Trichothecenes and lipases are host-induced and secreted virulence factors ofFusarium graminearum

Abstract

We investigate secreted virulence factors of F. graminearum , namely trichothecenes and lipases. The first gene of the trichothecene pathway, the trichodiene synthase ( Tri5 ), was disrupted in different F. graminearum wild-type strains, producing high or medium amounts of deoxynivalenol (DON) or nivalenol. All disruption mutants ceased to produce trichothecenes and showed a similar reduced virulence on wheat but unchanged virulence to barley. Nivalenol proved to be a weak virulence factor to maize, whereas DON production displayed no influence on maize infection. Therefore, trichothecenes are host specific virulence factors. Mutants lacking DON colonized only the inoculated wheat spikelets. These spikelets showed heavy cell-wall thickening that seemed to prevent the mutant from growing through the rachis node into the rachis. No such symptoms were found in spikelets inoculated with the wild type. Disruption mutants of FGL1 , a secreted lipase, showed similar symptoms on wheat spikelets as the Δ tri5 muta...