Assessment of Drought Responses of Wild Soybean Accessions at Different Growth Stages

Drought is a significant abiotic stress that limits crop production. Soybeans [Glycine max (L.) Merr.] are regarded as drought-sensitive. In the present study, the drought responses of wild soybean accessions were evaluated at different growth stages. Based on the leaf wilting index of 411 accessions at the vegetative stage, seven highly tolerant (HT) and 24 tolerant (T) accessions were identified, although most wild soybeans were classified as moderate (M), sensitive (S), and highly sensitive (HS) genotypes. In addition, with selected wild soybeans, stomatal density decreased in HT accessions but increased in HS accessions under drought conditions at the vegetative stage. However, for cultivated soybeans, the stomatal density of the drought-tolerant and drought-sensitive were not significantly different between the two conditions. The expression levels of drought-related transcriptional factors indicated that the HT genotype showed a higher expression level of drought-related genes than that of the HS genotype at the vegetative stage. At the reproductive stages, 12 wild soybeans randomly selected from HT, T, S, and HS based on assessment at the vegetative stage showed consistent drought responses with seed yield, root development, and water status. However, the extent of the detrimental effect of drought on the germination rates and root length of 165 wild soybeans at the germination stage varied depending on the genotype, indicating that there may not be a robust correlation between phenotypic measurements at the germination stage and drought-related assessments at the two growth stages. The information from this study can provide useful breeding materials for the development of drought-tolerant cultivars from wild soybeans.