** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** SUSCEPTIBILITY OF COMMERCIAL APPLE CULTIVARS TO APPLE SCAB ALONG WITH THE CONTINUAL EMERGENCE OF NEW PATHOGENIC STRAINS HAVE PREVENTED WIDESPREAD ADOPTION OF LOW-INPUT APPLE PRODUCTION, ESPECIALLY IN THE HUMID EASTERN AND MIDWESTERN U.S. SOURCES OF APPLE SCAB RESISTANCE HAVE BEEN IDENTIFIED, BUT THEIR USE IN BREEDING IS HINDERED BY LACK OF CHARACTERIZATION OF FUNCTIONAL ALLELES AND AVAILABILITY OF DIAGNOSTIC MARKERS. LINKAGE GROUP 1 OF APPLE HARBORS TWO MAJOR APPLE SCAB RESISTANCE LOCI IN CLOSE PROXIMITY TO A PREVIOUSLY WELL-CHARACTERIZED APPLE SCAB RESISTANCE GENE HCRVF2. HERE, WE PROPOSE TO FINE-MAP, IDENTIFY, AND VALIDATE CANDIDATE GENE FUNCTION, AS WELL AS DEVELOP DIAGNOSTIC MARKERS FOR TWO MAJOR APPLE SCAB RESISTANCE LOCI. AVAILABILITY OF TIGHTLY-LINKED DIAGNOSTIC MOLECULAR MARKERS AND CHARACTERIZED FUNCTIONAL ALLELES FOR THESE LOCI WILL PROVIDE OPTIONS TO DEVELOP APPLE CULTIVARS WITH DURABLE DISEASE RESISTANCE BY PYRAMIDING MULTIPLE SCAB RESISTANCE LOCI THROUGH BREEDING AND BIOTECHNOLOGY. TO FINE-MAP THIS GENOMIC REGION AND IDENTIFY CANDIDATE GENES, WE WILL ALSO ASSEMBLE A HIGH-QUALITY GENOME OF 'ANTONOVKA', AN IMPORTANT CULTIVAR FOR APPLE BREEDING. THE GENOME ASSEMBLY WILL BE VALUABLE TO PURSUE FURTHER GENOMICS, GENETICS, AND BREEDING OF OTHER COMMERCIAL APPLE TRAITS. THIS PROJECT ADDRESSES THE 'PRE-BREEDING AND GERMPLASM ENHANCEMENT' PRIORITY OF THE A1141 PROGRAM AND ALL USDA ROADMAP FOR PLANT BREEDING PRIORITY NEEDS, PARTICULARLY (I) CHARACTERIZATION OF GENETIC RESOURCES; AND (IV) DEVELOPMENT OF NOVEL TOOLS TO EXPLOIT GENETIC RESOURCES. ULTIMATELY, THE OUTCOMES OF THIS PROJECT WILL SIGNIFICANTLY REDUCE FUNGICIDE USE, COST OF SPRAYS, AND SOCIAL AND ECONOMIC IMPACTS OF FRUIT QUALITY LOSS FROM APPLE SCAB