Ecological properties and stability of benomyl resistance of three benomyl-resistant mutants of nonpathogenicFusarium-isolates antagonistic to fusarium wilt in carnation, and three benomyl-resistant mutants of a pathogenic isolate ofFusarium oxysporum f.sp.dianthi were evaluatedin vitro and in glasshouse experiments. The benomyl resistance of the nonpathogenic mutants was stable under all conditions tested, also after a 1000-fold increase of the population in sterilized soil. Mutants of the pathogen were stable during allin vitro tests, but after proliferation in carnation stems only part of the population was benomyl resistant.Compared to the wild type, mutants of the pathogen were less pathogenic, also if thein vitro propeties were similar. Colonization of carnation by benomyl-resistant nonpathogenicFusarium in the presence of the pathogen showed that the antagonistic effect correlated with the presence of the nonpathogenic isolates within the carnation stem. The wild types and two of the mutant nonpathogenicFusarium-isolates controlled fusarium wilt in the susceptible cultivar Lena for 50% or more.UV-induced benomyl resistance appeared to be a valuable marker to distinguish between differentFusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prerequisite since alterations in antagonism and pathogenicity can occur.
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