Response of Soybeans to High Temperature During Germination 1

The variability among soybean [ Glycine max (L.) Merr.] genotypes for tolerance to above optimal temperatures during germination was evaluated. In an initial screening, germination of 289 genotypes in maturity groups VIII, IX, and X was tested at 32 and 38 C. Forty‐eight of these genotypes germinated as well at 38 as at 32 C and were selected for further study. Absolute response of the selected genotypes to temperature in subsequent tests depended on previous history of the seed. Germination of all selected genotypes was significantly reduced at 38 C in tests utilizing seeds stored for 15 to 18 months. Germination of stored seed of 21 genotypes was not significantly affected by temperatures as high as 36 C. When germination of fresh seed harvested at maturity or 3 weeks afterwards was compared at 32 and 38 C, the increase in temperature was found to reduce germination in both harvests, but most markedly among genotypes which were delay‐harvested. Genotypes represented within each source (stored, harvested at maturity, and delay‐harvested) were classified for relative tolerance. A confidence interval drawn about the mean germination at 36 (stored seed) or 38 C (seed harvested at maturity and delay‐harvested seed) was used for dividing the genotypes into three classes: those with above, intermediate, and below average tolerance to high temperature. Four genotypes (PI 259538, PI 346304, PI 374166, and PI 374174) were consistently classified as having above average tolerance to high temperature, while four others (PI 174860, PI 203405, ‘Cherokee’, and ‘Hardee’) were consistently classified as having below average tolerance. Results presented indicate that consistent genotypic differences exist for tolerance to high temperature during germination and that these differences can be most effectively identified among genotypes which have not been subjected to prior stress.