Quantitative trait loci from the host genetic background modulate the durability of a resistance gene: a rational basis for sustainable resistance breeding in plants

The combination of major resistance genes with quantitative resistance factors ishypothesized as a promising breeding strategy to preserve the durability of resistantcultivar, as recently observed in different pathosystems. Using the pepper (Capsicumannuum)/Potato virus Y (PVY, genus Potyvirus) pathosystem, weaimed at identifying plant genetic factors directly affecting the frequency of virusadaptation to the major resistance gene pvr2³ and atcomparing them with genetic factors affecting quantitative resistance. The resistancebreakdown frequency was a highly heritable trait (h²=0.87).Four loci including additive quantitative trait loci (QTLs) and epistatic interactionsexplained together 70% of the variance of pvr2³breakdown frequency. Three of the four QTLs controlling pvr2³breakdown frequency were also involved in quantitative resistance, strongly suggestingthat QTLs controlling quantitative resistance have a pleiotropic effect on the durabilityof the major resistance gene. With the first mapping of QTLs directly affecting resistancedurability, this study provides a rationale for sustainable resistance breeding.Surprisingly, a genetic trade-off was observed between the durability of PVY resistancecontrolled by pvr2³ and the spectrum of the resistanceagainst different potyviruses. This trade-off seemed to have been resolved by thecombination of minor-effect durability QTLs under long-term farmer selection.