2012 Annual Report 1a.Objectives (from AD-416): 1. Develop and characterize cucumber and melon populations segregating for fruit size. A set of segregating populations from cucumber will be analyzed for fruit size phenotype. 2. Combine genomic tools, segregating populations, and phenotypic characterization to identify loci associated with fruit size. Genetic analysis using the SNP arrays developed in this project and segregating populations for fruit size will identify QTL associated with fruit size. 1b.Approach (from AD-416): Three mapping populations will be used for phenotyping of fruit size (RIL and F2:3 families). Phenotypic data will be collected from field trials in three years (2011, 2012, and 2013) at both greenhouse and field conditions. Whole genome scan of different population segregating for fruit size will be conducted for QTL analysis to establish marker-fruit size trait associations. 3.Progress Report: Development of mapping populations. F6 and F7 recombinant inbred lines were advanced to F7 and F8, respectively by single seed descent in the greenhouse. In the 2012 field season, 145 F7/F8 recombinant inbred lines (RILs) were planted in replicated trials to collect phenotypic data for fruit size (fruit length ad diameter). Development of an integrated genetic-physical map. A high-density linkage map for cucumber was developed with simple sequence repeat (SSR) markers. The completeness of this linkage map was verified with fluorescence in situ hybridization (FISH) in the pachytene stage. Quantitative trait loci (QTL) mapping of fruit size was conducted using F3 fruit size data and the linkage mapping data. Three QTLs were identified for fruit length and diameter. Deoxyribonucleic acid (DNA) is being extracted from F7/F8. RILs will be sent to collaborators for single-nucleotide polymorphism (SNP) genotyping. This research relates to Objective 1, Determine the genetic basis of and initiate selection for carrot, onion, cucumber, and melon quality attributes influencing human nutrition and health, disease resistances, and yield and quality components, and stress tolerance in cucurbits, and perform field performance and quality trials; Objective 2, Utilize current biotechnology to discover and evaluate genetic variation and to map agriculturally important traits in Allium, Cucurbit, and Daucus germplasm, and to develop genetic and breeding stocks.