t i l l dependent on endosperm. Under such c o n d i t i o n s one would expect the c o r r e l a t i o n to be low. S i m i l a r c o r r e l a t i o n s were found by Brougham (1950) i n s e v e r a l v a r i e t i e s of dicotyledons and monocotyledons, J a k r l o v a (1967) i n a meadow community, P i l a t (1967) i n f i v e species of meadow community and Bray (19 60) i n various p l a n t communities. Oelke and Andrews (1966) on the other hand d i d not f i n d any r e l a t i o n s h i p i n corn. Carbohydrates and T o t a l Ash T o t a l carbohydrate and ash content w i l l be d i s -cussed i n the l i g h t of the observation that at 8 weeks f l o r a l i n i t i a t i o n had taken place i n Kangni at 35/26.5 10-hour photoperiod i n Caloro at 35/26.5, 8, 10 and 12 hours and i n Dokri at 35/26.5, 10 hours as determined by d i s s e c t i o n of the apex. In no case was f l o r a l i n i t i a t i o n v i s i b l e at 35/35. 160 Carbohydrate alone or carbohydrate plus ash were not highest i n these treatments i n which f l o r a l i n i t i a t i o n had taken p l a c e . In f a c t concentrations were g e n e r a l l y higher at 35/35 than at 35/26.5. S i m i l a r l y at 8 weeks, i n p l a n t s at 12- and 14-hour photoperiod the carbohydrate conce n t r a t i o n was higher than at 8 and 10 hours. I t i s c l e a r t h a t f l o r a l i n i t i a t i o n d i d not p a r a l l e l carbohydrate contents or carbohydrate plus ash contents. There was a l s o g e n e r a l l y no increase i n the two components w i t h age. The present f i n d i n g does not support the hypothesis of Grainger (1948, 1964) who b e l i e v e d t h a t f l o r a l i n i t i a t i o n does not occur unless a s u f f i c i e n t number of l e a f i n i t i a l s have developed and unless there i s a s u f f i c i e n t l y high value of the combined per cent of t o t a l carbohydrate and ash. The present f i n d i n g s a l s o do not agree w i t h those of Tsybulko (1965). 161 SUMMARY AND CONCLUSIONS In order t o i n v e s t i g a t e the e f f e c t of photoperiod and temperature and t h e i r i n t e r a c t i o n a s e r i e s of experiments were conducted on 4 v a r i e t i e s of r i c e from d i f f e r e n t l o c a t i o n s . P l a n t s were grown t o maturity under c o n t r o l l e d c o n d i t i o n s of temperature and photoperiod i n one experiment and i n other experiments various measurements and analyses were performed at 2, 4, 6 and 8 week. i n t e r v a l s . From the r e s u l t s of these experiments the f o l l o w i n g conclusions may be drawn: 1. The nature and i n t e n s i t y of th<2 e f f e c t of photoperiod and temperature depends upon the age of the pl a n t and the v a r i e t y used. V a r i e t i e s from the temperature regions are a f f e c t e d more by temperature and v a r i e t i e s from s u b - t r o p i c a l regions more by photoperiod. The v a r i e t i e s from the sub-tr o p i c s are b e t t e r adapted to high temperatures. 2. Very long or very short photoperiods delay f l o w e r i n g . Low temperatures accentuate the e f f e c t of short day and moderate the e f f e c t of long day. The reverse i s true f o r high temperatures. 3. Dry matter production i s a f u n c t i o n of v a r i e t y , photoperiod and temperature. Dry matter does not so much depend"upon photoperiod as upon 162 d u r a t i o n of l i g h t , i n c r e a s i n g w i t h i n c r e a s i n g periods of l i g h t . Both high day and high ni g h t temperature increased the t o t a l dry matter production. P a n i c l e c h a r a c t e r i s t i c s are not a f f e c t e d by temperature. Photoperiod a f f e c t s the c h a r a c t e r i s t i c s but not according t o a uniform p a t t e r n . S t e r i l i t y i s a f f e c t e d by both photoperiod and temperature. Both very short and very long photoperiods increase s t e r i l i t y . Very high day and very high night temperatures increase s t e r i l i t y . The optimum temperature f o r veget a t i v e growth i s q u i t e d i f f e r e n t from t h a t f o r reproductive growth. Conditions which may not have any d e l e t e r i o u s e f f e c t s on ve g e t a t i v e growth can s e r i o u s l y a f f e c t r eproductive growth. The r a t e of net photosynthesis i s a f f e c t e d by both temperature and photoperiod. P l a n t s otherwise s i m i l a r but grown i n s h o r t e r photo-period record a higher r a t e of net photo-synthesis than p l a n t s grown i n longer photoperiods. P l a n t s grown i n a p a r t i c u l a r temperature become adapted to that temperature and show higher r a t e s of net photosynthesis 163 at that temperature than do p l a n t s grown at another temperature. Net photosynthesis r a t e i s a l s o a f f e c t e d by age. 7. High photosynthetic r a t e s do not n e c e s s a r i l y lead t o high dry matter production nor does net a s s i m i l a t i o n r a t e m i r r o r photosynthetic r a t e . Leaf area, number of t i l l e r s and period of growth are important c o n t r i b u t i n g f a c t o r s . 8. 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