Location: Crop Genetics and Breeding Research
2022 Annual Report
Objectives
1. Identify and characterize nematode resistance genes and work with breeders to combine them with commercially valuable agronomic traits in cotton and peanut.
1.A. Determine the phenotypic expression of Meloidogyne arenaria resistance in peanut isolines 48 (moderate resistance) and 46 (high resistance).
1.B. Evaluate the phenotypic expression of the Meloidogyne incognita resistance QTLs qMi-C11 and qMi-C14 in cotton isolines.
1.C. Identify sources of resistance to Meloidogyne incognita in cotton that differ from Auburn 623 RNR.
1.D. Identify specific Meloidogyne-resistance genes within quantitative trait loci (QTL) regions and determine their functions in cotton and peanut.
2. Evaluate antagonist-nematode interactions, and develop novel integrated strategies, including biological control methods for management of nematodes in cotton, peanuts, and biofuel crops.
2.A. Evaluate environmental factors that influence Pasteuria penetrans endospore movement in soil and attachment to nematodes.
2.B. Monitor changes in adhesion phenotypes of Pasteuria penetrans to determine the drivers of phenotypic/genetic changes occurring in a population of the bacterium and its host, Meloidogyne arenaria.
2.C. Evaluate factors that affect the general suppression of Meloidogyne spp. in field soil.
2.D. Evaluate integrated management options including resistance, suppressive cover crops, and an improved decision model for managing Meloidogyne incognita.
Approach
Field and greenhouse experiments will be conducted to develop management options for root-knot nematodes in cotton and peanut. We plan a multi-tactic approach utilizing host-plant resistance (Objective 1), crop rotation, antagonistic crops, seed treatments, and biological control (Objective 2). Host-plant resistance to nematodes is the cornerstone of our strategy. We will determine mechanisms of resistance in cotton and peanut, determine effects of nematode resistance genes on the Fusarium wilt disease complex in cotton, and try to identify new resistance QTLs in cotton. However, we cannot rely exclusively on host-plant resistance for managing nematodes. We will also investigate ecologically based control strategies that can be integrated with resistant cultivars to increase the durability of resistance and control a broader spectrum of nematodes. Specifically, we will evaluate factors that influence the ability of the nematode-parasitic bacterium Pasteuria penetrans to suppress nematodes; determine whether frequency-dependent selection occurs between the bacterium and its host; and determine whether considering P. penetrans abundance improves nematode management decisions. We will evaluate the effects of winter cover crops on the natural suppressiveness of soils to nematodes; evaluate integrated management options including combining high residue rye with resistant cotton cultivars and nematicidal seed treatments; and evaluate nematode suppression and crop damage in the novel crop rotation of cotton with double cropped sweet sorghum (summer crop) and sugar beet (winter crop).
Progress Report
This is the final report for project 6602-21220-016-000D (terminated March 28, 2022), which has been replaced by a new project 6048-21220-019-000D, "Integrated Management of Nematodes in Southeastern Field Crops".
We demonstrated that the two known quantitative trait loci (QTLs) in cotton for resistance to root-knot nematode (RKN) have different modes of action with one inhibiting an early stage of nematode development and the other inhibiting a later stage. We further demonstrated that despite having different modes of action, both QTLs equally reduce the number of nematode eggs per egg mass. Although only one QTL interferes with the nematode establishing a feeding site, neither QTL significantly increases nematode egression from cotton roots nor reduces the size of the root gall created by the nematode. The specific resistance genes within the two QTLs are not known. We identified differentially expressed genes within the two QTLs in susceptible and resistant cotton during nematode infection and development, which allowed us to identify genes possibly involved in the resistance response. Currently, there is only one available source of resistance to the peanut root-knot nematode (PRKN) in peanut. Using marker-assisted selection (MAS), two new genes for resistance to PRKN were transferred from the wild peanut species Arachis stenosperma into cultivated peanut thereby imparting high levels of resistance. We successfully used MAS to rapidly incorporate a high level of RKN resistance into a diverse group of previously susceptible sorghum lines thereby proving that the resistance gene could be widely and easily utilized in sorghum breeding.
