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Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2017)

In this paper, we study the Cohen-Macaulay property of a general commutative ring with unity defined by Hamilton and Marley. We give sufficient conditions on pullback constructions, fixed rings, and normal monoid rings to all be Cohen-Macaulay in this sense. We also exhibit a class of quasi-local rings where the top Čech cohomology module with respect to a sequence generating the maximal ideal up to radical is non-vanishing.

    Cover page: On a Notion of Cohen-Macaulay and the Non-vanishing of Čech Cohomology ModulesCreative Commons 'BY' version 4.0 license
    • Thesis
    • Peer Reviewed
    UC Davis Electronic Theses and Dissertations (2022)

    The accumulation of salts in plant rootzones, known as “salinization,” is often a gradual process that can degrade soil structure and cause permanent plant damage. Salinization caused by ever increasing water demands and an increasingly dry climate is becoming problematic for agriculture in semi-arid to arid regions, including California’s Central Valley, which produces about one-quarter of the United States' food supply and almost half of its nuts and fruits, including grapes, according to the USGS California website (https://ca.water.usgs.gov). While grapevines are considered moderately salt tolerant (Walker et al. 2002), the current rate of salinization in many of California's vineyards is contributing to reduced crop yields and lower fruit quality (Keller 2020). Once symptoms of salt toxicity appear on the leaves, vine growth and crop yield may already be in serious decline (Fort and Walker 2011). To prevent salt toxicity from occurring in grapevines, the Walker Lab at UC Davis is applying traditional plant breeding techniques to some of the native population of wild North American grapevine species to improve the salt tolerance of commercial rootstocks (Fort et al. 2013). In recent years, the Walker Lab discovered a wild grapevine species called Vitis acerifolia 9018, which has consistently proven to be more salt tolerant than the most salt tolerant commercial rootstocks (Chen 2021). These physiological traits could be bred into existing popular commercial rootstocks to improve their salt tolerance. The research for this thesis was performed to observe the stress response and compare the salt tolerance of the recently discovered salt tolerant wild rootstock V. acerifolia 9018, against commercial rootstocks widely planted in California and other salinization-affected places, including Ramsey, 1103 Paulson and 140 Ruggeri.

      Cover page: Breeding Salt Tolerant Grapevine Rootstocks
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2016)
      The piercing-sucking mouthparts of the true bugs (Insecta: Hemiptera: Heteroptera) have allowed diversification from a plant-feeding ancestor into a wide range of trophic strategies that include predation and blood-feeding. Crucial to the success of each of these strategies is the injection of venom. Here we review the current state of knowledge with regard to heteropteran venoms. Predaceous species produce venoms that induce rapid paralysis and liquefaction. These venoms are powerfully insecticidal, and may cause paralysis or death when injected into vertebrates. Disulfide-rich peptides, bioactive phospholipids, small molecules such as N,N-dimethylaniline and 1,2,5-trithiepane, and toxic enzymes such as phospholipase A2, have been reported in predatory venoms. However, the detailed composition and molecular targets of predatory venoms are largely unknown. In contrast, recent research into blood-feeding heteropterans has revealed the structure and function of many protein and non-protein components that facilitate acquisition of blood meals. Blood-feeding venoms lack paralytic or liquefying activity but instead are cocktails of pharmacological modulators that disable the host haemostatic systems simultaneously at multiple points. The multiple ways venom is used by heteropterans suggests that further study will reveal heteropteran venom components with a wide range of bioactivities that may be recruited for use as bioinsecticides, human therapeutics, and pharmacological tools.
        Cover page: Venoms of Heteropteran Insects: A Treasure Trove of Diverse Pharmacological Toolkits
        • Article
        • Peer Reviewed
        Proceedings of the Annual Meeting of the Cognitive Science Society, Volume 36 (2014)
          Cover page: A Preliminary Meta-analysis On the Influence of Scaffolding Characteristics and Study and Assessment Quality on Cognitive Outcomes in STEM Education
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2021)

          Background

          Introgressive hybridization can reassort genetic variants into beneficial combinations, permitting adaptation to new ecological niches. To evaluate evolutionary patterns and dynamics that contribute to introgression, we investigate six wild Vitis species that are native to the Southwestern United States and useful for breeding grapevine (V. vinifera) rootstocks.

          Results

          By creating a reference genome assembly from one wild species, V. arizonica, and by resequencing 130 accessions, we focus on identifying putatively introgressed regions (pIRs) between species. We find six species pairs with signals of introgression between them, comprising up to ~ 8% of the extant genome for some pairs. The pIRs tend to be gene poor, located in regions of high recombination and enriched for genes implicated in disease resistance functions. To assess potential pIR function, we explore SNP associations to bioclimatic variables and to bacterial levels after infection with the causative agent of Pierce's disease (Xylella fastidiosa). pIRs are enriched for SNPs associated with both climate and bacterial levels, suggesting that introgression is driven by adaptation to biotic and abiotic stressors.

          Conclusions

          Altogether, this study yields insights into the genomic extent of introgression, potential pressures that shape adaptive introgression, and the evolutionary history of economically important wild relatives of a critical crop.
            Cover page: Introgression among North American wild grapes (Vitis) fuels biotic and abiotic adaptation.
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2023)
            Xylella fastidiosa is a bacterium that infects crops like grapevines, coffee, almonds, citrus and olives. There is little understanding of the genes that contribute to plant resistance, the genomic architecture of resistance, and the potential role of climate in shaping resistance, in part because major crops like grapevines (Vitis vinifera) are not resistant to the bacterium. Here we study a wild grapevine species, V. arizonica, that segregates for resistance. Using genome-wide association, we identify candidate resistance genes. Resistance-associated kmers are shared with a sister species of V. arizonica but not with more distant species, suggesting that resistance evolved more than once. Finally, resistance is climate dependent, because individuals from low ( < 10 °C) temperature locations in the wettest quarter were typically susceptible to infection, likely reflecting a lack of pathogen pressure in colder climates. In fact, climate is as effective a predictor of resistance phenotypes as some genetic markers. We extend our climate observations to additional crops, predicting that increased pathogen pressure is more likely for grapevines and almonds than some other susceptible crops.
              Cover page: Multigenic resistance to Xylella fastidiosa in wild grapes (Vitis sps.) and its implications within a changing climate.
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