Genetic Similarity among Isolates of Pyrenophora tritici-repentis, Causal Agent of Tan Spot of Wheat

Tan spot, a foliar disease of wheat, is caused by the fungus Pyrenophora tritici-repentis. On susceptible wheat cultivars, P. tritici-repentis induces two distinct symptoms: tan necrosis and extensive chlorosis. Presently isolates of P. tritici-repentis are classified into 11 races based on their virulence on a set of wheat differential genotypes. In nature, this pathogen reproduces both sexually and asexually, but the extent of genetic variability in the P. tritici-repentis population of western Canada is unknown. This study was conducted to assess the genetic variability among different isolates of P. tritici-repentis and to determine if similarities among isolates are correlated with race classification or geographic origin of the isolates. Thirty-three isolates of P. tritici-repentis and one isolate each of P. teres f. sp. teres, P. teres f. sp. maculata, P. graminea, Helminthosporium sativum and an uncharacterized isolate were studied with 30 random amplified polymorphic DNA (RAPD) primers. Cluster analysis showed that all isolates had unique banding patterns and that clustering of isolates was independent of their race designation or geographic origin. Analysis of molecular variation (amova) showed that 96.8% of variability occurred among isolates and among race variability accounted for only 3.2% of the total variability.