Abstract
The threshold level of the oospore density of Pythium aphanidermatum and P. spinosum causing damping-off in spinach seedlings was evaluated by a greenhouse assay using pasteurized soil. The severity of damping-off decreased with the decrease in the oospore density in both Pythium spp. The threshold level of the inoculum density was 2 oospores per gram of dry soil in both Pythium spp. under favorable conditions of temperature and soil water content for disease development.
