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A study of postharvest moisture loss in carrots (Daucus carota L.) during short term storage Shibairo, Solomon Igosangwa 1996

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A STUDY OF POSTHARVEST MOISTURE LOSS IN CARROTS (Daucus carota L.) DURING SHORT TERM STORAGE by SOLOMON IGOSANGWA SHIBAIRO B.Sc. Agric. (Hons), The University of Nairobi, 1985 M.Sc. Agronomy, The University of Nairobi, 1989 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Plant Science) We accept this thesis as conforming to the required standard THE UNIVERSITY 6F BRITISH COLUMBIA October, 1996 © SOLOMON IGOSANGWA SHIBAIRO In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of 9 U^hOTT ^ C l ^ S " C ^ The University of British Columbia Vancouver, Canada Date b C ^ s W j 1<T 11 Abstract Postharvest moisture loss leads to wilting of horticultural produce which shortens their shelf life and reduces their commercial value. Effects of preharvest water stress, potassium (K), cultivar, water vapour pressure deficit (WVPD) and recharging (rehydration in water) on postharvest moisture loss of carrots (Daucus carvta L.) during short term storage were studied. In greenhouse experiments, carrots subjected to water stress for 4.5 weeks preceding harvest had higher postharvest moisture loss, compared to unstressed carrots. Root water potential followed by relative solute leakage (RSL), accounted for most of the variation in moisture loss. It is suggested that preharvest water stress increases carrot tissue permeability which enhances moisture loss. Increase in K fertilization to 1.0 mM increased carrot size and lowered cell \\k and osmotic potentials (ip^ and RSL from the root tissue. Regression analysis showed that K affects moisture loss mainly by influencing carrot size and tissue permeability, and that the benefit of K fertilization in improving shelf life is limited to conditions of low K availability. Consistent differences in postharvest moisture loss among eight field-grown, late harvested carrot cultivars were observed at low relative humidity. These differences, which accounted for up to 6 days of difference in shelf life, were associated with specific surface area and transpiration coefficient of carrot roots. Carrots at high WVPD lost more moisture. The results showed carrot tissue permeability increases during storage at high WVPD which further enhances the rate of moisture loss. Increase in duration of recharging increased carrot weight gain but had no effect on the rate of moisture loss during subsequent storage. Weight gain was greatest during the first week after harvest. Recharging, therefore, should be explored as a means to replace moisture lost and extend shelf life of carrots. The effects of preharvest water stress, nutrition and cultivar on specific surface area, \j4 and tissue permeability were found to be important in determining the shelf life of carrots, It may be possible to improve the shelf life by reducing preharvest water stress, K fertilization, cultivar selection, storage at high relative humidity, and recharging. iv Table of Contents Abstract ii Table of Contents iv List of Tables viii List of Figures x List of Appendices xii Abbreviations xiii Acknowledgements xv General Introduction 1 Research objectives 4 Chapter L literature review 6 Origin of carrots 6 Importance of carrots 6 Carrot production in B.C 6 Definition of shelf life 7 I. Physical and physiological factors affecting postharvest moisture loss 7 A. Physical factors 7 (i) Plant size and shape 7 (ii) Plant surface . 8 B. Physiological factors 9 C. Tissue permeability 10 II. Preharvest factors determining shelf life 10 A. Water stress 10 B. Plant nutrition 11 C. Cultivar differences 13 III. Postharvest factors affecting moisture loss 15 A. Effect of WVPD 15 (i) Effects of temperature 15 (ii) Effects of RH 17 B. Recharging 18 Chapter IL Influence of preharvest water stress on postharvest moisture loss of carrots 20 Abstract 20 Introduction 20 V Materials and methods 22 A. Carrot size and shape 23 B. Moisture loss during storage 24 C \ | V measurements 24 D. RSL measurement 25 E. Statistical analysis 26 Results 27 A. Carrot size and shape 27 B. Moisture loss during storage 27 C. v ,^ V|4 and 31 D. RSL 31 E. Stepwise multiple regression analysis 31 Discussion 34 Chapter I1L Potassium nutrition and postharvest moisture loss in carrots 37 Abstract 37 Introduction 37 Materials and methods 39 A. Carrot size and postharvest moisture loss measurements 40 B. and Vj/^ measurements 40 C. RSL measurements 40 D. K concentration in tissue (TK) 41 E. Statistical analysis 41 Results 42 A. Carrot size and postharvest moisture loss 42 B. and \\f^ 42 C. RSL 45 D. TK 45 E. Stepwise multiple regression analysis 45 Discussion 49 Chapter IV. Moisture loss characteristics of carrot cultivars during short term storage at 13°C 52 Abstract 52 Introduction 52 Materials and Methods 54 A. Carrot size and shape measurements 55 B. Moisture loss characteristics of cultivars 55 C. ipk and Vj/rtR measurement 56 D. Relative electrolyte leakage (REL) 56 E. Statistical analysis 57 vi Results 58 A Size, shape and surface area to volume ratio of cultivars 58 B. Moisture loss characteristics of cultivars 58 C. Cultivar i|4 and vpf^  and REL 62 D. Multiple regressions between W* and various physical and physiological attributes 65 Discussion 67 A. Cultivar Differences 67 B. Multiple regressions between W* and the various physical and physiological attributes 68 Chapter V: Effect of moisture loss on water potential, osmotic potential and tissue permeability during short term storage of carrots 71 Abstract 71 Introduction 71 Materials and Methods 73 A Effect of WVPD on root moisture loss 73 B. 1)4 and VJ/^ R measurements 74 C. REL measurement 74 D. Statistical analysis 75 Results 76 A. Effect of WVPD on root moisture loss 76 B. V|4 and v^. 76 C. REL 80 D. Regressions between W* and various parameters. 80 Discussion 82 Chapter VI: Replacement of postharvest moisture loss by recharging and its effect on subsequent moisture loss during short term storage of carrots 87 Abstract 87 Introduction 88 Materials and methods 89 A. Single recharging treatments 89 (i) Recharging duration 89 (ii) Ternperature and duration of recharging 90 B. Repeated recharging treatments 91 (i) Duration and frequency of recharging 91 (ii) Recharging on bruised carrots 92 Results 93 A Single recharging of carrots 93 (i) Recharging duration 93 (ii) Ternperature and recharging duration 93 vii B. Repeated recharging 96 (i) Duration and frequency of recharging 96 (ii) Recharging on bruised carrots 99 Discussion 103 A. Single recharging of the carrots 103 B. Repeated recharging of carrots 105 Chapter VII. Conclusions and Recommendations 108 Bibliography 114 Appendices 123 viii List of Tables Table 1. Effect of preharvest water stress on root length (L), crown diameter (D), weight (W), C-value, and specific surface area (SSA) in Eagle and Paramount cultivars of carrots . 28 Table 2. Effect of preharvest water stress on leaf water potential (v )^, root water potential (vj^ ), osmotic potential (11/,^ ), and relative solute leakage (RSL) in Eagle and Paramount cultivars of carrots 32 Table 3. Parameters and statistics for multiple regression models of the relationship between moisture loss (W) and the various attributes for carrots stored at 13°C and 32% relative humidity 33 Table 4. Parameters and statistics for multiple regression models of the relationship between percent moisture loss (W) and the various attributes for carrots stored at 13°C and 32% relative humidity 47 Table 5. Root specific surface area (SSA) (cm2 g"1) of carrot cultivars harvested early and late in 1993 and 1994 59 Table 6. Percent moisture losses at 7, 14, and 21 days (d) of storage at 13°C and either 80% (HRH) or 35% (LRH) relative humidity from carrots harvested early and late in 1993 60 Table 7. Percent moisture losses at 7, 14, and 21 days (d) of storage at 13°C and either 80% (HRH) or 35% (LRH) relative humidity from carrots harvested early and late in 1994 61 Table 8. Transpiration coefficient (mg mm'2) of carrot cultivars at 13°C and either 80% (HRH) or 35% (LRH) relative humidity in early and late harvests of 1993 and 1994 63 Table 9. Water potential (\j^ ), osmotic potential (vpL^ ) and relative electrolyte leakage (REL) at 13°C and 35% (LRH) relative humidity for late harvested carrots in 1993 and 1994 64 Table 10. Parameters and statistics for best subset multiple regression models of the relationship between moisture loss (W*) and various attributes for carrots stored at low relative humidity (LRH) in late harvest in 1993 and 1994 66 Table 11. Effect of water vapour pressure deficit (WVPD) on percent moisture loss per KPaper day 78 ix Table 12. Parameters and statistics for best subset multiple regression model of the relationship between moisture loss (W*) and the various carrot variables 81 Table 13. Weight gain upon recharging and the rate of moisture loss of carrots recharged for different durations at day 3.5 and stored at 13°C and 35% RH for 21 days 94 Table 14. Weight gain upon recharging and the rate of moisture loss of carrots recharged at various temrx^ ratures for different durations at day 3.5 and stored at 13°C and 35% RH for 21 days 95 Table 15. Percent weight gain of carrots recharged every 3.5, 7 and 14 days for a duration of 6 h and stored at 13°C and 35% RH for 21 days 100 X List of Figures Figure 1. Time course of percent moisture loss in cultivars Eagle and Paramount stored at 13°C and 32% relative humidity 29 Figure 2. Transpiration coefficient (TC) in cultivars Eagle and Paramount stored at 13°C and 32% relative humidity for 20 days 30 Figure 3. The relationship between potassium concentration in growth medium ([K+]) and (A) moisture loss (%) (Wp) and (B) transpiration coefficient (mg mm"2) (TC) of carrots following 14 days of storage 43 Figure 4. The relationship between potassium concentration in growth medium ([K+]) and (A) carrot root weight (W), (B) water potential (\|4), and (C) osmotic potential (\\f^) 44 Figure 5. The relationship between potassium concentration in growth medium ([K+]) and (A) relative solute leakage (RSL) and (B) potassium concentration in tissue (TK) 46 Figure 6. The relationship between moisture loss (%) (W) and (A) carrot root weight (W)and(B) relative solute leakage (RSL) 48 Figure 7. Moisture loss (%) of carrots stored under different water vapour pressure deficits (WVPD) 77 Figure 8. (A) Water potential, (B) osmotic potential and (C) relative electrolyte leakage of carrots stored at different water vapour pressure deficits (WVPD). . . . 79 Figure 9. The relationship between carrot moisture loss (arcsin transformed) (W*) and (A) water potential (B) osmotic potential (\\f^t), and (C) relative electrolyte leakage (REL).. 83 Figure 10. (A) weight gain (%), (B) weight gain (% h"1 of recharging) and (C) apparent weight loss (%) of carrots recharged for different durations and stored at 13°C and 35% RH for 21 days 97 Figure 11. The effects of repeated recharging every 3.5 days for 0, 3, 6 and 9 h (from left to right) on the colour and flexibility of carrots 98 Figure 12. Apparent weight loss (%) of carrots recharged for 6 h every 3.5, 7 and 14 days and stored at 13°C and 35% relative humidity for 21 days 101 xi Figure 13. Effects of recharging every 3.5 days for a duration of 6 h on (A) weight gain (%) during recharging and (B) apparent weight loss (%) of recharged and non-recharged bruised carrots stored at 13°C and 35% relative humidity for 21 days 102 Figure 14. The effect of bruising on surface coloration in (A) recharged and (B) non-recharged carrots 104 xii List of Appendices Appendix 1. Combined exponential and power functions (Y = a x [K+]b x c^+]) fitted among potassium concentration in growth medium ([K+]) and root length (L) and the widest diameter of the root (D) 123 Appendix 2. Length (L), C-value (C), weight per root (W) and surface area (A) of carrot cultivars harvested in 1993 124 Appendix 3. Length (L), C-value (C), weight per root (W) and surface area (A) of carrot cultivars harvested in 1994. . 125 xiii Abbreviations A Carrot surface area As Arcsin AWL Apparent weight loss . b Partial regression coefficient V Standard partial regression coefficient bx, to bn Partial regression coefficients C C-value (indicator of shape) Cp Mallow's coefficient Cv Cultivar d Storage duration (days) D Greatest carrot root diameter (crown diameter) h hour HRH High relative humidity [K+] Potassium concentration in growth medium L Carrot root length LRH Low relative humidity r2 Partial correlation coefficient R 2 Model correlation coefficient REL Relative electrolyte leakage RH Relative humidity RSL Relative solute leakage A/V Surface area to volume ratio SSA Specific surface area (surface area to weight ratio) TC Transpiration coefficient (moisture loss per unit surface area) (TK) Potassium concentration in root tissue V Root volume W Carrot root fresh weight w* arcs in transformed percent moisture loss w percent moisture loss (expressed as a percentage of the root fresh weight) W W Water vapour pressure WVPD Water vapour pressure deficit Water potential Osmotic potential Carrot root osmotic potential WL Carrot leaf water potential Carrot root water potential X V Acknowledgements I wish to thank the University of British Columbia and the University of Nairobi CIDA linkage for a postgraduate scholarship. My sincere appreciation goes to Dr. M Pitt for the valuable coordination of the program, support and constructive criticism during this study. I also thank the Natural Sciences and Engineering Research Council of Canada, Science Council of B.C., B.C. Agricultural Research Council, and B.C. Coast Vegetable Cooperative for financial support. My inmost appreciation goes to my research supervisor, Dr. M.K. Upadhyaya, for his guidance, patience and support during the course of the study. I am, also, thankful to the other members of my research committee, Drs, P. Jolliffe, A. Bomke and P .MA Toivonen for their valuable guidance. This study would not have been possible without the support of the staff and the students of the Department of Plant Science whom I thank most. Special thanks goes to my friends M Upenyu, F. Njenga, J. Odhiambo, R Biegon, N. Furness, F. Wanjau, M Tesfaye, E. Srinivasan and M Srinivasan. I also thank the whole Kenyan community for their endless help in all aspects of my life at this University. I dedicate this thesis to my father Shibairo and mother Khasoa and my loving wife Khasoa, son Murira and daughter Mwani in appreciation for their love, support and strong endurance during my stay without which this study would not have been possible. Praise be to our Heavenly Father for whose love and wish we are all able to do this. 1 General Introduction Carrot (Daucus carota L.) is the second most important vegetable crop of British Columbia (B.C.), Canada, with an annual sale of 5.97 million dollars (Anon., 1988-94). The crop, however, has faced a continuous decline in acreage during the 1989 to 1994 period; the acreage under this crop declined from 646 acres in 1989 to 575 acres in 1994. The decline was partly due to replacement by other vegetables (e.g. potatoes) and partly to shorter shelf life of B.C. grown carrots as compared to Washington and California imports. Allegedly, B.C. grown carrots are more susceptible to wilting and become commercially unacceptable faster than imports. Trie problem of short shelf life also occurs in developing countries (e.g. Kenya), where carrots (and vegetables in general) are harvested and put on the shelf for immediate sale. Moisture loss from carrots not only makes them shrivel but also changes their colour and texture, making them less appealing. Understanding the factors which regulate moisture loss is essential to improve shelf life and, therefore, the commercial value of this crop. Several factors have been implicated in moisture loss in root crops. Environmental factors (e.g. ternperature and relative humidity) (van den Berg and Lentz, 1966; van den Berg, 1981), physical factors (e.g. root size, shape and anatomy) (Apeland and Baugenad, 1971; den Outer, 1990) and the physiological status of the root at harvest (Nilsson, 1987) determines weight loss in carrots which is predominantly due to moisture loss. Most fresh market vegetables are stored and marketed under water stressed [high water vapour pressure deficit (WVPD)] conditions. It is well established that the rate of transpiration from a plant organ is proportional to the WVPD (Apeland and Baugenad, 1971; 2 Kays, 1991). However, knowledge of the physiological changes as well as of the extent of damage that occurs during harvesting and storage for carrots is lacking. Such knowledge can help in the development of improved postharvest handling methods to preserve produce quality. Produce with greater surface area have high rate of transpiration (Apeland and Baugered, 1971; Kays, 1991). Large-sized produce loses moisture at a lower rate when expressed on per unit weight basis than smaller produce (Apeland and Baugerod, 1971; Ketsa, 1990). Surface area to volume ratio (A/V) of produce has been suggested to be a better indicator of the rate of moisture loss compared to either the surface area (A) or weight (W) (Sastry et al., 1978; Wills et al., 1981). A higher A/V, which means a larger area per unit volume, results in greater moisture loss. Carrot periderm 'skin' thickness and composition (Esau, 1940; Knowles and Flore, 1983) and interstitial and cell wall resistances (Russel and Goss, 1974) could determine transpiration loss during short term storage. How these factors affect the shelf life of carrots has not been investigated. Such information could lead to development of improved preharvest and postharvest practices to enhance the shelf life of carrots. Carrot is an underground storage root that is harvested in the first year when it is metabolically very active. Carrot harvest, therefore, represents an artificial interruption of what naturally should be a two year life cycle (Nilsson, 1987). Physiological and metabolic changes that have been reported to occur during storage include: changes in cell turgor, respiration, soluble sugar content, level of amino acids, organic acids and phenolic substances (Phan et al., 1973; Finlayson et al., 1989). These changes may alter total solute content of 3 cells which determines their osmotic potential (ij/J, a component of water potential \\f gradient is one of the driving force for water movement across a membrane. The dissolved substances, which include ions (K+, N03", Ca2+), organic molecules (sugars and amino acids) and proteins, make \\f more negative. K + is the major contributor to cell \\fn in plants (Salisbury and Ross, 1992). Intact plants with a negative \]7 tend to have low transpiration rates. However, it is not known whether carrots harvested at low \\J have a lower postharvest transpiration compared to those harvested at higher \\J. Factors which affect a cell's V}/ include soil moisture tension, nutrition (especially K +) and genotype. The extent to which these factors determine \\J and hence postharvest moisture loss in carrots has not been investigated. In addition to \\f, water movement is governed by the conductance of the flow path (Boyer, 1985; Salisbury and Ross, 1992). In intact plants, the plasma membrane offers resistance to water movement between cells. In storage, tissue permeability can be affected by many factors. Finlayson et al. (1989) observed increased electrolyte leakage with increase in ternperature during carrot storage. Potato cultivars with higher fatty acid unsaturation levels have been shown to have lower membrane leakage (Spychalla and Desborough, 1990). Many tissues have been shown to increase the proportion of unsaturated fatty acids in response to low temrx^ ratures (Thompson, 1984; Yoshida, 1984). However, the significance of tissue permeability in determining moisture loss from carrots during short term storage is not known. Since carrot quality loss during the short term storage is mainly due to moisture loss, replacement of the lost water could be an option to extend shelf life. It is an industry practice to submerge carrots in water before packaging for either field heat removal or fungicide 4 application. However, submerging carrots in water to replace the transpired moisture (recharging) is not practiced. Development of a system to replace water to enhance cell turgidity could improve the shelf life of carrots. The influence of duration and frequency of recharging and of temperature during recharging on carrot quality need to be explored. Research objectives The research in this thesis investigates the factors affecting postharvest moisture loss in carrots, and attempts to determine whether recharging can replace the lost moisture and/or lower the rate of moisture loss during storage in carrots. The specific objectives are to determine: 1. if preharvest water stress influences postharvest moisture loss from carrots, and the physical and physiological basis of this influence, 2. the effect of potassium (K) nutrition on postharvest moisture loss, and the physiological basis of this effect, 3. if carrot cultivars differ in their postharvest moisture loss characteristics during short term storage at 13°C, and whether these differences could be attributed to differences in physical and/or physiological characteristics of carrot roots, 5 4. the effect of WVPD on carrot root moisture loss, V J ; ^ and tissue permeability in terms of cellular leakage, and the relationships among postharvest moisture loss and V J J ^ , vj/^  and tissue permeability, 5. the effects of duration and frequency of recharging, temperature during recharging and recharging of bruised carrots on root weight gain during recharging and moisture loss during subsequent storage. Organization of the thesis. Chapter I is an introductory chapter which includes a review of the literature on factors affecting moisture loss in horticultural produce during storage. The research to fulfil objectives 1 to 5 is reported in Chapters II, III, IV, V and VI, respectively. The last chapter (Chapter VII) gives general conclusions drawn from the research presented in this thesis. Chapter L Literature review Origin of carrots Carrots (Daucus carvta var sativa L.) belong to the family Apiaceae (Umbelliferae) (McCollum, 1980; Pierce, 1987). Although both annual and biennial forms exist, the cultivars grown in North America are biennial. Carrots are believed to have originated in the Middle Asia and were first domesticated in Afghanistan around 600 AD from where they spread to the Mediterranean region and to the rest of the world (McCollum, 1980; Pierce, 1987). Importance of carrots Of all root crops, carrot is the most important (Pierce, 1987). Early use of the plant was mainly medicinal, prescribed for curing stomach problems and treating wounds, ulcers, and liver and kidney ailments. The carrot crop is now grown worldwide as a major source of vitamin A and a good source of vitamins B l 5 and C (McCollum, 1980). For fresh market carrots, moisture loss leads to loss of quality and shortens the shelf life. The features that consumers use as measures of freshness include colour, crispness, firmness, succulence and sweetness (Ben-Yehoshua, 1987; Ryall and