Effect of Disruption of the Enniatin Synthetase Gene on the Virulence of Fusarium avenaceum. Matthias Herrmann. Institut fur Biochemie und Molekulare Biologie, Technische Universitat Berlin, Franklinstr. 29, D-10587 Berlin, Federal Republic of Germany. Rainer Zocher, and Angela Haese Institut fur Biochemie und Molekulare Biologie, Technische Universitat Berlin, Franklinstr. 29, D-10587 Berlin, Federal Republic of Germany. MPMI 9:226-232. Accepted 15 February 1996. Copyright 1996 The American Phytopathological Society.

Production of the phytotoxic compound enniatin has been proposed to play a role during the infection process of plants by enniatin-synthesizing Fusarium species. Enniat-ins are cyclohexadepsipeptides synthesized by the multifunctional enzyme enniatin synthetase. To test the hypothesis that enniatin contributes to pathogenicity, enniatin-nonproducing mutants were constructed by gene disruption of the enniatin synthetase gene of a virulent Fusarium avenaceum strain. Four independent enniatin-nonpro-ducing mutants were characterized that did not express enniatin synthetase, as proved by RNA and protein blot analysis. The virulence on potato tuber tissue of the en-niatin-nonproducing strains was significantly reduced compared with the virulence of the parent strain and three enniatin-producing transformants. Therefore, we conclude that enniatin production contributes to the virulence of Fusarium avenaceum.