A research experiment entitled “Phenology and physiological responses of Bt cotton genotype RCH 776 regulated through application of chemical growth retardants under various sowing times in semi-arid ecosystem” was carried out at Research area of Cotton Section of Chaudhary Charan Singh Haryana Agricultural University, Hisar. The experiment was replicated thrice in split plot design during kharif season (2021-22). The experiment included three sowing times in main plots: M1 (First fortnight of April), M2 (Second fortnight of April), M3 (Mid of May) and six chemical growth retardant treatments application in sub plots: S1 (Control), S2 (Lihocin @ 50 ml/ha at 45 DAS), S3 (Lihocin @ 50 ml/ha at 60 DAS), S4 (Mepiquat chloride @ 300 ml/ha at 60 DAS), S5 (Mepiquat chloride @ 300 ml/ha at 75 DAS) and S6 (Mepiquat chloride @ 300 ml/ha at 60 and 75 DAS). M1 (First fortnight of April) took slightly more number of days to achieve different phenological stages (days to 50% squaring, 50% flowering and 50% boll development). M1 (First fortnight of April) recorded maximum relative water content (RWC), chlorophyll content and photosynthetic rate which was significantly higher than M2 (Second fortnight of April) and M3 (Mid of May). M1 (First Fortnight of April) and M2 (Second fortnight of April) times of sowing recorded significantly higher seed cotton yield than M3 (Mid of May). Application of different chemical growth retardants significantly influenced the phenological behaviour & commencement of 50% flowering and 50% boll formation. Maximum chlorophyll content, RWC, photosynthetic rate and maximum seed cotton yield were recorded with application of S6 (Mepiquat chloride @ 300 ml/ha at 60 and 75 DAS) which was significantly higher than rest of the treatments.

Bt Cotton Genotype, Semi-Arid Climate, Sowing Times, Mepiquat Chloride