Drought Stress Effects During Seed Fill on Soybean Seed Germination and Vigor

Abstract

Environmental stress exerts a substantial effect on leaflet productivity and yield, but its effect on germination and vigor is poorly understood. The objective of this study was to relate drought stress intensity during soybean [ Glycine max (L.) Merr.) seed fill to reductions in seed yield, mass, germination, and vigor. Drought was imposed on pot‐grown plants (cv. Gnome) in the greenhouse by applying differing volumes of water during seed fill. Stress intensity was measured by summing stress degree days (SDD), the daily difference between the leaf and air temperature, measured using an infrared and shielded thermometer, respectively. As SDD values increased from 46.2 to 141.2, leaf resistance increased 68%, transpiration decreased 44%, and apparent photosynthesis decreased 71%, verifying that severe drought had been imposed. Seed yield was linearly reduced 38 and 58% by drought in 1985 and 1986, primarily because few seeds were produced. Seed germination and vigor decreased as SDD increased. The effect of drought on germination and vigor was substantially less than that on yield and was inconsistent across years. Drought reduced standard germination percentage and seedling axis dry weight 5 and 12%, respectively and increased single‐seed conductivity 19%. Seed quality loss was correlated with reduced single‐seed mass. Severe drought that occurred throughout seed fill reduced yield and seed number at a faster rate than seed mass, germination, or vigor, and maintained the development of at least some viable and vigorous seeds.