Fine Mapping of Chilling Requirement and Bloom Date to Enable Marker-Assisted Breeding of Climate Resilient Peach

Peach (Prunus persica (L.) Batsch) fruit is a delicious summer treat appreciated for its sweet, juicy, and aromatic taste all over the globe. With only 44 calories and zero fat per fruit, peach has a great popularity among consumers and producers for its nutritional and economic value. Peach production is threatened by unpredictable climate changes, rising temperatures that reduce winter chill, especially in the warmer growing areas, resulting in fruit and yield loss. Therefore, it is necessary to develop cultivars that are resilient to environmental changes. Peach breeding takes a long time, and this process can benefit from the development of tools that can improve breeding efficiency and potentially shorten the breeding cycle. The objective of this work was to investigate the molecular basis of chilling requirement with a goal to enable breeding for targeted chilling requirement using DNA information. To accomplish this goal, we have utilized an F2 population segregating for chill requirement, to narrow down previously reported genetic regions associated with chill requirement, and germplasm to investigate haplotype diversity for this important trait in the U.S. peach breeding germplasm. This has facilitated the discovery of 34 alleles associated with different chill requirements in three major regions on chromosomes 1, 4 and 7 in peach genome. This information has been further converted to the Pp.CR Kompetitive Allele Specific PCR (KASP) based DNA assays capable of predicting chilling requirement genotype and phenotype with 95% and 69% accuracy, respectively. The observed discrepancy between the KASP predicted and actual phenotype suggests further investigation is needed in potential epistasis between the three major chilling requirement QTL regions on chromosomes 1, 4, and 7. The assays developed and validated in this project provide a rapid, user-friendly, and cost-effective option for breeders to select material with desirable CR to assist in developing peach cultivars with desired phenotype for targeted region. These assays can also be used to predict chilling requirement in peach cultivars available on the market to assist growers in choosing those that are suitable for their environment