Temperature Tolerance in Soybeans. II. Evaluation of Segregating Populations for Membrane Thermostability1

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Abstract
Genetic variability for heat tolerance has been alluded to in several crop species but few reports of inheritance or heritabilities of the trait are reported. Some screening for heat tolerance, employing controlled environmental chambers, has been reported but only limited numbers of plants can be evaluated in such facilities. 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 1076 and 1977. Significant genetic variance for heat tolerance was observed in all populations in both years. The mean of the progeny in tolerant ✕ 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 from 16 to 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. It appears that substantial genetic variability for membrane thermostability exists in soybeans and selection for heat tolerance types is feasible.