The necrotrophic fungal pathogen Pyrenophora tritici-repentis (Ptr) is the causal agent of tan spot, a significant foliar disease of wheat worldwide. Ptr is known to produce at least three necrotrophic effectors (NEs), namely, Ptr ToxA, Ptr ToxB and Ptr ToxC, to cause disease in wheat. Both Ptr ToxA and Ptr ToxB are a protein and the coding genes for them have been cloned. In contrast, Ptr ToxC was partially characterized over 20 years ago as a low molecular weight secondary metabolite, but its production in fungal pathogen remains unknown. In addition, many lines of evidence have shown that the fungal pathogen produces additional NEs for virulence. We recently developed a novel approach to further dissecting the genetics of fungal virulence in Ptr. Using the approach, we have successfully mapped the genetic locus (ToxC) conditioning Ptr ToxC production in a biparental population between a Ptr ToxC producing isolate and Ptr ToxC nonproducing isolate. Four genes in that locus (...).