Effects of Bacterial Blight on Soybean Yield. E. W. Park, Graduate Research Assistant, Agricultural Research Service, U.S. Department of Agriculture, and Department of Plant Pathology, University of Illinois, Urbana 61801. S. M. Lim, Plant Pathologist and Professor, Agricultural Research Service, U.S. Department of Agriculture, and Department of Plant Pathology, University of Illinois, Urbana 61801. Plant Dis. 70:214-217. Accepted for publication 16 September 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/PD-70-214.

The effects of bacterial blight 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 soybean 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 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 300-seed weight (r = –0.53 to –0.55, P = 0.01). In 1982, only 300-seed weight of Wells II 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.

Keyword(s): Glycine max, Pseudomonas syringae pv. glycinea.