Relationships between climatic factors and square, flower and boll production in Bt cotton (Gossypium hirsutum L.) under rainfed condition

The present field research experiment entitled ‘relationships between climatic factors and square, flower and boll production in Bt cotton (Gossypium hirsutum L.) under rainfed condition' was carried out during kharif season 2015-16 at experimental farm, Department of Agricultural Meteorology, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani and which was laid out in split plot statistical design with four sowing dates June 16, 2015; June 23, 2015; June 30, 2015; and July 7, 2015 as main plots and three hybrids viz., Mallika, Ajith-155 and Rasi-799 as sub plot with three replications. The flowering stage of cotton was found most sensitive to >30^oC maximum temperature, <20^oC minimum temperature, and its regimes alter the boll development, boll size and the maturity period both decreased as the temperature amplitude increased. And increases the maximum temperature above 32^oC, boll growth decreased significantly and bolls sheds more than 2-3 days after blossoming. The higher temperature coincided with soil moisture stress induced due to midseason and terminal drought, resulted into low conversion mean ratio of flowers (white/yellow + pink/red) to open balls (20%) and squares to open balls (16%). The water stress, higher afternoon relative humidity and daily evaporate rate increase at yield attribute stages, decreased boll retention in plant and decreased seed cotton yield. The significantly highest cotton seed yield was recorded in 24^th MW sowing (6.76 q/ha) and which was on par with 25^th MW sowing (6.67 q/ha), thereafter, drastically it was reduced by 71.3 and 73.5% in 26^th and 27^th MW, respectively. The overall mean of all sowing dates recorded lower seed cotton yield observed during this experimental year compared to normal climatic year due to the early, mid season and terminal drought condition.