Restoration of pathogenicity of a penetration-deficient mutant of Collectotrichum lagenarium by DNA complementation.

Infection by Colletotrichum lagenarium requires formation of an appressorium and of a penetration peg. A mutant, 83,348, defective in morphogenesis of the penetration peg was unable to penetrate into cellulose membranes or infect cucumber leaves. DNA transformation using a wild-type genomic library constructed in pKVB resulted in two transformants, Ppr1 and Ppr2, with restored penetration peg formation, from 2,000 benomyl-resistant transformants. However, penetration into cellulose membranes by these transformants ranged from 30 to 40% compared to greater than 90% by wild-type. Southern-blot hybridization showed that a single copy of a cosmid clone had integrated into the genome of the transformants. A 12.0-kbp fragment of the cosmid vector with the flanking region of wild-type genomic DNA was recovered by plasmid rescue from Ppr1. Using the flanking DNA sequences as a probe for colony blot hybridization, a genomic clone was identified and designated pRP46. Transformants obtained following transformation with pRP46 were able to penetrate cellulose membranes. The penetration frequency of pRP46 transformants ranged from 25 to 65%. Transformants were also pathogenic on cucumber.