DISTRIBUTION OF VIRULENCE IN 2 POPULATIONS OF PUCCINIA-CORONATA F-SP AVENAE IN CANADA

The distributions of virulence in the eastern (Ontario and Quebec) and prairie (Manitoba and Saskatchewan) populations of Puccinia coronata f.sp. avenae in Canada were examined from virulence survey data in 1974 and 1990 to determine if these populations resemble previously characterized sexual or asexual cereal rust populations. Single uredinial isolates from both populations were evaluated for virulence phenotype on single gene differential host lines. The eastern and prairie populations in 1974 were dominated by relatively simple phenotypes that were avirulent or virulent to one of the single gene lines. In 1990, after virulence to crown rust resistance genes Pc39 and Pc38/Pc39 increased in frequency in the eastern and prairie populations, respectively, the eastern population had an increased proportion of isolates with virulences to one to two genes, and the prairie population was dominated by isolates with one to four virulences. Increasing virulence to Pc39 in the eastern population and Pc38 and Pc39 in the prairie population also contributed to a greater number of phenotypes in both populations in 1990 compared with 1974. The distributions of virulence differences among isolates in both populations in 1974 and 1990 appeared to be nearly random, approximating Poisson distributions. Associations between pairs of specific virulences to 10 single gene lines were examined in both populations during 1974 - 1990. Relatively few pairs of virulences in both populations were found to be nonrandomly associated. No associations between pairs of virulences persisted for more than 3 years in either population. Sexual recombination most likely functions in evenly distributing virulences among phenotypes in both populations.