Drought‐Induced Stress Effect on Soybean Seed Calcium and Quality

Abstract

Drought stress can lower seed quality of soybean [Glycine max (L.) Merr.], possibly from stress related changes in seed‐nutrient concentration. Determinate soybean plants were grown under a mobile weather‐shelter near Ames, IA in 1985 and 1986 to determine if the timing of drought stress could influence seed‐Ca concentration and, subsequently, seed germination and quality. A randomized complete‐ block design was used to test the effect of withholding water during flowering (R2), full pod (R4), seed formation (R5), and full seed (R6) on the quality of the harvested seed. Drought stress was quantified by monitoring leaf temperatures. Each drought‐stress period received an equivalent amount of drought stress. Seed from a R5 drought stress had 85% germination compared with 96% germination for the nonstressed seed. This reduction in seed germination coincided with a 343 μg g−1 decrease in seed‐Ca concentration from a Ca level of 1648 μg g−1 in the nonstressed seed. Electrolytic conductivity per seed and seed‐Ca concentration were negatively correlated (r = −0.50). Germination percentage was significantly correlated (r = + 0.57) with seed‐Ca concentration and negatively correlated with P, Fe, and Zn (r = −0.49, −0.44, and −0.43, respectively). Application of 2.0 g L−1 of Ca(NO3)2 to the germination media of the R5‐stressed seed improved germination to the level obtained by nonstressed seed. The application of Ca(NO3)2 also improved the germination of R6‐stressed seed, which had a concentration of seed Ca equal to the control. This suggests that seed‐Ca concentration is not solely responsible for the decrease in germination percentage of drought‐stressed seed. Results indicate that drought stress during seed formation can reduce seed‐Ca concentration, but additional work is needed to clarify the role that Ca and other seed nutrients play in the germination of drought‐stressed seed.