Coevolution of the bean rust pathogen Uromyces appendiculatus with its wild, weedy and domesticated hosts (Phaseolus spp.) at its center of diversity

The virulence of the bean rust pathogen, Uromyces appendiculatus collected from wild, weedy and cultivated Phaseolus species was examined in 28 locations across Honduras. A total of 385 U. appendiculatus isolates were characterized on the 12 bean rust differentials. No significant difference in mean disease score was found between locations. However, there were significant differences among the host variants within locations. Moreover, when locations were compared on the basis of pathotype occurrence and frequency, differences among locations were evident.; A total of 74 bean accessions, including wild P. vulgaris, P. vulgaris landraces, P. lunatus, and wild and domesticated P. coccineus from Honduras were evaluated for rust resistance. A high level of resistance was identified in P. coccineus and P. lunatus and some P. vulgaris landrace accessions. Wild P. vulgaris accessions were highly susceptible. Thirty-two (52%) of the accessions showed intermediate to high levels of resistance under greenhouses conditions but a higher number of resistant accessions was observed in the field screening tests. The high percentage of intermediate and highly resistant accessions identified supports the hypothesis that collecting host plants from a center of pathogen diversity, or from locations with high incidence of disease and pathogen diversity, is a very efficient approach to identification of new sources of disease resistance.; The molecular diversity of 39 U. appendiculatus isolates representative of the most common and virulent pathotypes collected in Honduras was examined using AFLP. A total of 137 easy-to-score, repeatable polymorphic bands were used for similarity and correlation analyses. A high degree of polymorphism between isolates of similar virulence phenotype was detected. No two isolates had the same AFLP pattern for any of the primer pairs used in this study. Low correlation, however, was found between molecular and virulence data. No virulence, geographical or host origin correlation was detected between isolate clusters based on the similarity matrices.