Lipton, 1979). Maintenance of these qualities at a level similar to that at harvest is a major challenge in postharvest handling of carrots. Carrot production in B . C Over 80% of the carrots in the Fraser Valley of B.C. are grown on muck soils [> 30% organic matter with pH 5.5 to 7.0 (A. Bomke, Soil Science Department, U.B.C., personal communication)] and the rest on deep well drained, sandy loam. Almost all the carrots are produced for fresh market sales and none for processing. In general, carrots are seeded in late April and harvested from the end of July until 7 November. Carrots are handled and distributed to wholesalers and retailers by the local cooperatives or are sold on farm and roadside. The carrots are, therefore, stored and marketed under a wide range of WVPD conditions. In this study, storage at 13°C and 35% (LRH) was used to simulate the retail shelf conditions prevalent in B.C.. Definition of shelf life Shewfelt (1986) defined shelf life as "the time period that a product can be expected to maintain a predetermined level of quality under specified storage conditions". In asparagus, Hurst et al. (1993) defined shelf life as "the number of days at 20°C before asparagus reaches the end of its marketable life". Shelf life can be defined as "the time period a vegetable product can stay in storage and/or on the retail shelf while maintaining an acceptability to the consumer, similar to produce harvested at an optimum stage for immediate consumption" (Dennis, 1981). Carrots shelf life has been defined as "the number of days carrots can stay at specified storage conditions before they attain the maximum permissible moisture loss which is 8% of the initial root weight" (Robinson et al., 1975). Postharvest weight loss in perishable crops is a widely used indicator of storage life (Ben-Yehoshua et al., 1983 and Hurst et al., 1993) and is used as a index of shelf life in this thesis. I Physical and physiological factors affecting postharvest moisture loss A. Physical factors (i) Plant size and shape Variation in vegetable size and shape may influence the rate of moisture loss from produce. In carrots, root fresh weight has been reported to determine moisture loss (Apeland and Baugerod, 1971). Apeland and Baugered (1971) working with different size 'Nantes' 8 carrots observed an increase in postharvest weight loss with a decrease in initial root weight; an approximate doubling of weight loss, expressed as a percentage of the initial root weight, occurred as the initial weight decreased from 120 g to 15 g. A/V is a better indicator of transpiration than W (Sastry et al., 1978). The rate of moisture loss is directly proportional to A/V of the transpiring structure (Apeland and Baugerod, 1971; Sastry et al., 1978; Wills et al., 1981; Kays, 1991). Since specific gravity of carrots is approximately unity (Bleadsdale and Thompson, 1963), carrot weight in grams gives an accurate measure of root volume. Hence, the surface to weight ratio, referred to as specific surface area (SSA), is a good indicator of A/V. In carrots with similar shapes, weight loss has been shown to be inversely proportional to the diameter of the root crown (D) (Apeland arid Baugerod, 1971). The shape of the root, as indicated by C-value [an index calculated using W, D and length (L)] (Bleadsdale and Thompson, 1963; Apeland and Baugerod, 1971), also correlated with weight loss. A cone-shaped root (C = 0.33) lost 50% more weight than a cylindrical root (C - 1.00) of equal D and W. Soil moisture tension (Stanhill, 1977) as well as soil fertility (Beverly et al., 1993) are the environmental factors which affect plant size and shape. Carrot cultivars differ in size and shape (Reynolds, 1968; Stanhill, 1977 and Hole et al., 1983). The extent to which the size and shape differences as affected by soil, moisture tension, nutrition and cultivar contribute to carrot shelf life has not been investigated. (ii) Plant surface The outer layer of a carrot, often referred to as "skin' or periderm consists of three 9 parts: phellogen, phellem, and phelloderm (Esau, 1965). Carrots have been reported to differ in periderm weight (Knowles and Flore, 1983) and the suberin and lignin deposition in its component cells (Esau, 1965). These properties of the periderm may also be determined by the environment. For example, tissues exposed to excess moisture have reduced suberization (den Outer, 1990). Differences in storage conditions and the structure of evaporating surfaces influence transpiration coefficient (TC; an indicator of the rate of moisture loss per unit surface area of a plant surface) in vegetables (van den Berg, 1987). The effect of the evaporating surface (periderm) on TC and hence the moisture loss during storage in carrots has not been investigated. B. Physiological factors The total solute content of a cell determines its osmotic property. K + , N03", Ca 2 +, and organic molecules such as sugars and amino acids, and some proteins (Salisbury and Ross, 1992) make the cell's \\f more negative. Since \\f gradient is the driving force of water into plant roots, root cells with low \\f may resist water loss by transpiration. Evers (1989a-d) showed that fertilization increased the amount of K + and other inorganic ions in carrot roots. Higher soil moisture at harvest can result in high \\f of carrots, which could make them more vulnerable to water loss during storage. Carrots may adjust to water stress by decreasing their \\fm and hence reduce postharvest moisture loss. The extent to which a decrease in Vj/ at harvest, caused by increased ionic fertilization or soil moisture tension, may affect postharvest moisture loss in carrots is not known. 10 C. Tissue permeability Cell membrane permeability may change with senescence. This may result in leakage of dissolved materials from cells (Berard and Lougheed, 1982) and affect cell turgor. Since the plasma membrane offers resistance to water movement (Boyer, 1985), an increase in membrane permeability either at harvest or during storage will increase apoplastic water flux leading to an increase in transpiration. Electrolyte (Finlayson et al., 1989; Knowles and Knowles, 1989) and solute (Pooviah and Leopold, 1976; Toivonen, 1992) leakage have been used as indicators of membrane permeability in vegetable crops. Several factors have been implicated in the change of membrane integrity during storage of vegetables. Finlayson et al. (1989) observed increased electrolyte leakage and disruption of membranes with increase in temperature for diseased carrots. Carlin et al. (1990) observed an increase in K + leakage in carrots with increase in C 0 2 or a decrease in 0 2 concentration. In potatoes, cultivars with higher levels of unsaturated fatty acids had lower rates of membrane leakage (Spychalla and Desborough, 1990). Thompson (1984) and Yoshida (1984) reported that the degree of fatty acid unsaturation in many tissues increased in response to low temperature. However, the relationship between membrane permeability and postharvest moisture loss during short term storage in carrots has not been investigated. IL Preharvest factors determining shelf life A. Water stress From the above discussion, it is inferred that root size, periderm, and physiological characteristics can influence postharvest moisture loss from carrots. Water stress causes cell 11 turgidity to drop significantly which in turn affects cell expansion. An increase in water stress beyond a limit could decrease cell wall and protein synthesis and increase respiration and proline and sugar accumulation (Hsiao, 1973). Some plants exposed to periods of low water availability become more resistant to subsequent stress, a process called acclimatization or hardening. It is suggested that vegetables subjected to conditions where they become acclimatized to water stress have lower postharvest moisture loss. Plants have evolved different mechanisms for acclimatization, e.g., increase in leaf cuticle thickness, periderm changes in roots, and modification of size and shape. Plants may lower cell vj/ro via active accumulation of solutes (Turner and Jones, 1980), which in turn lowers \\i allowing water absorption to occur (Kramer, 1983). Kays (1991) suggested that water content at the time of harvest may affect the rate of moisture loss during postharvest storage in perishable plant products. Products with a lower water content lose water at a slower rate during storage than products with a higher water content. Hurst et d. (1993) reported that early-season asparagus spears, which contained more water compared to mid- or late-season spears, also lost more fresh weight during storage. Whether moisture status at the time of harvest affects postharvest moisture loss in carrots is not known. B. Plant nutrition In addition to carbon, hydrogen and oxygen, plants require 14 essential inorganic nutrients to complete their life cycles. Nutrients are needed for photosynthesis, metabolism, carbohydrate transport, protein synthesis and plasma membrane and cell wall integrity. 12 Of the cations, K + is most abundant in plant cells (Salisbury and Ross, 1992). Apart from increasing solute concentration, K + ions are charged, hence hydrophillic and therefore, increase the osmotic pull of cells. Preharvest applications of K, therefore, could lower the \\fn of carrot roots at harvest. The lowering of \\fn would reduce postharvest moisture loss during storage. K is also required for normal plant performance and maximizing crop yields. It increases cell turgor and volume (Raschke, 1979) and is, therefore, important in cell extension and growth. K enhances the development of tubers and/or roots by enhancing a less competitive shoot sink and stimulating phloem loading and translocation of assimilates (Beringer et al., 1990). It is well established that increase in dry matter and accumulation of K in plant cells saturate beyond a certain [K+] (Glass and Siddiqi, 1984). In carrots, a decrease in the level of total sugars and an increase in sucrose with increasing K application rates has been observed in low-K peat and loam soils (Habben, 1972). Biegon (1995) found no effect of K on yield or postharvest weight loss in high-K muck soil. However, the effects of low levels of K on postharvest moisture loss have not been studied. K + is required in catalytic amounts for activation and stabilization of enzymes and membranes (Clarkson and Hanson, 1980; Evans and Sorger, 1966). It is required for membrane transport systems (Hodges, 1976) and for the tWckening of cell walls, which increases tissue stability (Beringer and Nothdruft, 1985). Membrane integrity is essential for regulation of solute transport (Zeiger, 1983) and maintenance of the osmotic pull. K + interacts with many other ions in affecting crop yield and quality (Daliparthy et al., 1994). This interaction can occur in the soil or in the plant. In soils containing 2:1 expanding 13 clay minerals, K + modifies N H / fixation thereby influencing N availability (Tisdale et al., 1993). On the other hand, an antagonistic effect between K + and N H / absorption can restrict K + absorption. Similarly, Mg 2 + or Ca 2 + deficiency in acid soils results from their antagonism with exchangeable K + (Loue, 1977). Short distance ion transport studies show K + channels are regulated by other ions including Ca 2 + and Ba 2 + (Kohler et al., 1986; Tahler et al., 1987). Such interactions may limit K + availability. Because of these interactions, crop yields may increase in response to K + application even on soils with high K. For example, in basaltic soils of north-west Tasmania, potato yield increased in response to K fertilization even on sites with up to 300-400 mg/kg bicarbonate-extractable K + (Chapman et al., 1992). Apart from its effect on tuber size, K + has been shown to affect the susceptibility of potatoes to bruising. Both internal bruising (Maier et al., 1986) and periderm bruising (Chapman et al., 1992) were reduced in potatoes with high K + application. C. Cultivar differences Reynolds (1968) grouped 387 commercial main-crop carrot cultivars into five groups on the basis of shape, size and the optimum time of harvest. The cultivars, in increasing order of weight were: Amsterdam Forcing, Nantes, Berlicum, Chantenay and Autumn king. Many hybrids have been bred from these major groups of carrots. Hole et al. (1987) in a study of differences in carrot root weights, found that the highest weights were associated with larger shoots. The relative growth rates were similar for all carrots during the first 41 days after sowing, but changed thereafter. It was suggested that genetic factors affect partitioning between the shoot and root in the latter stage of carrot growth, causing differences in root 14 size with the time of harvest. A wide diversity in carrot shape among and within cultivars has been reported (Banga, 1962; Umiel et al., 1972). This diversity includes differences in W, D, root core and cortex diameters, and relationships between these size parameters (Umiel et al., 1972; Bleadsdale and Thompson, 1963). The relationship between these parameters and shelf life of commercial cultivars has not been investigated. Carrot cultivars are known to differ in periderm characteristics. Knowles and Flore (1983) observed that the weight per unit area of isolated periderm varied with cultivar and ranged from 470 to 790 \ig cm"2. Burton (1982) suggested that the compactness and thickness of cuticle or periderm could result in moisture loss differences among commodities, varieties and species. How these genetic differences in periderm characteristics influence moisture loss in carrots has not been investigated. The shelf life of carrots could be improved by breeding for desirable periderm characteristics to reduce transpiration loses. Cultivars differ in physiological characteristics such as cell turgor, respiration, soluble sugar content, and the levels of amino acids, organic acids and phenolic substances (Phan et al., 1973). The sugar content of a cell, a major contributor to V | ^ , increases during growth (Fritz and Weichmann, 1979; Weichmann and Kappe, 1977) and decreases during storage (Ben-Yehoshua, 1987; Nilsson, 1987). The relationship between carrot core and whole root diameter ratio and soluble solids has been shown to vary with cultivar (Bassett, 1973). The large-cored cultivars have low soluble solids. Whether these differences cause differences in shelf life of cultivars is not known. Also, whether carrot cultivars differ in their \\J at harvest, and the relationship between \\f and postharvest moisture loss has not been studied. 15 III. Postharvest factors affecting moisture loss A. Effect of WVPD Transpiration in vegetables is a mass transfer process in which water vapour moves from the produce surface to the surrounding air. The driving force for transpiration (i.e. WVPD) is the difference between water vapour pressure (WVP) in the air and the equilibrium WVP of the vegetable (van den Berg, 1987). The relationship of WVPD and the rate of transpiration is curvilinear (Burton, 1982). At a constant temperature, a 5% change in relative humidity (RH), has a much larger effect on transpiration at high than at low RH; e.g. a decrease from 98 to 93% RH increases transpiration by 250% whereas a decrease from 85 to 80% results in an increase of only 33% (Burton, 1982). (i) Effects of temperature As discussed above, temperature affects the rate of transpiration from vegetables by affecting the WVPD. Increase in temperature increases transpiration by increasing WVPD (Apeland and Baugerod, 1971; van den Berg, 1987; Kays, 1991) as well as increasing the rate of diffusion of water (Boyer, 1985; Kays, 1991). Temperature also affects metabolic rates of vegetables in storage. For example, respiration is significantly reduced by lowering of temperature (Weichmann, 1987). Low temperatures increase the activity of enzyme invertase in carrots making them 'sugary' (Phan, 1987); the invertase breaks sucrose into monosaccharides, fructose and glucose. The depleted sucrose is replaced by the breakdown of starch reserve. In low ternperature sensitive vegetables, e.g. okra and cucumber (Kader, 1987), chilling increases the rates of glycolysis 16 and mitochondrial respiration. In addition, low temperatures lower membrane integrity and increase solute leakage which is one symptom of for chilling injury in perishable plant products (Kays, 1991). van den Berg and Lentz (1966) reported that carrots stored at low temperature (0 to 1°C) remained crispy and juicy like fresh carrots while those stored at 2.3 to 3.9°C desiccated after 9 months of storage at 98 to 100% RH. However, van den Berg and Lentz (1973) found no effect of an increase in temperatures up to 4.5°C on weight loss in carrots. The weight loss observed at this temperature was due to its effect on the activity of decay-causing microorganisms. Smith (1967) suggested that temperatures in the range of 0 to 3°C are critical for storing carrots up to two months; 1°C appeared to be the optimum for longer storage. Studies by van den Berg and Lentz (1966) showed that respiration accounted for very little of the weight loss (0.1% per month) at 0°C during short term storage. Apeland and Hoftun (1974) observed an evolution of 4, 5 and 7 mg C 0 2 kg"1 of carrots h"1 at 0, 2 and 5°C, respectively. Assuming a respiration quotient of 1 (i.e. oxidation of glucose equivalents), these rates would account for 0.11, 0.15, and 0.21% of the weight loss per month at 0, 2 and 5°C, respectively. To date, information on the effects of the high temperatures commonly found at retail shelves on carrot weight loss is not available. Storage of produce at temperatures higher than its "biologically safe" range increases lipid liquification and membrane damage (Kays, 1991). These changes could lead to increase in apoplastic water flux (Boyer, 1985) and transpiration. Whether temperature affects postharvest moisture loss from carrots through its effect on membrane characteristics has not been established. 17 (ii) Effects of RH Recommended levels of RH for storing vegetables are a trade-off between desiccation of the products at low humidity and an increase in decay at high humidity (van den Berg and Lentz, 1966; van den Berg, 1981). The recommended optimum RH for carrots, however, is close to 98 to 100% because decay at the low temperatures used is not a serious problem. Quality assessment of carrots by van den Berg and Lentz (1966) showed that storage at high RH (98-100%) substantially lowered their moisture loss for up to 9 months. The carrots remained crisp and juicy as freshly harvested carrots. The unexpected reduction in decay at high RH, even when moisture condensation occurred on the carrot surface, was in part due to a reduction in the pectolytic activity of the decay-causing microorganisms at high humidity (Smith and Yang, 1969). Desiccation, wilting and some incidence of disease has been reported to occur in carrots stored at lower RH (92 to 96%) (van den Berg and Lentz, 1966; van den and Lentz, 1973). Thus, storage at high RH is essential to prolong shelf life of carrots. For long term storage, jacketed and Filacell systems provide practical and economical ways of maintaining a water saturated atmosphere during storage (Raghavan et al., 1980). The jacketed storage provides high humidity and maintains a uniform temperature and air movement (Lentz and Rooke, 1957). Other humidification systems include plastic packaging. Raghavan et al. (1980) used sealed boxes and constant temperature cold rooms, and obtained the same benefit as jacketed storage at high RH. Since at the retail level carrots are stored under variable temperatures and RHs for only a few days, the use of Filacell and jacketed storage to reduce transpiration may not be 18 economical. Alternative methods for short term storage to reduce postharvest moisture loss are, therefore, needed. Before the development of such technologies, an understanding of the changes that occur in carrot roots under the retail shelf conditions is essential. As discussed above, \\f and plasma membrane integrity could determine the rate of moisture loss of carrots. The effect of WVPD on these factors and their relationships with postharvest moisture loss need to be elucidated. B. Recharging Since carrot quality deterioration during storage is mainly due to moisture loss, reduction of moisture loss or replacement of the lost moisture may improve carrot shelf life. Reduction of moisture loss is achieved by refrigeration, which slows evaporation, and by storage in jacketed rooms, Filacell systems or sealed boxes in cold rooms (Raghavan et al., 1980), all of which decrease WVPD around the produce. However, these options are expensive to build and maintain at the retail level. Carrots are usually hydrocooled after harvest to remove field heat, brushed to remove dirt, and graded on "carrot line" before storage. Other methods of field heat removal include dipping in a water-tank carriage, or placement in bins that are passed under a system of showers, or placement in bins on a carriage that is entirely immersed in a water pool, generally with disinfecting chemicals added, before conveying to the storage rooms (Phan, 1987). Direct humidification, where water is sprayed on top of bulk-stored carrots with refrigerated air moving down through the product, is also practiced (van den Berg, 1987). However, these systems involve submerging carrots in water for only short durations, which 19 may not provide enough time to allow carrots to absorb water for shelf life improvement. Recharging by submerging carrots in water in order to increase their turgidity and extend shelf life has not been explored. In other crops e.g. Denarobiwn flower, submerging influorescences in water immediately after harvest did not significantly increase postharvest life; submerging in water after harvest, before packing, and again after unpacking shortened their shelf life (Dai and Paul, 1991). Lentz (1966) observed that carrots which had lost as much as 7 to 8% moisture regained 2.6% water in 24 h when immersed in ice-water, and 3.0% after one week when held in drained ice. However, these studies did not examine effects of recharging on transpiration loses during subsequent storage. The effects of the duration and frequency of recharging and of the temperature during recharging have not been investigated. 