Simple sequence repeats and diversity of globally distributed populations ofPyrenophora tritici-repentis

Genetic diversity and relatedness in Pyrenophora tritici-repentis, the causal agent of tan spot disease of wheat, were examined in a geographically diverse collection of 80 isolates representing the eight races of the pathogen. Thirty-one simple sequence repeat markers were designed from the P. tritici-repentis genome which amplified 31 different loci in the isolates tested. Data were examined using: (i) Nei's analysis of genetic diversity and genetic distance, (ii) analysis of molecular variance (AMOVA), and (iii) clustering by the unweighted pair group method using arithmetic averages (UPGMA). A significant genetic differentiation (ΦPT = 0.153, P ≤ 0.001) was detected among populations, with isolates from different origins having similar levels of genetic diversity. Nei's analysis of genetic distance revealed that isolates of P. tritici-repentis can be grouped into four distinct populations based on their region of origin. The AMOVA showed that Canadian isolates have less than 9% genetic dissimilarity with isolates from the Caucasus region, while they have up to 32% genetic dissimilarity with isolates from the Fertile Crescent. Isolates were also compared by race, genetic distance and cluster analysis based on pooled allele frequency. Ptr ToxA non-producing isolates clustered together but were distantly related to Ptr ToxA-producing isolates, suggesting that the host-specificity imposed by the different Ptr toxins could lead to differentiation among isolates of P. tritici-repentis.