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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Research Project #441435

Research Project: Validating Bacterial Spot Resistant Markers to Ensure Reliable Marker-assisted Selection of Peaches

Location: Fruit and Tree Nut Research

Project Number: 6042-21000-006-009-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Oct 1, 2021
End Date: Jun 30, 2025

This is a new proposal requesting for funding for the first year of a 4-year project. The bacterial spot resistance/susceptibility rating data will be collected in leaf thrice and fruit once (whenever ripe and ready for evaluation) each year from peach cultivars and advanced selections maintained in the variety blocks at the USDA-ARS-SEFTNRL stone fruit breeding program. Three years of replicates are essential for rigorous statistical analysis because the trait can be influenced by weather conditions and other non-genetic factors (e.g., orchard management). The markers in the mapped bacterial spot resistance region will be used to genotype all the same materials and collect the marker and allele data. The goal is to collect both phenotypic and genotypic data on bacterial spot resistance that can be used to validate in a large number of peach materials. The data is also helpful for breeders to determine the haploid types or alleles specific to resistance and susceptibility in peaches and use the information in marker-assisted selection in peach breeding.

The proposed research includes field rating of bacterial spot resistance/susceptibility and lab genotyping to collect marker allele data on about 700 peach materials maintained in the variety blocks at the USDA-ARS Southeast Fruit and Tree Nut Research Laboratory, Byron, Georgia. Bacterial spot resistance/susceptibility will be rated on leaf and fruit at a 0-5 scale, respectively, as previously described (Yang et al., 2013). Briefly, for leaf, a rating of 0 – no symptomatic leaf and 1-5 – diseased or defoliated leaves at approximately 1-5%, 6-10%, 11-25%, 26-50%, and >50%, respectively. For fruit, a rating of 0 – no symptomatic fruit and 1-5 – approximately 1-5%, 6-10%, 11-25%, 26-50%, and >50% sampled fruit with lesions, respectively. Each year the rating of leaf will be performed thrice (April, July, and October) and that of fruit once (whenever ready for fruit evaluation). DNA extraction and marker genotyping will be performed in the first two years following the protocols used in the lab (Chen and Okie, 2017). Briefly, tender leaves will be collected and used in the DNA extraction. Marker genotyping will be performed in an ABI Genetic Analyzer 3500 (Thermo Fisher Scientific, Waltham, MA) and the chromatographic files will be analyzed using GeneMarker (SoftGenetics, State College, PA) to generate the alleles from all the peach materials. A statistical analysis will be performed in the third year on the field phenotypic rating data that will subsequently be compared with the marker genotyping data to validate the reliability and level of association between the bacterial spot resistance trait and the alleles. Meanwhile, new markers in the mapped regions will be developed from the peach reference genome in the third and fourth years and tested in additional genotyping to refine the markers in the mapped regions and improve the trait and marker association and the marker specificity. The research will primarily be done at the USDA-ARS-SEFTNRL, Byron, Georgia.