A field investigation was carried out to characterize the growth and development of Bt cotton hybrids by detopping and use of plant growth retardants during the rainy (kharif) season of 2011 and 2012. The experimental site had loamy sand soils with normal in reaction. The experiment (split plot) involved three Bt cotton hybrids (MRC 7017, MRC 7031 and RCH 314) in main plots and growth regulation treatments (Mepiquat chloride (MC) @ 300 ppm, 2, 3, 5-tri iodo benzoic acid (TIBA) @ 100 ppm and Maelic hydrazide (MH) @ 250 ppm) in sub plots with four replications. Hybrid MRC 7017 produced significantly higher (p<0.01) seed cotton yield which was attributed to the maximum number of sympodial branches plant-1, total number of flowers and picked bolls plant-1. Application of MC @ 300 ppm, TIBA @ 100 ppm and MH @ 250 ppm reduced plant height, leaf area index and total dry matter accu-mulation than control. Detopping treatment significantly (p<0.01) reduced plant height than control but attained more plant height than all the PGRs. MC @ 300 ppm, TIBA @ 100 ppm and MH @ 250 ppm at 80 days after sowing had beneficial effect on seed cotton yield. Detopping done at 80 days after sowing failed to influence the seed cotton yield dur-ing both the years. The results revealed that foliar application of MC @ 300 ppm yielded more seed cotton by improv-ing the setting percentage and therefore, increased number of picked (open) bolls plant-1 without exhibiting any ad-verse effect on quality traits.
Bt cotton hybrids, Maleic hydrazide (MH), Mepiquat chloride (MC), Plant growth regulators, Seed cotton yield, 2,3,5-tri iodo benzoic acid (TIBA)
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