Colonization of Plant Residues in Idealized Field Soil by Pythium vanterpoolii with Acquired Resistance to Fungicide

Abstract

A sensitive field isolate UOP 392 (=IFO32589) of Pythium vanterpoolii was compared for competitive saprophytic ability with its acquired resistant isolate UOP 393 (=IFO32590) to metalaxyl. The results obtained are as follows.
(1) The EC₅₀values for metalaxyl of acquired resistant isolate as well as its hyphal tip cultures were 400 μg/ml of active ingredient, and those of sensitive field isolate and its hyphal tip cultures were in the range of 0.1-1.0μg/ml.
(2) Competitive saprophytic ability by propagules of acquired resistant isolate was the same or somewhat higher level than that of sensitive field isolates.
(3) The rates of colonization of plant residues by oospores of acquired resistant isolate were the same as those of sensitive field isolate.
(4) Both high sensitivity and its acquired resistance retained even after competitive saprophytic ability and colonization tests.
(5) The size and form of reproductive structures such as oogonium, oospore and oospore wall were the same in sensitive field isolate as well as its acquired resistant isolate even after competitive saprophytic ability and colonization tests.