Browsing by Subject "Phylloxera"

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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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    Investigating Novel de Novo Meristem Induction Through a Direct Delivery Gene Editing Technique in Greenhouse Grown Apple and Grape
    (2023-02) Spicer, Robert
    Apple and grape are woody fruit crops with a significant global market. The process of conventional breeding of woody fruit crops is a lengthy process that takes decades to produce commercially viable cultivars due to heterozygosity, self-incompatibility, and long juvenile periods. Genome editing technologies have become an alternative breeding method to traditional plant breeding techniques to bypass the time and resource limitation in current breeding programs. Currently, one of the most prominent gene editing technologies in plants is CRISPR/Cas9 that can be used to produce targeted changes for specific attributes comparable to conventional breeding but in a faster and more predictable manner. The efficiency of Cas9 for crop improvement has been studied in grape and apple as explants or somatic embryos but the efficiency of this technology in soil grown plants is understudied. This study investigates novel de novo meristem gene editing in soil grown apple and grape to develop and test methods for direct delivery of Cas9 and sgRNA for targeted gene knockouts in non-model species. Plasmids programmed with Cas9, sgRNA, developmental regulators, and bioluminescent reporter were injected into designated nodes in planta at different growth stages with varying Agrobacterium cell concentration treatments. We also investigated variations in preparing plants for injection by node ablation, tissue types, plant preparation, and experimental setups. After selecting for shoots with suspected gene edits, tissue was assayed for luciferase expression and knockout verification using PCR. No evidence of a gene knockout was observed through phenotypic observations or with luciferase and PCR assays. Early preliminary experiments had high rates of plants with inactive shoot growth but were useful in designing optimized experiments with substantially lower rates of inactivity. Abnormal shoot growth was observed in apple seedling experiments as well as gall-like formations. Both abnormal shoot growth patterns and gall-like formations were observed ubiquitously in all treatment groups. Young non-woody plant tissue was more susceptible to desiccation than lignified tissue, but some plants were capable of new shoot growth despite having desiccated stems. Method development remains important to improve the efficiency regeneration and increase the likelihood of gene edits.