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2024-2026 IB2024 SPE INRAE

Coordinators: Maël Baudin and Bruno Le Cam

Venturia inaequalis is the causal agent of apple scab, a world-wide spread disease responsible for about half of the pesticide treatments in apple orchards. To reduce the use of fungicides, research institutes including INRAE have developed resistant varieties such as Ariane, Initial, Story, Pitchounette. These breeding programs are particularly long and expensive and rely on the introgression of resistance genes into agronomically interesting apple trees. The host resistance genes recognize avirulent genetic determinants on the pathogen side. Unfortunately, under the selection pressure, the fungus can rapidly lose or modify these determinants which greatly diminish the efficiency of the resistance. Identifying the fungal avirulent determinants ahead of the breeding program can therefore help to better evaluate the durability of the resistance and develop diagnostic tools to survey the presence of virulent isolates in the environment.

With the ICARUS project, we aim to find the unknown fungal avirulent determinants cognate to 13 resistance loci identified in apple germplasms. To do so we will use the very well-established method of UV-induced random mutagenesis. With the ease of generating mutations and the sequencing technologies available, the only bottle neck left to this type of approaches is the phenotyping of mutants. In our case, we use a suppressive screen where only the potential virulent strains survive which makes this workflow simple, cheap and reliable.

Once the avirulent candidate genes are identified, it opens the way to multiple follow up research programs such as: (i) Analyses of the natural diversity of these determinants which help us assess the durability of the resistance ; (ii) Interatomic and cellular biology to help identifying the gene underlying apple resistance loci; (iii) Evolution and molecular biology to better understand the co-evolution of V. inaequalis with its hosts.