P-077 - The robustness of Stb resistance genes

Genetic resistance is one of the most agroecologically relevant strategies to protect wheat from Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici. To date, 23 Stb wheat resistance genes have been identified, some of which following a gene-for-gene model. However, in field conditions, efficiency of these resistance highly depends on factors such as the environment and the fungal pressure. To assess the robustness of resistance, we studied the impact of high fungal inoculum on Stb16q resistance by phenotyping near-isogenic lines with 11 isolates of Z. tritici using increased spore concentrations. Under these conditions, Stb16q efficacy decreased, with up to 50% leaf covered by pycnidia, as compared to no pycnidia at low concentrations. At high inoculum levels, 75% of stomata, considered a barrier to Z. tritici, experienced penetration attempts, while only 20% closed, potentially explaining efficacy loss. One of the five identified AvrStb16q alleles identified among the 11 isolates was associated with a greater loss of Stb16q efficacy suggesting a role of AvrStb16q alleles recognition in this loss. Unlike Stb16q, Stb6 remains fully effective using high inoculum concentration. These findings demonstrate that, resistance confer by major Stb genes is more quantitative than qualitative with gene-dependent efficacy influenced by environmental factors.