Factors Affecting the Reaction of Soybeans to Phytophthora megasperma var. sojae in Hydroponic Culture1

Three factors (nutrients, light intensity, and type of inoculum) were examined for their effects on the hydroponic method used to test soybean [Glycine max (L.) Merr.] cultivars for susceptibility to Phytophthora megasperma Drechs. var. sojae Hildeb. The most rapid kill of the greatest number of plants was obtained using a 25% Hoagland's nutrient solution, shading the plants for 3 days after adding the inoculum, and using infected fresh plants as inoculum. Shading the plants was essential for high mortality of susceptible genotypes. Susceptible plants grown in distilled water were killed as rapidly as those grown in nutrient solution if infected fresh plants were used as inoculum and plants were shaded.