2018 ASHS Annual Conference

Peach is one of the most important fruit crops in the world, with the global annual production exceeding 24.9 million tons. The United States is the fourth largest producer after China, Spain and Italy. Peach consumption has decreased over the last decade, most likely due to inconsistent quality of the fruit in the market. Fruit weight (FW) and diameter (FD) are important traits for market success, since consumers tend to prefer homogeneous fruits of large size. Marker assisted selection for FW and FD is at the top of the wish list for fresh market peach breeding programs and one of the major goals of the RosBREED project. The ability to use DNA information to select desirable fruit size would enable peach breeders to efficiently plan crosses and select seedlings with large FW and FD, early in the selection process before even seeing the fruit. Therefore, to understand genetic background of FW and FD in peach, we assembled pedigree connected breeding material of 620 individuals from three public fresh market peach breeding programs (Arkansas, Texas and South Carolina). The material was genotyped using 9K SNP array and FW and FD were phenotyped over two seasons. Pedigree based analysis (PBA) using both additive and dominance genetic effects identified seven QTLs on three chromosomes. Three QTLs were associated with FW on linkage groups (LG) 1 (qPP-FW_1.1), 4 (qPP-FW_4.1), and 6 (qPP-FW_6.1). Four QTLs were associated with FD; two on LG 1 (qPP-FD_1.1; qPP-FD_1.2), and one on each LG 4 (qPP-FD_4.1) and 6 qPP-FD_6.1). The strong positive correlation between FW and FD was reflected in clustering of the QTL for the two traits on LG 4. Haploblock/haplotype analyses revealed 1-3 haploblocks per QTL region with 7-31 haplotypes per haploblock. The highest number of haploblocks was detected on LG 4 (qPP-FD_4.1) and the highest number of haplotypes within the haploblock were detected in QTL qPP-FD_4.1_Hap1. The validation and characterization of functional alleles for fruit weight and size and their predictive effects, frequency and distribution in U.S. peach breeding germplasm will be presented.