REDUCED VIRULENCE OF GIBBERELLA-ZEAE CAUSED BY DISRUPTION OF A TRICHOTHECENE TOXIN BIOSYNTHETIC GENE

The production of trichothecene mycotoxins by some plant pathogenic sp ecies of Fusarium is thought to contribute to their virulence, Gibbsre lla zeae (F. graminearum) is an important cereal pathogen that produce s the trichothecene deoxynivalenol, To determine if trichothecene prod uction contributes to the virulence of G. zeae, we generated trichothe cene-deficient mutants of the fungus by gene disruption. The disrupted gene, Tri5, encodes tile enzyme trichodiene synthase, which catalyzes the first step in trichothecene biosynthesis. To disrupt Tri5, G. zea e was transformed with a plasmid carrying a doubly truncated copy of t he TRi5 coding region interrupted by a hygromycin B resistance gene. T ri5(-) transformants were selected by screening for the inability to p roduce trichothecenes and by Southern blot analysis. Tri5(-) strains e xhibited reduced virulence on seedlings of Wheaten wheat and common wi nter rye, but wild-type virulence on seedlings of Golden Bantam maize. On Caldwell and Marshall wheat and Porter oat seedlings, Tri5(-) stra ins were inconsistent in causing less disease than their wild-type pro genitor strain, Head blight developed more slowly on Wheaten when inoc ulated with Tri5(-) mutants than when inoculated with wild-type strain s. These results suggest that trichothecene production contributes to the virulence of G. zeae on some hosts.