20 Chapter II. Influence of preharvest water stress on postharvest moisture loss of carrots Abstract In order to understand the relationship between preharvest water stress and postharvest moisture loss, carrot cultivars Eagle and Paramount were grown in muck soil in 6-litre pots (8 carrots per pot) in a greenhouse at the University of British Columbia. The plants were watered to field capacity every second day for 5.5 months prior to receiving 100, 75, 50 and 25% field capacity water stress treatments (for 4.5 wk), henceforth referred to as low, medium, high and severe water stress respectively. Postharvest moisture loss of carrots stored at 13°C and 32% relative humidity was monitored every second day for three weeks. The percent moisture loss was low in low water stressed, and high in severely water stressed carrots of both cultivars. Root crown diameter, weight, and water and osmotic potentials decreased, whereas specific surface area and relative solute leakage increased with increasing preharvest water stress. The results show that carrots adjust to water stress by lowering water and osmotic potentials. Root water potential, followed by relative solute leakage, were the variables which accounted for most of the variation in moisture loss. It is suggested that preharvest water stress lowers membrane integrity of carrot roots, and this may enhance moisture loss during storage. Introduction Preservation of carrot freshness after harvest depends on storage conditions, as well as structural and physiological characteristics of roots (Fritz and Weichmann, 1979; van den 21 Berg, 1981). Increased moisture loss and respiration result in weight loss of carrots during storage. Such carrots are wilted, have poor coloration, are prone to infection by pathogens, and hence have lower consumer appeal. Low temperature storage has become a common practice to reduce weight loss and maintain quality of carrots. Washing and hydrocooling with a fungicide in the water at 4 to 7°C for 2 to 3 min after harvest (Punja and Gaye, 1993), and storage at a constant temperature just above 0°C and a humidity level approaching saturation (Stoll and Weichmann, 1987; Apeland and Hoftun, 1974) are recommended in order to reduce moisture loss from carrots. Root size and shape, structure of evaporating surfaces (Benjamin and Sutherland, 1989; Kays, 1991, Wills et al., 1981), and tissue water potential, which contributes to the driving force for water movement in and out of living cells (Salisbury and Ross, 1992), may all affect postharvest weight loss in carrots. Plant size and structure are greatly affected by the soil water status (Stanhill, 1977). Soil moisture stress reduces leaf water potential which in turn may reduce transpiration (Kramer, 1983). Plants adjust to mild soil water tension by lowering their water potential, thereby allowing water absorption when transpiration rates are low (Kramer, 1983; Chapman and Auge, 1994). Whether preharvest water stress influences postharvest moisture loss in carrots is not known. This information is essential to facilitate development of an irrigation regime to enhance the shelf life of freshly harvested carrots. The objectives of this study were to determine: (1) if preharvest water stress influences postharvest moisture loss from carrots and (2) the physical and physiological basis of this influence. 22 Materials and methods Seeds of carrot cultivars Eagle (a Berlicum x Nantes hybrid, Stokes Seed Ltd., St. Catharines, ON) and Paramount (Asgrow Seed Co., Newmarket, ON) were sown in muck soil (8 seeds in 4 kg soil per 6-litre pot) between May and October (in 1994) and January and July (in 1995) in a greenhouse at the University of British Columbia. 'Osmocote' (14:14:14 N:P:K, Grace Sierra, Milpitas, CA), a controlled-release fertilizer was added to the soil (3 g kg"1 soil) before planting. Carrots were grown in pots in a greenhouse to facilitate preharvest soil moisture stress treatments. Before seeding, the soil was flooded with water and allowed to drain over night. The amount of water held by soil at field capacity was calculated as the difference between the weight of soil plus water at field capacity (4.9 kg) and the oven dried weight (105°C for 48 hours) of the soil (3.2 kg). The soil was watered to field capacity every second day up to 145 days (d) in 1994 and 167 d in 1995. The plants were sprayed weekly with VendexTm (fenbutatin-oxide) (Dupont Co., Wilmington, DE) (for mite control) and Safer's Insecticidal Soap (Safer Inc., Concord, MA) (for white fly control). The daily average greenhouse temperature varied between 18 and 24°C in 1994 and between 18 and 30°C in 1995. Maximum daytime solar irradiance varied between 150 and 300 [xmoi m"2 s"1 in 1994 and between 150 and 465 umol m"2s' in 1995. A completely randomized design with the four water stress treatments and the two cultivars in a factorial arrangement was used. There were three replications (pots) per treatment. The water stress treatments, which were started after 145 d of sowing in 1994 and 167 d in 1995j included watering to 100, 75, 50 and 25% field capacity, henceforth referred to as 23 low, medium, high and severe water stress, respectively. Water was applied every second day at noon. The pots were watered to 4.9, 4.5, 4.1 and 3.6 kg to achieve low, medium, high and severe water stress, respectively. Soil water tension was measured using a soil moisture tensimeter (Tensimeter, Soil Measurement Systems, Las Cruces, NM) buried to a depth of 0.1 m in each pot. Readings were taken 24 h after each watering. The soil tension values averaged over the experimental period at low, medium, high and severe water stress were 17.0 ± 4.3, 40.3 ± 4.6, 53.8 ± 4.6 and 73.9 ± 4.3 KPa, respectively. To quantify the water stress within plants, leaf water potential (i|4J was measured two days prior to root harvest. Plants were harvested 174 and 199 d after sowing in 1994 and 1995, respectively. Soil was carefully removed from the roots, which were then separated from the shoots. The carrot roots were gently cleaned with paper towels and used for various measurements as follows: three carrots from each replication (pot) were used to monitor weight loss during storage, one carrot to determine root water (vjk) and osmotic (vj/^ potentials, and one carrot to determine the relative solute leakage (RSL). A. Carrot size and shape The carrot root weight (W), crown diameter (D) and length (L) were measured. The C-value (which indicates carrot shape) was calculated using the Bleadsdale and Thompson (1963) formula and surface area (A) using the Baugerod formula (H. Baugerod, Dept. of Vegetable Crops, Agric. College of Norway, Vollebekk, Norway, personal communication) given below: 24 C = W/(3.142 x R 2 x L) A = (4 x C x 3.142 x R x L)/(l + C) where R = D x 0.5. Since the specific gravity of carrots is approximately unity (Bleadsdale and Thompson, 1963), carrot weight in grams (W) gives an accurate measure of root volume (V). The surface area/weight ratio [the specific surface area (SSA)] was, therefore, used to estimate the surface area/volume ratio. Weight loss per unit surface area [transpiration coefficient (TC)] was also calculated. B. Moisture loss during storage After carrot size and shape measurements were recorded, the carrots were placed in 0.10 m x 0.22 m plastic bags (Super Pack kitchen bags, Scotch Buy, Glencourt Distributers, Vancouver, B.C.), perforated near the bottom end with nine (4 mm diameter) holes to facilitate air and moisture movements. The bags were placed in incubators at 13°C and 32 ± 4% RH (Model 52 Incubator, Sheldon Manufacturing Inc., Cornelius, OR). Carrot weight loss was monitored every second day for 20 days. Carrots with higher weight loss were considered to have a shorter shelf life. Preliminary studies showed that weight loss during storage at 13°C and 32% relative humidity was mainly due to moisture loss. Respiration accounted for a negligible portion of weight loss during 21 d of storage under these conditions. C. i|4 and measurements Using a cork borer, 3 mm diameter discs were excised from the third leaf from the shoot tip. The discs were placed in the sample well of a Thermocouple Psychrometer chamber 25 (Model C-52, Wescor Inc., Logan, UT) and connected to a Dewpoint Microvoltmeter (Model HR-33T, Wescor Inc., Logan, UT) in the psychrometer mode calibrated vvith NaCI standards. During \|^ measurement, the sample well was placed in a polystyrene container to rninimize thermal gradients; the temperature was maintained at 22 ± 2°C. Samples were left for 30 min, which was found in preliminary studies to be adequate to establish thermal and vapour equilibriums. V } ^ was measured 2 h after harvesting. Cores (30 mm long) excised longitudinally from the phloem parenchyma using a cork borer were cut into 1 mm thick x 3 mm diameter discs and was measured using the psychrometric method described above. Y } / ^ measurements were made on the same carrots used for % measurements described above. Shredded phloem parenchyma tissue was stored in a freezer at -85°C for 2 wk, thawed at room temperature for 10 min, crushed with a mortar and pestle, and the sap expressed through a double layer of Miracloth (Calbiochem-Novabiochem Corporation, La Jolla, CA). VJJL^ of the sap was measured by the depression of freezing point method using a thermocouple connected to a micrologger (21-Micrologger, Campbell Scientific Inc., Logan, UH) which was calibrated with NaCI standards. D. RSL measurement RSL from the carrot root tissues from different water stress treatments was measured to determine cell membrane integrity. Carrot root cores (30 mm long), excised longitudinally from the phloem parenchyma using a cork borer, were cut into 1 mm thick x 4 mm diameter discs. The discs were rinsed (3x) and incubated in 25 mL of deionized distilled water in 50 mL glass jars (20 discs per jar) at 26 ± 2°C. After 24 h, absorbance of the incubation medium 26 at 280 nm was measured using a spectrophotometer (Model UV 160, Shimadzu, Japan) to determine its solute content (Toivonen, 1992). Following measurements, the tissue integrity was destroyed by freezing at -85°C as described above. After thawing, absorbance of the bathing medium was measured to determine the total solute content of the tissue. RSL was expressed as the ratio of the absorbance before freezing to after tissue disintegration by freezing. E. Statistical analysis Analysis of variance and regression analysis were carried out using the SYSTAT software (Wilkinson et al., 1992) and means separated by the least significant difference (LSD) method. To determine which factors explain the variation in postharvest moisture loss most, stepwise multiple regression analysis on the variables which were significantly affected by preharvest water stress was carried out. Trie water stress treatments were coded 1, 2, 3 and 4 in order of increasing percent moisture loss (W). Data were fitted to the model: W = Constant + bx * WS + b2 x Cv + b3 x W + b4 x D + b5 x SSA + b6 x 1|/R + bn x \|/^  + b% x RSL where D is the crown diameter, Cv, cultivar and bx to b%, the partial regression coefficients. The best fit model was determined from a set of models on the basis of a high R 2 value and the optimum Mallow's coefficient (Cp value) (Neter et al., 1990). The 1994 carrots generally lost more moisture than those of 1995 at all water stress levels. This occurred mainly because the carrots were harvested later than those of 1994. 27 However, similar trends at the different water stress treatments of the different variables measured were observed in both experiments. Hence, only the results of 1995 are presented. Results A. Carrot size and shape Carrot D and W decreased with increase in preharvest water stress in both cultivars (Table 1). Water stress had no significant effect on carrot L in either cultivar. Similarly, there was no effect of preharvest water stress on the C-value. However, the SSA increased with increase in water stress. The SSA of the two cultivars did not differ. B. Moisture loss during storage In general, both 'Eagle' and 'Paramount' carrots lost the least moisture at low preharvest water stress and the most at severe water stress (Fig. 1). In 'Eagle', the differences were significant after day four when severely water stressed carrots started to lose more moisture than carrots from other treatments. There was no significant difference in moisture loss between treatments in 'Paramount' for up to 12 d, when the moisture loss of the severely stressed carrots was significantly higher than the three other treatments. The percent moisture losses in low and severely water stressed carrots were 14.1 and 20.5, respectively in 'Eagle' and 13.7 and 19.7, respectively in 'Paramount' on the 20th day of storage. TC was significantly lower in low compared to severe water stressed carrots (Fig. 2). It was higher in medium and high, compared to low water stressed carrots but the difference was not significant. TABLE 1. Effect of preharvest water stress on root length (L), crown diameter (D), weight (W), C-value, and specific surface area (SSA) in Eagle and Paramount cultivars of carrots. Cultivar Water L D W C SSA (Cv) Stress (WS) (mm) (mm) (g) (cm2 g"1) 'Eagle' Low 146.3 33.1a 79.18a 0.61 1.37b Medium 142.2 30. lab 65.03ab 0.61 1.57b High 136.8 26.9ab 48.82bc 0.61 1.83b Severe 130.6 22.8b 28.85c 0.57 2.06a 'Paramount' Low 150.2 36.8a 96.64a 0.61 1.52c Medium 159.7 32.9a 78.08ab 0.57 1.67b High 149.2 29.4ab 51.87bc 0.52 1.87b Severe 139.8 24.8b 40.12c 0.67 2.35a Significance WS Ns * * Ns * Cv Ns Ns Ns Ns Ns WsxCv Ns . Ns . Ns Ns Ns * and Ns, significant and not significant at P < 0.05. Means within a column followed by different letters are significantly different by LSD, P<0.05. 29 Days in storage Figure 1. Time course of percent moisture loss in cultivars Eagle and Paramount stored at 13°C and 3 2 % relative humidity. 12 Low Medium High Severe Water stress level Figure 2, Transpiration coefficient (TC) in cultivars Eagle and Paramount stored at 13°C and 3 2 % relative humidity for 20 days, C. Y|4, \fc and MV \|4 decreased vvith increase in preharvest water stress in both cultivars (Table 2). The iji of high and severely water stressed 'Eagle' carrots were significantly lower than the low and medium water stressed carrots. The low water stressed 'Paramount' carrots had the highest \ | i and the severely stressed carrots the lowest. Hk significantly decreased in the high and severely, compared to low and medium water stressed carrots in both cultivars. There was no difference in \pk between the low and medium water stressed carrots, and between the high and severe water stressed carrots. HW decreased with increasing water stress in 'Eagle'. However, it was lower only in the severely water stressed 'Paramount' carrots. D. RSL The RSL was significantly higher in the severely water stressed 'Eagle' carrots compared to other treatments (Table 2). In 'Paramount' carrots it was low in both low and medium water stressed carrots and high in high and severely water stressed carrots. E. Stepwise multiple regression analysis The best subset model obtained by backward stepping and the optimum Mallow's coefficient (Cp value) (R2 = 0.49, P < 0.05, Cp = 0.61) showed that most of the variation in postharvest moisture loss could be explained by and RSL (Table 3). Thus, postharvest moisture loss increased with decrease in i|4 and increase in RSL. because of its high TABLE 2. Effect of preharvest water stress (WS) on leaf water potential root water potential (VJ/R), root osmotic potential (VJ/^R), and relative solute leakage (RSL) in Eagle and Paramount cultivars of carrots. Cultivar Water Mi RSL (Cv) stress (WS) (MPa) (MPa) (MPa) (%) 'Eagle' Low -1.69a -0.62a -2.00a 5.90b Medium -1.89a -0.77a -2.33ab 6.34b High -2.35b -1.40b -2.77bc 19.23b Severe -2.33b -1.66b -3.24c 33.96a 'Paramount' Low -1.86a -0.91a -2.34a 9.37b Medium -2.07ab -0.91a -2.37a 8.04b High -2.29b -1.47b -2.87a 39.73a Severe -2.94c -1.56b -3.61b 39.98a Significance WS * * * * Cv Ns Ns Ns Ns WsxCv Ns Ns Ns Ns * and Ns, significant and not significant at P < 0.05. Means within a column followed by different letters are significantly different by LSD, P< 0.05. TABLE 3. Parameters and statistics for multiple regression models of the relationship between moisture loss (W) and the various attributes for carrots stored at 13°C and 32% relative humidity. Full model Best model Variable b V b b' r2 Constant -0.09 - 0.20 - -WS -0.02 -0.57 - - -Cv 0.02 0.23 - - -W 0.01 0.27 - - -D 0.01 0.20 - - -SSA 0.09 0.88 - - -% -0.06 -0.77 -0.07 -0.07 0.84 M>*R -0.02 -0.36 - - -RSL -0.01 -0.49 -0.01 -0.01 0.04 R2 0.35 0.49 Cp 0.61 WS = water stress level, Cv = cultivar, 1)4 = root water potential (MPa), \\f^ = root osmotic potential (MPa), RSL = relative solute leakage, D = root crown diameter (mm), SSA - specific surface area (cm2 g'1), W = root weight (g), - = parameter not selected in the best model, Cp = Mallow's coefficient, R2 = model coefficient of determination, r2 partial coefficient of determination, b = partial regression coefficient, V - standard partial regression coefficient. 34 standard partial regression coefficient (b) and high partial coefficient of determination (r2), was more important than RSL in estimating postharvest moisture loss. Significant (P < 0.05) positive relationships between W and WS and SSA, and negative relationships between W and D, W, and vj/^ were observed. Hence, carrots with low D, W, i)/^ and high SSA and WS had high, whereas those with high D, W, V|/^ and low SSA and WS had low postharvest moisture loss. D, W, SSA, WS and Cv were not selected in the best subset model indicating their lesser contribution to the variation in postharvest moisture loss. Discussion Soil fertility, temperature and water content can affect postharvest moisture loss by affecting plant growth (Stanhill, 1977), structure of evaporating surface, and/or plant composition (e.g. sugars, amino acids and ionic substances). In this study, preharvest water stress increased postharvest moisture loss from carrots. Stepwise multiple regression analysis showed that most of the variation in moisture loss could be explained by \J4 and RSL. Water movement in plants is governed by \\f gradients and the conductance of the flow path. Plants respond to soil moisture stress (Turner and Jones, 1980; Chapman and Auge, 1994) by lowering their cell \\fn due to accumulation of solutes (Turner and Jones, 1980), which lowers their \\f. Such plants lose less moisture through transpiration (Kramer, 1983). However, in this study, roots with low V]4 had high postharvest moisture loss. This suggests involvement of factors other than Vj^ in regulation of postharvest moisture loss. For \\f gradient to draw water into cells and tissues, proper runctioning of the plasma membrane is essential. In this study, RSL, a measure of plasma membrane permeability and cellular integrity (Poovaiah and Leopold, 1976; Toivonen, 1992), increased with increase in preharvest water stress. It positively correlated to moisture loss in the best subset model estimating postharvest moisture loss. An increase in plasma membrane permeability may, therefore, have countered the effects of a reduced vp^ and resulted in high postharvest moisture loss. Plant structures differ in TC, an index of the ease with which a plant surface allows transpiration to occur (van den Berg, 1987), due to differences in interstitial, cell wall and plasma membrane resistances (Kays, 1991), as indicated by RSL. Plant tissues with higher RSL would allow a greater flux of water through the evaporating structures, which in turn would result in a higher TC. In this study, carrots at low water stress showed low RSL and had low TC during storage at 13°C and 32% relative humidity. Conversely, the carrots at severe water stress showed high RSL and had high TC. It has been shown that larger sized produce which has lower SSA loses less moisture in storage compared to smaller produce with higher SSA (Wills et al., 1981). This proved true in this study. The smaller carrots (with low W and D) from the severe water stress treatment had higher SSA and lost the most moisture. Conversely the moisture loss was lower in the bigger carrots with lower SSA However, while SSA, D, W and Cv influenced postharvest moisture loss, their contribution was lower compared to RSL (as they were not included in the best subset model). Since the carrots had similar L- and C-values, preharvest water stress did not influence postharvest moisture loss by changing the carrot length or shape. Cultivar 36 differences played a minor role in determining postharvest moisture loss in carrots in this study. In conclusion, the results of this study show that preharvest water stress increases postharvest moisture loss of carrots thereby, reducing their shelf life. Preharvest water stress influences the shelf life of carrots by reducing root size and by increasing membrane permeability as measured by relative solute leakage. It is, therefore, recommended that carrots should not be harvested when soil is under water stress. Irrigation to decrease soil water stress may improve the shelf life of carrots by reducing the rate of postharvest moisture loss. 37 Chapter III. Potassium nutrition and postharvest moisture loss in carrots Abstract The effect of potassium nutrition on the shelf life of carrots (Cv. Paramount) was studied using a hydroponic system involving rockwool slabs as support. Carrots were grown for 192 days under greenhouse conditions and supplied with 0, 0.1, 1.0, 10 or 15 raM K in the nutrient medium. Increases in K concentration up to 1 mM decreased postharvest moisture loss. Carrot root weight and tissue potassium concentration increased, and water potential, osmotic potential and relative solute leakage decreased with increasing potassium concentration up to 1 m M Concentrations greater than 1 mM had little or no effect on postharvest moisture loss, root weight, root water and osmotic potentials and relative solute leakage. The best subset model obtained by backward stepping and the optimum Mallow's coefficient showed that carrot root weight and relative solute leakage accounted for most of the variation in moisture loss. Root weight correlated negatively and relative solute leakage positively to moisture loss. Water potential and osmotic potential correlated less strongly to the moisture loss. These results suggest that potassium concentrations below 1 mM influence postharvest moisture loss by affecting carrot size and tissue permeability. Effects on cell water and osmotic potentials are also important, but to a lesser extent. Introduction Wilting and shrivelling due to transpirational moisture loss lower the quality of vegetables (Lutz and Hardenburg, 1968). Postharvest moisture loss increases susceptibility to disease (van den Berg and Lentz, 1973), reduces vitamin C and carotene contents, marketable weight, and the economic value of vegetables (Lutz and Hardenburg, 1968). Air velocity, 38 temperature, relative humidity, plant nutrition, and physical and physiological conditions of the produce all influence moisture loss in fruits and vegetables during storage (Fockens and Meffert, 1972; Ben-Yehoshua, 1987). Plant nutrition can influence the rate of postharvest moisture loss through its effect on produce size and physiology. In carrots, the effect of potassium (K) on root growth and size depends on soil type. Habben (1972) reported an increase in root size with increasing level of K fertilization when carrots were grown in low-K peat and loam soils. Biegon (1995), however, found no effect in high-K muck soil. Whether the size differences observed in low K soils lead to differences in postharvest moisture loss is not known. K plays an important role in activation and stabilization of enzymes and membranes (Wyn Jones and Pollard, 1983; Suelter, 1985), protein and starch synthesis (Hsiao, 1976), and transport across membranes (Cheeseman and Hanson, 1980). It is needed for the operation of the K+-shuttle system, which mediates the transport of nutrients and photosynthates between roots and shoots (Ben-Zioni et al., 1971), regulation of osmotic and turgor pressures, and cell volume maintenance (Raschke, 1979). In growing plants, it is a major contributor to osmotic potential (v|/J, a component of water potential (i|/) which