ToxA Is Present in the U.S. Bipolaris sorokiniana Population and Is a Significant Virulence Factor on Wheat Harboring Tsn1

Abstract

ToxA, a necrotrophic effector originally identified from the tan spot fun-BsToxA did not induce necrosis on any of the lines. Culture filtrates gus Pyrenophora tritici-repentis in 1987, was subsequently identified of the four BsToxA-containing isolates induced necrosis on the wild from Parastagonospora nodorum in 2006. More recently, the ToxA type (Tsn1) lines but not on the corresponding tsn1 mutant lines. Sen-gene was identified in the spot blotch fungus Bipolaris sorokiniana sitivity to these culture filtrates also mapped to the previously identiin Australia. Here we show that the ToxA gene is also present in the fied location for Tsn1 in the winter wheat mapping population Arina × B. sorokiniana population in the winter wheat region of southcentral Forno. Inoculation of one of these ToxA-producing isolates on the Texas. Leaves from ‘Duster’ wheat showing strong necrotic lesions same population showed that the Tsn1 locus accounted for 24.4% of were collected in Castroville, TX. Fifteen single-spore isolates were the disease variation. All 13 isolates harbored the same BsToxA nuclecollected from separate lesions, and 13 of them harbored the BsToxA otide sequence, which was identical to one of the two haplotypes pregene and secreted ToxA in culture based on sensitivity of BG261, the viously identified in Australia. Sensitivity to ToxA is prevalent in differential line containing the dominant ToxA sensitivity gene, Tsn1. popular hard winter wheat cultivars in the central and southcentral Four isolates harboring BsToxA and one deficient in BsToxA were winter wheat regions of the United States, showing the potential of used to infiltrate two wheat lines harboring Tsn1 as well as their cor-a selective advantage for B. sorokiniana isolates that harbor the ToxA responding tsn1 mutant lines. Culture filtrates of the isolate lacking gene.