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ARS Home » Southeast Area » Charleston, South Carolina » Vegetable Research » Research » Research Project #434575

Research Project: Genomics and Genetic Improvement of Disease Resistance and Horticultural Characteristics of Watermelon, Broccoli, and Leafy Brassicas

Location: Vegetable Research

Project Number: 6080-21000-019-00-D
Project Type: In-House Appropriated

Start Date: Apr 11, 2018
End Date: Apr 10, 2023

Objective:
Objective 1. Develop genomic tools and use them to develop and release watermelon germplasm with improved disease resistance, combined with desirable fruit quality and other consumer- and commercially-relevant horticultural traits. Sub-objective 1.A. Utilize an identified major quantitative trait locus (QTL) for Fusarium wilt Race 2 resistance to develop sequence-based markers as selection tools to aid the incorporation of resistance into enhanced watermelon germplasm with desirable fruit characteristics. Sub-objective 1.B. Utilize the watermelon genome sequence to develop a single nucleotide polymorphism (SNP)-based linkage map for the desert watermelon (Citrullus colocynthis) and identify markers associated with resistance to Papaya ring spot virus (PRSV). Sub-objective 1.C. Develop and release watermelon germplasm with improved disease resistance from a wild watermelon type combined with improved fruit characteristics of cultivated types. Objective 2. Develop and release broccoli germplasm with improved adaptation to high temperature environments and other commercially- and consumer-relevant horticultural traits. Sub-objective 2.A. Breed and release broccoli lines with enhanced tolerance to high temperature by exploiting additional, new tolerance alleles, and identify genomic sequences associated with the tolerant phenotype. Sub-objective 2.B. Determine if elite broccoli inbreds that are vigorous and highly self-compatible can produce head yield and quality comparable to that of commercial hybrid broccoli cultivars. Objective 3. Utilize genetic diversity in leafy green Brassicas (B.) to develop germplasm with improved commercially- and consumer-relevant traits. Sub-objective 3.A. Determine mode of inheritance of resistance to Pseudomonas cannabina pv. alisalensis (Pca) in a B. rapa accession with turnip-like leaves. Sub-objective 3.B. Exploit phenotypic diversity in a unique collection of collard landraces collected from southern seed savers to develop a B. oleracea collard with resistance to Pca and another collard that expresses relatively high levels of the glucosinolate glucoraphanin.

Approach:
Parental lines of watermelon, broccoli or leafy green Brassicas will be selected based on phenotypic expression of resistance, tolerance or quality traits under study. The selected parental lines will then be utilized to construct conventional (i.e., F2, BC1, recombinant inbred) and doubled haploid (for broccoli only) populations segregating for the traits of interest. These populations will in turn be used in studies to determine mode of inheritance of each character or to select new, more superior lines. Modern techniques like genotyping by sequencing or quantitative trait locus (QTL) seq will be employed to identify DNA sequences associated with the traits of interest and to locate controlling genes on genetic linkage maps. Key DNA sequences will be used to develop strategic markers, e.g. kompetitive allele specific primer (KASP) markers, that are closely linked to the traits under study and that can be used in marker-assisted selection strategies. Knowledge gained in the above studies will be applied in developing improved breeding approaches and in fine-tuning marker-assisted methods to use in the further development of enhanced horticultural lines or hybrids that express improved resistances or tolerances and other traits of interest and that also produce high quality vegetable products. The improved plant germplasm will be made available through public releases or commercial licensing. Ongoing searches for new resistances or tolerances among watermelon and vegetable Brassica accessions from the U.S. Plant Introduction and other collections will also be conducted.