Host susceptibility and fungal virulence in the wheat-Parastagonospora nodorum interactions

Abstract

The fungus Parastagonospora nodorum is responsible for substantial economic losses of wheat worldwide. P. nodorum secretes multiple proteinaceous host-specific toxins known as necrotrophic effectors (NE) that induce compatible interactions with hosts possessing the corresponding dominant susceptibility (S) genes. In this study, the reaction of 40 wheat genotypes including 19 Iranian cultivars, 16 world cultivars and five differential genotypes against 33 P. nodorum isolates was investigated. In addition, the occurrence of known NEs and their corresponding S genes was assessed. Wheat genotypes were classified into six groups based on their variable reaction towards P. nodorum isolates. The S gene Tsn1 was present in 70% of highly susceptible cultivars and was completely absent in all resistant cultivars. The cultivars possessing all three S genes Tsn1, Snn1 and Snn3 were susceptible to all P. nodorum isolates. S gene Snn3 was detected in all Iranian wheat cultivars whereas the proportion of this gene in world cultivars was 62.5%. SnTox1-Snn1 was the most abundant NE-S gene frequency (100%) in Iranian P. nodorum isolates and Iranian cultivars. Furthermore, SnToxA was produced in Pichia pastoris and infiltration of SnToxA resulted in necrosis response exclusively on wheat cultivars harboring the Tsn1 sensitivity gene indicating that toxin infiltration can be used as a quick and accurate assay in breeding programs. Overall, these findings extended our substantial knowledge about P. nodorum-wheat interactions and their underlying molecular basis in Iran, a country located in the Fertile Crescent where both wheat and its pathogens coevolved.