determines water uptake by roots. It also plays an important role in the regulation of stomatal opening in leaves (Salisbury and Ross, 1992) thereby affecting foliar transpiration. Although K has been shown to improve storability of potatoes and onion bulbs (Kunkel, 1947; Lune and Goor, 1977), the mechanism of this effect is not understood. Biegon (1995) found no effect of K level and source (KCI vs K 2S0 4) on postharvest moisture loss from carrots grown on high-K muck soil. The influence of lower levels of K on postharvest moisture loss in carrots has not been investigated. The objectives of this study were, therefore, to determine: (1) the effect of various levels of K nutrition on postharvest moisture 39 loss in carrots and (2) the physiological basis of this effect. Materials and methods Carrot (Cv. Paramount; Asgrow Seed Co., Newmarket, ON) seeds were grown between May and November (in 1993) and February and August (in 1995) in rockwool slabs (Pargro Ltd., Caledonia, ON) placed in 6-liter plastic pots (10 seeds per pot) in a greenhouse at the University of British Columbia. Each pot contained two 70 mm wide x 150 mm long x 222 mm high rockwool slabs. Seedlings were thinned to 3 per slab (6 per pot) 1 month after sowing. A modified Hoagland and Arnon (1950) No. 2 solution was used as nutrient medium. The treatments were 0.0, 1.0, 10 and 15 mM of K in 1993. The same treatments in addition to application of 0.1 mM K were used in 1995. K 2 S0 4 in place of KN0 3 was used as a source of K (since the use of the latter would lead to a variation in plant N, a major plant nutrient). Other salts added to the medium were: 4 mM Ca(N0 3 ) 2 «4H 2 0, 1 mM NH4FLPO4, 2 mM MgS0 4 «7H 2 0, 9 uM MnCMH 2 0, 46 uM H 3B0 3 , 0.8 uM ZnS04-7H20, 0.2 uM CuS0 4 «5H 2 0 and 0.1 uM Mo0 3. Iron was supplied as sequestrene at 5.0 ppm. The pots were arranged in a completely randomised design and replicated six times. The nutrient solution was applied at the rate of 200 mL per pot twice a week except on the weekends when the rockwool was flushed with tap water to wash away excess nutrients. The flushing water contained 5.2 uM K and was the only source of K responsible for growth of carrots at the lowest K treatment. A 1/4, 1/2 and full strength nutrient solution was applied in the first, second and third month of growth, respectively. The plants were sprayed with Vendex (fenbutatin-oxide) (Dupont Co., Wilmington, DE) (for mite control) and Safer's insecticidal soap (Safer Inc., Concord, MA) (for white fly control) every 7th day. The average greenhouse temperature varied between 18 to 30°C, and 40 the relative humidity between 35 to 65%. Solar irradiance varied between 150 and 465 umol m s^"1. Plants were harvested after 192 days. Harvesting was done by carefully separating the rockwool material from the roots followed by removal of the leaf stalk. Three carrots from each pot (replicate) were used to determine postharvest moisture loss, one for root (vj^ ) and osmotic (vj/^ potential at harvest, and one for the relative solute leakage (RSL) characteristic of the carrot tissue at harvest. A. Carrot size and postharvest moisture loss measurements The carrot root weight (W), the widest diameter of the root (D) and root length (L), C-value and surface area (A) were measured on the three carrots sampled, for moisture loss studies, as described above. The carrot shape (indicated by the C-value) and surface area (A) were calculated as described in Chapter II. Carrot weight was monitored every second day and percent moisture loss (W) and transpiration coefficient (TC) were measured as described in Chapter II. B. vj^ and vp^ measurements Using a cork borer, 30 mm long cores were excised longitudinally from phloem parenchyma 2 h after harvesting. was measured using the psychrometric method as described in Chapter II. \\Jn measurements were made on the same carrots used for \pk measurements, if/^ was measured on shredded pieces of phloem by the molecular depression of freezing point method as described in Chapter II C. RSL measurements RSL of the phloem parenchyma tissue from carrots grown under different 41 concentrations of K in growth medium ([K+]) was measured as described in Chapter II. D. K concentration in tissue (TK) The tissue bathing medium, before and after the destruction of tissue integrity, which was used for determination of the total solute content (described above) was also used to determine TK. Aliquots (0.5 mL) of the medium were diluted with 6 mL of deionized distilled water. TK was measured using an atomic absorption flame photometer (Perkin-Elmer 806, Mountain Sites, Montreal, Quebec) at 766 nm, and KC1 standards. E. Statistical analysis Nonlinear regression analysis among [K+] and the various dependent variables was carried out using SYSTAT software (Wilkinson et al., 1992). Combined exponential and power functions, and hyperbolic, linear and quadratic models were fitted. Combined exponential and power function: Y = a * [K+]b x c^+] (1) where Y = is the dependent variable (W, D, L, W, VJ/R, V J / ^ RSL and TK), and a, b and c are parameters. The models reported here are those with the highest coefficient of determinations (R2 values). Stepwise multiple regression analysis using the means of W, \|^, V]/^ RSL and TK (independent variables) and W (dependent variable) were carried out. The best fit model was determined from a set of models on the basis of a high R 2 value and the optimum Mallow's coefficient (Cp value) (Neter et al., 1990). Combined exponential and power functions, and hyperbolic, linear and quadratic models were again fitted between each of the independent Hyperbolic: Y = a + b x (1/[K+]) + c x [K+] Linear: Y = a + b x [K+] Quadratic: Y = a + bx[K + ] + cx (pC])2 (2) (3) (4) 42 variables chosen in the best model and W . While only four levels of [K+] were used in 1993 compared to five in 1995, similar trends at the different [K+] of the various attributes measured were observed in both experiments. Hence only the results of 1995 experiment are presented. Results A. Carrot size and postharvest moisture loss Percent moisture loss of carrots grown under different [K+] differed following 14 days of storage (Figure 3A). An increase in [K+] up to 1.0 mM decreased postharvest moisture loss. There was no difference in moisture loss among carrots grown at 1.0, 10 and 15 mM K. The relationship between K nutrition and moisture loss was best described by equation 1 (R2 = 0.81). An increase in [K+] up to 1.0 mM also resulted in decreased moisture loss when expressed on per unit surface area basis (TC) (Figure 3B). There was also no difference in TC among carrots grown at 1.0, 10 and 15 mM K. Equation 1 (R2 = 0.60) best described the relationship between K nutrition and TC as well. Increase in [K+] up to 1.0 mM increased carrot root weight (Figure 4A). Higher concentrations did not change the carrot size. Similarly, D and L increased up to 1.0 mM K and then levelled off (Appendix 1). Equation 1 best described the relationship between [K+] and W, D and L. B. \fc and ife \|4 of the carrot roots decreased with increasing [K+] up to 1.0 mM and then levelled off (Figure 4B). decreased sharply as [K+] increased from 0 to 1.0 mM; the decrease was more gradual between 1.0 and 15 mM K (Figure 4C). The relationships between [K+] and and Yj/j^ were best described by equation 1. 0 200 150 100 0 5 10 15 20 Potassium concentration in growth medium (mM) Figure 3: The relationship between potassium concentration in growth medium (|K1) and (A) moisture loss (%) (W°) and (B) transpiration coefficient (mg mm"2) (TC) of carrots following 14 days of storage. Nonlinear regression equations are: (A) W D = 32.42 x [KT°' 1 B x K 1.01IK*'. r 2 = 0.60. 1,02" 0.81, (B) T C = 88.98 x [KT -1.50 ' 1 1 1 1 1 0 5 10 15 20 Potassium concentration in growth medium (mM) Figure 4: The relationship between potassium concentration in growth medium ([K*D and (A) carrot root weight (W). (B) water potential, (\|/E) and (C) osmotic potential (v^). Nonlinear regression equations are: (A) W = 20.51 x [K 4] 0 3 3 x 0.97 IK*'. r 2 = 0.78, (B) y R = -0.68 x [ K 1 0 0 6 x 0.99 I K*'. r 2 = 0.69 and (C) v * = -1.05 x [ K ? 0 2 x 1.00**'. r 2 = 0.46. 45 C. RSL RSL of carrot tissue decreased with increase in [K+] up to 1.0 mM and then levelled off (Figure 5A). The relationship between [K+] and RSL was best described by equation 2 (R2 = 0.71). D. TK TK increased steadily with increasing [K+] (Figure 5B). The rate of this increase was highest up to 1 mM K in the growth medium, and gradually decreased thereafter. E. Stepwise multiple regression analysis The best subset model obtained by backward stepping and the optimum Mallow's coefficient (Cp value) (R2 = 0.81, P < 0.05, Cp = 2.63) showed that W and RSL accounted for most of the variation in W (Table 4). Further analysis showed a significant quadratic relationship (equation 4) between W and W (R2 = 0.91, P < 0.05), with W increasing with decrease in W (Figure 6A). Similarly, a significant quadratic relationship between RSL and W (R2 = 0.72, P < 0.05), with W increasing with increase in RSL, was found (Figure 6B). Significant (P < 0.05) linear relationships among W, and vj% vp^ TK and [K+], with W decreasing with decrease in \pk V j /^ and increase in TK and [K+], were observed (Table 4). However, ipk, ip^ TK and [K+] were not selected in the best subset model that explained the variation in W. S? 3 0 -S 20 E 50 CD CO CO ~ 40 2 3 0 "c CD O c o o E 20 10 0 B i o 1 o o -/ o -do 1 i 1 1 0 5 10 15 20 Potassium concentration in growth medium (mM) Figure 5: The relationship between potassium concentration in growth medium G O and (A) relative solute leakage (RSL) and (B) potassium concentration in tissue (TK). Nonlinear regression equations are: (A) R S L = 14.80 + 0.29 x (1 / [K l ) + -0 .13 x |K1. r 2 = 0.71, (B) TK = 14.7 x [Ki 0.99 IK*', r2 = 0.93. 47 Table 4. Parameters and statistics for multiple regression models of the relationship between percent moisture loss (W) and the various attributes for carrots stored at 13°C and 32% relative humidity. Model Full Best Variable b b' b b' CON 91.98 - 47.98 -[K+] 1.08 0.31 - -W -1.73 -0.97 -0.96 -0.54 -34.96 -0.17 - -54.36 0.33 - -RSL 0.54 0.35 0.72 0.47 TK 172.72 0.16 - -R 2 0.81 0.81 Cp 2.63 Significance * * CON = intercept, [K+] = potassium concentration in growth medium (mM), W = carrot root fresh weight (g), \\fR= water potential (MPa), \\f^ = osmotic potential (MPa), RSL = relative solute leakage, TK = K concentration in tissue (M), R 2 = model coefficient of determination, - = parameter not selected in the best model, Cp = Mallow's coefficient, * = significant at P < 0.05, b = partial regression coefficient, and b' = standard partial regression coefficient. 100 80 60 .» 40 o E 20 V o I I A o \ c \ o -- o \ ^ v O -I I o o 100 10 20 30 carrot root weight (g) 40 10 20 30 40 Relative solute leakage (%) Figure 6: The relationship between moisture loss (%) and (A) carrot root weight (W) and (B) relative solute leakage (RSL). Nonlinear regression equations are: (A) W D = 93.93 + -5.0 x W + 0 0 9 x W 2 r 2 = 0.91 and (B) W° = -6.17 + 3.29 x RSL + -0.03 x R S L 2 r 2 = 0.72. 49 Discussion Moisture loss from carrot roots occurs by diffusion mainly through the periderm and lenticels (Esau, 1965). Plant characteristics including size (Apeland and Baugerod, 1971), \|4 and its components (Salisbury and Ross, 1992), and tissue integrity may affect the rate of moisture loss. The results of this study suggest that K nutrition decreases postharvest water loss by affecting these characteristics. Backward stepping showed that W and RSL were the two independent variables which accounted for most of the variation in W 5. The W, with high standard partial regression coefficient, was more important than RSL in this regard. An increase in [K+] increased the size of carrot roots, which in turn decreased their surface area/volume ratio. A lower surface area/volume ratio lowered moisture loss per unit weight of carrot. Conversely, smaller carrots, with higher surface area/volume ratios, lost more moisture than the larger carrots. V J / R is the driving force for water flux in plant tissues (Boyer, 1985; Salisbury and Ross, 1992). Plant tissues with a low Vjj^  have a smaller vapour pressure deficit in relation to the surrounding air (Kays, 1991) and, therefore, lose moisture at a slower rate than the tissues with a high In this study, carrots grown under high [K+] had a low X J J ^ , and lost less water. Conversely, carrots grown under low [K+] had a high VJJ^ and lost more moisture. However, the best subset model to explain the variation in W did not include ipk, suggesting that \jk affects postharvest moisture loss to a lesser extent than W. Apart from \\f, water flux is determined by the resistance to water movement (Boyer, 1985). The plasma membrane offers resistance to water movement, which reduces the apoplastic flux (Boyer, 1985). A reduction in tissue integrity would lower this resistance and 50 increase apoplastic flux, causing the cells to lose more moisture. Interstitial and cell wall resistances may also affect transpiration (Kays, 1991). Cells with thick walls would offer greater resistance and lower the flux of water to the evaporating surfaces. The ease with which a plant surface allows transpiration to occur is indicated by the amount of moisture loss per unit surface area [(TC) (van den Berg, 1987)]. Cells which offer higher resistance to water flux have lower TC. RSL has been used as an indicator of plasma membrane permeability (Pooviah and Leopold, 1976) and cellular integrity (Toivonen, 1992). Plant cells with higher RSL, therefore, would exhibit higher TC. The high postharvest moisture loss (W and TC) observed in this study at low [K+] could, therefore, be due to an increase in permeability of the cells to water. K is required for the production of proteins and carbohydrates (Hsiao, 1976), which are necessary for plasma membrane synthesis, and for activation and stabilization of enzymes and membranes (Wyn Jones and Pollard, 1983, Suelter, 1985). The 0.05 M TK observed in the carrots grown at the highest [K+] in this study agrees with the high level of K found in plant cells (Salisbury and Ross, 1992). Assuming that each K + is associated with an anion to maintain electrical neutrality, the increase in TK from 0.01 to 0.05 M in this study can account for only 5.6% (0.05 MPa) and 21.1% (0.24 MPa) of the at the lowest and the highest [K+], respectively. This suggests that the benefits of TK were not mainly through a lowering of ipk but through its effect on other plant functions. The response of carrot yield to K fertilization has been shown to depend on K status of the soil. For example, Bishop et al. (1973) observed a linear increase in the marketable yield of carrots in response to K fertilization in sphagnum peat soil, but not in mineral soil. 51 Greenwood et al. (1980) observed that increasing K fertilization to 100 Kg/ha, on sandy loam with 69 ppm of K, increased yield of carrots. Above this level, the yield increased but not significantly. Biegon (1995), observed no effect of K fertilization on carrot shoot growth and marketable yield in muck soil containing 503 to 693 ppm K. Carrot weight loss during short term storage was also not affected by the rate or the source of K (KN0 3 vs K 2S0 4). Evers (1989), on the other hand, found a negative effect of fertilization on storability of carrots. In our study, the nonlinear regression models fitted for the independent attributes W , W, and RSL shows response to [K+] up to 1.0 mM; the effect levelled off thereafter. It is, therefore, suggested that K fertilization could improve the shelf life of carrots by reducing postharvest moisture loss from carrots grown in soils with very low K content. In conclusion, K affects the postharvest weight loss in carrots during short term storage by increasing root size (weight) and by decreasing membrane permeability. The benefit of K fertilization in terms of improved shelf life, however, is limited to the conditions of low K availability. c, 52 Chapter IV. Moisture loss characteristics of carrot cultivars during short term storage at 13°C Abstract Differences in moisture loss characteristics of carrot cultivars Irnperator Special 58, Gold Pak 28, Caro-pride, Paramount, Eagle, Celloking, Top Pak and Caro-choice during short term storage at 13°C and either 80 ± 5% or 35 ± 3% relative humidity were investigated. Experiments were conducted over two years with an early and late harvest in each year. Moisture loss was significantly greater at low relative humidity compared to high relative humidity. Consistent cultivar differences in moisture loss characteristics were observed in the late harvested carrots at low relative humidity. Cultivars with higher specific surface area, relative electrolyte leakage, and lower water and osmotic potentials exhibited high moisture losses. However, moisture loss differences among cultivars were mainly associated with root surface area to volume ratio (the specific surface area) and the transpiration coefficient. Introduction A desirable characteristic for fresh market carrots is a long shelf life. Postharvest moisture loss causes carrots to become shrivelled (Hruschka, 1977), lose their bright orange appearance, and become susceptible to postharvest decay (van den Berg and Lentz, 1973). Generally, the rate of moisture loss is proportional to the surface area of the carrot root and the WVPD (Apeland and Baugerod, 1971), which is determined by the temperature and RH of the surrounding air (van den Berg, 1987). Differences in size and shape may affect moisture loss from fruits and vegetables. For example, smaller tangerines have a shorter shelf life due to greater moisture loss compared to 53 larger tangerines (Ketsa, 1990). Lownds et al. (1994) reported that surface area, surface area to volume ratio, and the amount of epicuticular wax in different pepper varieties correlated with the rate of moisture loss from the fruit. Apeland and Bauger0d (1971) observed that the postharvest moisture loss in TSfantes' type carrots increased as their root size decreased. V|4 and membrane permeability are important factors in determining moisture loss. The levels of sucrose and hexoses, which are major determinants of \]/,^  in carrot roots, decrease during storage (Nilsson, 1987; Ben-Yehoshua, 1987). Changes in turgor pressure and lead to changes in ij^. At low VJ4, roots draw moisture from the soil. Whether a low ipk at harvest helps carrots retain moisture during postharvest storage has not been investigated. Plasma membrane semipermeability is essential for maintaining the osmotic balance and hence of a cell. The plasma membrane permeability increases during storage in carrots (Finlayson et al., 1989) and potatoes (Spychalla and Desborough, 1990). This increase has been attributed to changes in fatty acid composition of the plasma membrane (Thompson, 1984; Yoshida, 1984). A differential increase of plasma membrane permeability during storage may cause differences in moisture loss characteristics of carrot cultivars. Little information is available on moisture loss characteristics of carrot cultivars during short term storage under retail shelf conditions. An understanding of physical and physiological characteristics that influence moisture loss during short term storage can contribute to the development of ways to enhance shelf life of carrots. The objectives of this study were to determine: (1) if carrot cultivars differ in their postharvest moisture loss characteristics during short term storage at 13°C, and (2) whether these differences could be attributed to differences in physical and/or physiological characteristics of carrot roots. 54 Materials and Methods Carrot cultivars Irnperator Special 58, Gold Pak 28, Caro-pride, Paramount, Eagle, Celloking, Top Pak and Caro-choice, which are grown in the Fraser Valley of British Columbia, were used. Cultivars Gold Pak 28, Eagle, Irnperator Special 58, Celloking and Top Pak seeds were supplied by the Stokes Seed Ltd. (St. Catharines, Ontario) and Caro-pride, Caro-choice and Paramount seeds by the Asgrow Seed Company (Newmarket, Ontario). Carrots were grown at the Totem Park Field Station of the University of British Columbia between May and November, 1993. The experiment was repeated during the same period in 1994. The soil was a sandy loam with pH 6.0 (H20), 8.9% organic matter and 9.4, 74.6, 100, 52, 100, and 16 kg ha"1 of nitrate, phosphate, calcium, magnesium, potassium, and sodium respectively. The nitrate, phosphate, calcium, magnesium, potassium, and sodium had been determined by Kelowna extraction method (e.g. van Lierop, 1989) by mixing dried soil sample with extraction solution (soiksolution ratio = 1:5). Fertilizers 21:0:0, 0:20:0 and 0:0:50 (N:P:K) were broadcast to provide the recommended rates of 70, 8.7 and 62.2 kg of N, P, K ha"1 respectively, and incorporated by raking before seeding. N at 40 kg ha'1 was top-dressed two months after planting (Anon., 1992). Carrots were grown in a randomized complete block design replicated four times. Each replication was a 2 m x 5 m plot with five rows spaced 0.35 m apart. Carrots were seeded on May 15 in 1993 and on May 17 in 1994 using a Heistair-Stanhay precision seeder. Seedlings were thinned to 60 to 80 plants per meter row length three weeks after planting. Overhead irrigation was used to supplement rainfall as needed. 