Interaction of wheat-Parastagonospora nodorum isolates: Exploring host susceptibility and fungal virulence

Abstract

The fungus Parastagonospora nodorum causes substantial economic losses in wheat worldwide. P. nodorum secretes multiple proteinaceous necrotrophic effectors (NEs) that induce compatible interactions with hosts possessing corresponding dominant susceptibility (S) genes. This study focused on unraveling the virulence pattern and presence of NEs secreted by 33 isolates of P. nodorum in the context of its interaction with 40 wheat genotypes. Wheat genotypes were classified into six groups based on their variable responses to P. nodorum isolates. The S gene Tsn1 was present in 70 % of the highly susceptible cultivars and completely absent in all resistant cultivars. Cultivars possessing all three S genes, Tsn1, Snn1, and Snn3, were susceptible to all P. nodorum isolates. The S gene Snn3 was detected in all Iranian wheat cultivars, whereas its proportion in the world's cultivars was 62.5 %. SnTox1-Snn1 was the most abundant NE-S gene (100 %) in the Iranian P. nodorum and Iranian cultivars. Furthermore, SnToxA was produced in Pichia pastoris, and infiltration of SnToxA resulted in necrosis response exclusively in wheat genotypes harboring the S gene Tsn1. Overall, these findings extend our substantial knowledge of P. nodorum-wheat interactions and their underlying molecular basis in Iran, a country in the Fertile Crescent where both wheat and its pathogens coevolved.