SOYBEAN SEED QUALITY AS AFFECTED BY SHRIVELING DUE TO HEAT AND DROUGHT STRESSES DURING SEED FILLING

A high level of shriveled soybean (Glycine max (L.) Merrill) seeds was reported in several regions in Brazil in 1990. The occurrence of shriveled soybean seeds is also reported in some areas in the U.S.A. This problem is observed in Florida (USA) and Parana (Brazil) almost annually. The occurrence of shriveling means losses to the producers of soybean seed and grain. Shriveling results from the occurrence of heat (air temperature above 30-degrees-C) and drought stresses during seed fill. These stresses may result in 100% shriveled seeds in some cultivars, such as 'Bragg'. The objectives of these experiments were: a) to determine the effects of different levels of shriveling on the quality of soybean seeds; and b) to determine the critical level of shriveling that can be accepted in a seed lot without reducing its quality. Two genotypes were studied: 'Forrest,' produced in Gainesville in 1987, and the breeding line BRAS 85-1821, produced in Londrina in 1989. Seed samples were prepared with different levels of shriveling from 0 to 100%. Dry weight (g/100 seeds) decreased as shriveling increased. Seed quality, determined using germination, tetrazolium (vigor and viability), blotter, and emergence in sand tests, was significantly reduced as the level of shriveling increased. The reduction in quality was greater for seeds of Forrest because the plants were subjected to high temperature and rainfall during maturation. The distribution of shriveling within a soybean plant varies, the incidence of shriveled seed from the upper third of the plant exhibiting the highest levels of shriveled seed. The observed trends for reduction in seed quality due to shriveling were similar for the studied parameters despite the effects of different genotypes and production sites.