Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (2 results)

  • Multimedia
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2024)

Tomatoes are among the most important vegetable crops in human society. As the world population grows and global climate shifts, improving the long-term sustainability of tomato production is crucial. Agricultural research is currently focused on crop sustainability and productivity, and researchers are increasingly using high-throughput biological technologies to identify nuanced biological aspects of agricultural systems. There is much scientific opportunity to characterize these systems in a holistic yet incredibly detailed way by integrating results of multiple high throughput technologies towards the goal of crop system improvement. In this work, I used large-scale biological analyses to characterize tomato plant and soil biology in two greenhouse and one field experiment and identify the biological changes caused by nitrogen availability, soil stress, and differing soil management practices. I analyzed these changes to pinpoint specific molecules, pathways, and microorganisms that were especially impacted by the variables tested in each experiment. In Chapter 1, I reviewed the current use and promise of high-throughput biological technologies to inform targeted agricultural improvements. In Chapter 2, I explored the effects of chemical nitrogen fertilizer on the morphology and molecular biology of tomato plants and the composition of soil bacterial communities, allowing for a multi-layered, integrative view of exogenous nitrogen’s impact on the biological system of tomatoes grown in agricultural soil. I described the effects of agronomic management practices on soil and leaf metabolomes in a California cropping system in Chapter 3. Finally, in Chapter 4, I identified metabolic changes to soil, rhizosphere, and roots caused by soil stress and compost amendment. Taken together, my work contributes to the growing field of agricultural omics and identifies several key targets for future research aimed at improving the sustainability and productivity of tomato growing.

  • 1 supplemental ZIP
  • Article
  • Peer Reviewed
UC Irvine Previously Published Works (2020)
Contamination of edible produce leaves with human bacterial pathogens has been associated with serious disease outbreaks and has become a major public health concern affecting all aspects of the market, from farmers to consumers. While pathogen populations residing on the surface of ready-to-eat produce can be potentially removed through thorough washing, there is no disinfection technology available that effectively eliminates internal bacterial populations. By screening 303 multi-gene deletion (MGD) mutants of Salmonella enterica serovar Typhimurium (STm) 14028s, we were able to identify ten genomic regions that play a role in opening the stomatal pore of lettuce leaves. The major metabolic functions of the deleted regions are associated with sensing the environment, bacterium movement, transport through the bacterial membrane, and biosynthesis of surface appendages. Interestingly, at 21 days post inoculation, seven of these mutants showed increased population titers inside the leaf, two mutants showed similar titers as the wild type bacterium, whereas one mutant with a large deletion that includes the Salmonella pathogenicity island 2 (SPI-2) showed significantly impaired persistence in the leaf apoplast. These findings suggest that not all the genomic regions required for initiation of leaf colonization (i.e., epiphytic behavior and tissue penetration) are essential for continuing bacterial survival as an endophyte. We also observed that mutants lacking either SPI-1 (Mut3) or SPI-2 (Mut9) induce callose deposition levels comparable to those of the wild type STm 14028s; therefore, these islands do not seem to affect this lettuce defense mechanism. However, the growth of Mut9, but not Mut3, was significantly impaired in the leaf apoplastic wash fluid (AWF) suggesting that the STm persistence in the apoplast may be linked to nutrient acquisition capabilities or overall bacterial fitness in this niche, which are dependent on the gene(s) deleted in the Mut9 strain. The genetic basis of STm colonization of leaves investigated in this study provides a foundation from which to develop mitigation tactics to enhance food safety.
    Cover page: Salmonella enterica Serovar Typhimurium 14028s Genomic Regions Required for Colonization of Lettuce LeavesCreative Commons 'BY' version 4.0 license
    Top