55 The carrots were harvested 87 days (early harvest) and 120 days (late harvest) after seeding in 1993. Early and late harvests were carried out 98 days and 164 days after seeding, respectively, in 1994. In 1994 the carrots in the second block were not of uniform size due to flooding that occurred during a rain storm two weeks after planting and, therefore, were not harvested. The carrots were hand harvested from the middle three rows and, their shoots were removed. The carrots were put in polyethylene bags, transported to the laboratory less than 1 km away, washed in cold water, gently blotted with paper towels, and subjected to various treatments. A. Carrot size and shape measurements Carrot root length (L), greatest diameter (D), and weight (W) were measured. The carrot shape (C-value), and surface area (A) and specific surface area (SSA) (estimator of surface area to volume ratio) were calculated as described in Chapter II. B. Moisture loss characteristics of cultivars Six carrots were chosen randomly from carrots harvested from each plot. Three individually marked carrots were placed in each of two 0.51 x 0.56 m plastic bags perforated with 18, 4 mm diameter holes, to facilitate air and moisture movements. The bags were placed in incubators at 13°C and 35 ± 3% or 80 ± 5% RH to provide low (LRH) and high (HRH) RH conditions, respectively. Carrot weights were measured periodically over a three-week period. Moisture loss (W) was expressed as a percentage of the carrot fresh weight as well as on per unit surface area basis [Transpiration Coefficient (TC)]. Preliminary studies showed that respiration accounted for only a negligible portion of the total weight loss during 56 21 days of storage under similar conditions. Therefore, weight loss was used as a measure of moisture loss and hence the shelf life of carrots. C. V J / R and \\J^ measurement Three "Gold Pak 28', 'Paramount', 'Eagle' and 'Celloking* carrots harvested from each plot were placed in perforated plastic bags and incubated at LRH as described above. The Vj4 and Yj/^ were measured immediately after harvest and after 7, 14 and 21 days of storage. Carrot discs (5 mm diameter x 20 mm thickness) from the mid-section of the carrot root were excised longitudinally from phloem parenchyma using a cork borer, ipk was determined at room temperature (22 ± 2°C) by the constant mass method using 0.0, 0.15, 0.2, 0.25, 0.3 and 0.35 molal polyethylene glycol (PEG 4000; Sigma Chemical Co. Louis, MO) solutions. The i|/ of the PEG solution where no change in the carrot disc weight occurred was considered equal to the of the carrot discs. The water potential of the PEG solutions was calculated according to Steuter et al. (1981). Vj/^ of the carrots used for measurement was also measured. \ | V of the sap was measured using the molecular depression of freezing point method as described in Chapter II. D. Relative electrolyte leakage (REL) REL of three carrots was measured after 0, 7, 14 and 21 days of storage to assess the influence of moisture loss on tissue permeability. Carrot root cores (30 mm-length and 4 mm diameter) from the mid-section of the carrot root excised longitudinally from the phloem parenchyma using a No. 2 cork borer, were cut into 1 mm-thick discs and rinsed (3x) with deionized distilled water. The discs (25) were placed in 25 mL deionised, distilled water in 50 mL glass jars and incubated at 22 ± 2°C. After 24 h of incubation the increase in the 57 conductance of the bathing medium was measured using a conductivity bridge (Model FCM-2A, Weather Measure Corp., Sacramento, CA) to determine electrolyte leakage. At the end of the measurements, the tissue integrity was destroyed by freezing at -85°C. After thawing for 24 h, a second conductivity measurement was made. REL was expressed as the ratio of conductivity before and after tissue disintegration by freezing. E. Statistical analysis Analysis of variance among the treatments was carried out using SYSTAT software (Wilkinson et al., 1992). For each treatment, the percent moisture loss data were not normally distributed. They were, therefore, arcsin transformed prior to analysis using the following formula: W* = As x (V(W/100), where, W* is the arcsin transformed data, As, arcsin, and W, percent moisture loss. Stepwise multiple regression analysis between W* and the attributes measured was performed for late harvested 'Gold Pak 28', 'Eagle', 'Paramount' and 'Celloking' carrots at LRH. Cultivars were re-corded 1, 2, 3 and 4 for 'Eagle', 'Gold Pak 28', 'Paramount' and 'Celloking', respectively, in order of increasing W*. Data were fitted to the model: W* = Constant + bx x B + b2 x Cv + b3 x d + b4 -x SSA + b5 x \|4 + b6 x \ | /^ + 67 x REL + Z ? 8 x C v x d + 6 9 x C v x SSA + 610 x Cv x U4 + ^ n x Cv x + Z>12 x Cv x REL + bu x d x \|4 + bu x d x vj/^ + bl5 x d x REL + bl6 x Cv x d x \|4 + bxl x Cv x d x v j j r^ + bx% x Cv x d x REL, 58 where B is the block effect, bx to bl& are partial regression coefficients, Cv, cultivar and d, storage duration (days). The best fit model was chosen: from several models on the basis of a high R 2 value and the optimum Mallow's coefficient (Cp value) (Neter, et al., 1990). Results A. Size, shape and surface area to volume ratio of cultivars There was no difference in the C-value, which indicates carrot shape (Bleadsdale and Thompson, 1963), among cultivars in either year (Appendix 2 and 3). 'Paramount' had the highest SSA in the late harvest of 1993, but it was statistically different only from 'Eagle' (Table 5). 'Paramount' and 'Gold Pak 28' had significantly (P < 0.05) higher SSA than 'Eagle', 'Iinperator Special 58' and 'Caro-pride' in the late harvest of 1994. There was no difference among cultivars in SSA in the early harvests in both years. SSA was generally lower in 'Caro-choice', 'Eagle' and 'Celloking' in 1993, and in all cultivars in 1994 in late, compared to early, harvests. B. Moisture loss characteristics of cultivars For both early and late harvests in 1993 and 1994, carrots stored at LRH generally lost more moisture than those stored at HRH (Tables 6 and 7). There were no significant differences among cultivars in moisture loss at HRH for the early harvest of 1993, but in the late harvest 'Gold Pak 28' and 'Celloking1 lost more moisture than the other cultivars studied. No differences in moisture losses were observed at HRH for either harvest in 1994. Table 5. Root specific surface area (SSA) (cm2 g"1) of carrot cultivars harvested early and late in 1993 and 1994. 1993 1994 Cultivar Early Late Early Late harvest harvest harvest harvest Caro-choice 1.79 1.67ab 1.92 1.5 lab Gold Pak 28 1.76 1.77ab 2.16 1.92a Eagle 1.72 1.44b 1.97 1.41b Paramount 1.92 1.99a 2.17 1.74a Irnperator Special 58 1.69 1.64ab 2.07 1.49b Caro-pride 1.82 1.80ab 2.10 1.53b Celloking 1.82 1.69ab 2.00 1.61ab Top Pak 1.88 1.90ab 1.87 1.59ab S.E. 0.06 0.06 0.04 0.04 Cv Ns * Ns * *, and Ns, significant and not significant at P < 0.05. S.E. = standard error of means. Means in a column followed by different letters are significantly different by Bonferroni procedure (P < 0.05). 60 Table 6. Percent moisture losses at 7, 14, and 21 days of storage at 13°C and either 80% (HRH) or 35% (LRH) relative humidity for carrots harvested early and late in 1993. Early harvest Late harvest HRH LRH HRH LRH d 7 14 21 7 14 21 7 14 21 7 14 21 Caro-choice 5.7 12.5 19.0 4.8 13.3 19.8 3.6 5.2 7.1 13.1 18.1 21.5 Gold Pak 28 4.2 11.8 14.9 5.5 12.2 15.4 6.8 10.5 14.1 12.9 17.7 24.6 Eagle 3.5 8.8 11.8 6.8 16.8 26.3 3.5 4.9 6.6 1.9 9.4 13.4 Paramount 3.3 8.2 10.6 12.6 20.9 27.3 4.0 6.8 8.8 10.6 16.1 24.9 Imperator 3.3 10.0 12.6 5.3 15.2 21.1 3.5 5.1 7.0 4.5 9.0 12.8 Caro-pride 3.5 8.7 11.9 6.1 17.2 21.2 3.4 5.6 8.0 8.0 12.4 17.0 Celloking 3.3 7.6 11.0 5.1 12.3 17.4 5.6 8.2 10.5 17.4 19.8 25.6 Top Pak 6.8 12.8 14.6 5.7 14.3 17.5 3.8 5.4 7.1 10.4 17.8 23.4 S.E. 0.8 1.2 1.4 1.2 1.8 1.8 0.7 0.9 1.1 1.6 1.9 1.9 Cv Ns * * * d * * * * Cv x d Ns * * * * and, Ns, significant and not significant at P < 0.05 level, respectively. 'Imperator' is the cultivar Imperator Special 58. Cv is cultivar, d is storage duration (days) and S.E. = standard error of means. 61 Table 7. Percent moisture losses at 7, 14, and 21 days of storage at 13°C and either 80% (HRH) or 35% (LRH) relative humidity for carrots harvested early and late in 1994. Early harvest Late harvest HRH LRH HRH LRH d 7 14 21 7 14 21 7 14 21 7 14 21 Caro-choice 6.5 9.2 12.1 8.9 14.3 18.5 4.3 5.5 9.2 9.5 16.1 22.5 Gold Pak 28 4.3 6.7 9.6 13.3 19.3 23.3 4.6 6.7 9.6 12.0 19.5 27.2 Eagle 4.1 6.4 8.5 6.8 12.7 15.0 3.3 5.3 7.3 7.1 12.1 16.6 Paramount 6.7 10.9 14.3 8.9 13.1 15.9 4.6 7.0 9.5 12.9 21.6 30.2 Irnperator 5.1 8.0 9.8 7.3 11.7 14.2 2.8 5.1 7.4 9.0 12.6 18.0 Caro-pride 7.5 11.1 14.0 10.3 16.3 21.2 3.8 6.0 8.5 9.5 15.3 21.6 Celloking 6.1 9.1 11.1 12.5 19.2 23.1 3.9 8.9 13.1 9.1 16.9 23.6 Top Pak 5.8 8.6 11.9 9.6 14.5 17.9 3.2 5.4 7.1 8.5 14.4 •19.3 S.E. 0.7 1.0 1.1 1.4 1.8 2.0 0.6 0.9 0.9 1.2 1.2 1.3 Cv Ns * Ns * d * * * * Cv x d Ns * Ns * * and, Ns, significant and not significant at P < 0.05 level, respectively. 'Irnperator' is the cultivar Irnperator Special 58. Cv is cultivar, d is storage duration (days) and S.E. = standard error of means. 62 Moisture loss differences among cultivars were found in the early harvest of each year at LRH, however the ranking of cultivars was not the same in both years. 'Paramount' and 'Eagle' lost the greatest moisture in the early harvest of 1993, whereas 'Gold Pak 28' and 'Celloking' lost the most moisture in the early harvest of 1994 under LRH conditions. Differences among cultivars held at LRH were consistent in the late harvests in both years. In 1993, 'Eagle' and 'Imperator Special 58' lost the least moisture at LRH and 'Celloking1, 'Gold Pak 28', and 'Paramount' the most (Table 6). The same was true in the late harvest carrots held at LRH in 1994 (Table 7). 'Top Pak1, 'Caro-choice' and 'Caro-pride' lost more moisture than 'Eagle' and 'Imperator Special 58' but the differences were not significant. Conversely, 'Top Pak', 'Caro-choice' and 'Caro-pride' lost less moisture than 'Celloking', 'Gold Pak' and 'Paramount' but the differences were not significant. The TC was generally higher in carrots at LRH compared to HRH (Table 8). There was no difference in the TC among cultivars under both storage conditions in the early harvest of 1993. However, in the late harvest, 'Eagle' and 'Imperator Special 58' had low TC values at LRH. In the early harvest in 1994, 'Eagle', 'Paramount', and 'Imperator Special 58' had low TC compared to the other cultivars at LRH. 'Eagle', 'Imperator Special 58', and 'Top Pak' had low, while 'Paramount' and 'Celloking' had high TC at LRH in the late harvest in 1994. C. Cultivar % and ip^ and REL While only results for VJ4, VjV and REL at day 7, 14 and 21 are presented (Table 9), results similar to those at day 7 were obtained at day 0 in both years. Table 8. Transpiration coefficient (mg mm2) of carrot cultivars at 13°C and either 80% (HRH) or 35% (LRH) relative humidity in early and late harvests of 1993 and 1994. 1993 1994 Early Late Early Late harvest harvest . harvest harvest HRH LRH HRH LRH HRH LRH HRH LRH Caro-choice 1.06 1.12 0.46 1.38 0.62 0.98 0.48 1.21 Gold Pak 28 0.87 0.85 0.79 1.52 0.46 1.06 0.42 1.11 Eagle 0.70 1.53 0.44 0.81 0.44 0.77 0.43 0.97 Paramount 0.56 1.41 0.47 1.30 0.66 0.76 0.47 1.55 Irnperator 0.68 1.33 0.41 0.77 0.48 0.69 0.41 0.98 Caro-pride 0.69 1.21 0.46 1.02 0.69 0.97 0.46 1.09 Celloking 0.61 0.96 0.59 1.93 0.57 1.13 0.71 1.26 Top Pak 0.76 0.96 0.37 1.24 0.65 0.97 0.39 0.99 S.E. 0.07 0.10 0.05 0.10 0.05 0.10 0.06 1.10 Cv Ns * * * H * * * * Cv x H Ns * * * * and, Ns, significant and not significant at P < 0.05 level, respectively. 'Irnperator' is the cultivar Irnperator Special 58. Cv is cultivar, H is storage condition (relative humidity). 64 Table 9. Water potential (v )^, osmotic potential (VJ/^R) and relative electrolyte leakage (REL) of carrot cultivars at 13°C and 35% (LRH) relative humidity for late harvested carrots in 1993 and 1994. \j4(MPa) \|4R (MPa) REL (%) T 14 21 7 14 21 7 14 21 1993 Gold Pak 28 -0.8 -0.8 -1.0 -1.3 -1.2 -1.7 43 46 55 Eagle -0.8 -0.7 -0.9 -1.2 -1.1 -1.5 41 45 51 Paramount -0.9 -1.0 -1.0 -1.2 -1.7 -2.1 55 65 63 Celloking -0.7 -0.8 -0.9 -1.1 -1.2 -1.6 32 38 76 S.E. 0.02 0.05 3.1 Cv * * * d * * * Cv x d * * * 1994 Gold Pak 28 -0.8 -0.7 -0.9 -1.1 -1.3 -1.6 30 29 34 Eagle -0.7 -0.7 -0.8 -1.2 -1.2 -1.3 31 33 33 Paramount -0.8 -0.8 -1.0 -1.1 -1.4 -1.8 31 37 44 Celloking -0.7 -0.7 -0.9 -1.0 -1.3 -1.5 25 39 44 S.E. 0.01 0.02 0.90 Cv * * * d * * * Cv x d * * * * and, Ns, significant and not significant at P = 0.05 level, respectively. 'Imperator' is the cultivar Imperator Special 58. Cv is cultivar, d is storage duration (days) and S.E. = standard error of means. 65 Except for 'Paramount' in 1993, decreased after day 14 in all carrots in both years (Table 9). At the end of storage, Vj4 was low for 'Paramount' and high for 'Eagle' in both years. In 'Eagle', 'Gold Pak 28' and 'Celloking" in 1993, ip^ did not change up to day 14 and decreased sharply thereafter. XjV declined continuously in 'Paramount' over the storage period. In 1994, ip!^  of 'Eagle' did not change up to day 14 but declined thereafter. It declined continuously in 'Gold Pak 28', 'Paramount' and 'Celloking" over the storage period. At the end of storage, ijV was low for 'Paramount' and high for 'Eagle' in both years. REL increased in 'Paramount' up to day 14 and did not change thereafter in 1993. In 'Eagle' and 'Gold Pak 28' it increased steadily over the storage period. 'Celloking1 had the lowest REL up to day 14 but increased sharply at day 21 in 1993. In 1994, REL in 'Eagle' did not change significantly. The REL of 'Gold Pak 28 did not change up to day 14 but increased thereafter. 'Paramount' and 'Celloking" steadily increased in REL over the entire 1994 storage period D. Multiple regressions between W* and the various physical and physiological attributes The SSA was the attribute that could explain, because of a high partial coefficient of determination (r2), most of the variation in W* in both years (Table 10). SSA followed by due to their high standard partial regression coefficients (#), were more important than the other attributes measured in 1993 in estimating W* (Table 10). However, in 1994 the interaction Cv x REL followed with SSA had high standard partial regression coefficients. 66 Table 10. Parameters and statistics for best subset multiple regression models of the relationship between moisture loss (W*) and various attributes for carrots stored at low relative humidity (LRH) in late harvest 1993 and 1994. Cp = 9.2 and R2 = 0.89 for 1993, and Cp = 4.15 and R2 = 0.88 for 1994. 1993 1994 Potential independent variable b b' r2 b b' r2 Constant 0.52 - - 0.05 - -B 0.02 0.04 0.14 - - -Cv -0.11 -0.20 0.14 -0.08 -0.01 0.13 SSA -0.42 -0.87 0.25 0.21 0.29 0.42 -1.70 -0.29 0.03 0.01 0.01 0.01 REL 0.12 0.22 0.02 - - -d><V|4 -0.01 -0.01 0.22 - - -d x REL - - - 0.02 0.02 0.10 Cv x d - - - 0.01 0.01 0.20 Cv x SSA 0.10 0.16 0.24 - - -Cv x REL - - - 0.24 0.34 0.14 Cv x d x REL - - -0.02 -0.02 0.18 - = parameter not selected in the moisture loss model, Cp = Mallow's coefficient, R' = model coefficient of determination, b = partial regression coefficient, V = standard partial regression coefficient and r2 = partial coefficient of determination. B = the block effect, Cv = cultivar, d duration in storage, SSA = specific surface area (cm2 g"1), % - water potential (MPa), V j / ^ = osmotic potential (MPa) and REL = relative electrolyte leakage. 67 Discussion A. Cultivar Differences Except for the more mature carrots (late harvest), the cultivar differences in moisture loss characteristics at LRH were not consistent in the two years of this study. 'Eagle' and 'Irnperator Special 58' lost the least moisture and 'Paramount', 'Gold Pak 28', 'Celloking' and 'Caro-choice' the most. There is no evidence in the literature that relates cultivar differences and maturity to postharvest moisture loss during the short term storage. Carrot cultivars, however, have been shown to differ in size, during growth (Hole et al., 1987). Hole et al. (1987) reported that growth rates of nine carrot cultivars were similar during the first 41 days after sowing, but changed thereafter. They suggested that genetic factors affect partitioning between the shoot and root in the later stages of growth of carrots, causing differences in root size with time of harvest. This is in agreement with the results of this study where cultivar differences in SSA, which partly depends on carrot size, were more pronounced in late harvested carrots. Such size differences may explain the cultivar differences in moisture loss at the LRH in late harvested carrots. This study, therefore, suggests that maturity at the time of harvest is important when evaluating cultivars for shelf life improvement. Carrot shelf life has been defined as "the number of days carrots can stay at specified storage conditions before attaining the maximum permissible moisture loss of 8% of the initial root weight" (Robinson et al., 1975). The carrots with high moisture loss would become unmarketable earlier than those with less moisture loss. In contrast, carrots which lose less moisture will wilt more slowly and hence are acceptable to consumers for longer periods on the retail shelf. The results of this study show that the cultivars differ by up to 4 to 6 days 68 in their shelf life. 'Eagle' and 'Irnperator Special 58' carrots from the late harvest lost 8% moisture after about 13 and 9 days of storage at LRH, in 1993 and 1994, respectively, whereas 'Paramount', 'Gold Pak 28' and 'Celloking* lost 8% moisture following 7 and 5 days of storage at LRH, in 1993 and 1994, respectively. Carrots stored at LRH lost more moisture than those at HRH. This is in agreement with the findings of van den Berg and Lentz (1966, 1973) and van den Berg (1981) who showed that moisture loss from carrots can be greatly reduced by increasing RH up to nearly 100%. The driving force for transpiration is WVPD gradient, which depends on RH. The rate of moisture loss is lower at HRH because of reduced WVPD between carrot surface and the surrounding air (Ben-Yehoshua, 1987). Inconsistent (in 1993) or lack of (in 1994) differences among cultivars in moisture loss at HRH suggests greater importance of RH, compared to cultivar differences, in determining the moisture loss during storage of carrots. B. Multiple regressions between W* and various physical and physiological attributes Physical attributes of carrots can influence moisture loss. The carrot cultivars in this study had similar C-values (Appendix 2 and 3) indicating that differences in shape cannot explain the differences in their moisture loss characteristics. The average C-value was found to be 0.5, indicating a conical shape (Bleadsdale and Thompson, 1963). The SSA, an indicator of A V ratio, did show a significant relationship with moisture loss in both years. SSA was the first and second in ranking in standard partial regression coefficient in 1993 and 1994, respectively, and exhibited high partial coefficient of determinations in both years, suggesting that it was highly associated with the moisture loss 69 characteristics of these cultivars. In fact 'Eagle' and 'hnperator Special 58', the cultivars that showed the lowest moisture loss at LRH in late harvests, had the smallest SSA in both years. Conversely, 'Paramount', 'Gold Pak 28' and 'Celloking', which showed high storage moisture loss, had high SSA in both years. It is, therefore, suggested that SSA could be important in deterrnining the moisture loss of carrots and should be taken into consideration when selecting cultivars for longer shelf life. The TC is an index of the ease with which the surface of produce allows transpirational moisture loss (van den Berg, 1987). The TC is influenced by temperature and humidity (i.e. WVPD) of the storage environment, periderm thickness, and interstitial, cell wall and plasma membrane resistances (Kays, 1991). REL has been used as an indicator of plasma membrane permeability and cellular integrity (Finlayson et al., 1989). Plant cells with higher REL, therefore, are expected to exhibit higher TCs. In the late harvest at LRH, 'Eagle', the cultivar with the lowest moisture loss, had low REL while 'Paramount' and Celloking', which exhibited highest moisture loss had high REL at any given WVPD. In addition, the interaction Cv x REL was selected in the best model for the 1994 data. This suggests that cellular membrane integrity characteristics are associated with the high moisture loss response in the mature carrots in this study. Water movement in plants is governed by \|/ and the conductance (permeability) of the flow path (Salisbury and Ross, 1992). Plant structures with low \\f lose less moisture through transpiration (Kramer, 1983). However, in this study the cultivars with low V j ^ exhibited high W*, suggesting involvement of other factors in the regulation of moisture loss. It is possible the effects of a lowered \|4 were counteracted by loss of membrane integrity, indicated by an 70 increase in REL. A decrease in cell membrane integrity may therefore be important in deterrnining the TC and hence the moisture loss during storage. The significance of attributes accounting for the variation in moisture loss differed for the two years (Table 10). For example, SSA were more important in accounting for the variation in W* in 1994 than in 1993. This could possibly be due to the fact that harvesting was done much later in 1994 when cultivar size differences were more pronounced. In conclusion, the differences in moisture loss characteristics of cultivars became apparent only when the carrots were stored at low relative humidity. At high relative humidity, the cultivars did not differ significantly. Consistent cultivar differences are seen only with more mature (late harvested) carrots. The differences in moisture loss characteristics appear to be due to differences in the surface area to volume ratio (SSA) and transpiration coefficient, which is determined in part by tissue permeability. 