Molecular-based race classification of Pyrenophora tritici-repentis causing tan spot of wheat in Japan

Tan spot, a foliar disease of Triticum spp. such as bread wheat (T. aestivum L.) and durum wheat (T. turgidum ssp. durum (Desf.) Husn.) caused by the filamentous fungus Pyrenophora tritici-repentis (Died.) Drechsler leads to serious losses of crop yield and quality in some areas in Japan. P. tritici-repentis is classified into eight races according to the combinations of three necrotrophic effectors, PtrToxA, PtrToxB, and PtrToxC encoded by ToxA, ToxB, and ToxC1, respectively. Race classification has been based on reaction of a differential variety to necrotrophic effectors, which is tested by inoculation. Recent identification of the Tox genes and development of specific DNA markers have enabled us to classify races of P. tritici-repentis collected in Japan by Tox gene genotyping. We found that 17 strains collected from Triticum spp. in Japan were mainly race 1 or 2, because they carried ToxA as a toxin gene by current race classification; wheat genotype tsn1 is resistant to ToxA. Establishment of wheat cultivars carrying tsn1 would be most effective for decreasing agronomic losses caused by the disease in Japan.