Sensitivity to three Parastagonospora nodorum necrotrophic effectors in current Australian wheat cultivars and the presence of further fungal effectors

Parastagonospora nodorum is a major fungal pathogen of wheat in Australia, causing septoria nodorum blotch (SNB). Virulence of P. nodorum is quantitative and depends largely on multiple effector-host sensitivity gene interactions. The pathogen utilises a series of proteinaceous, necrotrophic effectors to facilitate disease development on wheat cultivars that possess appropriate dominant sensitivity loci. Thus far, three necrotrophic effector genes have been cloned. Proteins derived from these genes were used to identify wheat cultivars that confer effector sensitivity. The goal of this study was to determine whether effector sensitivity could be used to enhance breeding for SNB resistance. We have demonstrated that SnTox1 effector sensitivity is common in current commercial Western Australian wheat cultivars. Thirty-three of 46 cultivars showed evidence of sensitivity to SnTox1. Of these, 19 showed moderate or strong chlorotic/necrotic responses to SnTox1. Thirteen were completely insensitive to SnTox1. Disease susceptibility was most closely associated with SnTox3 sensitivity. We have also identified biochemical evidence of a novel chlorosis-inducing protein or proteins in P. nodorum culture filtrates unmasked in strains that lack expression of ToxA, SnTox1 and SnTox3 activities.