Dissecting the genetic basis of susceptibility to Flavescence dorée in a Vitis vinifera progeny

Abstract

Flavescence dorée (FD) is one of the most destructive epidemic diseases affecting yields of cultivated grapevine (Vitis vinifera L.) in Europe. FD is caused by a phytoplasma (FDp) classified as quarantine organism and transmitted by the leafhopper vector Scaphoideustitanus Ball. As no curative treatment against FDp is available, FD control relies on vineyard surveys, the uprooting of symptomatic grapevines, chemical control of the vector, and the use of disease-free propagation material. In the context of sustainable viticulture, alternative control strategies are therefore urgently needed. Several studies have reported differential susceptibilities among grapevinecultivars, although none are resistant.

Interestingly, the highly susceptible Cabernet Sauvignon (CS) and poorly susceptible Merlot (M) share a common parent, Cabernet Franc (CF), which displays intermediate susceptibility to FD. In contrast, the second parent of CS, Sauvignon Blanc, is highly susceptible, whereas the second parent of M, Magdeleine Noire des Charentes (MAG), exhibits low susceptibility. Therefore, the following question arises: is the reduced susceptibility observed in M heritable from MAG? To answer this question, we investigated the genetic determinismof two phenotypic traits: (i) the proportion of FD-infected plants and (ii) the mean of FDp titer in infected plants. Crosses between MAGand CF (MAG x CF; CF x MAG) and resulting from a self-fertilization of MAG (MAG x MAG) were performed to generate a progeny of125 individuals. We determined the susceptibility of the progeny, for both phenotypic traits, using a controlled FDp transmission assay byS. titanus under confined greenhouse conditions. In parallel, genomic analyses were conducted on healthy progeny plants using a genotyping-by-sequencing approach to identify potential constitutive biomarkers. Phenotypic assays revealed a wide range of susceptibility levels within the progeny. After filtering of the genotyping data, 11,942 SNP markers were retained, and genomic heritabilityvalues for both phenotypic traits were high (> 0.8). GWAS analyses and predictive modelling were then performed to identify SNP markersassociated with low susceptibility to FD. These results will contribute to a better understanding of the genetic basis of grapevine susceptibility to FD and provide valuable perspectives for grapevine breeding.

Acknowledgements

We would like to thank J.E. Masson and M. Perrin (UMR SVQV, INRAE Colmar) for their participation in phenotyping trials and scientific discussions.