Browsing by Subject "Biocontrol"
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Item Characterizing A Soybean Cyst Nematode Mycobiome From Waseca Long-term Soy-corn Rotation Experiment in Search of Fungal Biological Control Agents and Bio-nematicides(2020-05) Rajendran, DeepakThe Soybean Cyst Nematode (SCN, Heterodera glycines) is the most economically consequential pathogen of the soybean plants worldwide. Integrated management of this pathogen currently relies on using genetic resistance and crop rotation with a non-host such as corn. Additional help from chemical and biological agents could lead to better management of this pathogen by supplementing the biological limitations of genetic resistance and economical limitations of using a non-host crop. Identifying natural antagonists of SCN is a good first step towards finding potential biocontrol agents. In this study, I have cultured and identified fungi from 6000 SCN cysts obtained from a long-term soy-corn rotation experiment with no nematicide applied, over a period of 3 years. ITS barcode sequences from all the isolates (about 5000 from 6000 cysts) obtained from these cysts, as well as their colony morphologies were used to identify the fungi against NCBI database. ITS sequences were then used to cluster them into 326 OTU groups based on at least 99% sequence similarity. OTU cluster representatives were evaluated in vitro for their ability to produce anti-nemic metabolites and to directly parasitize SCN eggs. Ten high anti-nemic metabolite producers (‘A’ through ‘J’) and ten high parasitic fungi (‘K’ through ‘T’) were then evaluated in vivo using a growth chamber-based cone-tainer assay. Top three performers in the cone-tainer assay, isolates ‘D’, ‘E’ and ‘T’ were subsequently evaluated in greenhouse potted plant assays. Isolates ‘E’ and ‘T’ were as good as commercially available biocontrol agent Melocon WG, even at 40-400 folds lower concentration.Item Control of the common carp through species-specific toxin delivery systems and biocontrol by bluegill sunfish(2018-03) Poole, JoshuaThe Common carp (Cyprinus carpio, or ‘carp’) is an invasive fish native to Eastern Europe and Asia and is one of the world’s most ecologically harmful species. It is known to cause issues with water clarity, increase nutrient levels, reduce aquatic vegetation, and impact waterfowl. There are many existing strategies to control carp, however, each have various issues. This has led to the search for more practical, sustainable, or broadly applicable control strategies. I investigated two emerging control strategies for carp: biocontrol of carp by bluegill sunfish, and selective toxin delivery systems. Biocontrol has been used successfully for decades in the agriculture industry; however, biocontrol for aquatic pest control is still rudimentary. Previous evidence has suggested that bluegill sunfish (Lepomis macrochirus) may be capable of controlling carp recruitment by consuming eggs and larvae of carp, however, this has never been tested in natural, whole-lakes. To test if bluegill were capable of limiting carp recruitment in natural lakes, I conducted a two-year experiment where carp were stocked into natural lakes, and bluegill were stocked in half of the lakes. The recruitment success of carp was assessed at various stages in first growing season of development: (1) the egg stage, (2) the post-larval juvenile stage, and (3) the end-of-season juvenile stage. The results indicate that bluegill predation had a major effect on the egg stage and the abundance of post-larval carp, but the abundance of end-of-season carp were affected by other processes (such as density-dependence). This is the first experiment to my knowledge that has conducted an experiment on biocontrol of a fish using multiple whole-lake manipulations. This may provide the most robust evidence to date that bicontrol of a fish is possible in natural systems. Next, I performed an analysis to examine lake characteristics that cause bluegill abundance to be low, and thus define conditions where bluegill density is too low to control carp through biocontrol. My model incorporated 12 lake and watershed variables that were used to explain variation in bluegill sunfish catch-per-unit-effort (CPUE). Of those variables, depth and water clarity had the largest effect. Specifically, bluegill abundance declined rapidly in lakes with maximum depths of less than 7 m, and a secchi disk depth less than 0.7 m. These conditions are indicative of lakes that winterkill, thus aeration may be a feasible way to stabilize bluegill populations in these systems. Last, I incorporated antimycin-a (ANT-A), a known