Browsing by Subject "Grape"

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    Genetic analysis and characterization of variegation in hybrid grape populations (Vitis spp.)
    (2020-09) Olson, Jack
    Variegation is a plant trait defined by “plants which develop patches of different colors in the vegetative parts”, although variegation can express in reproductive parts of plants as well (Kirk and Tilney-Bassett, 1978). Variegation is a common trait found among a wide variety of plant species and has been reported in V. vinifera, sport mutations, and segregating in hybrid grape populations (Reisch and Watson, 1984; Filler et al., 1994; personal observation). Variegation is highly desirable in ornamental plant breeding for its showy colors and patterns, but in grape seedlings, it has been observed to have deleterious effects in the form of shorter and less vigorous plants than their wild-type siblings. Mapping the locus or loci associated with variegation would allow for the development of markers to identify parents that may carry the recessive allele for the trait, allowing for more informative decisions on population size and parental combinations when making crosses (Chapter 2). Three different mapping approaches - bulked segregant analysis (BSA), Genome-wide association study (GWAS), and genetic mapping - were utilized to detect and validate associated loci. A total of 9 hybrid grape populations were utilized in mapping, of which all 9 were used in BSA, 3 (GE1642, GE1703, GE1895) were used in GWAS and 2 (GE1642, GE1703) were used in QTL genetic mapping. BSA detected four highly significant SNP markers on chromosome 14 between the physical positions of 21,425,721 to 21,425,734 Mbp. GWAS identified 24 significantly associated markers on chromosome 14 from 27.1 to 30.1 Mbp in GE1642 and GE1895; however, 9 markers on chromosome 11 from 12.1 to 18.4 Mbp were significantly associated with variegation in GE1703. Genetic mapping of GE1642 and GE1703 mapped the variegation the same regions, which validated the region identified in GWAS. Thus, two major loci on chromosomes 11 and 14 were associated with variegation in separate hybrid grape populations. Candidate genes for variegation were identified in the two locus regions for future studies. The effects of variegation on hybrid grape were examined in a variety of experiments in which it was discovered that variegation resulted in a reduction in photosystem II efficiency; reduced leaf chlorophyll and carotenoid concentration; altered leaf palisade mesophyll structure; and had significant reductions in plant growth-related traits (Chapter 3).
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    Genetic understanding of resistance to foliar phylloxera, Daktulosphaira vitifoliae Fitch, in cold-hardy hybrid grapes
    (2020-06) Yin, Lu
    Phylloxera is an important pest infesting foliage of North American native Vitis species and cold-hardy hybrids between V. vinifera and V. riparia. Currently, chemical control is the only commonly used management method. There is a need to development integrated pest management strategies including the use of resistant varieties (Chapter 1). The effects of foliar phylloxera infestations on four grape varieties were a numeric reduction in unit yield of cluster weight, photosynthesis rate, and photosystem II efficiency. This reduction in cluster weight can be economically important to growers (Chapter 2). Most genetic studies in grape for resistance to phylloxera limited to the root. A previous study using a population, GE1025 (N=~125), detected the first quantitative trait locus (QTL), a ~15-cM region, for foliar resistance on chromosome 14. To fine map the QTL, a larger population, GE1783 (N=~1023), was created and genotyped with the rhAmpSeq technology with conserved haplotype markers across Vitis species. Through selective phenotyping using a 0-7 severity rating scale among other phylloxera severity traits on 188 potential recombinants of GE1783, we fine mapped the QTL to 2.1-4.9 Mbp on chromosome 14. A most probable candidate resistance gene plays a role in gallic acid formation (Chapter 3). To investigate antixenosis as a possible resistance mechanism, leaf trichome density was mapped in GE1025 with genotype-by-sequencing and phenotypic scores collected using a 0-6 trichome density scale at several leaf positions. Evaluations were done on forced dormant cuttings in two years and on field-grown leaves in one year. There was a ~ -0.2 correlation (r) between trichome density and phylloxera resistance. Two regions on chromosomes 1 and 10 were repeatedly detected for multiple trichome density traits. We fine mapped the chromosome 1 QTL to a 140-kb region using selective phenotyping in GE1783. We found insertion/deletion variations of the parents of the population in one candidate pseudogene in this region and three other candidate genes proposed previously (Chapter 4). In all, we identified closely linked markers that can be used for marker-assisted breeding for foliar phylloxera resistance to improve the cold-hardy hybrid grape germplasm and potential candidate resistance genes for future investigations.
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    Source, Spring-Summer 2007
    (University of Minnesota Extension, 2007) University of Minnesota Extension