Occurrence and characteristics of Fusarium oxysporum f.sp.dianthi (Prill et Del.) Snyder et Hansen strains resistant to systemic fungicides

Abstract

Strains of Fusarium oxysporum 1 sp. dianthi (Prill et Del.) Snyder et Hansen, highly resistant to benomyl (Benlate), carbendazim – MBC (Bavi-stin) and methylthiophanate (Topsin M) were observed for the first time. They grew well in the presence up to 1000 ppm of MBC. The resistant strains usually grow considerably slower than the sensitive ones on unpoisoned media. Sporadic cases were noted of increasing transitional adaptative tolerance to MBC, after several transfers of sensitive strains onto media with low concentrations of the fungicide. An increasing frequency of resistant strains was observed under production conditions. Of the fungitoxicants used, MBC was more active towards the sensitive strains while the resistant strains tolerated considerably lower concentrations of benomyl than that of MBC.