The ascomycete fungus Pyrenophora tritici-repentis is the causal agent of tan spot of wheat. The disease can occur on both common wheat (Triticum aestivum) and durum wheat (T. turgidum ssp. durum) and has potential to cause significant yield and quality losses. The fungal pathogen is known to produce necrotrophic effectors (NEs) that act as important virulence factors. Based on the NE production and virulence on a set of four differentials, P. tritici-repentis isolates have been classified into eight races. Race 4 produces no known NEs and is avirulent on the differentials. From a fungal collection in North Dakota, we identified several isolates that were classified as race 4. These isolates caused no or little disease on all common wheat lines including the differentials; however, they were virulent on some durum cultivars and tetraploid wheat accessions. Using two segregating tetraploid wheat populations and quantitative trait locus mapping, we identified several genomic regions significantly associated with disease caused by two of these isolates, some of which have not been previously reported. This is the first report that race 4 is virulent on tetraploid wheat, likely utilizing unidentified NEs. Our findings further highlight the insufficiency of the current race classification system for P. tritici-repentis.

子囊真菌Pyrenophora tritici-repentis是小麦棕褐色斑点的致病因子。所述疾病可发生在两个普通小麦（普通小麦）和硬粒小麦（Ť。圆锥小麦SSP。硬粒小麦），并且具有可能造成显著的产量和质量的损失。已知真菌病原体会产生坏死性效应子（NEs），这些作用是重要的毒力因子。基于NE的产生和在一组四个差异P. tritici-repentis上的毒力分离株已分为八个种族。种族4不产生已知的NE，并且在差异上无毒。从北达科他州的一个真菌收集物中，我们鉴定出了几种被归类为第4种的分离株。但是，它们对一些硬质小麦和四倍体小麦品种有毒。使用两个分离的四倍体小麦群体和数量性状基因座作图，我们鉴定了几个与这些分离物中的两个引起的疾病显着相关的基因组区域，其中一些以前未曾报道过。这是第四个种族在四倍体小麦上有毒的第一个报道，可能利用未鉴定的NE。我们的发现进一步凸显了当前的种族分类系统的不足三角假单胞菌。