VIRULENCE AND MOLECULAR POLYMORPHISM IN PUCCINIA-RECONDITA F SP TRITICI IN CANADA

Sixty-four representative single-uredinial isolates of Puccinia recond ita f. sp. tritici collected from wheat in the eastern (Ontario and Qu ebec), prairie (Manitoba and Saskatchewan), and Pacific (Alberta and B ritish Columbia) regions of Canada were analyzed for virulence polymor phism on 19 near-isogenic wheat differential lines and for randomly am plified polymorphic DNA (RAPD) using 10 arbitrary decamer primers. Thi rty-seven phenotypes of P. r. tritici were distinguished by the 19 hos t differential lines. Fifteen molecular phenotypes were distinguished by the 10 primers in the RAPD analysis. Forty-five unique phenotypes o f P. r. tritici were distinguished by combined virulence and RAPD data . Molecular variation was greatest between isolates of different virul ence phenotypes. There was some molecular variation among isolates wit h identical virulences. Virulence and RAPD data were used separately a nd combined in cluster analyses. Two major clusters were distinguished with the combined data sets. The first cluster consisted of isolates virulent or avirulent to both resistance genes Lr2a and Lr2c, and the second cluster consisted of isolates avirulent to Lr2a and virulent to Lr2c. The molecular polymorphisms were more effective in distinguishi ng between the major clusters of P. r. tritici compared to the virulen ce polymorphisms. However, virulence polymorphisms were more effective in distinguishing between isolates within the major clusters compared to the molecular polymorphisms. There was a correlation of 0.58 betwe en the virulence and molecular dissimilarity matrices. The cluster ana lyses indicated a general relationship between virulence and molecular polymorphism in P. r. tritici in Canada. There are currently two majo r groups of P. r. tritici in Canada. One group consists of isolates fo und in the prairie and eastern regions. Isolates in this group have li mited molecular polymorphisms and consist of many virulence phenotypes that are either virulent or avirulent to both Lr2a and Lr2c. Isolates in the second group are found in eastern Canada and in the Pacific re gion. These isolates are avirulent to Lr2a and virulent to Lr2e and ha ve molecular phenotypes distinct from isolates in the first group. The molecular data support conclusions from virulence survey data that di stinct geographic populations of P. r. tritici exist in Canada and tha t new virulences arise and increase in the prairie population by mutat ions from preexisting phenotypes.