FUNGICIDE SENSITIVITY IN SOMATIC HYBRIDS OF PHYTOPHTHORA-CAPSICI OBTAINED BY PROTOPLAST FUSION

Near-isogenic strains of Phytophthora capsici resistant to either metalaxyl (Metr) or phosphorous acid (PAr) were treated with MNNG and selected on agar amended with p-fluorotryptophan (FTP) to obtain double drug-resistant mutants. Protoplasts were successfully isolated from wildtype and mutant strains using Driselase or Cellulase CP. Putative somatic hybrids were recovered following fusions between protoplasts from strains either resistant to metalaxyl (Metr) or phosphorous acid and fluorotryptophan (PArFTPr) by selection on agar amended with metalaxyl and FTP. Hybrid strains from this cross were resistant to FTP and phosphorous acid, but showed intermediate resistance to metalaxyl, similar to the phenotype reported for sexual progeny of other Oomycetes heterozygous for metalaxyl resistance. Zoospore progeny from the putative hybrids retained this phenotype, suggesting that nuclear fusion had taken place. Somatic hybrids and their zoospore progeny were pathogenic to green pepper seedlings. © 1990.