Protecting the durability of major resistance genes to plant viruses with quantitative resistance
Abstract
The deployment of virus-resistant crops often leads to the emergence of resistance-breaking (RB) pathogens that suppress the yield benefit provided by the resistance (Fabre et al,2012). Although breakdowns are well known for qualitative resistances conferring total resistance to the virus, they are still poorly understood for quantitative resistances conferring partial resistance. Furthermore, it has been proved for several pathosystems that combining qualitative and quantitative resistances can increase the durability of the qualitative resistance (Palloix et al, 2009, Quenouille et al, 2013). Two mechanisms can explain this result : either (i) an increase of genetic drift in the virus population, or (ii) a decrease of the selection advantage of the RB mutant. The purpose of the ongoing work presented here is to disentangle the role of these two mechanisms on the durability of plant qualitative resistances to viruses.To investigate this, we concentrated on a pepper Potato virus Y (PVY) pathosystem on which we report consistent variability in bottlenecks undergone by viral populations at inoculation and in viral accumulation, both determined by the host genotype. We follow by high-throughput sequencing the within-host demo-genetic dynamics of several virus variants in contrasted plant genotypes, carrying a qualitative resistance and different combinations of quantitative resistances. The respective effects of genetic drift and selection are evaluated by fitting models to these data (Fabre, 2012). We further aim at predicting the potential of combining qualitative and quantitative plant resistances to achieve sustainable plant resistance management at the epidemic scale.