71 Chapter V: Effect of moisture loss on water potential, osmotic potential and tissue permeability during short term storage of carrots Abstract Carrots were stored for 30 days at 2°C and 80 ± 3% relative humidity (RH), 13°C and 79 ± 5% RH, or 13°C and 31 ± 3% RH, providing low (0.07 KPa), medium (0.23 KPa) and high (0.64 KPa) water vapour pressure deficits (WVPD), respectively. Carrots at high WVPD lost the most moisture followed by those at medium and low WVPD. Water potential (\\Jp) and osmotic potential (vpL^ ) of the carrots at medium and high WVPD did not change significantly for up to 6 days, but decreased thereafter. No statistically significant change in \|4 and V)/^ occurred in carrots at low WVPD. A significant quadratic relationship (P < 0.05, r = 0.75, N = 43) between \|k and carrot moisture loss, and a significant negative linear relationship (P < 0.05, r = -0.82, N = 43) between \|/^ and moisture loss were observed. Relative electrolyte leakage (REL) increased after 12 days at high and after 18 days at medium WVPD; no change occurred in carrots stored at low WVPD. A positive linear relationship between REL and carrot moisture loss was observed. Moisture loss was best predicted by equations which utilized coefficients for ip^and Vj/^. It is concluded that postharvest water stress alters carrot tissue permeability, resulting in an increase in water loss. Introduction Physiological status of the vegetable root crops at harvest, and subsequent storage conditions can influence postharvest weight loss through respiration and moisture loss (Nilsson, 1987). Respirational losses, however, are relatively small at the low temperatures 72 commonly used during storage (van den Berg and Lentz, 1966). At higher temperatures, respiration rate increases, and crops can be stored for short periods only. The rate of water loss from a plant organ is proportional to its surface area and WVPD (Apeland and Baugerod, 1971; Kays, 1991). The WVPD gradient increases with a decrease in ambient RH at a given temperature and increases with air temperature at a given RH (van den Berg, 1987). Crop harvest abruptly disrupts water uptake by roots and lowers cell turgidity, which is mainly determined by tissue \\f, \\fn and matrix potentials. Since many biochemical reactions operate well only within a narrow range of V|/ (0 to -2.0 MPa; Hsiao, 1973), severe changes in vj/ may influence plant metabolism and disrupt cellular functions. Physiological changes that have been reported to occur during storage include changes in cell turgor, respiration, and levels of soluble sugars, amino acids and phenolic substances (Phan et al., 1973). Most fresh market vegetable root crops are stored and marketed under water stress (in high WVPD) conditions. Variation in storage temperature and RH can expose produce to fluctuating WVPDs. Knowledge of physiological changes and the extent of tissue damage that occurs during the harvesting and storage in response to WVPD can help in the development of improved postharvest handling methods to preserve produce quality. Shelf life of carrots is generally defined in terms of percent weight loss after harvest (Robinson et al., 1975). Since carrots harvested from different locations at the same time may differ in their water status due to differences in soil moisture stress at these sites, the postharvest weight loss expressed as percent of carrot weight at harvest may not indicate the actual moisture status of roots. \j/ is a good indicator of tissue water status (Salisbury and Ross, 1992) and firmness (McGarry, 1995). Whether freshness of carrots can be expressed in 73 terms of water status and/or tissue deterioration parameters is not known. The objectives of this study were: (i) to investigate the effect of WVPD on carrot root moisture loss, xpk, ip^ and tissue permeability in terms of cellular leakage, and (ii) to determine the relationships among postharvest moisture loss and ipk, ip^ and tissue permeability. Materials and Methods Carrots (cv. Eagle, a Berlicum x Nantes hybrid; Stokes Seeds Ltd., St. Catharines, Ontario) from the large cultivar field experiment described in Chapter IV were used. To obtain carrots in the least stressed condition, harvesting was done the morning after a rainy day. Carrots were hand-harvested from the middle three rows at 186 and 178 days after sowing in 1993 and 1994, respectively. In 1994, carrots in the second block were not of uniform size due to flooding that occurred during a rain storm two weeks after planting and, therefore, were not harvested. Carrots were placed into polyethylene bags, transported to the laboratory at the University of British Columbia (<1 km away), washed in cold water, and gently blotted with paper towels. Weight (W), length (L) and greatest diameter (D) of the carrot roots were recorded as described in Chapter JJ. Carrots were placed in 0.51 m x 0.56 m plastic bags perforated with 18, 4 mm diameter holes and subjected to WVPD treatments described below. A. Effect of WVPD on root moisture loss Twelve carrots harvested from each plot were divided into three groups. Groups of four carrots were placed in perforated plastic bags and stored under the three WVPD 74 conditions: 2°C and 80 ± 3% RH (low WVPD), 13°C and 79 ± 5% RH (medium WVPD), and 13°C and 31 ± 3% RH (high WVPD) in incubators. A small fan was placed in each incubator to facilitate air circulation. These conditions provided 0.07 KPa, 0.23 KPa and 0.64 KPa WVPDs, respectively. Carrot water loss was monitored by weighing the carrots every second day over a period of 24 and 30 days in 1993 and 1994, respectively. Preliminary studies showed that respiration accounted for a negligible proportion of the total weight loss during 21 days of storage under similar conditions. B. 1)4 and \\J^ measurements. For each observation time and storage condition, two carrots from each plot were placed in perforated plastic bags and incubated under the three WVPD conditions described above. of the carrot tissue was measured at day 0, 6, 12, 18 and 24 in 1993 and up to day 30 in 1994. Using a 3 mm diameter cork borer, 30 mm long cores were excised longitudinally from phloem parenchyma and cut into 1 mm thick discs. The discs l|4 were determined by the psychrometric method described in Chapter II. ij/^ of the carrots stored at various WVPDs as described above was measured, of the phloem sap was measured using the molecular depression of freezing point method as described in Chapter II. C. REL measurement. Electrolyte leakage from tissues stored at the different WVPDs for 0, 6, 12, 18 and 24 in 1993 and up to day 30 in 1994 was studied as an indicator of membrane permeability. Two carrots per plot for every measurement time and storage condition were placed in perforated plastic bags and incubated at the three WVPDs described above. Relative electrolyte leakage 75 of carrot root discs cut from root cores excised from the phloem parenchyma was determined as described in Chapter IV. D. Statistical analysis. Analysis of variance among the treatments was carried out using SYSTAT software, and means were separated by the LSD procedure (Wilkinson et al., 1992). For each treatment, percent weight loss data were not normally distributed. The data were, therefore, arcsin transformed prior to analysis using the following formula. W* = As x (V(WP/100) (1) where, W* is the arcsin transformed percent moisture loss, As, arcsin, and W, untransformed percent moisture loss. Data were fitted to the model: W* = Constant + bx x B + b2 x WVPD + b3 x d + b4 x WVPD x d + b5 x v|4 + b6 x WVPD xu4 + 6 7 x v | 4 x d +6 8 x WVPD x d x \^ + b9 x + bxo x WVPD x Wi& + bn x d x v j j r^ + bn x WVPD x d x xj/^ + b13 x REL + bH x WVPD x REL + bl5 x d x REL + bl6 x WVPD x d x REL (2) where, B is the block effect, d, the duration in storage (days), and bx to bX6 the partial regression coefficients. Stepwise multiple regression analysis was carried out to determine the attributes which explained the variation in carrot moisture loss the most. From a set of models, the best fit model was determined on the basis of a high R 2 value and the optimum Mallow's coefficient (Cp value) (Neter et al., 1990). 76 Lower R 2 values among the various attributes measured and W* were observed in 1993 than in 1994. The low R 2 were attributed to the fewer observations made, since the experiment was terminated earlier in 1993. However, similar trends at the different WVPD treatments of the various variables measured were observed in both experiments. Hence, only the results of 1994 are presented. Results A. Effect of WVPD on root moisture loss. Carrots at high WVPD lost more moisture than those at low or medium WVPD (Figure 7). Carrots at low and medium WVPD did not differ significantly in moisture loss up to 6 days. Thereafter, the carrots at medium WVPD lost more moisture than those at low WVPD. The maximum moisture loss at medium and high WVPD was higher, compared to that at low WVPD, than that expected from the 0.64:0.23:0.07 ratio of the WVPDs of these treatments. When moisture loss was expressed as percent per KPa WVPD per day, more moisture loss occurred at the low compared to the medium and high WVPDs during the first 6 days of storage (Table 11). However, carrots lost more moisture (i.e percent per KPa WVPD per day) after 18 days of storage at medium and after 30 days at high WVPD compared to those stored at low WVPD. B. \J4 and v^. 1)4 of carrots at different WVPDs did not differ significantly (P > 0.05) for up to 6 days of storage (Figure 8A). Thereafter, the \)4 at medium and high WVPD was significantly (P < 0.05) lower than that of carrots at low WVPD. There was no change in V)4 of carrots at the low WVPD up to 30 days. Figure 7. Moisture loss (%) of carrots stored at different water vapour pressure deficits (WVPD). Vertical bars represent S.E.M. 78 Table 11. Effect of water vapour pressure deficit (WVPD) on percent moisture loss per KPa per day. Duration of storage (days) WVPD Slope 6 12 18 24 30 Low -1.2 x 10"3a* 2.67a 1.84ab 1.43b 1.20b 1.12c Medium 3.7 x lO^b 1.74ab 2.30a 2.37a 2.62a 3.05a High 9.2 x i o 5 b 1.58b 1.56b 1.69ab 1.72ab 1.80b *Values in a column followed by different letters are significantly different by LSD (P < 0.05). 79 Figure 8. (A) Water potential, (B) osmot ic potential and (C) relative electrolyte leakage of carrots stored at different water vapour pressure deficits (WVPD). Vertical bars represent S .E .M. 80 The carrots at high WVPD had the lowest ip^ (Figure 8B). The vp^ for carrots at medium and high WVPD decreased after 6 days. There was no statistically significant change in the ip^ at low WVPD up to 30 days. C. REL. REL from carrots increased after 12 days at high and 18 days at medium WVPD; it levelled off after 24 days under these conditions. There was no change in REL for carrots at low WVPD for up to 30 days (Figure 8C). D. Regressions between W* and various parameters. Stepwise multiple regression analysis showed that the interaction WVPD x d followed by WVPD x d x REL were the attributes that could explain, because of their high partial coefficient of determinations (r2), most variation in W* (Table 12). However, since a unit change in an independent variable with a high standard partial regression coefficient (b') results in a greater change in the dependent variable (Steel and Torrie, 1987), the interactions WVPD x d and WVPD x d x REL, due to their low standard partial regression coefficients, would be less important in estimating W*. Though the partial coefficient of determinations between the water status parameters (\p^  and vp^ and W* were low, these parameters had high standard partial regression coefficients suggesting their greater usefulness, than other attributes, in estimating W*. For each experiment, a polynomial model was fitted to the mean values of each replicate of all of the treatments. A significant quadratic relationship (P < 0.05, r = 0.75, N = 43) between \pk and W*, showing a decrease in \pk with an increase in moisture loss, was 81 Table 12.. Parameters and statistics for best subset multiple regression model of the relationship between moisture loss (W*) and the various carrot variables (Cp = 2.5, N = 43 and R 2 = 0.96). Attribute b b' r2 Constant -0.52 - -W V P D 0.05 0.16 0.28 W V P D x d 0.01 0.02 0.94 W -0.19 -0.42 0.66 -0.44 -0.85 0.75 W V P D x VJV 0.06 0.15 0.46 0.02 0.04 0.61 d x REL 0.04 0.03 0.62 W V P D x d x REL -0.01 -0.02 0.80 Cp - Mallow's coefficient, N - number of observations and R 2 = model coefficient of determination, b = partial regression coefficient, b' - standard partial regression coefficient and r2 - partial coefficient of determination, WVPD : water vapour pressure deficit (KPa), d = duration in storage (days), \J4 - water potential (MPa), ijV = osmotic potential (MPa), and REL -relative electrolyte leakage. 82 observed (Figure 9A). A simple linear equation, showing that V ) / ^ decreased with an increase in moisture loss, best described the relationship between ip^ and W* (Figure 9B). The variation in W* which could be explained by \\f^ (the r-value) was high (r = 0.82, N = 43). A positive linear relationship (P < 0.05, r = 0.60, N = 43) between REL and W*, showing an increase in REL with increase in moisture loss, was observed (Figure 9C). Discussion The results of this study show that carrot moisture loss expressed as percent of initial weight increased with increasing WVPD. However, the percent moisture loss per KPa WVPD per day during the first six days of storage was greater at low, compared to medium and high WVPD. It has been shown that the relationship between WVPD and evaporation from the surface of a plant commodity is curvilinear (van den Berg, 1987; Burton, 1982). This would result in higher rate of evaporation (per KPa WVPD per day) at low WVPD and could explain the lower than expected percent moisture loss (per KPa WVPD per day) during storage at high, compared to low, WVPD during the first six days of storage. With storage beyond six days, moisture loss (percent per KPa WVPD per day) at low WVPD decreased significantly as indicated by the significant negative slope (Table 11). Carrots at medium and high WVPD continued to lose water even though their moisture content decreased with time. This suggests that factors apart from WVPD may be involved in controlling the rate of moisture loss from carrot roots. Such factors may include membrane permeability and a direct effect of ternperature on root cell metabolism. 83 Water potential (MPa) Osmotic potential (MPa) Relative electrolyte leakage Figure 9. The relationship between carrot moisture loss [arcsin transformed (W*)] and (A) water potential (\|fR). (B) osmotic potential (v|/,R). and relative electrolyte leakage (REL). Best fit regressions are: (A) is W* = -0.16 + 0 . 8 2 ^ (r = 0.75, p < 0.05), (B) is W* = -0.56 - 0.62v r t (r = 0.82. P < = 0.05) and (C) is W* = -0.51 + 1.43 REL (r = 0.60, p < 0.05). 84 \\fn of plant cells decreases with moisture loss either directly, due to an increase in concentration of solutes, or indirectly due to an increase in the level of hydrolytic enzymes which break starch and other polysaccharides into monomers (Jefferies, 1981; Morgan, 1984). Accordingly, at high WVPD, \\f of carrot cells should decrease, due to increase in solute concentration, which in turn should reduce moisture loss. However, this reduction in the rate of water loss did not occur, suggesting involvement of other factors in regulation of water loss. Nilsson (1987) showed an increase in hexose content during storage at low ternperature. Such an increase in sugar content could lower the cell Vj/^ However, in our study did not decrease significantly (P < 0.05) when carrots were stored at low temperature (2°C) for 30 days. Hence, an increase in sugar content at low temperature was not a major factor in determining \\J^ in this study. Apart from \\f gradient, another major factor governing water movement in plants is conductance of the water flow path (Boyer, 1985, Salisbury and Ross, 1992). In intact plants, the plasma membrane offers resistance to apoplastic water movement. Electrolyte leakage has been used to study plasma membrane permeability (Simon, 1974). REL, therefore, can indicate cellular disintegration and/or a change in the cell's ability to accumulate ions and hence maintain vj/^ . In this study, REL increased during storage at high WVPD indicating an increase in membrane permeability which would reduce resistance to water flux and increase water loss. Conversely, REL did not increase during storage at low WVPD, indicating that membrane integrity was maintained, and therefore water loss did not increase. 85 A decrease in relative humidity (Walters et al., 1990) and senescence have been reported to increase membrane leakiness. Storage conditions have also been shown to influence membrane composition. In potatoes, cultivars with a higher level of unsaturated fatty acids have low rates of membrane leakage (Spychalla and Desbough, 1990). The level of fatty acids in potato tubers decreased in response to water loss at 18°C (Mazliak, 1987). This decrease was accompanied by a decrease in membrane permeability. Thompson (1984) and Yoshida (1984) reported increases in the degree of fatty acid unsaturation in several species in response to low temperature. Whether storage of carrots at 13°C influences tissue permeability by influencing membrane composition remains to be determined. Toivonen (1992) reported that ascorbic acid and a combination of calcium chloride and citric acid effectively reduced browning in parsnips by reducing membrane leakiness. Chemical or genetic manipulation of plasma membrane permeability may offer ways to reduce postharvest moisture loss in carrots. Percent loss of fresh weight is generally used to describe freshness of vegetables. For example, carrots are considered unmarketable after losing 8% or more of their fresh weight (Robinson et al., 1975). This value can, however, be misleading because the water content of carrots harvested from soils with different moisture contents and under a variety of weather conditions would be different. Parameters such as \|4 and V | / ^ may more accurately estimate the water status of carrot roots. Using regression equations for relationships between moisture loss and \]4 and i p ^ it was deduced that moisture loss (W*) is approximately equal to: -0.16 + 0.82 VJ/R2 (r = 0.75, N = 43) (Figure 3A) or -0.56 - 0.62 ipLj, (r = 0.82, N = 43) (Figure 3B) (3) (4) The results of this study show that while the membrane permeability parameter REL may be used to estimate the freshness of vegetables (Figure 9C), V|4 and are better estimators of moisture loss as indicated by their high r-values and standard partial regression coefficients (Table 12, Figure 9). The low r-values for leakage could be due to the fact that the change in membrane leakiness occurred after changes in VJJ^ and The experiments in this study were conducted on a single cultivar of carrots grown in a sandy loam soil. Environmental and genetic differences may affect carrots size, composition (e.g sugars, amino acids and minerals) and periderm characteristics. Equations (3) and (4) should, therefore, be used with caution when soil type, climate, or cultivar are different. 87 Chapter VI: Replacement of postharvest moisture loss by recharging and its effect on subsequent moisture loss during short term storage of carrots Abstract The replacement of postharvest moisture loss in carrots (cv. Caro-choice) by single and repeated recharging (i.e. rehydration in water) treatments, the interaction between the duration of recharging and the temperature during recharging, and the effects of these treatments on moisture loss during subsequent short term storage were studied. With single recharging treatments, carrot weight gain increased with increase in recharging duration. Recharging at 13°C or 26°C for 9 h led to highest weight gains. The rate of moisture loss (% day"1) during subsequent storage, however, was not affected by recharging duration or the temperature during recharging. With repeated recharging (every 3.5 days), increase in recharging duration up to 9 h increased carrot weight gain. Most of the weight gain occurred between 0 to 7 days. These recharging treatments, however, did not affect rate of moisture loss during subsequent storage. The percent apparent weight loss (AWL) (without correction for weight gain during recharging) decreased with increase in recharging duration. At 17.5 days of storage, AWL of carrots recharged for 9 h was only one-third that of the control. Carrots recharged every 3.5 days, compared to every 7, 14 days and the control, gained more weight and had the least AWL. Abrasion of carrots increased weight gain upon recharging, and reduced AWL. In contrast, abrasion increased AWL in non-recharged carrots. Overall, the magnitude of reduction in AWL due to recharging was low in single recharging and high in repeated recharging treatments. It is suggested that recharging should be further investigated as an option to improve the shelf life of carrots. 88 Introduction Quality and storage life of fruits and vegetables are reduced by moisture loss, physiological breakdown and decay. Carrots stored at high temperatures tend to wilt, have poor appearance, and hence a short shelf life. Controlled atmosphere during storage and chemical treatments have been used to slow down physiological changes and decay in carrots. Wills et al. (1979) reported that lowering the 0 2 :C0 2 ratio during storage reduced respiration and physiological breakdown of carrots. Use of calcium propionate or potassium sorbate during hydrocooling has been shown to reduce postharvest development of black root rot in carrots (Punja and Gaye, 1993). However, because of consumer concern for use of chemicals on food, development of non-chemical means to maintain carrot quality during storage is needed. Several methods have been used to reduce moisture loss from fruits and vegetables during storage. Most crops benefit from refrigeration, which slows metabolism and reduces water loss. Use of jacketed room storage and Filacell systems (Raghavan et al., 1990) increases relative humidity, thereby reducing moisture loss. However, these systems can be expensive to build and are long term storage strategies and therefore are not designed for retail market systems. One possible option to enhance the shelf life of carrots is to replace the lost moisture by recharging (i.e. rehydration in water). It is an industry practice to wash and hydrocool vegetables to remove field heat before storage, packaging and transportation (Phan, 1987). While some reabsorption of moisture may occur during hydrocooling, because of its short duration, carrots do not fully regain their turgjdity. Lentz (1966) observed that carrots which 89 had lost 7 to 8% weight regained as much as 2.6% weight within 24 h of immersion in ice-water, and 3.8% within one week of storage in drained ice. Carrots can be recharged either immediately after harvest or later during holding. It is not known whether recharging merely replenishes the lost moisture, or whether it also affects the rate of moisture loss during subsequent storage. The optimum duration and frequency of recharging, effect of temperature during recharging and the effect of recharging on abraded or damaged carrots has not been investigated. The specific objectives of this study were to determine the effects of: (1) duration and frequency of recharging, (2) temperature during recharging and (3) recharging of abraded carrots on root weight gain during recharging and root moisture loss during subsequent short term storage. Materials and methods A. Single recharging treatments Carrots (Cv. Caro-choice, Asgrow Seed Company. Newmarket, ON) were hand-harvested 164 days (in 1993) and 175 days (in 1994) after sowing from a large field experiment described in Chapter IV. The carrots were placed into polyethylene bags, transported to the laboratory at the University of British Columbia (<1 km away). They were washed in cold water, gently blotted with paper towels to remove excess water, and subjected to the following treatments. (i) Recharging duration A randomized complete block design with three replications was used. Carrots were 90 allowed to lose moisture by storing for 3.5 days at 13°C and 35% RH and then recharged for 0, 3, 6, 9, 12 and 15 h. Recharging was achieved by dipping carrots in water in 0.30 x 0.21 x 0.07 m plastic trays at 22 ± 2°C. Carrots were blotted dry and reweighed. Preliminary studies showed that carrots absorb moisture most readily between 3.5 and 7 days of storage. (ii) Temperature and duration of recharging A randomized complete block design with three replications of five carrots each in a factorial arrangement with three temperatures (0°C, 13°C and 26°C) and three durations of recharging (3, 6 and 9 h) was used. Recharging was achieved by dipping carrots in water in 0.30 x 0.21 x 0.07 m plastic trays at these temperatures. After recharging and reweighing, the carrots were incubated in perforated plastic bags (0.51 x 0.56 m) at 13°C and 35% RH and their weight was monitored every 3.5 days for 21 days. Weight gain upon recharging was analyzed using a general linear model (Wilkinson et al., 1992). Single degree polynomial contrasts were fitted using the means of various treatments for trend analysis using SYSTAT statistical software. Slope analysis was performed on weight loss (% day"1) to determine the rate of moisture loss during short term storage following recharging. A total of five carrots per replicate in 1994 compared to three in 1993 were used to increase precision since harvesting was only performed from three blocks. However, the carrots of 1994 compared to 1993 showed less variability among the various treatments. 