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Poster: Biology & Disease Mgmt: Oomycetes


Pathogenicity and Virulence of Oomycete Species on Common Bean
D. ROSSMAN (1), M. Chilvers (1), A. Rojas (2), J. Jacobs (2) (1) Michigan State University, U.S.A.; (2) Michigan State University, U.S.A.

Common bean is often affected by soilborne oomycetes that cause seed and seedling rot. A study was conducted to determine the pathogenicity and virulence of 24 Pythium spp. and Phytopythium aff. vexans on two common bean (Phaseolus vulgaris) cultivars, ‘Red Hawk’ kidney bean and ‘Zorro’ black bean from Andean and Meso-American gene pools, respectively. A seedling assay was conducted at 20°C in a growth chamber. Oomycete inocula were added to the root zone at the time of planting, and seedlings were harvested after 12 days. Root length, root area, root dry weight, and emergence were quantified. Seedling assay results indicated that 12 species caused significant root length and root area reductions from the control. Similarly, 11 of the same oomycete species caused significant reductions in root dry weight. Four Pythium spp. and Phytopythium aff. vexans caused significantly lower emergence than the control and were considered to be seed rot pathogens. An in vitro seed assay was conducted at 20°C and 26°C, in which disease ratings were assessed. In this assay, 13 species caused disease severity that was significantly higher than the control. Moreover, it was observed that the virulence of certain oomycete species varied depending temperature and host gene pool. Findings help elucidate the oomycete species that are most aggressive and identify factors that may influence oomycete species virulence on common bean.