fish toxicant, into a corn-based bait and conducted a series of experiments to determine its toxicity, leaching rate, and species-specificity. My results showed that ANT-A was lethal to carp at doses ≥ 4 mg/kg and that the amount of ANT-A that leached out of the bait in 72 h was not lethal to carp or bluegill (Lepomis macrochirus). Species-specificity trials were conducted in 227 L tanks, in which carp were stocked with three native species representing families that occur sympatrically with carp in my study region: the fathead minnow (Pimephales promelas), yellow perch (Perca flavescens) and bluegill. These trials showed high mortality of carp (46%) and fathead minnows (76%) but no significant mortality of perch or bluegill. Finally, a pond study, which used the same species composition except for fathead minnows, resulted in 37% morality among adult carp and no mortality among perch or bluegill. My results suggest that corn-based bait that contains ANT-A could be used to selectively control carp in ecosystems dominated by percids or centrarchids, such as lakes across the Great Plains ecoregion of North America, where carp are especially problematic.Item The Development of a Plant-Growth Promoting Biocontrol Cocktail Using Microbiological Methods and Functional Genomics to Mitigate Salmonella enterica Typhimurium 4/74 Contamination in Alfalfa Sprouts(2022-08) Vitt, JacobSalmonella enterica is a serious threat to public health that is responsible for the vast majority of reported Salmonella outbreaks annually. Despite interventions from private industry and governmental agencies, Salmonella’s main mode of transmission continues to be foodborne, thus eliminating Salmonella reservoirs in the food supply chain is critical to controlling this pathogen. Fresh sprouts present a unique food safety challenge due to minimal processing and ideal growth conditions created during sprouting. Currently, sprout producers have implemented interventions such as seed decontamination, regular pathogen testing of irrigation water and harvested sprouts, and post-harvest treatments. However, an intervention has yet to be introduced during the sprout germination process when conditions are the most optimal for Salmonella growth and proliferation. To address the current gap in pathogen reduction, great interest has been put towards the use of bacterial biocontrol agents to reduce Salmonella contamination during sprout germination.In this thesis, two research goals were established. The first goal was focussed on isolating/characterizing plant-associated bacteria from alfalfa sprouts and subsequently formulating a cocktail of plant-associated bacteria that would function as a biocontrol agent to reduce Salmonella contamination on alfalfa sprouts. This biocontrol cocktail was then assayed for its ability to positively impact alfalfa biomass production and reduce Salmonella cell density on alfalfa sprouts. A plant-associated bacterial cocktail was composed of Pantoea agglomerans, Priestia megaterium, Pseudomonas koreensis, and Pseudomonas putida KT-2440. With a complex community of plant-associated bacteria, the cocktail was found to increase alfalfa biomass production by 25% when compared to uninoculated seeds while not causing a detriment to the overall shelf-life of harvested alfalfa sprouts. Furthermore, the cocktail led to a 3.1 log reduction of Salmonella Typhimurium 4/74 on the sprout surface after six days of germination. The second goal was centered on utilizing a functional genomics approach through transposon insertion sequencing to determine Salmonella conditional gene essentiality to the colonization and infection of alfalfa sprouts. From identified conditionally essential metabolic genes, metabolites produced by alfalfa or metabolites inherent to the sprout germination environment can be targeted for consumption by biocontrol agents. Therefore, the results of the transposon insertion sequencing study could then be used to guide the process of formulating a biocontrol cocktail specifically tailored towards the consumption of metabolite targets to ultimately decrease Salmonella cell density on alfalfa sprouts. Due to time limitations, the results of the transposon insertion sequencing study were not available prior to the submission of this thesis for review, and the results were not included.Item The ecology and evolution of an invasive perennial plant (Lythrum salicaria) in the context of biological control by specialist herbivores (Galerucella spp.)