TEMPERATURE TOLERANCE IN SOYBEANS .2. EVALUATION OF SEGREGATING POPULATIONS FOR MEMBRANE THERMOSTABILITY

A technique measuring membrane thermostability (heat tolerance) was used to screen segregating soybean (Glycine max (L.) Merr.) populations derived from crosses of heat tolerant and intolerant parents grown in 1976 and 1977. Significant genetic variance for heat tolerance was observed in all populations in both years. The mean of the progeny in tolerant .times. intolerant cross was intermediate although closer to the tolerant parent. No definitive conclusions could be reached as to the number of genes involved due to the relatively small number of progeny examined. Heritability estimates obtained from 1976 data were relatively high indicating that selection for heat tolerance would be effective. Calculated expected gains from selection ranged 16-18%. Phenotypic and genotypic correlations of heat tolerance with other traits were near zero and nonsignificant except for the genotypic correlation of heat tolerance and maturity. Substantial genetic variability for membrane thermostability [apparently] exists in soybeans and selection for heat tolerance types is feasible.