APS Homepage

Poster: Biology & Disease Mgmt: Mycology


Effects of inoculum substrates on root rot of soybean caused by Fusarium oxysporum and Fusarium graminearum
D. CRUZ (1), D. Mayfield (2), Y. Meng (1), G. Munkvold (1), L. Leandro (1) (1) Iowa State University, U.S.A.; (2) Iowas State University, U.S.A.

Fusarium oxysporum (Fo) and F. graminearum (Fg) are associated with the Fusarium seedling disease and root rot complex in soybeans. Published soil infestation methods have limitations in the expression of disease. Our objective was to compare the efficacy of infested substrates for generating root rot caused by Fo and Fg and evaluate adverse effects of non-infested substrates on roots. Autoclaved millet and rice hulls infested with Fo and Fg were added to soil at a rate of 5% (by vol.). Susceptible cultivars Jack and MN1805 were evaluated 2 weeks after planting for root length and root rot using the WinRhizo image analysis software; root rot was also estimated visually on a percent scale. Cultivars did not differ in root length and root rot assessed by image analysis, but visually-assessed root rot was greater in Jack (P=0.008). There was a significant interaction between substrate and Fusarium species for root rot assessed by both methods (P<0.0001). Millet infested with Fg produced the greatest root rot severity (37%), followed by millet infested by Fo (24%), whereas infested rice hulls resulted in low root rot (15 and 10% for Fo and Fg, respectively). Root rot for non-inoculated substrates was less than 5%. Infested and non-infested millet reduced root length compared to rice hulls. Pathogen colonization was assessed using qPCR. Our study suggests that millet is more effective for producing seedling root rot but can cause some adverse effects on root growth.