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 ben omyl-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 evaluat ed in vitro and in glasshouse experiments. The benomyl resistance of t he nonpathogenic mutants was stable under all conditions tested, also after a 1000-fold increase of the population in sterilized soil. Mutan ts of the pathogen were stable during all in vitro tests, but after pr oliferation in carnation stems only part of the population was benomyl resistant. Compared to the wild type, mutants of the pathogen were le ss pathogenic, also if the in vitro properties were similar. Colonizat ion of carnation by benomyl-resistant nonpathogenic Fusarium in the pr esence of the pathogen showed that the antagonistic effect correlated with the presence of the nonpathogenic isolates within the carnation s tem. The wild types and two of the mutant nonpathogenic Fusarium-isola tes controlled fusarium wilt in the susceptible cultivar Lena for 50% or more. UV-induced benomyl resistance appeared to be a valuable marke r to distinguish between different Fusarium isolates and to study the population dynamics, but intensive screening of the mutants is a prere quisite since alterations in antagonism and pathogenicity can occur.