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Polygenic Resistance of Pepper to Potyviruses Consists of a Combination of Isolate-Specific and Broad-Spectrum Quantitative Trait Loci

At least six potyviruses infect pepper crops around the world. Only monogenic resistance with isolate-specific effects or broad-spectrum effects against potyviruses has been identified. Quantitative trait loci (QTLs) for resistance to two potato virus Y (PVY) isolates and to potyvirus E have been mapped in a doubled-haploid progeny from the hybrid between the line Perennial with resistance factors against several potyviruses and the line Yolo Wonder, with 172 DNA markers. Eleven chromosomal regions were found to be associated with quantitative resistance to PVY and potyvirus E by both analysis of variance and non-parametric tests. This resistance results from the association of a major-effect QTL and several minor-effect QTLs. Two minor-effect QTLs originated from the susceptible parent. In addition to additive-effect QTLs, interactions between QTLs were also identified. Based on their spectrum of action, we discriminated QTLs with PVY isolate-or potyvirus-specific effect and loci involved in the resistance to several distinct potyviruses. The locations of QTLs were compared with loci having known qualitative effects against potyviruses; QTLs for PVY and potyvirus E resistance were detected in the vicinity of the pvr2 and pvr6 loci. The origin of the broad-spectrum resistance against potyviruses and the relationships between major genes and QTLs are discussed.