ABSTRACT
Production of macroconidia by the causal agent of sudden death syndrome, Fusarium solani f. sp. glycines, occurred on lower stems and roots of soybean plants symptomatic for the disease in Illinois, Indiana, Kentucky, Mississippi, and Tennessee. Most of the sporulation was light to dark blue to blue-green in color. Microscopically (15×) visible sporulation occurred on plants in 26, and macroscopically visible sporulation occurred on plants in 15, of 32 fields inspected. In some fields, the incidence of plants with microscopically visible sporulation was as high as 70%, and the incidence of plants with macroscopically visible sporulation reached 50%. Sporulation varied from pinpoint microscopic areas to macroscopically visible masses 4 to 6 cm2 or larger. Areas of microscopically visible sporulation occurred on lower stems and roots within 2.5 cm above and below the soil line on about 50% of the plants, and areas of macroscopically visible sporulation occurred within the same region on about 60% of the plants. Both microscopic and macroscopic sporulation also occurred on taproots as far as 10 cm or more below the soil line. Severe foliar symptoms and root decay were associated with a greater incidence of plants with sporulation. The occurrence of sporulation should help distinguish sudden death syndrome from other diseases of like foliar symptomatology and help confirm its diagnosis. It is presumed from the results that sporulation eventually contributes to the inoculum density of F. solani f. sp. glycines in soybean fields.
