Prevalence and importance of the necrotrophic effector gene ToxA in Bipolaris sorokiniana populations collected from spring wheat and barley

Bipolaris sorokiniana is a nectrophic fungal pathogen that causes foliar and root diseases on wheat and barley. Theose diseases are common in all wheat- and barley-growing regions with more severe outbreaks occurring in under warm and humid conditions. areas. The fungus B. sorokiniana can also infect a wide range of grass species in Poaceae and secrete ToxA, an important necrotrophic effector also identified other wheat leaf spotting pathogens. ToxA is an important effector gene that has been identified in several wheat fungal pathogens including B. sorokiniana. In this study, we investigated the prevalence and virulence role of ToxA were investigated in a collection of 278 B. sorokiniana populations isolates that were mainly collected from spring wheat and barley in the Upper Midwest of the United States or other places, including . A total of 278 B. sorokiniana isolates were evaluated including 169 from wheat leaves, 75 from wheat roots, 30 from barley leaves and four from wild quack grass leaves. ToxA was detected present in the isolates from wheat leaves, wheat roots and wild grass leaves, but was absent notfrom isolates collected in those from barley leaves. Prevalence of ToxA in wheat leaf isolates (34.3%) was much higher than that in wheat root isolates (16%). Sequencing analysis revealed the presence of two haplotypes with the majority being BsH2. All ToxA+ isolates produced the functional effector in liquid cultures. Pathogenicity assays revealed that ToxA+ isolates caused significantly more disease on spring wheat lines harboring Tsn1 than their tsn1 mutants, suggesting the ToxA-Tsn1 interaction plays an important role in spot blotch development. This work confirms the presence and importance of ToxA in B. sorokiniana populations from infecting wheat and thus, the need to eliminate breeding of Tsn1 out from spring wheat cultivars can to reduce susceptibility to spot blotch.