Impact of benzimidazole resistance on fitness parameters and fumonisin B1 production in Fusarium verticillioides (Sacc) Niremberg

Abstract

Fusarium verticillioides laboratory isolates resistant to carbendazim were readily obtained after mutagenesis with UV-irradiation. Three resistant phenotypes that included highly (HR, Resistant factors>30), moderately (MR, Rf: 14–25) and low (LR, Rf: 2–5) resistant isolates to carbendazim were identified by fungitoxicity tests in vitro. Mutant isolates were simultaneously resistant to thiabendazole and benomyl but not to the also tubulin-blocking fungicides diethofencarb and zoxamide. No cross resistance relationship was found between carbendazim and fungicides with different modes of action such as the dicarboximide iprodione, the QoI pyraclostrobin, the imidazole prochloraz, the triazoles flusilazole and epoxiconazole. Mutation(s) for resistance to benzimidazoles did not significantly affect mycelial growth rate whereas sporulation and pathogenicity were adversely affected in most of the resistant mutants. Moreover, low temperatures suppressed the expression of carbendazim-resistance in all resistant phenotypes. Most mutant isolates produced Fumonisin B1 in similar or less quantities than the wild-type isolate both in vitro and in vivo in the absence of carbendazim with the exception of one HR isolate which had up to 3-fold increased FB1 production. Sub lethal doses of carbendazim in the growth medium in vitro resulted in a significant reduction in FB1 levels in all cases even though most mutant isolates produced higher FB1 quantities than the wild type. A significant correlation was found between F. verticillioides sporulation and FB1 production on maize seeds. The potential risk of food and feed contamination by FB1 producing F. verticillioides isolates resistant to benzimidazoles and implications on resistance management strategies are discussed.