Virulence Patterns of Uromyces appendiculatus from Different Geographical Areas and Implications for Finding Durable Resistance to Rust of Common Bean

Single-uredinium cultures of Uromyces appendiculatus (Pers) Unger from Honduras, Dominican Republic, Puerto Rico, Tanzania and USA were evaluated for virulence on 19 standard bean {Phaseolus vulgaris) rust differential lines, cultivars that had been previously selected on the basis of resistance to bean rust, A disease rating scale, based on uredinium diameter, was used to study pathogenic variability of the bean rust fungus. Virulence of the cultures was measured by the vector of disease score (mds) on all 19 differentials and the nearest centroid sorting algorithm was used to cluster the cultures according to virulence similarity, A total of 373 different virulence patterns was identified from more than 2000 cultures and were grouped into four virulence clusters. None of the cultures produced a susceptible reaction on all the differentials. Cultures that produced uredinia > 0,5 mm in diameter in 15 differentials were considered to have high virulence. About 59, 15, 20, 5 and 0%, respectively, ofthe Honduran., Dominican, Puerto Rican, USA and Tanzanian cultures were highly virulent. The lines/cultivars Ecuador 299, Mexico 235, 51051, NEP-2, Mexico 309, California Small White 643, A x S 37, and Aurora had a high degree of resistance to most cultures and can be used as sources of broad resistance. Virulence patterns ofthe differentials indicated redundancy in some host parasite interactions and the need to modify the composition of the differential lines/cultivars