Location: Crop Genetics and Breeding Research
2024 Annual Report
Objectives
1. Deployment of root-knot nematode resistance in cotton and peanut.
1.A. Determine the economic value of growing nematode-resistant vs. a susceptible cultivar in continuous and rotated peanut.
1.B. Evaluate the economic effect of growing M. incognita-resistant cotton in fields with damaging levels of the nematode.
2. Identify and screen nematode resistant crops that can be grown in rotation with cotton and peanut.
2.A. Identify sources of resistance to Meloidogyne incognita in sorghum that differ from known sources of resistance.
2.B. Identify sorghum cultivars that are poor hosts for Pratylenchus brachyurus and Meloidogyne arenaria.
3. Increased understanding of the interactions between plant-parasitic nematodes and the soil microbiology community and how that contributes to disease.
3.A. Evaluate the interactions of nematode parasitism, the salicylic acid (SA) and jasmonic acid (JA) plant defense pathways, and Fusarium oxysporum f.sp. vasinfectum in the Fusarium wilt disease complex in cotton.
3.B. Investigate the contribution of predatory nematodes in suppressing root-knot nematodes.
3.C. Identify the host and environmental factors that influence the attachment of Pasteuria penetrans spores to Meloidogyne arenaria.
Approach
The long-term goal of our research is to develop integrated approaches for managing plant-parasitic nematodes in cotton and peanut. Host-plant resistance is the most consistent means of reducing yield losses from nematodes. Our research will investigate the most effective deployment of resistance in cotton and peanut for improving yield and economic returns. For sustainable long-term production, farmers cannot rely solely on host-plant resistance for managing plant-parasitic nematodes. Therefore, we will investigate other management options. We will identify crops that can be grown in rotation with cotton and peanut that will reduce population densities of damaging nematodes. Biological control organisms are being marketed for use in cotton and peanut, and they also occur naturally in fields. We will investigate the contribution of predatory nematodes to suppression of root-knot nematodes and the environmental factors that influence the susceptibility of these nematodes to their host-specific bacterial pathogen, Pasteuria penetrans. Nematodes commonly interact synergistically with other plant pathogens to cause greater crop losses. We will investigate how nematodes interact with cotton’s innate defense systems and whether that plays a role in the Fusarium wilt disease complex.
Progress Report
Both technician positions on this CRIS were new hires in the summer of 2023, so training in the standard nematology methods used in these research projects (e.g., culturing and using nematodes for inoculum, extracting nematodes from soil samples, and nematode identification) took significant time, which delayed progress on some projects. Additionally, a new scientist, who also started in the summer of 2023 and took over the projects originated by her predecessor, was on medical and maternity leave for several months during the year, which delayed progress on some projects. However, progress was made on all three objectives.
The field project to evaluate the economic value of resistant peanut (Subobjective 1A) was delayed because the new scientist did not start until midway through the 2023 crop season. However, that project is now underway.
The field experiment to evaluate the economic benefit of growing nematode-resistant cotton (Subobjective 1B) had lower than desired nematode damage in 2023, so an additional (final) year of field testing is being conducted in 2024.
The greenhouse project to identify new sources of resistance to Meloidogyne incognita in sorghum (Subobjective 2Aa) is in its final stages and a manuscript is in preparation. Unfortunately, we were unable to identify significant new sources of resistance in commonly used breeding material. Phenotyping the sorghum association panel (SAP) is underway (Subobjective 2Ab). The project evaluating candidate resistance genes in mutant sorghum lines (Subobjective 2Ac) was unsuccessful because the mutants had far more mutations than we originally believed and therefore were unsuitable for the planned experiments. The series of greenhouse experiments to identify sources of resistance to Meloidogyne arenaria and Pratylenchus brachyurus (Subobjective 2B) were delayed until the new scientist joined the CRIS, but they are underway now.
Projects to evaluate the interactions of nematode parasitism, the salicylic acid (SA) and jasmonic acid (JA) plant defense pathways, and Fusarium wilt in cotton (Subobjectives 3Aa, 3Ab, and 3Ac) were delayed by critical technician vacancies. Additionally, the methods reported for measuring SA and JA in other plant species did not work for cotton, so significant time has been spent developing new methods of measuring those compounds in cotton. Those methods have now been established and the planned experiments are being started.
