Screening for Drought Tolerance: Soybean Germination and its Relationship to Seedling Responses

Seventeen determinate soybean ( Glycine max L.) cultivars from maturity groups V through VIII were screened for drought tolerance during germination and seedling stages. Germinating seeds and hydroponically-grown seedlings were subjected to osmotic stresses of -0.3 and -0.5 MPa using polyethylene glycol M.W. 8000. Genotypic variability was found among the cultivars for all the parameters analyzed in both germination and seedling tests. Germination stress index was lower for seeds exposed to -0.5 MPa than for -0.3 MPa osmotic stress. Lower osmotic potential in the treatment medium was also correlated with lower leaf water potential in seedlings subjected to it. A significant relationship was found between fresh weight and height stress indices. The cultivars that grew taller under drought stress conditions had greater dry matter accumulation and higher germination stress indices indicating the reliability of height to predict cultivar performance under such conditions. The cultivars Lee-74 and Wright had higher dry matter accumulation, greater height, and better germination under stress conditions than the other cultivars tested. Conversely, the cultivars Ra 401 and Bay performed poorly in the drought tests at both levels. In the seedling tests, there was no strong relationship between the leaf water potential and the overall performance of the plant suggesting no clear osmoregulatory mechanism. Based on results from germination and seedling tests, the cultivars Lee-74, Wright , and Ra 401 were selected for further studies in greenhouse and field trials.