Stomatal Closure, a Conserved Spore Concentration‐Dependent Response Mediated by Different Stb Genes to Avirulent Isolates of Zymoseptoria tritici

Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici , is one of the most damaging diseases of wheat ( Triticum spp.) worldwide. To date, 23 Stb resistance genes have been identified, including the cloned Stb6 and Stb16q genes, both encoding receptor‐like kinases (RLKs). Upon recognition of an avirulent isolate, these two genes trigger a strong inhibition of pathogen penetration into leaf tissues at the stomatal level and promote a transient stomatal closure that could be involved in preventing pathogen entry. The objective of this study was to better understand the magnitude of this stomatal closure in incompatible interactions. Increasing inoculum concentrations of an avirulent isolate, thereby enhancing Z . tritici penetration attempts, caused a nonlinear response in Stb16q ‐induced stomatal closure, with 71% penetration attempts leading to only 21% of closed stomata. Another avirulent isolate also triggered stomatal closure, indicating that Stb16q ‐dependent stomatal closure is not specific to one particular avirulent isolate. Likewise, the near‐isogenic line carrying Stb9 displayed a significantly higher proportion of closed stomata (18%) under incompatible interactions using a high inoculum concentration compared to the water‐inoculated control (8%). Altogether, these results confirm that stomatal closure is a shared spore concentration‐dependent response induced by Stb genes during incompatible interactions to likely limit fungal penetration.