Possible role of trichothecene mycotoxins in virulence of Fusarium graminearum on maize

Trichothecene-producing and -nonproducing Fusarium graminearum strains were tested for their ability to cause Gibberella ear rot in field trials at tw o locations-Ottawa, Ontario, and Peoria, Illinois-in 1996. Maize ears were inoculated with wild-type or transgenic F. graminearum strains in which the trichothecene biosynthetic pathway had been disabled by the specific disru ption of the trichodiene synthase gene and with a derivative revertant stra in in which trichothecene production had been restored through recombinatio n. A silk channel inoculation method was employed at both locations. In add ition, a kernel puncture inoculation method was used at the Ontario locatio n. Harvested maize ears were analyzed for visual disease severity, grain yi eld, deoxynivalenol (DON) concentration, and fungal biomass by quantitative polymerase chain reaction (PCR) and/or ergosterol quantitation. There was a significant correlation (r = 0.86) between data obtained from the two dif ferent methods of quantifying fungal biomass. The trichothecene-nonproducin g strains were still pathogenic but appeared less virulent on maize than th e trichothecene-producing progenitor and revertant strains, as assayed by m ost parameters. This suggests that the trichothecenes may act as virulence factors to enhance the spread of F. graminearum on maize.