YIELD AND SEED QUALITY OF SOYBEAN CULTIVARS INFECTED WITH SCLEROTINIA-SCLEROTIORUM

Sclerotinia stem rot (SSR) is one of the most important diseases of so ybean in the United States. Five maturity group III cultivars, Asgrow A3304 STS (A3304), Pioneer Brand 9342 (P9342), Pioneer Brand 9381 (P93 81), Probst, and Yale, grown in fields in east-central Illinois, were used to determine the relationship of SSR incidence to yield, 100-seed weight, seed protein and oil content, visual seed quality, and seed g ermination. In addition, the number of sclerotia in seed samples and t he seedborne incidence of Sclerotinia sclerotiorum were determined. Fo r each cultivar, at least 23 two-row plots, 3 m long, that represented a range of SSR incidence from low to high, were used to count the num ber of plants with and without SSR stem symptoms and were used to esti mate yields and evaluate seed quality. Disease incidence ranged from 2 to 45% for Probst, 0 to 65% for P9381, 0 to 68% for P9342, 1 to 93% f or Yale, and 0 to 95% for A3304. Regression of yields on SSR incidence s for each cultivar was significant (P < 0.05); for every 10% increase in SSR incidence, yields were reduced by 147, 194, 203, 254, and 263 kg/ha for Probst, A3304, P9342, Yale, and P9381, respectively. Disease incidence was negatively correlated (P < 0.05) with seed germination for all cultivars but Probst, and to oil content and seed weight for P 9381 and Yale. Disease incidence was positively correlated (P < 0.05) with seed quality for all cultivars and to the number of sclerotia in harvested seeds for P9342, P9381, and Probst. The seedborne incidence of S. sclerotiorum was 0.3, 0.3, 0.3, 0.4 and 0.7% in A3304, P9381, Ya le, Probst, and P9342, respectively, and represents a significant pote ntial for further spread of this pathogen and disease.