CUTINASE GENE DISRUPTION IN FUSARIUM-SOLANI F SP PISI DECREASES ITS VIRULENCE ON PEA

Fusarium solani f sp pisi (Nectria haematococca) isolate 77-2-3 with o ne cutinase gene produced 10 to 20% of the cutinase produced by isolat e T-8 that has multiple cutinase genes, whereas cutinase gene-disrupte d mutant 77-102 of isolate 77-2-3 did not produce cutinase. On the sur face of pea stem segments, lesion formation was most frequent and most severe with T-8, less frequent and less severe with 77-2-3, and much less frequent and much milder with the gene-disrupted mutant. Microsco pic examination of the lesions caused by the mutant strongly suggested that it penetrated the host mostly via the stomata. In seedling assay s, 77-2-3 caused severe lesions on every seedling and stunted growth, whereas the mutant showed very mild lesions on one-third of the seedli ngs with no stunting. Thus, cutinase gene disruption resulted in a sig nificant decrease in the pathogenicity of F. s. pisi on pea.