Race structure and distribution of Pyrenophora tritici-repentis in Tunisia

Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is a widespread foliar disease of wheat, which is becoming important in North Africa particularly in Tunisia. To assess the pathogenic variation of Ptr in Tunisia, characterized 84 single conidium isolates of Ptr were characterized from durum wheat cultivars, sampled during the 2017-2018 cropping season. The virulence of isolates were assessed, under controlled conditions, on a standard differential set of six wheat genotypes. Ptr races 2, 4, 5, 6, 7 and 8 were identified, the first such information available for Tunisia. Race 2, commonly found in North America, South America and Asia, was identified for the first time in North Africa, at a low frequency of 5%. Races 5 and 7 were the most frequent, representing, respectively, 39% and 43% of the isolates tested. Only 8% of the isolates were classified as race 8, while 4% were identified race 6. Race 6 was only detected at the experimental station in the North Western region of Tunisia and in a nearby farm field. Only one Ptr isolate was avirulent on all six differential genotypes, and was therefore designated race 4. The identification of six races of Ptr on durum wheat demonstrates the high diversity of the pathogen population in Tunisia.