91 While only results of the experiments conducted in 1994 are presented, results suggesting similar conclusions were obtained in 1993. B. Repeated recharging treatments Carrots for this study were grown on a commercial field (Hing Sing Farm) in Cloverdale, B.C., Canada The soil had 5.3 pH and 48.9% organic matter. The field was cropped to lettuce during the previous two years. Fertilizer N:P:K (5:12:16) was broadcast to provide the recommended (Anon., 1992) rates of 45, 23.6 and 59.8 kg of N, P, K ha"1 respectively, and incorporated by raking into the soil before seeding. Carrot seeds (Cv. Caro-choice; Asgrow Seed Co. Kalamazoo, M ) were sown on April 28 in 1994 and on May 19 in 1995 using a Hestair Stanhay S 870 planter with a precision seeder. Three rows (0.35 m apart) with three lines (10 mm apart) in each row were seeded per bed. Paraquat (pre-emergent) and linuron (post-emergent) were used for weed control and cyrjermethrin, parathion and diazinon for insect control. Overhead irrigation was used to supplement rain water as needed. The carrots were harvested from a 1.32 m wide and 10 m long area 90 days (in 1994) and 105 days (in 1995) after sowing. Carrots used in the study involving abraded carrots were harvested 125 days (in 1994) and 120 days (in 1995) after sowing. Carrots were put in polyethylene bags, taken to the University of British Columbia (52 km away), gently washed to remove dirt, blotted dry with paper towels, and subjected to the following treatments. (i) LXiration and frequency of recharging Carrots (five per replicate) were weighed and then recharged for 0, 3, 6 and 9 h to 92 determine the effect of duration of recharging. Recharging was repeated every 3.5 days. In a separate experiment, carrots were recharged for 6 h every 3.5, 7 or 14 days to detennine the effects of frequency of recharging. The non-recharged carrots served as controls. (ii) Recharging of abraded carrots. Periderm surface area was determined by the equations described in Chapter II. Surface area (0, 20 and 40%) of six carrots (per treatment) was abraded by placing a cardboard template over the carrot surface and scrubbing three times with a nylon nail brush using a moderate force. The carrots were then divided into two lots of three carrots each. One lot was recharged for 6 h every 3.5 days while the other served as a non-recharged control. Recharging was achieved by dipping carrots in water at 22 ± 2°C as described above. Carrots were weighed before and after recharging, and placed in 0.51 m x 0.56 m plastic bags perforated with 18, 4 mm diameter holes. The weight and surface colour changes (visually evaluated) of carrots were monitored at 13°C at 35% RH every 3.5 days for 21 days. The duration and frequency of recharging studies were laid out as a completely randomized design with four replications. The recharging study on abraded carrots was laid out as a completely randomized design in a split-plot arrangement. The recharging conditions were arranged as the main plots and carrot abrasion levels as subplots. Repeated measures analysis was done on the weight gain (following recharging) and on the apparent percent weight loss (AWL) (without correcting for weight gained during recharging) in all the experiments using the SYSTAT statistical program (Wilkinson et al., 1992). Slope analysis was performed on weight loss (% day"1) to quantify the rate of moisture 93 loss during the storage after recharging. Treatment means in the duration of recharging and recharging of abraded carrots experiments were fitted to single degree polynomial contrasts for trend analysis. In the frequency of recharging experiments, the means were separated by the Fisher's LSD procedure. While only results of the experiments conducted in 1995 are presented, similar results were obtained in 1994. Results A Single recharging of carrots (i) Recharging duration Weight gain, expressed as percent of fresh root weight increased with the duration of recharging (Table 13) The relationship between weight gain and duration of recharging was linear and quadratic. However, the rate of this increase decreased with recharging duration longer than 12 h. Although the rate of moisture loss during storage of the recharged carrots was 20 to 41.7% lower compared to non-recharged carrots, the effect was not statistically significant. No change in carrot colour (not shown) after recharging was observed. (ii) Temperature and recharging duration The interaction between the effects of ternperature and recharging duration on carrot weight gain was not significant. Weight gain increased with increase in recharging duration (Table 14) at all recharging temperatures. It also increased with increase in the temperature of recharging water from 0°C to 13° or 26°C at all recharging durations. Table 13. Weight gain upon recharging and the rate of moisture loss of carrots recharged for different durations at day 3.5 and stored at 13°C and 35% RH for 21 days. Recharging Weight gain Moisture loss duration (h) (%) (% day1) 0 - 1.19 3 1.08 0.85 6 1.44 0.96 9 2.00 0.71 12 2.45 0.91 15 2.51 0.70 S.E. 0.14 0.06 Significance L,Q Ns L, Q and Ns are linear, quadratic and not significant at P = 0.05, respectively. S.E. = standard error of mean Table 14. Weight gain upon recharging and the rate of moisture loss of carrots recharged at various temperatures for different durations at day 3.5 and stored at 13°C and 35% RH for 21 days. Recharge temperature (°C) Recharge duration (h) Weight gain (%) Weight loss (% dayT) 0 3 0.70 1.21 6 0.94 1.19 9 0.99 0.91 S.E. 0.02 0.34 Significance L Ns 13 3 0.84 1.11 6 1.68 0.95 9 1.82 1.03 S.E. 0.03 0.28 Significance L,Q Ns 26 3 1.08 1.07 6 1.60 1.15 9 2.14 1.00 S.E. 0.06 0.28 Significance L,Q Ns Recharge duration * Ns Recharge temperature Ns Recharge duration x Recharge temperature Ns Ns L, Q and Ns are linear, quadratic and not significant at f< U.05, respectively. S.E.= the standard error of the mean 96 The rate of weight loss (% day"1) during storage of recharged carrots was not affected by the duration of recharging or ternperature of the recharging water (Table 14). No changes in colour (not shown) of the carrots upon recharging were observed. B. Repeated recharging (i) Duration and frequency of recharging Increase in recharging duration increased water uptake by carrots at all times of recharging except on day 0 (Figure 10A). The weight gain (%) was greatest on day 3.5 with recharging. Weight gain (%) decreased after day 3.5 in all treatments. With the exception of day 14, the rate of weight gain (% h"1) was lower in carrots recharged for 9 h and 6 h compared to 3 h (Figure 10B). The recharging duration affected AWL of carrots during incubation at 13°C at 35% RH (Figure IOC). Carrots recharged for 9 h had the lowest AWL followed by 6 and 3 h. The non-recharged carrots had the highest weight loss. The rate of increase in AWL of carrots recharged for 9 h was about a third (0.4% day'1) that of the weight loss from the non-recharged controls (1.2% day"1) at 17.5 days. However, there was no difference in the actual rates of weight loss, i.e. following correction for the weight gain during recharging (data not shown) among various recharging treatments. An increase in the duration of recharging caused browning on the carrot surface following 21 days of storage at 13°C and 35% RH (Figure 11). Carrots repeatedly recharged for 9 h displayed prominent darkened areas particularly at the points of root hair attachment. The lower halves of the non-recharged controls and of the carrots repeatedly recharged for ^ 0 .8 "o 5 0 .6 — 0.4 0 .2 -B x S . E . I iTOlriJlJ 3.5 10.5 14 17 .5 40 =3- 30 -•- 0 h . 3 h -O 6 h -V- 9 h c 3.5 7 10 5 14 Observat ion time (d) 17.5 21 Figure 10. (A ) Weight gain (%), ( B ) weight gain (% I T 1 of recharging) and ( C ) apparent weight loss (%) of carrots recharged for different durations and stored at 13°C and 35% RH for 21 d. The fall at each observation time in (C) indicates weight gain during recharging which is plotted in ( A ) . S . E . = overall standard error of the mean. Figure 11. The effects of repeated recharging every 3.5 days for 0, 3, 6 and 9 h (from the left to the right) on the colour and flexibility of carrots, after 21 days. 99 3 h each time were very flexible; they could be bent to an angle of 90° without breaking. The carrots repeatedly recharged for 6 and 9 h could not be bent to the same angle without breaking, indicating their low flexibility. When carrots were recharged repeatedly every 3.5 days, the percent weight gain during recharging was highest on the first recharging and decreased thereafter (Table 15). Similarly, the highest weight gain occurred during the first recharging on day 7 for the carrots recharged every 7 days. Carrots first recharged on day 14 gained the least weight compared to weight gained during the first recharging in other treatments. The initial recharging weight gains in carrots recharged every 3.5 (2.19%) and 7 days (2.14%) were approximately double the weight gained by the carrots first recharged on day 14 (1.19%). Carrots recharged every 3.5 days had the lowest AWL compared to those recharged every 7 or 14 days (Figure 12). The weight loss was highest in the control (non-recharged carrots) while AWL was highest in carrots recharged on day 14 followed with those recharged every 7 days. However, there was no difference in the slopes of the actual weight loss (%) curves, i.e. following correction for the weight gained during recharging, for different recharging treatments. (ii) Recharging of abraded carrots Weight gain (%) of abraded carrots recharged for 6 h every 3.5 days increased with increase in the level of abrasion at 0, 3.5, 7, 10.5 and 17.5 days (Figure 13A). The increase was greatest on day 7. 100 Table 15. Percent weight gain of carrots recharged every 3.5, 7 and 14 days for a duration of 6 h and stored at 13°C and 35% RH for 21 days. Frequency of Observation time (d) recharging (d) 3.5 7.0 10.5 14.0 17.5 Control -3.5 2.19* 1.79a 1.37 1.35a 1.16 7.0 - 2.14a - 1.02b 14.0 - - - 1.19ab S.E. 0.15 0.21 0.04 0.06 0.07 S.E. is the standard error of the mean. Means within a column followed by different letters are significantly different at P = 0.05 with LSD. * a percentage of the fresh weight of the carrots. 101 4 0 3 0 Control 3.5 days 7.0 days 1 4.0 days CO CO o 2 0 CD g- 1 0 < I S . E . Oc o 3 . 5 7 1 0 . 5 1 4 1 7 . 5 21 Observat ion time (d) Figure 12. Apparent weight loss (%) of carrots recharged for 6 h every 3.5, 7 and 14 d and stored at 13°C and 3 5 % RH for 21 d. The fall at each observation time indicates weight gain. S.E. = overall standard error of the mean. 102 0 3.5 7 10.5 14 17.5 21 Observation time (d) Figure 13. Effects of recharging every 3.5 d for a duration of 6 h on (A) weight gain (%) during recharging and (B) apparent weight loss (%) of recharged and non-recharged abraded carrots stored at 13°C and 3 5 % RH for 21 d. The fall at each observation time in (B) indicates weight gain which is plotted in Figure (A). OA, 20A and 40A are non-recharged carrots with 0, 20 and 40 percent of their surface area abraded, respectively. R0A, R20A and R40A are recharged carrots with 0, 20 and 40 percent of their surface area abraded, respectively. S.E. = overall standard error of the mean. 103 Carrot abrasion had no significant effect on AWL in all treatments up to 17.5 days in recharged carrots (Figure 13B). AWL however, decreased significantly (P < 0.05) with increase in level of abrasion in recharged carrots following 21 days of storage. In contrast, an increase in abrasion level increased weight loss during storage in non-recharged carrots at 17.5 and 21 days. Overall, the AWL in recharged carrots was lower compared to weight loss in the non-recharged carrots. However, there was no difference in the rate of the actual weight loss, i.e. following correction for the weight gained during recharging, in different treatments. Recharged carrots with abraded surface developed a dark brown coloration after 10.5 days of storage (Figure 14A). Browning increased with the degree of periderm abrasion. A similar but less severe browning was observed on the non-recharged carrots with 40% of their surface area abraded (Figure 14B). Non-recharged carrots with 0% and 20% of their surface area abraded did not develop this discoloration within 17.5 days. Discussion A Single recharging of the carrots Storage under high humidity reduces moisture loss and maintains turgidity of horticultural produce (van den Berg, 1987). Recharging by dipping in water may increase turgidity of produce, making longer storage possible. During hydrocooling, carrots are plunged into cold water for a short period, which may not provide enough time to allow reabsorption of the lost water. In this study, the carrots which had lost 2.96% of their weight regained as much as 2.45% of the weight during recharging for 12 h. A further increase in Figure 14. The effect of increasing abrasion level on (A) surface coloration in recharged carrots and (B) surface coloration in non-recharged carrots. Values represent percent of surface area damaged for each pair. 105 recharging duration had little effect on weight gain. The benefit of recharging was manifested in the replacement of the lost moisture and not in the reduction of rate of moisture loss during storage of the recharged carrots. While these results suggest that recharging can replace most of the lost moisture, the practicality of this option remains to be investigated. There is no information available concerning the interaction between the effects of water temperature and recharging duration on carrot weight gain during recharging, and on moisture loss during storage of recharged is available. Lentz (1966) reported that carrots immersed either in ice-water or in drained-ice regained as much as half of their lost weight. In this study, the carrots recharged in water.at 13°C or 26°C for 9 h regained almost all of their lost weight compared to only half at 0°G, Thus, use of water at 13°C and 26°C, instead of 0°C, is preferential from the point of view of water absorption. Whether employment of these temperatures introduces other problems, e.g. increase in the incidence of diseases during storage, remains to be determined. B. Repeated recharging of carrots Although water is frequently sprayed on carrots on supermarket and store shelves, no information on the effects of repeated recharging on carrot weight gain during recharging, and moisture loss during storage of the recharged carrots is available. In this study, slopes of real weight loss (%) curves (i.e. following the correction for weight gain) were not affected by the recharging treatments suggesting that recharging does not influence the rate of transpiration. Hence, the observed decrease in AWL due to repeated recharging was due to an increase in the amount of moisture absorbed during the recharging of carrots. 106 In this study, carrots gained weight most readily during recharging at days 0 and 7; their capacity to absorb moisture following storage decreased progressively thereafter. Evidence presented in Chapter V suggests that carrot tissue deteriorates and loses its capacity to maintain \|^ after one week of storage at 13°C and 35% RH. It is possible that once carrots start to senesce and lose membrane integrity, their ability to absorb water during recharging may also be reduced. The storage potential of root vegetables is known to decrease with damage during harvesting (Karl and Weichmann, 1987). In this study, increase in the level of abrasion of non-recharged carrots led to greater weight loss during storage. Abrasion damage or possibly removal of the periderm affects this protective barrier against moisture loss in carrot roots (Esau, 1940). An increase in the percentage of carrot surface area abraded resulted in increased weight gain (%) during recharging, which lowered AWL. Since some abrasion usually occurs during harvest and postharvest handling, this damage may benefit these carrots by improving water absorption during recharging thereby extending shelf life. Prominent darkened areas developed around the points of root hair attachment in carrots repeatedly recharged for 9 h. It is possible that separation of the root hairs during harvesting caused damage on these spots. Dorrell and Chubey (1972) suggested that any damage to the carrot root stimulates suberization and accelerates surface browning, den Outer (1990) suggested that the drier conditions during storage cause death of the thin-walled cells, e.g. phellogen cells and the secretory cells of oil ducts in carrots. A layer of dead and crushed cells is formed, decreasing the brightness of the skin. In this study, browning increased with the degree of periderm abrasion in recharged carrots. The poor colour development may 107 adversely affect the market value, thus negating the advantage gained from recharging carrots. In conclusion, this study shows that recharging can replace most of the moisture lost during postharvest storage. The benefit of recharging is due to increased water gain and not due to decrease in moisture loss rate. Recharging at 13 or 26°C leads to greater weight gain than recharging at 0°C. Carrots benefit most from recharging within the first week following harvest. The magnitude of decrease in the AWL due to recharging is high with repeated recharging treatments, compared to single recharging treatments. Whether repeated immersion in water for the necessary period is practical remains to be determined. 108 Chapter VTJL Conclusions and Recommendations The work presented in this thesis has investigated the factors affecting postharvest moisture loss in carrots. Investigation into how preharvest factors such as soil water stress, K nutrition and cultivar affects postharvest moisture loss provided information which may lead to extension of shelf life in carrots. A study of the effects of moisture loss on 1)4 and ip^ and tissue deterioration revealed physiological changes associated with moisture loss during the short term storage of carrots. Finally, an attempt was made to replace carrot moisture through different recharging regimes and the effects of these treatments on moisture loss during subsequent storage was studied. The following conclusions and recommendations can be drawn from the results presented in this thesis. (A) Preharvest factors (soil moisture, cultivar, and K nutrition) (i) Preharvest water stress Preharvest water stress increased postharvest water loss from carrots. It is, therefore, suggested that carrots should not be harvested when soil is under water stress. Irrigation to decrease soil water stress may improve the shelf life of carrots by reducing postharvest moisture loss. Stepwise multiple regression analysis suggested that \|4 and RSL (an indicator of cell membrane integrity) accounted for most of the variation in moisture loss. Carrots adjusted to water stress by decreasing \J4. However, the carrots with low \\k exhibited high, instead of the expected low postharvest moisture loss. This suggests that other factors) may counter the 109 effects of a lowered \(4, and this imbalance caused increased moisture loss. The RSL increased with increase in water stress and was associated with high postharvest moisture loss. It is, therefore, suggested that preharvest water stress increases tissue permeability of carrots which may enhance moisture loss during storage. Increase in preharvest water stress increased SSA and lowered W and D. However, stepwise multiple regression analysis showed that SSA, W, D and cultivar were associated with postharvest moisture loss to a lesser extent than either \(4 or RSL. (ii) K nutrition A change in carrot size and 1(4, XJJLR and RSL with change in K availability during growth was observed. Backward stepping showed that W and RSL were the two variables which accounted for most of the variation in the postharvest moisture loss. Increase in K application up to 1 mM increased W which in turn lowered SSA and postharvest moisture loss. Carrots grown at low levels of K had high RSL and moisture loss, compared to those grown on high K levels. It is concluded that adequate K availability lowers cell membrane permeability and hence reduces transpiration losses. Increase in K application up to 1 mM lowered \|4 and \)/ .^ Moisture loss correlated positively with 1(4, and \\f^. Carrots grown at high K levels had low \|4 and low postharvest transpiration. It is, therefore, suggested that adequate K nutrition is essential for longer shelf life in carrots. Stepwise regression, however, showed that \|4 was associated with postharvest moisture loss to a lesser extent than either W or RSL. 110 Changes due to K application in various variables measured in this study were observed only up to 1. 0 mM; the effects levelled off thereafter. High K fertilization could, therefore, improve shelf life of carrots only under low K conditions. Conversely, high application of K in growth medium with adequate K is not beneficial in improving the shelf life of carrots. Supplementary K should only be added if the growth medium and/or plant K analysis shows K deficiency. (iii) Cultivar differences A wide range of carrot cultivars varying in size and shape are grown in N. America. Consistent cultivar differences in postharvest moisture loss characteristics were observed in the late harvested (more mature) carrots for these commonly grown cultivars. 'Eagle' and 'Irnperator Special 58' lost the least while 'Paramount', 'Gold Pak 28' and 'Celloking1 lost the most moisture. Differences in SSA (an indicator of A V ) among cultivars were more prominent in the late harvested carrots. This suggests that the time of harvesting should be considered while selecting cultivars for shelf life extension. The cultivars used in this study had similar C-values (indicator of shape). Hence differences in carrot shape cannot explain differences in moisture loss. Stepwise multiple regression showed that SSA was highly associated with moisture loss. The cultivars with low SSA tended to have low moisture loss, while those with high SSA had high moisture loss. Cell membrane permeability was the other variable that accounted for a high variation in moisture loss among the cultivars. The cultivars Paramount and Celloking with high cell membrane permeability, as measured by increased REL, had higher moisture loss than 'Eagle' I l l with low cell membrane permeability. Since one of the determinants of water movement in plant tissues is the resistance of the flow path, increase in cell membrane permeability would lead to faster water movement and hence higher transpiration. The fact that cultivar differences were apparent only at LRH but not at HRH suggested that storage conditions are more important than cultivar differences in determining the moisture loss characteristics of carrots. This suggests that the Fraser Valley of B.C. growers may not benefit much through choice of cultivars for shelf life improvement. Investment into facilities providing HRH conditions during storage would be worthwhile. Cultivar selection may, however, be important in situations where HRH storage facilities are not available. This study suggests that shelf life can be lengthened by 4 to 6 days by choosing cultivars tolerant to water loss, and this could translate into financial savings to carrot producers. (B) Effect of moisture loss on vj^ and tissue permeability during storage Storage of carrots at different WVPDs resulted in changes in moisture loss, M^R and cell membrane permeability. Increase in WVPDs increased the rate of moisture loss. Despite losing more moisture, the carrots at high WVPDs continued to lose more moisture (percent per KPa per day) compared to those at low WVPD. This suggests involvement of factors other than WVPDs in determining moisture loss. A decrease in vj^ with storage duration did not decrease moisture loss as expected. The REL of carrots at high WVPDs increased in comparison to that of the carrots at low WVPD. It is suggested that an increase in carrot tissue permeability may be responsible for the 112 increase in the rate of transpiration despite a decrease in \|^. vpkandvj/nR (as indicated by high r-values) were the variables that best predicted moisture loss. REL was a poor indicator of moisture loss (as indicated by low r-values) possibly because it occurred after changes in XJ/R and VJJL .