Influence of soil matric potential on the debilitation of oospores of Pythium aphanidermatum

The influnece of soil matric potential on the debilitation of oospores of Pythium aphanidermatum was assessed during incubation in Yanagido sandy loam and Kakamigahara clay loam soil in tensiometers at 0, −1, −5, −10 and −15 kPa ψm over a period of 80 days. Germinability in salts solution and viability in corn meal agar of oospores started to decline after 10 days incubation on both soils. Oospores incubated in water saturated soil (0 kPa ψm) rapidly declined in germinability and viability. By 80 days oospores incubated in soils at 0 kPa ψm failed to germinate in salts solution and their viability and pathogenic aggressiveness was decreased significantly (P = 0.05). However, oospores exposed to lower water potentials (−5 to −15 kPa ψm) maintained their germinability, viability and pathogenic aggressiveness.