Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Committee Chair/Advisor

Gasic, Ksenija

Committee Member

Reighard , Gregory

Committee Member

Liang , Haiying

Committee Member

Schnabel , Guido


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. To study the genetics of the peach response to Xap, an F2 segregating population between two peach cultivars, `Clayton', a resistant phenotype, and `O'Henry', which is very susceptible to Xap, was created. Phenotypic data for leaf and fruit response to Xap infection were collected over three years at two locations: the Sandhills Research Station, Jackson Springs, North Carolina (NC) and the Sandhill Research and Education Center, Pontiac, South Carolina (SC).
Phenotypic data for leaf and fruit organs were collected with 26 data points in total. Our phenotypic data suggest that Xap resistance in peach is a quantitative trait, and leaf and fruit resistance is regulated by separate genetic factors. In addition, relative humidity higher than 80% from petal fall to shucks off (gererally from March 15th to April 15th) plays a significant role on the occurrence of Xap disease incidence and severity.
A genetic map was initially developed using SSR markers, however, only thirteen SSR markers were put on the linkage map. Therefore, sixty three individuals exhibiting high tolerance/resistance to Xap were genotyped with an IPSC 9K peach SNP array v1. Out of 8,144 SNPs 1,341 were used to construct a high-density genetic linkage map. This map covers a genetic distance of 421.4 cM with an average spacing of 1.6 cM and is used for mapping QTLs responsible for Xap in peach. 95% of the mapped SNP markers on the linkage map showed consistency with the marker order on the peach genome v1.0 assembly. A QTL analysis revealed 14 QTLs involved in Xap resistance: 3 on linkage group (LG) 1; two on each LG2, 3, 4 and 8; and one on each LG5, 6, and 7. One major Xap.Pp.CO-4.1 on LG4 was associated with Xap resistance in leaf, and one major QTL Xap.Pp.CO-5.1 on LG5, was associated with Xap resistance on both leaf and fruit and two major QTLs. While Xap.Pp.CO-1.2 and Xap.Pp.CO-6.1 on LG1 and 6, was associated with Xap resistance in fruit.



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