Association of Weather Variables with Genotype × Environment Interactions in Grain Sorghum1

The objective of this study was to determine the relative contribution of several weather variables during various plant growth stages to variation in environment and genotype ✕ environment (GE) interactions of grain sorghum [Sorghum bicolor (L.) Moench] genotypes in different maturity groups. Three growth stages viz., planting to panicle initiation (GS1), panicle initiation to anthesis (GS2), and anthesis to physiological maturity (GS3), were approximated with three periods of crop season, each with an equal number of growing degree days. Variation in temperature and rainfall accounted for more than half of the environment and genotype ✕ environment interaction sums of squares for yield, and seed number and seed weight components of yield. However, the extent to which these variables contributed to differential genotypic response to environments varied among maturity groups and growth stages. Temperature was the most important factor affecting environmental variability for yield and seed number. Effects of temperature and rainfall in GS2 and GS3 were highly associated with GE interaction effects for yield in all maturity groups. Generally, minimum temperature was more important than maximum temperature especially for the early and the late maturing genotypes. Preseason precipitation contributed more than seasonal rainfall to the GE interaction sums of square for yield and seed number, however, the opposite was observed for seed weight. Variation in weather factors contributed more to GE interaction for yield of the late maturing genotypes than the early and medium maturing genotypes. More information on environmental factors is needed to better understand the nature of GE interaction in grain sorghum.