Quantitative Trait Loci ControllingPhytophthora cactorumResistance in the Cultivated Octoploid Strawberry (Fragariaxananassa)

Abstract

ABSTRACTThe cultivated strawberry,Fragaria x ananassa(Fragariaspp.) is the most economically important global soft fruit.Phytophthora cactorum, a water-borne oomycete causes economic losses in strawberry production globally. A bi-parental cross of octoploid cultivated strawberry segregating for resistance toP. cactorum, the causative agent of crown rot disease, was screened using artificial inoculation. Multiple resistance quantitative trait loci (QTL) were identified and mapped. Three major effect QTL (FaRPc6C,FaRPc6DandFaRPc7D) explained 36% of the variation observed and in total, the detected QTL explained 86% of the variation observed. There were no epistatic interactions detected between the three major QTLs. Testing a subset of the mapping population progeny against a range ofP. cactorumisolates revealed no major differences in host response, however, some lines showed higher susceptibility than predicted, indicating that additional undetected factors may affect the expression of some quantitative resistance loci. Using historic crown rot disease score data from strawberry accessions, a preliminary genome-wide association study of 114 individuals revealed additional loci associated with resistance toP. cactorum. Mining ofFragaria vescaHawaii 4 v1.1 genome revealed candidate resistance genes in the QTL regions.