Growth regulation and defoliation studies for source-sink optimization and synchronized maturity in soybean (Glycine max L. Merrill)
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Date
2016
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The present investigation entitled “Growth regulation and defoliation studies for source-sink optimization and synchronized maturity in soybean (Glycine max L. Merrill)” comprising of two field experiments was carried out at the Research Farm, Department of Agronomy, Punjab Agricultural University, Ludhiana, during kharif 2014 and 2015. Both field experiments were laid out in randomized complete block design (RCBD) with four replications each. Experiment I consisted of eight treatments viz. control, detopping (removal of 4-5 cm apical portion of main stem) at 50-55 days after sowing (DAS), mepiquat chloride @ 200 ppm (50-55 DAS), mepiquat chloride @ 200 ppm (50-55 + 65-70 DAS), mepiquat chloride 250 ppm (50-55 DAS), mepiquat chloride @ 250 ppm (50-55 + 65-70 DAS), mepiquat chloride @ 300 ppm (50-55 DAS) and mepiquat chloride @ 300 ppm (50-55 + 65-70 DAS). Experiment II consisted of seven treatments viz. control, thidiazuron @ 100 g/ha (110-115 DAS), thidiazuron @ 150 g/ha (110-115 DAS), thidiazuron @ 200 g/ha (110-115 DAS), ethrel @ 150 ppm (110-115 DAS), ethrel @ 200 ppm (110-115 DAS) and ethrel @ 250 ppm (110-115 DAS).
In experiment I, detopping had a non-significant effect on leaf area index, SPAD value and PAR interception but it significantly decreased plant height, increased dry matter accumulation per plant, foliage and pod dry weight, specific leaf weight, crop growth rate (CGR) and net assimilation rate (NAR) in comparison to control. A significant increase in number of flowers and pods per plant, pod setting percentage, seed yield and harvest index over control was also recorded during 2014 and 2015. Detopping resulted in highest dry matter accumulation per plant at all growth stages, specific leaf weight at harvest and number of flowers per plant than rest of the treatments during both 2014 and 2015.
Mepiquat chloride application had a non-significant effect on plant height, PAR interception and phenological stages but it significantly affected the leaf area index, specific leaf weight, SPAD value, dry matter accumulation and growth indices as compared to control in both 2014 and 2015. At 80 and 110 DAS, all the levels of mepiquat chloride significantly decreased the leaf area index with highest reduction by two foliar applications of mepiquat chloride @ 300 ppm as compared to control. Among all the treatments, highest specific leaf weight at 80 and 110 DAS, SPAD value, CGR, relative growth rate (RGR) and NAR was recorded in two foliar applications of mepiquat chloride @ 250 ppm. Among the chemical treatments, two foliar applications of mepiquat chloride @ 250 ppm resulted in highest specific leaf weight, dry matter accumulation per plant, pod dry weight and SPAD value at all the growth stages followed by two foliar applications of mepiquat chloride @ 200 ppm. Mepiquat chloride application significantly decreased abscission of reproductive parts, increased number of pods per plant, pod setting percentage, 100-seed weight, seed yield and harvest index as compared to control during both the years. During 2014, detopping out yielded all the treatments (17.81 q/ha) followed by two foliar applications of mepiquat chloride @ 250 ppm (16.97 q/ha). But in 2015, highest seed yield was realized by two foliar applications of mepiquat chloride @ 250 ppm (19.14 q/ha) followed by two applications of mepiquat chloride @ 200 ppm (18.57 q/ha) and detopping (17.99 q/ha). During 2014, highest B:C was recorded with detopping but in 2015, two foliar applications of mepiquat chloride @ 250 ppm resulted in highest B:C.
In experiment II, foliar application of thidiazuron and ethrel did not have a significant effect on plant height of soybean but a significant reduction in leaf area index and increase in dry matter accumulation was recorded as compared to control. Application of thidiazuron @ 200 g/ha and ethrel @ 250 ppm resulted in highest reduction in leaf area index and highest dry matter accumulation in comparison to rest of the treatments. All phenological parameters except days to physiological maturity were found to be non-significant. All the levels of thidiazuron and ethrel significantly decreased days to physiological maturity as compared to control. Foliar application of defoliants caused significant reduction in abscission of reproductive parts, increase in number of pods per plant, pod setting percentage, seed yield and harvest index as compared to control with highest effect by application of thidiazuron @ 200 g/ha and ethrel @ 250 ppm during both the years. Thidiazuron application @ 200 g/ha resulted in 16.66 and 15.74 q/ha and ethrel @ 250 ppm recorded 15.70 and 16.83 q/ha seed yield of soybean during 2014 and 2015, respectively. During 2014, highest B:C was recorded with application of thidiazuron @ 200 g/ha but in 2015, ethrel application @ 250 ppm resulted in highest B:C as compared to all the other treatments.