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Effect of 2, 4-Dichlorophenoxyacetic acid on the yield and metabolism of the bean plant Phaseolus vulgaris Chi, Chu-hsiang

Abstract

An investigation was designed to determine the effect of dusts and sprays of 2,4-D on growth, yield, enzyme activity, photosynthesis, respiration and photophosphorylation of bush bean plants. Beans (Phaseolus vulgaris, var. Top Crop) were grown under growth room conditions in five-inch tin cans filled with soil, and in six inch plastic pots filled with vermiculite. Vermiculite-grown beans were irrigated with a modified Shive's three-salt nutrient solution. Treatment unit of 8 to 10 plants was replicated 4 to 6 times. Dusts containing 2,4-D, NCL, NH4•2,4-D and minerals at a rate of 8 pounds per acre were applied to the foliage of plants when 13 or 14 days old. Sprays containing NH4•2,4-D were applied to the plants until run off. The soil-grown beans treated with 2,4-D in dust form were harvested when 8 weeks old. Growth (based on tops) and yield (based on pods) were then determined, and enzyme activity was measured 2, 5, 7, 11, and 14 days after treatment. The vermiculite-grown beans were treated with both dusts and sprays of 2,4-D. Growth and rates of photosynthesis and respiration were determined at one-week intervals for six consecutive weeks after treatment. Yield was determined by collecting pods at one-week intervals for three weeks starting at the fourth week after treatment. The gas exchange method was used for the determination of photosynthesis and respiration. Effects of NCL in dust form and NH4•2,4-D in spray form on chlorophyll content and photophosphorylation 7 days after treatment were studied. The results showed that dusts of 2,4-D significantly increased the number of pods, whereas sprays of NH4•2,4-D did not. NCL 0.12 and NH4•2,4-D 1.0 ppm increased seed yield by 18.52% and 12.66% over the controls. With the exception of NCL 0.12, all the 2,4-D treatments in dust form failed to show a significant effect on growth and yield. Sprays of NH^*2,4-D at 5 ppm significantly inhibited growth and yield. A higher dry weight and percentage dry weight were obtained in dust of 2,4-D treated vermiculite-grown beans. Beans dusted with NCL 0.12 showed a significant increase in fresh weight and dry weight of tops, and fresh weight of pods. The increases were 41.73%, 48.84% and 28.30% over the controls. Application of NCL 0.12 and 2,4-D 0.12 resulted in a significant stimulation of catalase activity in bean leaves but inhibited catalase activity in bean stems in 14 days. In the case of phosphatase, NCL 0.12 caused an inhibition in the enzyme activity of both leaves and stem in 5 days and a stimulation in 14 days. NCL 0.06 treated plants showed a lower catalase activity in 2 days and higher activity in 5, 7, and 14 days. Phosphorylase activity was stimulated in 2 days but was inhibited in 5 days. Minerals accelerated phosphorylase activity in 2 and 5 days. NCL dusts and NH4•2,4-D sprays caused a stimulation in the rate of photosynthesis one week after treatment. This was followed by an inhibition during the period from the second to sixth week after treatment. A higher rate of respiration was found in NH4•2,4-D treated plants whereas in the case of NCL treated plants a higher rate of respiration at the first and sixth week and a lower rate at the second to fifth, week were obtained. Photophosphorylation in plants treated with NCL dusts and NH4•2,4-D sprays was significantly higher than that in untreated plants except that NCL dust showed an uncoupling of phosphate uptake in noncyclic photophosphorylation.

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