EFFECT OF BACILLUS-CEREUS UW85 ON THE YIELD OF SOYBEAN AT 2 FIELD SITES IN WISCONSIN

Bacillus cereus strain UW85 was evaluated for its effect on the yield of three cultivars of soybean (Glycine max) over five seasons at two W isconsin field sites where Phytophthora sojae was present naturally an d that had low to severe disease potential for Phytophthora damping-of f and root rot. The soybean cultivars, selected on the basis of geneti c resistance to Phytophthora root rot, were 29725-15G (susceptible), D SR-262 (tolerant), and Elgin 87 (resistant, Rps1-k allele). Soybeans w ere treated at planting with spore-based formulations of B. cereus or metalaxyl, applied in-furrow or to the seed. At Racine, Wisconsin, hig her soybean yields were consistently associated with the genetically t olerant and resistant cultivars. Certain B. cereus treatments provided a significant yield benefit for the susceptible cultivar in all five growing seasons, and for all cultivars in 1990 when the disease pressu re was especially high. At Whitewater, Wisconsin, higher yields were n ot associated with genetic resistance to Phytophthora root rot and the re was evidence of pre-emergence damping-off. For the susceptible cult ivar, yields for B. cereus treatments and metalaxyl did not differ sig nificantly from the untreated control except in 1990, when yield and s tand counts benefited from those treatments. Yield of the resistant cu ltivar was improved significantly by treatment with either B. cereus o r metalaxyl in 1990, 1991, and 1992. The formulation of B. cereus infl uenced efficacy: clay granule formulations of UW85 applied in-furrow w ere the most consistent, but no single formulation of either B. cereus or metalaxyl exhibited efficacy at both sites and in all years. These data suggest that B. cereus improved soybean yield under conditions i n which Phytophthora root rot influenced yield as well as under condit ions in which other factors influenced yield.