Genetic diversity and pathogenic variation of Colletotrichum lindemuthianum in the three centers of diversity of its host, Phaseolus vulgaris

Population subdivision of Colletotrichum lindemuthianum, the causal agent of anthracnose, was studied in three regions located in three centers of diversity of its host, Phaseolus vulgaris. Random amplified polymorphic DNA (RAPD) markers, restriction endonuclease analysis of the amplified ribosomal internal transcribed spacer region, and virulence on a set of 12 cultivars were used to assess the genetic diversity of C. lindemuthianum strains isolated in Mexican, Ecuadorian, and Argentinean wild common bean populations. The three regions were significantly differentiated for molecular markers. For these markers, Mexico was the most polymorphic and the most distant from Ecuador and Argentina. The majority of the RAPD alleles present in Ecuador and Argentina were found in Mexico, suggesting that Andean populations have been derived from the Mesoamerican center. Pathogenicity tests on a set of 12 cultivars showed that all but one of the Mexican strains were virulent exclusively on Mesoamerican cultivars. Argentinean strains were virulent preferentially on southern Andes cultivars, and the Ecuadorian strains, except for one strain, were avirulent on all cultivars. These results suggest an adaptation of strains on cultivars of the same geographic origin. Thus, based on molecular and virulence markers, C. lindemuthianum strains isolated from wild common bean populations were divided into three groups corresponding to host gene pools.