Factors Influencing the Incidence of Embryo Infection byPythiumspp. During Germination of Wheat Seeds in Soils

The incidence of embryo infection (EI) by Pythium spp. in soil held at a matric potential (ψ m ) of -10 J/kg was a function of inoculum density (ID) at lower IDs and reached a plateau (EI max ) at higher IDs. In field soils, EI max (69.9-89.0%) was achieved at 150-200 propagules per gram. In pasteurized soil reinfested with P. ultimum var. sporangiiferum, EI max (≃100%) was achieved with only 50 propagules per gram. The incidence of EI was greatest at -10 J/kg, progressively less as soil was drier, and negligible at drier than -200 J/kg [...]