Methodological advances in characterizing Zymoseptoria tritici populations

Monitoring virulent strains within pathogen populations is crucial to improve host resistance deployment strategies.We developed a method for ‘bulk phenotyping on checkerboard microcanopies of wheat near-isogenic lines’ (BPC) for estimating the frequency of virulence against a resistance gene in mixed populations of the fungal pathogen Zymoseptoria tritici, the causal agent of Septoria tritici blotch (STB) in wheat, without the need for strain-by-strain pathogen phenotyping. Our method involves the uniform inoculation of a microcanopy of two wheat lines—one with the target resistance gene and the other without it—with a multistrain mixture of isolates representative of the population to be characterized, followed by the differential quantification of infection points (lesions). Using Stb16q, a wheat resistance gene that has recently broken down in Europe, we found a robust correlation between the ratio of the mean number of lesions on each wheat line and the frequency of virulent strains in the inoculum. This method appears to be a valuable tool for characterizing Z. tritici populations in contexts of specific varietal resistance deployment (such as regionalized varietal selection, optimization of varietal mixtures, etc.), complementing the molecular approaches currently being developed at BIOGER.

Suffert F, Le Prieur S, Gélisse S, Dzialo E, Saintenac C, Marcel TC. 2024. Estimating the frequency of virulence against an Stb gene in Zymoseptoria tritici populations by bulk phenotyping on checkerboard microcanopies of wheat NILs. Plant pathology. https://doi.org/10.1111/ppa.13894

Contact : frederic.suffert@inrae.fr