Traditional and molecular characterization of variability in Colletotrichum lindemuthianum

Colletotrichum lindemuthianum isolates were characterized into 41 races based on virulence to twelve differential cultivars of Phaseolus vulgaris. Races 7, 65, and 73 were widespread. No race was isolated from the Andean and the Middle American gene pools of P. vulgaris although 39% of the races were detected multiple times. Phenetic analyses showed no obvious geographical patterns correlated with virulence clusters. Genetic diversity of C. lindemuthianum was shown to be the greatest in Central America. Diversity was estimated using sequence homology and RFLP analysis of the ribosomal subunit spacer (ITS), and RAPD analysis of total genomic DNA. Polymorphism in the rDNA spacer region was not linked to any specific genetic factor. Parsimony and neighbor-joining analyses supported a monophyletic group formed by all except race 31. RFLP-ITS analysis placed Andean races predominantly into group I except race 23, which was placed within group II. The Middle American races were observed in both groups. Molecular polymorphism among isolates of similar virulence phenotype revealed a level of molecular variability within C. lindemuthianum greater than the variability characterized using virulence analysis. Thirty-four races of C. lindemuthianum were inoculated on sixty-two cultivars of P. vulgaris. Bean genotypes clustered based on the gene pool origin of the resistance genes present, regardless of the actual gene pool of the host genotype. Races of C. lindemuthianum with Middle American reaction showed broad virulence on germplasm from both gene pools, whereas races with Andean reaction showed high virulence only on Andean germplasm. The reduced virulence of Andean races on Middle American genotypes suggests selection of virulence factors congruent with diversity in P. vulgaris. The majority of races of C. lindemuthianum grouped according to specific gene pool (i.e., Middle American and Andean) based on principal component analysis, except a small group of isolates which appeared to possess factors of virulence to both host gene pools. No apparent geographic effect was observed. Virulence data supported variability in C. lindemuthianum structured with diversity in Phaseolus, whereas molecular data showed no congruence between pathogen and host populations.