Viability, vigor, and maturity of seed harvested from two soybean cultivars exposed to simulated acidic rain and photochemical oxidants

Tests were conducted on the viability and vigor of soybean seed harvested from plants grown in field chambers and treated with simulated acidic rain at two levels of photochemical oxidant. The plants (Glycine max [L.] Merr. cv ‘Beeson’ and ‘Williams’) were treated with simulated rain at pH values of 4.0, 3.4, or 2.8 in chambers supplied either with charcoal-filtered or unfiltered ambient air. At harvest, Beeson, a maturity class II cultivar, was at full maturity whereas Williams, a maturity class III cultivar, had not yet attained full maturity. There were no visual symptoms of acidic rain injury, but symptoms of oxidant injury were observed on all plants grown in unfiltered air.

In Beeson the germination of seeds was not affected by filtering the ambient air or by the acidity of simulated rain. Seeds from Williams had a lower germination rate than Beeson and were more sensitive to artificial aging stress. At each level of acidity, the proportion of seeds that germinated in Williams was greater in those obtained from plants grown in filtered air than in those from unfiltered air. Germination was greater at pH 4.0 than at pH 2.8 in both filtered and unfiltered air. In both cultivars, the average percentage of seed with green cotyledons approximated the average proportion of ungerminated seed. In Williams, the occurrence of green cotyledons was negatively correlated with viability. Therefore, coloration of the cotyledon was a good measure of seed maturity.

The results observed with Beeson agreed with previous reports that at full plant maturity, there are no measurable effects of oxidant on seed viability. However, the data obtained with Williams indicate that at earlier stages of plant growth oxidant or simulated acidic rain have a measurable effect on seed development.