(2013-09) Quiram, Gina LouiseThe introduction of non-native species to novel ranges has provided biologists the opportunity to study organisms experiencing sudden and sustained shifts in community composition and selection pressure. Management programs for invasive species can result in similar shifts. In classical biological control programs, non-native species are introduced to control invasive species. The short-term impacts of these introductions on invaded communities are often well documented, but the long-term impacts on the ecology and evolution of target invasive species are not well understood. Using a combination of field surveys, common garden techniques, and quantitative genetic models, I examined the effect of biological control by specialist herbivores (Galerucella spp.) on purple loosestrife (Lythrum salicaria L.) in southern Minnesota (MN), USA. Chapter 1 describes field surveys completed to determine the extent to which biological control directly reduces plant vigor, competitive performance, and reproduction. In Chapter 2, I quantify the extent to which population level variation in vigor, competitive performance, herbivore defense, and herbivore tolerance of L. salicaria reflects an evolutionary divergence following the introduction of biological agents. Finally, in Chapter 3 I assess the potential for L. salicaria to evolve in response to continued selection pressure. The results of these studies show that Galerucella spp. biocontrol agents remain established and continue to feed on L. salicaria in southern MN, but do not universally reduce the vigor, competitive performance, or reproduction of the plant in field populations as compared to populations lacking established populations of biocontrol agents. When grown in a common environment, an experimental garden, populations of L. salicaria having experienced herbivory by Galerucella spp. for 16 years are more vigorous, marginally more competitive, and marginally more tolerant of herbivory compared to populations lacking a historical association with the herbivore. In MN, L. salicaria is currently under selection pressure for increased vigor, and the plant has the genetic capacity to adapt in response to this selection pressure. Further evolution of L. salicaria could decrease the effectiveness of biological control by Galerucella spp.Item Effects of bluegill predation, lake productivity, and juvenile dispersal on common carp recruitment dynamics in lake-marsh systems in Minnesota(2016-02) Lechelt, JosephProcesses that regulate common carp (Cyprinus carpio) recruitment (i.e. survival of eggs, larvae and juveniles) are largely unknown. In interconnected lake-marsh systems of Minnesota, young of year (YOY) carp are generally found in marshes that winterkill and lack bluegill sunfish (Lepomis macrochirus), an abundant native predator. This suggests that bluegills might function as a biocontrol agent for carp. Further, whereas YOY carp are commonly found in winterkill marshes of south-central Minnesota, they are not found in similar systems in northern Minnesota where lake productivity is much lower, suggesting an aquatic productivity bottleneck on carp recruitment. Finally, in marshes where carp recruit (productive and bluegill-free), YOY must disperse into adjacent lakes to drive high population abundance. In this study, I conducted three experiments to test 1) the effect of bluegills on carp recruitment; 2) the effect of aquatic productivity on larval carp survival, growth and diet; 3) natural dispersal tendencies of YOY carp from a marsh into an adjacent lake. The first experiment employed four (20 m diameter) impermeable enclosures from 2011-2014. Each year, enclosures were stocked with carp eggs and every other one was stocked with bluegills. Backpack electrofishing surveys conducted five weeks later showed that carp catch per unit of effort (CPUE) was over 10-fold lower in the enclosures stocked with bluegills than in the controls. The second experiment, conducted in 2014 and 2015 used aquaria stocked with carp larvae and supplied with zooplankton densities and community structures from lakes of three different trophic states (oligo-, meso-, and eutrophic). It showed that carp larvae selectively consumed macrozooplankton (> 200 μm) and their growth rates were highest in the eutrophic lake and lowest in the oligotrophic lake. Survival, however, was high in all treatments. The third study was conducted in a natural lake-marsh system and utilized passive integrated transponder (PIT) tags to quantify the outmigration of YOY carp from the marsh to the lake. It showed that < 6% YOY carp outmigrated to the lake, supporting previous indirect estimates. The results of these three studies are important to understanding recruitment dynamics of carp in lake-marsh systems in Minnesota.