Biocontrol consortium
We use a synthetic community of rhizosphere bacteria to protect crop roots from soilborne pathogens. Specifically, we utilized seven species of corn rhizosphere bacteria and demonstrated that they protect corn against the root rot pathogen Pythium ultimum, using growth chamber studies and laboratory-based investigations. Out of these seven, we found that combinations of three bacterial species further enhanced plant growth and protection from the pathogen. The work is supported by the Minnesota Corn Research and Promotion Council. This work recently received support from the USDA-NIFA Pests and Beneficial Program.
Nitrogen fixation mediated by mycorrhizal fungi
We use root symbionts, particularly arbuscular mycorrhizal fungi, that colonize more than 70% of land plants to improve nitrogen uptake. Specifically, our isotope-labeling experiments show that the presence of these root endophytes facilitates better nitrogen uptake from N-fixing bacteria. The endophytic fungi and nitrogen-fixing bacteria appear to help each other by enhancing bacterial populations and endophytic fungal colonization. We built compartmented mesocosms to have mechanistic interactions between the fungi and the bacteria. We are also testing these interactions in dwarf corn to study nitrogen dynamics during the reproductive stages of corn.
Virulence Mechanisms of Bacterial Pathogens
Clavibacter nebraskensis - Goss's Wilt and Leaf Blight in Corn
Nonpathogenic strains of many bacterial pathogens have been reported to coexist with pathogenic strains in symptomatic plants. To understand the ecology and pathogenesis of the pathogen population, it is essential to study strain dynamics in the context of the host. We created a community of 13 strains exhibiting diverse virulence phenotypes and used this community to infect the host plant. We compared the strain frequency of these strains before and after the host infection. Contrary to our hypothesis of highly virulent strains being selected by the susceptible host, we found that weakly virulent strains were selected by both resistant and susceptible host lines. We identified several genes associated with strain frequency shifts, suggesting their role in strain colonization, virulence, and fitness.
Ralstonia pseudosolanacearum - Bacterial Wilt Pathogen
Ginger, a popular tropical plant known for its culinary and medicinal uses, has been successfully grown by some farmers in southeastern Minnesota despite the region’s cooler climate. In 2023 and 2024, these farmers reported a new and concerning disease affecting their ginger crops. The symptoms included wilting, yellowing leaves, stem collapse, and rotting rhizomes with a strong odor, resulting in significant crop losses of up to 50%. Tests conducted by the Minnesota Department of Agriculture and my lab confirmed that the disease was caused by Ralstonia solanacearum species complex (RSSC), specifically phylotype I, identified through molecular diagnostics and DNA sequencing. In controlled lab tests, ginger plants infected with this strain quickly developed severe symptoms, confirming its harmful impact. This discovery is significant because it marks the first known case of this bacterial pathogen in ginger in the U.S. and raises concerns about its potential spread and impact on other crops as climate change occurs.
Ralstonia solanacearum R3bv2
Ralstonia solanacearum race 3 biovar 2 strain (R3bv2) is a high-risk pathogen and poses a threat to the production of solanaceous crops such as potatoes, tomatoes, peppers, eggplant, weedy nightshades, and ornamental plants. R. solanacearum persists in the soil and irrigation waters for a long period of time. It is also known for latent infections and attends high populations in the reservoir plants, also known as alternate hosts, particularly the ones from the solanaceous family. Minnesota is among the top ten states in terms of potato production in the US. With an already established pathway of introducing R3bv2 through geranium import, potatoes growing in the northern regions are likely to be infested. The overall goals of our proposed project are to understand the interaction of R3bv2 with potential alternate hosts and under what conditions symptoms develop. We aim to screen potential alternate hosts that are usually found near potato-growing areas. The research work will help with the management of potato brown rot by knowing conditions that favor colonization of the alternate plants and guide the detection of the pathogen in alternate hosts, soil, and irrigation water when the concerned agencies need to track the spread of the pathogen
Xanthomonas campestris - Bacterial Blight pathogen
Once considered a winter weed, Pennycress is now being developed as a promising crop for biodiesel production and high-protein livestock feed, offering climate benefits such as reducing soil erosion and nitrate runoff. Integrating pennycress with soybean farming systems could boost seed oil yields and increase farm profits by approximately $100/acre. However, disease outbreaks affecting pennycress have become more prevalent as cultivation grows, especially in the Midwest. During 2022-23 and 2024, fields in Illinois, Wisconsin, and Minnesota reported significant disease impacts, affecting 30-50% of the pennycress plants. Symptoms included spots and lesions on leaves, stems, and pods, with bacterial streaming observed from cut tissues, indicating a bacterial pathogen.
Microbiome of high-tunnels vs fields in Minnesota
We screened 300 soil samples across Minnesota (as part of the 100 Farms project) to understand the soil biology and chemistry, which vary due to different agricultural practices. We found that soil nutrient levels were already high in several high tunnels and fields that can potentially impact beneficial soil microbial activity and soil health and water resources. We used these samples to understand the impact of high levels of ammonium, nitrate, phosphorous, organic matter, and soil pH on microbial composition and function. We sequenced conserved regions of bacteria and fungi and analyzed the sequence data. Microbes living in soil exhibited different patterns depending on whether crops are grown in high tunnels or traditional fields, primarily because tunnels have significantly higher levels of nutrients, such as nitrogen and potassium. While both settings support a broad mix of beneficial microbes, field soils have more tightly connected microbial communities, which may help plants utilize nutrients and resist disease more consistently.