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Race structure and genetic diversity of the Pyrenophora tritici-repentis population in North Dakota

Zhaohui Liu: North Dakota State University

<div>The fungus <em>Pyrenophora tritici-repentis</em> (<em>Ptr</em>) is the causal agent of tan spot, which is a major foliar disease of wheat (<em>Triticum </em>ssp.) worldwide. The fungal pathogen is known to produce three necrotrophic effectors (NEs), and eight races have been identified among globally collected isolates based on the production of different combinations of NEs. In this study, a total of 350 <em>Ptr</em> isolates collected from North Dakota (ND) in the last several years were characterized for race structure and genetic diversity. By using the <em>ToxA</em> and <em>ToxB</em> gene specific primers and greenhouse inoculations, race 1 isolates were found to be predominant (93%) with a small percentage of race 2 (5%) and race 4 (2%) isolates. Our results are similar to the previous finding with a population collected in ND two decades ago. A subset of race 1 isolates from different years was analyzed with five microsatellite markers that are dispersed on different chromosomes of the fungal genome. A high level of genetic diversity was detected with each microsatellite marker amplifying an average of 8.4 alleles. This work indicates that the race structure of the <em>Ptr </em>population in ND is relatively stable over the years, but small variability in virulence could exist within race 1 due to the genetic diversity.</div>