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Characterization of tan spot fungus populations from wheat in Oklahoma

Salome Suarez: Oklahoma State University

<div>Wheat ranks third among economically important crops in the United States. Reduced tillage or no-till practices in Oklahoma have contributed to a higher incidence of fungal leaf spot diseases, particularly tan spot caused by <em>Pyrenophora tritici-repentis </em>(PTR). The occurrence and genetic diversity of PTR in Oklahoma was determined. The identity of 311 isolates collected from 13 winter wheat fields across Oklahoma in 2016 and 2017 was confirmed using PTR-specific PCR primers. The genetic structure of PTR subpopulations from ten Oklahoma counties (n=100) in 2016 was assessed using eight simple sequence repeat (SSR) markers. AMOVA showed low but significant genetic differentiation among 2016 subpopulations. Four geographically distant fields were sampled again in 2017. Population structure analysis of the 2016 and 2017 subpopulations indicated significant differentiation among subpopulations as defined by location and year. Our results suggest local distribution and survival of PTR inoculum on site over time, occasional extensive long-distance movement of PTR inoculum, and frequent recombination among PTR populations. Presence of the cultivar-specific toxin genes was determined by PCR. Ninety-five percent of the PTR isolates were positive for <em>toxA</em> and none were positive for <em>toxB</em>. Thus, ToxA is the predominant toxin produced by PTR populations in Oklahoma. Further studies will phenotype PTR isolates for toxin production using differential lines of wheat.</div>