^ (C) Replacement of postharvest moisture loss by recharging. Increase in the recharging duration and of the temperature of recharging water to 13 or 26°C increased the carrot weight gain during recharging. However, the rate of moisture loss during storage of the recharged carrots at 13°C and 35% RH was not affected. This suggests that carrots benefit from the weight gain during recharging and not from the reduction in the rate of moisture loss during subsequent storage. In repeatedly recharged carrots, increase in recharging duration increased root weight gain leading to overall low AWL. Most of the weight gain occurred between 0 and 7 days of recharging. This shows that carrots would benefit from recharging particularly during the first week of storage. The most frequently recharged carrots (every 3.5 days) continued to regain weight even with later rechargings. Carrots recharged every 14 days gained less weight. This work, therefore, suggests that carrots should be recharged every 3.5 days. However, whether this is practical and economically justified remains to be determined. Abraded carrots gained more weight upon recharging than the non-abraded control. Since some abrasion usually occurs during harvest and postharvest handling, recharging may benefit these carrots by improving water absorption thereby extending their shelf life. 113 While these results show that recharging can replace most of the lost moisture and extend the shelf life of carrots, a number of practical issues need to be addressed before this practice can be exploited further. Whether immersion in water for the necessary period, frequency and ternperature is practical needs to be investigated. Poor coloration developed in some treatments. For example, carrots recharged repeatedly (every 3.5 days) for 9 h, and carrots with 40% of their periderm abraded developed surface browning, which may reduce their marketability. The reason for this browning remains to be investigated. Whether recharging introduces other problems, e.g. increase in incidence of diseases during storage, also remains to be determined. On the whole, whether the economic benefits obtained in extending carrot shelf life by recharging outweighs the costs of changing the present day carrot handling procedures should be determined. 114 Bibliography Anonymous. 1988-94. Annual statistics, B.C. Ministry of Agriculture, Fisheries and Foods, B.C. Anonymous. 1992. Vegetable production guide for commercial growers, p. 42-47. In: Province of British Columbia. Ministry of Agriculture, Fisheries and Foods. Apeland, J. and H. Baugerod. 1971. Factors affecting weight loss in carrots. Acta Hoit 20: 92-97. Apeland, J. and Hoftun, H. 1971. Physiological effects of oxygen on carrots in storage. Acta Hort. 20: 108-114. Apeland, J. and Hoftun, H , 1974. Effects of temperature-regimes on carrot during storage. Acta Hort. 38: 291-299. Banga, O. 1962. Main types of western carotene carrot and their origin. Tjeenk, W.E. (ed.). Willink. Zwolle, Netherland. Cited in: Umiel, N., Rust, A F . and Gabelman, W.H. 1972. A technique for studying quantitatively the variation in size and shape of carrot roots. HortSci. 7: 273-276. Bassett, M J . 1973. Relationship between core size, specific gravity, and soluble solids in carrots. HortSci. 8: 139. Benjamin, L .R and Sutherland, R A . 1989. Storage-root weight, diameter and length relationships in carrot (Daucus carvta) and red beet (Beta vulgaris). J. Agric. Sci. 113: 73-80. Ben-Yehoshua, S. 1987. Transpiration, water stress, and gas exchange, p. 113-170. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. Ben-Yehoshua, S., Shapiro, B., Chen, Z.E., Lurie, S. 1983. Mode of action of plastic film in extending life of lemon and bell pepper fruits by alleviation of water stress. Plant Physiol. 73: 87-93. Ben-Zioni, A., Vaadia, Y. and Lips, H.S. 1971. Nitrate uptake by roots as regulated by nitrate reduction products of the shoot. Physiol. Plant. 24: 288-290. Berard, L.S., and Lougheed, E.C. 1982. Electrolyte leakage from daminozide-treated apples held in air, low-pressure and controlled-atmosphere storage. J. Amer. Soc. Hort. Sci. 107: 421-425. 115 Beringer, H. and Nomdruft, F. 1985. Effects of potassium on plant structures, p. 352-363. In: Potassium in Agriculture. R.D. Munson (ed.). Amer. Soc. Agron., Madison, WI. Beringer, H., Koch, K and Lindhauer, M G . 1990. Source: sink relationships in potato (Solatium tuberosum) as influenced by potassium chloride or potassium sulphate nutrition, p. 639-642. In: Plant nutrition - physiology and applications, van Beusichem, M L . (ed.). Kluwer Academic Publishers, Norwell, M A Beverly, R.B., Latimer, J.G. and Smittle, D.A 1993. Preharvest physiological and cultural effects on postharvest quality, p. 73-99. In: Postharvest handling. A systems approach. Shewfelt, R.L. and Prussia, S.E. (ed.). Academic Press Inc., San Diego, C A Biegon, R.C. 1995. Effects of potassium fertilization and periderm damage on shelf life of carrots. MSc. Thesis. Dept. of Plant Science, Univ. of British Columbia, Vancouver, BC. Bishop, R.F., Chipman, E.W and MacEachern. 1973. Effect of nitrogen, phosphorus and potassium on yields and nutrient levels in carrots grown on sphagnum peat and mineral soils. Comm. Soil Sci. & Plant Anal. 4: 455-474. Bleadsdale, J . K A and Thompson, R 1963. An objective method of recording and comparing the shapes of carrot roots. J. Amer. Soc. Hort. Sci. 38: 232-241. Boyer, S.J. 1985. Water transport. Ann. Rev. Plant Physiol. 36: 473-516. Burton, W.G. 1982. The physiological implications of structure: water movement, loss and uptake, p. 43-68. In: Post-harvest physiology of food crops. Longman, London, U K Carlin, F., Nguyen-The C , Chambroy, Y. and Reich, M 1990. Effects of controlled atmospheres on microbial spoilage, electrolyte leakage and sugar content of fresh 'ready-to-use' grated carrots. Internatl. J. Food Sci. Tech. 25: 110-119. Chapman, D.S. and Auge, R M 1994. Physiological mechanisms of drought resistance in four native ornamental perennials. J. Amer. Soc. Hort. Sci. 119: 299-306. Chapman, K S . R , Sparrow, L A , Haedman, P.R, Wright, D.N and Thorp, J . R A 1992. Potassium nutrition of Kennebec and Russet Burbank potatoes in Tasmania: effect of soil and fertilizer potassium on yield, petiole and tuber potassium concentrations, and tuber quality. J. Amer. Soc. Hort. Sci. 32: 521-527. Cheeseman, J .M and Hanson, J.B. 1980. Does active K+influx to roots occur? Plant Sci. Lett. 18: 84-87. 116 Clarkson, D.T. and Hanson, J.B. 1980. The mineral nutrition of higher plants. Ann. Rev. Plant Physiol. 31: 239-298. Dai, J. and Paul, R E . 1991. Effect of water status on Dendrobium flower spray postharvest life. J. Amer. Soc. Hort. Sci. 11: 491-496. Daliparthy, J., Barker, A.V. and Mondal, S.S. 1994. Potassium fractions with other nutrients in crops: a review focus in on the tropics. J. Plant Nutr. 17: 1859-1886. den Outer, RW. 1990. Discolorations of carrot (Daucus carota L.) during wet chilling storage. Sci. Hort. 41: 201-207. Dennis, C. 1981. The effect of storage conditions on the quality of vegetables and salad crops, p. 329-339. In: Quality of stored and processed vegetables and fruits. Goodenough, P.W. and Atkins, R K . (ed.). Academic Press, London. Dorrell, D.G. and Chubey, B.B. 1972. Acceleration of enzymatic browning in carrot and parsnip roots by induced suberization. J. Amer. Hort. Sci. 97: 110-111. Esau, K. 1940. Development and anatomy of the fleshy storage organ of Daucus carota Hilgardia 13: 175-225. Esau, K. 1965. Periderm, p. 338-352, 511 and 719. In: Plant Anatomy. John Wiley & Sons, Inc. NY. Evans, H.J. and Sorger, G.J. 1966. Role of mineral elements with emphasis on the univalent cations. Annu. Rev. Plant Physiol. 17: 46-76. Evers, A M 1989a. Effects of different fertilization practices on the carotene content of carrot. J. Agric. Sci. Finland. 61:7-14. Evers, A M . 1989b. Effects of different fertilization practices on glucose, fructose, sucrose, taste and texture of carrots. J. Agric. Sci. Finland. 61: 113-122. Evers, A.M. 1989c. Effects of different fertilization practices on the quality of stored carrots. J. Agric. Sci. Finland. 61: 123-134. Evers, A M . 1989d. The role of fertilization practices in the yield and quality of carrot (Daucus carota L.). J. Agric. Sci. Finland. 61: 329-360. Finlayson, J.E., Pritchard, M K . and Rimmer, S.R 1989. Electrolyte leakage and storage decay of five carrot cultivars in response to infection by Sclemtinia sclerotiorum. Can. J. Plant Pathol. 11: 313-316. 117 Fockens, F.H. and Meffert, H.F.T. 1972. Biophysical properties of horticultural products related to loss of moisture during cooling down. J. Sci. Food & Agric. 23: 285-298. Fritz, D. and Weichmann J. 1979. Influence of the harvest date of carrots on quality and quality preservation. Acta Hort. 93: 91-100. Glass. A.D.M. and Siddiqi, M Y . 1984. The control of nutrient uptake rates in relation to the inorganic composition of plants, p. 103-147. In: Advances in plant nutrition. Tinker, P.B. and Lauchli, A. (ed.). Praeger Publishers. New York, NY. Greenwood, D.J., Cleaver, T.J., Turner, M.K., Hunt, J., Niendorf, K.B. and Loquens, S.MH. 1980. Comparison of the effects of potassium fertilizer on the yield, potassium content and quality of 22 different vegetables and agricultural crops. J. Agric. Sci. Camb. 95: 441-456. Habben, J. 1972. Quality constituents of carrots as influenced by nitrogen and potassium fertilization. Acta Hort. 29: 295-305. Hoagland, D.R. and Arnon, D.I. 1950. The water culture method of growing plants without soil. Calif. Agric. Expt. Sta. Circ. 347. Hodges. T.K. 1976. ATPase associated with membranes of plant cells, p. 260-283. In: Transport in plants. Luttge, U. and Pitman, M G . (ed.). Encyl. Plant Physiol., New Series, Vol 2A, Springier-Verlag, Berlin, Heidelberg, NY. Hole, C.C., Barnes, A. Thomas, T.H., Scott, P.A and Rankin, W.E.F. 1983. Dry matter distribution between the shoot and storage root of carrot (Daucus carota L.). I. Comparison of varieties. Ann. Bot. 51: 175-187. Hole, C.C., Morris, G.E.L. and Cowper, A S . 1987. Distribution of dry matter between shoot and storage root of field-grown carrots. I. Onset of differences between cultivars. J. Hort. Sci. 62: 335-341. Hsiao, T.C. 1973. Plant responses to water stress, p. 519-570. In: Ann. Rev. Plant Physiol, vol. 24. Briggs, W.R, Green, P.C. and Jones, R L . (ed.). Annual Reviews, Palo Alto, CA. Hsiao, T.C. 1976. Stomate ion transport, p. 195-221. In: Transport in plants. Luttge, U. and Pitman, M G . (ed.). Encycl. Plant Physiol., New Series. Vol. 2B, Springer-Verlag, Berlin, Heidelberg, NY. Hurschka, H.W. 1977. Post-harvest moisture loss and shrivel in five fruits and vegetables. U. S. Dept. Agric, Agric. Res. Ser., Marketing Res. Rep. No. 1059. 118 Hurst, P.L., Borst, W . M and Hannan, PJ. 1993. Effect of harvest date on the shelf life of asparagus. New Zealand J. Crop and Hort. Sci. 21: 229-233. Jefferies, R.L., 1981. Osmotic adjustment and response of halophytic plants to salinity. Bioscience 31: 42-46. Kader, A A 1987. Respiration and gas exchange of vegetables., p. 25-43. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. Karl, S. and Weichmann, J. 1987. Root vegetables, p. 541-553. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. Kays, SJ. 1991. Movement of gases, solvents, and solutes within harvested products and their exchange between the product and its external environment, p. 409-456. In: Postharvest physiology of perishable plant products. Van Nostrand Reinhold, New York, NY. Ketsa, S. 1990. Effect of fruit size on moisture loss and shelf life of tangerines. J. Hort. Sci. 65: 485-488. Knowles, L.O. and Flore, J A 1983. Quantitative and qualitative characterization of carrot root periderm during development. J. Amer. Soc. Hort. Sci. 108: 923-928. Knowles, N.R and Knowles, L.O. 1989. Correlations between electrolyte leakage and degree of saturation of polar lipids from aged potato (Solanum tuberosum L.) tuber tissue. Ann. Bot. 63: 331-338. Kohler, K , Steigner, W., Simonis, W., Urbach, W. 1986. Potassium channels in Eresmosphera viridis. Planta 166: 490-499. Kramer, PJ. 1983. Water relations of plants. Academic Press, NY. Kunkel, R 1947. The effect of various levels of nitrogen and potash on the keeping quality of onions. Proc. Amer. Soc. Hort. Sci. 50: 361-367. Lentz, CP. 1966. Moisture loss of carrots under refrigerated storage. Food Technol. 20: 201-204. Lentz, CP. and Rooke, E A 1957. Use of the jacketed room system for cool storage. Food Technol. 11: 257-259. Loue, A 1977. Fertilization and mineral nutrition of potato (In French). Imperimerie Alsace. Mulhouse: Dept. d'agronomie de la SPCA 119 Lownds, N.K., Banaras, M and Bosland, P.W. 1994. Postharvest water loss and storage quality of nine pepper (Capsicum) cultivars. HortScience 29: 191-193. Lune, P. van and van Goor, B.J. 1977. Ripening disorders of tomatoes as affected by the K/Ca ratio in the culture solution. J. Hort. Sci. 52: 173-180. Lutz, J .M and Hardenburg, R E . 1968. The commercial storage of fruits, vegetables and florist and nursery stocks. U.S. Dept. Agric. Handbook No. 66. Maier, N.A. Dahlenburg, A P . and Frensham, A B . 1986. Potassium nutrition of irrigated potatoes in south Australia. 3. Effect of specific gravity, size and internal bruising of tubers. Aust. J. Exp. Agric. 26: 737-44. Mazliak, P. 1987. Membrane changes and consequences for the postharvest period, p. 95-111. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. McCollum, W. 1980. Carrots, p. 273-282. In: Producing vegetable crops. Third edition. The Interstate Printers and Publishers, Inc. Danville, IL. McGarry, A. 1995. Cellular basis of tissue toughness in carrot (Daucus carota L.) storage roots. Ann. Bot. 75: 157-163. Morgan, J. M 1984. Osmoregulation and water stress in higher plants. Ann. Rev. Plant Physiol. 35: 299-348. Neter, J., Wasserman, W. and Kutner, H . M 1990, p. 386-287 and 447-450. In: Applied linear statistical models. Regression, analysis of variance, and experimental designs. Third edition, Irwin, Inc., Burr Ridge, IL. Nilsson, T. 1987. Carbohydrate composition during long-term storage as influenced by the time of harvest. J. Amer. Soc. Hort. Sci. 62:191-203. Pierce, L.C. 1987. Root crops, p. 225-258. In: Vegetable characteristics, production and marketing. John Wiley and Sons, Inc., NY. Phan, C.T., 1987. Temperature: Effects on metabolism, p. 173-180. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. Phan, C.T., Hsu, H. and Sarkar, S.K. 1973. Physical and chemical changes occurring in the carrot root during growth. Can. J. Plant Sci. 53: 629-634. Poovaiah, B.W. and Leopold, A 1976. Effects of inorganic salts on tissue permeability. Plant Physiol. 58: 182-185. 120 Punja, Z.K. and Gaye, M - M . 1993. Influence of postharvest handling practices and dip treatments on development of black root rot on fresh market carrots. Plant Dis. 77: 989-995. Raghavan, G.S.V., Bowell, R and Chayet, M 1980. Storability of fresh carrots in a simulated jacketed storage. Trans. Amer. Soc. Agric. Eng. 1521-1524. Raschke, K. 1979. Movements of stomate, p. 383-441. In: Physiology of movements. Haupt, W. and Feinleib, M E . (ed.). Encycl. Plant Physiol. New Series, Vol. 7, Springer-Verlag, Berlin, Heidelberg, NY. Reynolds, J.D. 1968. Main crop variety trials. J. Natl. Inst. Agric. Bot. 11: 307-21. Robinson, J.E., Browne, K . M and Burton, W.G. 1975. Storage characteristics of some vegetables. J. Food Qual. 10:157-177. Russel, RS. and Goss, M J . 1974. Physical aspects of soil fertility - The response to mechanical impedence. Neth. J. Agric. Sci. 22: 305-318. Ryall, A L . and Lipton, W.J. 1979. Handling, transportation and storage of fruits and vegetables and melons. AVI Publishing Co. Inc. Westport, CT. Salisbury, F.B. and Ross, C.W. 1992. Plant Physiology, p. 49-92. 4th edition. Wadsworth. Belmont, CA. Sastry, S.K., Baird, C D . and Burlington, D.E. 1978. Transpiration rates of certain fruits and vegetables. Amer. Soc. of Heating, Refrig., Air-conditioning Eng. Trans. 84: 237-255. Shewfelt, R L . 1986. Postharvest treatment for extending the shelf life of fruits and vegetables. Food Technol. 40: 70-89. Simon, E.W. 1974. Phospholipids and plant membrane permeability. New Phytol. 73: 377-420. Smith, W.H. 1967. Low temperature and storage of carrots. J. Fd. Technol. 2: 89-94. Smith, W.H. and Yang, S.M 1969. Effect of relative humidity on the production of extracellular pectolytic enzymes on Botrytis cinerea and Sclerotinia sclerotiorum. Can. J. Bot. 47: 1007-1010. Spychalla, J.P. and Desborough, S.L. 1990. Fatty acids, membrane permeability, and sugars of stored potato tubers. Plant Physiol. 94: 1207-1213. 121 Stanhill, G. 1977. Allometric growth studies of the carrot crop. I. Effects of plant development and cultivar. Ann. Bot. 41: 533-540. Steel, R.G.D. and Torrie, J.H. 1987. Principles and procedures of statistics. A biometrical approach. 2nd ed. McGraw-Hill Book Co., London, UK. Steuter, A.A., Mozafar, A and Goodin, J.R. 1981. Water potential of aqueous polyethylene glycol. Plant Physiol. 67: 64-67. Stoll, K and Weichmann, J. 1987. Root vegetables, p. 541-553. In: Postharvest Physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. Suelter, C H . 1985. Role of potassium in enzyme catalysis, p. 337-349. In: Potassium in Agriculture. Munson, RD. (ed.). Amer. Soc. Agr., Madison, WI. Tahler, M , Steigner, W., Kohler, K , Simonis, and W. Urbach, W., 1987. Release of repetitive transient potentials and opening of potassium channels by bacterium Eremosphaemviridis FEBS Lett. 219: 351-54. Thompson, J.E. 1984. Physical changes in the membrane of senescing and environmentally stressed plant tissues, p. 85-108. In: Physiology of membrane fluidity. Shinitzy, M (ed.). Vol. n . CRC Press, Boca Raton, FL. Toivonen, P . M A 1992. The reduction of browning in parsnips. J. Hort. Sci. 67: 547-551. Turner, N.C. and Jones, M M 1980. Turgor maintenance by osmotic adjustment: a review and evaluation, p. 87-103. In: Adaptation of plants to water and high temperature stress. Turner, N.C. and Kramer, P.J. (ed.). Wiley Interscience, NY. Tisdale, S.L., Nelson. W.L., Beaton, J.D. and Havlin, J.L. 1993. Soil and fertilizer potassium, p. 230-265. In: Soil fertility and fertilizers. Corey, P.F. (ed.). Fifth edition. MacMillan, New York, NY. Turner, N.C. and Jones, M M 1980. Turgor maintenance by osmotic adjustment: a review and evaluation, p. 87-103. In: Adaptation of plants to water and high temperature stress. Turner, N.C. and Kramer, P.J. (ed.). Wiley Interscience, NY. Umiel, K , Kust, A F . and Gabelman, W.H. 1972. A technique for studying quantitatively the variation in size of carrot roots. Hortscience 7: 273-276. van den Berg, L. 1981. The role of humidity, temperature, and atmospheric composition in mamtaining vegetable quality during storage, p. 95-107. In: Quality of selected fruits and vegetables of North America. Teranishi, R. and Barrera-Benitez, H. (ed.). Amer. Chem. Soc., Washington, DC. 122 van den Berg, L., 1987. Water vapour pressure, p. 203-230. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. van den Berg, L. and CP. Lentz. 1966. Effect of temperature, relative humidity and atmospheric composition on changes in quality of carrots during storage. Food Technol. 20: 104-107. van den Berg, L. and Lentz, CP. 1973. High humidity storage of carrots, parsnips, rutabagas and cabbage. J. Amer. Soc. Hort. Sci. 98: 129-132. van Lierop, W. 1989. Determination of available phosphorus in acid and calcareous soils with the Kelowna multi-element extractant. Soil Sci. 146: 284-291. Walters, Jr, J.R, Epley, D.G. and McFeeters, R.F. 1990. Effects of water stress on stored pickling cucumbers. J. Agr. Food Chem. 38: 2185-2191. Weichmann, J. 1987. Low oxygen effects, p. 231-237. In: Postharvest physiology of vegetables. Weichmann, J. (ed.). Marcel Dekker, NY. Weichmann, J. and Kappe, R 1977. Harvesting dates and storage-ability of carrots (Daucus carota L.). Acta Hort. 62: 191-194. Wilkinson, L., Hill, M A , Welma, P.J. and Birkenbeuel, K.G. 1992. SYSTAT for windows: Statistics, Version 5th ed. SYSTAT, Inc., Evanston, IL. Wills, R.B.H, Lee, T.H., Graham, D., McGlasson, W.B. and Hall, E.G. 1981. Water loss and humidity, p. 52-59. In: Postharvest: An introduction to the physiology and handling of fruit and vegetables. Third ed. AVI, Westport, CT. Wills, R.B.H., Wimalasiri, P. and Scott, K.J. 1979. Short pre-storage exposures to high carbon dioxide or low oxygen atmospheres for the storage of some vegetables. HortScience. 14: 528-530. Wyn Jones, R G. and Pollard, A 1983. Proteins, enzymes and inorganic ions, p. 528-562. In: Inorganic Plant Nutrition. Lauchli, A and Bieleski, R L . (ed.). Encycl. Plant Physiol., New Series, Vol. 15B. Springer-Verlag, Berlin, Heidelberg, NY. Yoshida, S. 1984. Chemical and biophysical changes in the plasma membrane during acclimation of mulberry bark cells (Moms bombycis Koidz. cv. Goriji). Plant Physiol. 76: 257-265. Zeiger, E. 1983. The biology of stomatal guard cells. Ann. Rev. Plant Physiol. 34: 441-475. Appendices Appendix 1. Combined exponential and power functions (Y = a x [K+]b x c^ *1) fitted among potassium concentration in growth medium ([K+]) and root length (L) and the widest diameter of the root (D). Variable a b c R 2 significance L (cm) 12.26 0.09 0.98 0.45 * D(cm) 2.01 0.13 0.99 0.83 * Y = dependent variable, [K+] = independent variable, a, b, and c are estimates, R 2 = coefficient of determination and * = significant at P < 0.05. 124 Appendix 2. Length (L), C-value (C), weight per root (W) and surface area (A) of carrot cultivars harvested in 1993. Early harvest Late harvest Cultivars L (cm) C W(g) A (cm2) L(cm) C W(g)A(cm2) Caro-choice 17.0ab 0.52 60.9 107.0 18.6ab 0.51 100.0 142.0 Gold Pak 28 16.3b 0.54 62.4 106.8 15.7b 0.55 68.4 109.3 Eagle 17.2ab 0.54 69.8 115.6 17.7ab 0.53 91.5 133.8 Paramount 19.9a 0.53 62.6 117.4 21.8a 0.57 85.6 143.1 Imperator 19.4ab 0.54 84.0 134.1 16.8b 0.55 74.7 117.6 Caro-pride 18.7ab 0.50 83.1 127.3 18. lab 0.53 81.3 126.4 Celloking 18.7ab 0.53 69.6 120.3 17.5ab 0.55 76.0 121.3 Top Pak 17.4ab 0.50 58.2 105.3 16.3b 0.54 57.4 101.0 Means in a column followed by different letters are significantly different by Bonferroni procedure (P< 0.05). 125 Appendix 3. Length (L), C-value (C), weight per root (W) and surface area (A) of carrot cultivars harvested in 1994. Early Harvest Late Harvest Cultivars L (cm) C W(g) A (cm2) L (cm) C W(g)A(cm2) Caro-choice 15.2ab 0.55 52.3 94.2ab 16.8b 0.57 91.5abl31.7a Gold Pak 28 11.9c 0.59 33.2 67.0b 12.2d 0.66 40.3b 76.2b Eagle 14.7ab 0.58 45.2 87.2ab 16.3bc 0.62 101.0a 138.4a Paramount 17.1a 0.57 43.3 91.5ab 20.1a 0.60 80.6ab 136.7a Irnperator 14.5abc 0.58 43.7 84.8ab 16.3b 0.68 93.1a 134.3a Caro-pride 16.4ab 0.49 42.0 86.8ab 16.5b 0.56 83.5ab 124.9a Celloking 14.0bc 0.59 42.2 82.5ab 15.9bc 0.65 73.9ab 117.8ab Top Pak 15.9ab 0.54 54.2 98.1a 17.2ab 0.65 83. lab 130.0a Means in a column followed by different letters are significantly different by Bonferroni procedure (P< 0.05). 

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