Modelling Effector-Receptor Interactions and Susceptibility to Septoria nodorum Blotch in Wheat

Fungal effector-host sensitivity gene interactions play a key role in determining the outcome of septoria nodorum blotch (SNB) on wheat. These interactions are quantitative and involve the interactions of multiple effector-sensitivity gene systems. Three effectors are well characterised in this pathosystem; SnToxA, SnTox1 and SnTox3. SnTox1 recognition is encoded by Snn1 and SnTox3 recognition is encoded by Snn3. We used a  double haploid (DH) population derived from the wheat cultivars Calingiri and Wyalkatchem (CxW) to study the roles of two interactions (SnTox1-Snn1 and SnTox3-Snn3; neither parent is sensitive to SnToxA) and of disease susceptibility. Interval QTL mapping showed that SnTox1-Snn1 interaction was the main contributor to the development of SNB on seedlings as well as adult plants using various evaluation indicators. Surprisingly, no effect of the SnTox3-Snn3 interaction was observed. Significant difference in SnTox1 expression was observed between progeny carrying Snn1 and snn1; while there wasnot any difference in SnTox3 expression. We suggest that differential expression of effectors may explain the relative impact of SnTox1-Snn1 and SnTox3-Snn3 interactions on the outcome of the disease.

This study also identified another QTL, on 4BL, was associated with CxW response to semi-purified Tox3 and QTLs on 2AS, 3AL and 6B were only detected at SNB seedling in greenhouse and adult field trial, respectively. Outcomes from this study confirmed that sensitivity gene Snn1 responding to SnTox1 effector appear as the main SNB contributor on the CxW DH mapping population from seedling to adult plants in different environments and explained the dominance of SnTox1-Snn1 over SnTox3-Snn3 interactions.