Roles of Fusarium oxysporum and F. solani in Essex Disease of Soybean in Virginia

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Abstract
Fusarium oxysporum and F. solani were isolated with high frequency from hypocotyl lesions on soybean cultivar Essex seedlings grown in naturally infested soil at -0.01 MPa water potential and 15, 20, or 25 C. F. oxysporum was isolated at high frequency from cotyledon lesions at 20 C, and Rhizoctonia solani was isolated at high frequency from hypocotyl lesions at 25 C. Thirteen days after planting, disease severity ratings were greatest at 20 C. In incubator trials using artificially infested soil, 41% of 102 representative F. oxysporum, F. solani, and R. solani isolates gave disease severity ratings on Essex soybean that were significantly higher than those for the pasteurized soil control at 20 C and -0.01 MPa water potential. In soil-temperature tank tests, all F. oxysporum and F. solani isolates tested delayed seedling emergence and caused significant reductions in stem length and plant fresh weight at 20 C and -0.01 MPa water potential. F. oxysporum and F. solani appear to be part of a complex that may cause Essex disease in Virginia.