BENOMYL-RESISTANT FUSARIUM-ISOLATES IN ECOLOGICAL-STUDIES ON THE BIOLOGICAL-CONTROL OF FUSARIUM-WILT IN CARNATION

Ecological properties and stability of benomyl resistance of three benomyl-resistant mutants of nonpathogenic Fusarium-isolates antagonistic to fusarium wilt in carnation, and three benomyl-resistant mutants of a pathogenic isolate of Fusarium oxysporum f.sp. dianthi were evaluated in 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 all in 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 the in vitro properties were similar. Colonization of carnation by benomyl-resistant nonpathogenic Fusarium 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 nonpathogenic Fusarium-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 different Fusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prerequisite since alterations in antagonism and pathogenicity can occur.