Stress Tolerance in Soybeans. I. Evaluation of Three Screening Techniques for Heat and Drought Tolerance1

Three screening techniques for characterizing drought tolerance were evaluated using 20 soybean Glycine max (L.) Merr. genotypes. These techniques involved: 1) germinating seed in polyethylene glycol‐600 (PEG) at −0.6 MPa osmotic pressure, 2) subjecting seedlings to PEG‐600 at −0.6 MPa osmotic pressure in hydroponic solution for 14 days, and 3) a heat tolerance test based on the cellular membrane thermostability. Genotypic variability associated with drought tolerance was demonstrated by the evaluation techniques. Based on these procedures, 2 of the 20 cultivars tested were relatively drought tolerant, 2 were relatively susceptible, and the remaining cultivars fell into an intermediate group. Highly significant correlations were found between the hydroponic seedling and heat tolerance tests, indicating that both drought and heat tolerance were identified in the same cultivars under the conditions of this study. It is doubtful that the seed germination test could be used as a reliable procedure for identifying drought tolerant cultivars because it tended to reflect differences in seed quality and had no relation to field performance. Although reproducibility and consistency of genotypic differences did exist using the heat tolerance tests, comparisons with more yield data are needed to evaluate this technique. Of the three procedures evaluated in this study, the hydroponic seedling test seemed to be the most reliable and potentially useful as a means for screening for drought tolerance in soybeans.