VIRULENCE OF UREDIAL AND AECIAL ISOLATES OF PUCCINIA CORONATA CORDA F.SP. AVENAE IDENTIFIED IN CANADA FROM 1952 TO 1966

Abstract

Isolates of Puccinia coronata f.sp. avenae collected during a 15-year period were tested for virulence on the crown rust differential oat varieties. The proportion of cultures virulent on Landhafer increased relative to others during this period, and was related to the release in the United States of commercial varieties that contained this type of resistance. These varieties served to reduce the proportion of races avirulent on Landhafer in the crown rust population that reached Canada.The occurrence and subsequent increase in frequency of isolates virulent on Victoria was correlated with the release of the oat varieties Rodney and Garry which possess part of the crown rust resistance of Victoria. The increased proportion of cultures that attacked Ukraine also paralleled the release of these two commercial varieties. This suggests that Ukraine either contains the Victoria Pc-11 gene for crown rust resistance that was transferred to Rodney and Garry, or that it contains another gene in common with these varieties.Races of crown rust that are differentially virulent on the varieties Landhafer and Santa Fe have recently been found in Canada. One culture was virulent on the variety Bondvic but not on Trispernia. No increase in race 264 of crown rust, which attacks all the differential sources of resistance except Saia, has been observed since it was first identified in Canada in 1957.Presentation of the virulence of crown rust isolates for individual types of resistance was found to express the results of race surveys in terms which were more meaningful to the oat breeding program. This form of analysis also produced valuable information on the possible relationships of genes for resistance in different oat varieties not readily obtainable from conventional information on the occurrence and distribution of physiologic races of crown rust.