Effects of Bacterial Blight on Soybean Yield

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Abstract
The effects of bacterial blight [Pseudomonas syringae pv. glycinea] on soybean yield and 300-seed weight of two soybean cultivars. Wells II and Williams 79, were studied in 1981 and 1982. Inoculations at five soybeans growth stages resulted in bacterial blight development at different levels in the plant canopy. A decrease in disease severity was observed at midseason during both years. In 1981, bacterial blight severity at R6 ranged from 0 to 36% for Wells II and from 0 to 29% for Williams 79. Yield and 300-seed weight of Wells II were significantly different between treatments in 1981, but only 300-seed weight was different in 1982. Compared with yield and 300-seed weight of control plots, reductions in yield and 300-seed weights of inoculated or naturally infected plots of Wells II in 1981 and were 5-15% and 5-9%, respectively. In 1982, significant 300-seed weight reductions of 7.6 and 5.4% occurred when Wells II was inoculated at V3 and R3, respectively. Bacterial blight severity rated at R6 correlated negatively only with yield of Wells II (r= -0.39, P = 0.05) in 1981, whereas the severities rated at R4, R5, and R6 correlated negatively with bacterial blight severity rated at each of three growth stages (r= -0.39 to -0.47, P = 0.01). Yield and 300-seed weight of Williams 79 did not differ significantly between treatments in either year.