DROUGHT RESISTANCE STUDIES IN SOYBEANS (RESTRICTED SOIL PROFILE, WATER STRESS)

Five experiments were conducted to investigate a basis of selection for drought resistance in soybeans (Glycine max L. Merr.);Experiment II addressed the subject of soil fertility effects of soybean growth and development in droughty conditions and the possible use of sites with low soil fertility in drought resistance selection programs. Nodulation and the internal water retention ability of the plants were greatly reduced by suboptimum soil fertility. Use of both low soil fertility and suboptimum environments improved the predictive value of the yield components for seed yield.;In Experiment III leaf water potentials, canopy temperature, plant height, flower and pod counts, and growth stages were monitored throughout the growing season on six genotypes grown in restricted soil profiles, in an effort to associate these characteristics and seed yield. No relationship was evident between seed yield and the measured characteristics owing to the unique influence of restricted soil plots on growth.;Experiment IV investigated the effects of restricted soil profiles on root development of soybeans growing in the restricted soil profiles. Most root development was in the top 15 cm of the soil and within 6 cm of the row. Shallower soil profiles promoted relatively more root growth closer to the soil surface, which were more prone to drying and had shorter plants.;Experiment I evaluated the basis of wide acceptance, among Missouri soybean producers, of eight commercial and research genotypes. All genotypes yielded similarly, however, 'Cumberland' was the most consistent yielding genotype while 'MFA Mosoy PV42' was the least consistent with potentially higher seed yield than the others; this suggested the other genotypes owed their poularity to factors not measured in the experiment.;In Experiment V genetic components of variance were estimated from 49 genotypes growing in restricted soil profile, to define the most suitable soil profile for use in drought resistance selection programs. Restricted profiles were found unsuitable for use in such selection programs.;Evidence from this investigation suggests that selection for drought resistance might be best accomplished through use of integrative traits such as seed yield obtained from multilocation trials.