Virulence Variability of Puccinia coronata f. sp. avenae Isolates Collected in Three Counties from Rio Grande do Sul State, Brazil.

Using isolates collected in three counties of Rio Grande do Sul State, Brazil, the goals of this work were to determine (i) the pattern of virulence or avirulence of the isolates to 25 Pc resistance genes, (ii) the similarity in virulence among Puccinia coronata f. sp. avenae isolates considering their pattern of virulence or avirulence, (iii) the race code for each isolate by the North American system of nomenclature, and (iv) the supplemental Pc genes potentially useful as local differentials for P. coronata f. sp. avenae races. The results indicate that the southern Brazilian rust isolates presented a high level of virulence, because 66% of inoculations manifested the high infection type. Only the Pc 68 gene was effective against all tested isolates. In general, each isolate presented a different pattern of virulence or avirulence, which indicates the high variability for virulence that the fungus presents at the sampled sites. However, the North American system of nomenclature was not completely sufficient in distinguishing southern Brazilian races. Thus, the genes Pc 36, Pc 53, Pc 55, and Pc 63 represent a possible gene combination to be incorporated into the North American system of nomenclature.