The project to investigate the role of predatory nematodes in the suppression of root-knot nematodes (Subobjective 3B) was delayed until the new scientist joined the CRIS, but those studies are underway now.
Progress was made regarding studies to identify the host and environmental factors that influence the attachment of Pasteuria penetrans to Meloidogyne arenaria (Subobjectives 3Ca and 3Cb) through the publication of a journal article in Evolutionary Applications (Do biological control agents adapt to local pest genotypes? A multiyear test across geographic scales). Local adaptation of a parasite to its pest host has rarely been studied in agricultural systems. In collaboration with scientists from the University of Virginia, we evaluated attachment of the bacterium Pasteuria penetrans to its nematode host, root-knot nematodes (Meloidogyne arenaria), both within and between peanut fields. In only one of four years did we find that P. penetrans had greater attachment to its local host compared to distant hosts; therefore, we conclude no strong support for local adaptation of P. penetrans to root-knot nematodes. Regarding soil type and crop plant influence, a field trial was established in June 2024 that will be sampled over the growing season for P. penetrans and M. arenaria. Vetch was planted in this field in late 2023 to assist in maintaining population densities of M. arenaria.
Additionally, ARS researchers at Tifton, Georgia are involved in the Fertilize 4 Life initiative, which is an agreement involving USDA-ARS, Embrapa, USDA-FAS, the University of Florida, and the International Fertilizer Development Center. Money received from this agreement will aid ARS researchers in Tifton, Georgia to advance soil health assessments in the U.S. and Brazil. We will determine site-specific effects of agricultural conservation practices on biological, physical, and chemical soil health indicators and soil functions. Furthermore, we will evaluate and improve dynamic assessment tools (i.e., SHAPE, SoilBio, and nematode ecological indices) to quantify site-specific soil health response to land management. Literature review is underway. This work is related to Objective 3.
We also received funds from the OTT Pilot Initiative (ARSX 2022) to perform work on improved nematode extraction methods. Nematode cultures were started in the greenhouse to begin this project.
Accomplishments
1. New methods were developed for measuring jasmonic acid (JA) levels in cotton. Jasmonic acid and salicylic acid (SA) are primary compounds involved in the innate plant defense systems against pathogens, including nematodes. However, published methods for measuring JA levels in plants were found to be unsuccessful for measuring the levels in cotton. ARS and University of Georgia researchers in Tifton, Georgia developed new methods for measuring JA levels in cotton. This new method will allow research into the role of the SA and JA plant defense systems in host-plant resistance and pathogen interactions in cotton, including the interaction of nematodes and a fungal pathogen in Fusarium Wilt disease of cotton.
2. No clear evidence for local adaptation of a parasite to its nematode host. Local adaptation of a parasite to its pest host has been rarely studied in agricultural systems. ARS scientists in Tifton, Georgia in collaboration with scientists from the University of Virginia evaluated attachment of the bacterium Pasteuria penetrans to its nematode host, root-knot nematodes (Meloidogyne arenaria), both within and between peanut fields. In only one of four years they found that Pasteuria had greater attachment to its local host compared to distant hosts; therefore, there was no strong support for local adaptation of Pasteuria to root-knot nematodes. This work paves the way for future research in biologically based disease management strategies and furthers our understanding of this important predator-prey relationship.
Review Publications
Schumacher, L.A., Liao, H., Small, I.M., Grabau, Z.J. 2024. Vertical distribution of plant-parasitic nematodes in peanut-cotton cropping systems. Applied Soil Ecology. 200:105445. https://doi.org/10.1016/j.apsoil.2024.105445.
Davis, R.F., Harris-Shultz, K.R., Knoll, J.E., Krakowsky, M.D., Scully, B.T. 2024. A quantitative trait locus on maize chromosome 5 is associated with root-knot nematode resistance. Phytopathology. 114(7):1657-1663. https://doi.org/10.1094/PHYTO-08-23-0286-R.