2019 ASHS Annual Conference

Bacterial spot, caused by Xanthomonas arboricola pv. pruni, is a serious economic disease causing severe defoliation and black surface pitting, cracking or blemishes on peach fruit worldwide. A management option for control and meeting consumer demand for chemical-free, environmentally friendly fruit production is the development of resistant or tolerant cultivars. Resistance to bacterial spot in peach cultivars is under polygenic control. Several controlling loci in the peach genome conferring quantitative resistance were recently discovered in an F2 population. The frequency and effect of two quantitative trait loci (QTLs) with the largest effects on bacterial spot resistance in peach fruit, Xap.Pp.OC-1.2 and Xap.Pp.OC-6.1, were evaluated in a large collection of U.S. peach breeding germplasm. Previously developed SSR tests Ppe-Xap-LG1 and Ppe-Xap-LG6 (www.rosbreed.org) were partially accurate in determining Xap alleles in breeding material. Therefore, we developed Ppe-Xap DNA test based on KASP technology to aid in accuracy and efficiency in culling seedlings at the greenhouse stage. The objective of this research was to validate newly developed Ppe-Xap DNA tests, targeting the two major QTLs for fruit resistance in peach, for their prediction of fruit response to bacterial spot infection. Ppe-Xap KASP test genotyping efficiency in new peach breeding germplasm and its prediction accuracy and breeding utility in Clemson University peach breeding program will be presented.