Mapping quantitative trait loci associated with resistance to bacterial spot (Xanthomonas arboricola pv. pruni) in peach

Bacterial spot, caused by Xanthomonas arboricola pv. pruni (Xap), is a serious disease that can affect peach fruit quality and production worldwide. This disease causes severe defoliation and blemishing of fruit, particularly in areas with high rainfall, strong winds, high humidity, and sandy soil. The molecular basis of its tolerance and susceptibility in peach is yet to be understood. An F2 population of 63 genotypes derived from a cross between peaches “O’Henry” (susceptible) and “Clayton” (resistant) has been used for linkage map construction and quantitative trait loci (QTL) mapping. Phenotypic data for leaf and fruit response to Xap infection were collected over 2 years at two locations. A high-density genetic linkage map that covers a genetic distance of 421.4 cM with an average spacing between markers of 1.6 cM was developed using the International Peach Single Nucleotide Polymorphism Consortium (IPSC) 9K array v1. Fourteen QTLs with an additive effect on Xap resistance were detected, including four major QTLs on linkage groups (LG) 1, 4, 5, and 6. Major QTLs, Xap.Pp.OC-4.1 and Xap.Pp.OC-4.2, on LG4 were associated with Xap resistance in leaf; Xap.Pp.OC-5.1 on LG5 was associated with Xap resistance in both leaf and fruit, while Xap.Pp.OC-1.2 and Xap.Pp.OC-6.1 on LG1 and LG6, respectively, were associated with Xap resistance in fruit. This suggested separate regulation of leaf and fruit resistance for Xap in peach as well as participation of genes involved in general plant response to biotic stress. The potential for marker-assisted selection for Xap resistance in peach is discussed.