Genetic and physiological characterization and ecological management of non-target site resistance in multiple herbicide resistant Avena fatua L.
Burns, Erin Elizabeth
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Extensive herbicide usage has led to the evolution of resistant weed populations that cause substantial crop yield losses and increase production costs. The multiple herbicide resistant (MHR) Avena fatua populations utilized in this study are resistant to members of all selective herbicide families, across five modes of action, available for A. fatua control in small grain production, and thus pose significant agronomic and economic threats. Resistance to ALS and ACCase inhibitors is not conferred by target site mutations, indicating that non-target site resistance (NTSR) mechanisms are involved. The objectives of this dissertation were to investigate the following features of NTS MHR in comparison to herbicide susceptible (HS) A. fatua: 1) inheritance and genetic control, 2) the involvement of glutathione-related enzymes, 3) differentially expressed stress-related proteins in HS and MHR redox and phosphoproteomes, and 4) the influence of abiotic and biotic stress on A. fatua demography. First, NTSR in MHR A. fatua is controlled by three separate, closely-linked nuclear genes for flucarbazone-sodium, imazamethabenz-methyl, and pinoxaden. Second, a combination of proteomic, biochemical, and immunological approaches showed that constitutive glutathione-S-transferase (GST) activities and other glutathione-related enzymes are not directly involved in enhanced rates of fenoxaprop-P-ethyl and imazamethabenz-methyl metabolism in MHR A. fatua. Instead, we hypothesize that constitutively elevated GST enzyme rates and amounts are representative of a global suite of abiotic stress-related changes in MHR plants. Third, post-translation modifications including protein phosphorylation and oxidation were compared in two-dimensional gels, showing that MHR plants contain constitutive changes very similar to systemic acquired resistance and systemic acquired acclimation to biotic and abiotic stressors, respectively. And fourth, we investigated the influence of nitrogen fertilizer rate and spring Triticum aestivum seeding density on the demography of MHR and HS A. fatua under two cropping systems (continuous cropping and crop-fallow rotation). In both systems, MHR seedbank densities were negatively impacted by increasing nitrogen fertilization rate and T. aestivum density, and density-dependent seed production was the most influential parameter impacting population growth rate. Overall, this work provides significant insights into the genetic and physiological mechanisms that confer NTS MHR in A. fatua, and presents realistic ecologically-based approaches for management.