Pasteuria penetrans, a bacterial parasite of RKN, is endemic to sandy soils in the Southeast. We demonstrated that when the nematodes are exposed to root exudates, they were more resistant to Pasteuria spore attachment than were nematodes not exposed to exudates, which suggests that nematodes will be less susceptible after they enter the root zone. We showed that application of Pasteuria spores to the planting furrow was more effective than around the seed in reducing nematode numbers entering roots, perhaps because spores were concentrated in the root zone in the seed application. We demonstrated rapid, local evolution in host specificity of Pasteuria such that as the nematode becomes resistant to Pasteuria attachment, the bacterium changes so that it can attach to the nematode in a process that is akin to an arms race. Scientists have largely ignored the role of predatory nematodes in the suppression of plant-parasitic nematodes, but we demonstrated that survival of RKN decreased with increasing proportions of predatory species in the nematode community. These results suggest that predatory nematodes can play an important role in natural suppression of nematodes. We showed that female RKN raised under crowded conditions produce offspring that are more resistant to infection by Pasteuria than females raised under non-crowded conditions: if these nematodes reach high populations, they will be more difficult to control with Pasteuria because of their greater resistance to the bacterium. Therefore, Pasteuria should be integrated with other control tactics such as crop resistance and rotation.
Accomplishments
1. Moderate resistance in cotton has no carry-over benefit for the next crop. The southern root-knot nematode (RKN) is an important pathogen of cotton in the southeastern United States. Cotton varieties with resistance to this nematode are commercially available, with some varieties having a single gene conferring moderate resistance and others having two genes conferring high resistance. In a field study, ARS researchers in Tifton, Georgia, showed that, although the cotton variety with a single gene for resistance reduced nematode populations in the year it was planted, it did not have a carry-over benefit to a susceptible variety planted the next year in terms of reducing damage from RKN or improving yield. It is recommended that growers wanting to plant a susceptible crop after a moderately resistant cotton variety use a nematicide.
Review Publications
Grabau, Z., Timper, P. 2021. Managing Meloidogyne arenaria in peanut with old and new tools in the south-eastern USA. In Sikora, R.A., editor. Integrated nematode management: state-of-the-art and visions for the future. Boston, MA: CABI International. p. 145-151. https://doi.org/10.1079/9781789247541.0021.
Davis, R.F., Harris-Shultz, K.R., Knoll, J.E., Wang, H. 2021. Transfer of Meloidogyne incognita resistance using marker-assisted selection in sorghum. Journal of Nematology. 53:e-2021-087. https://doi.org/10.21307/jofnem-2021-087.
Galbieri, R., Kobayasti, L., Albuquerque, M., De Sa, R., Dutra, S., Boldt, A., Timper, P. 2021. Castor bean as an option for Meloidogyne incognita management in cotton. International Journal of Pest Management. https://doi.org/10.1080/09670874.2021.1953633.
Ballen-Taborda, C., Chu, Y., Ozias-Akins, P., Holbrook Jr, C.C., Timper, P., Jackson, S.A., Bertioli, D.J., Leal-Bertioli, S. 2022. Development and genetic characterization of peanut advanced backcross lines that incorporate root-knot nematode resistance from Arachis stenosperma. Frontiers in Plant Science. 12:785358. https://doi.org/https://doi.org/10.3389/fpls.2021.785358.
Davis, R.F., Kemerait, R.C. 2021. Integrated management of Meloidogyne incognita, the most economically damaging pathogen of cotton in the south-eastern United States. In Sikor, R.A., Desaeger, J., Molendjik, L.P.G., editors. Integrated nematode management: state-of-the-art and visions for the future. Wallingford, UK: CABI International. p. 87-93. https://doi.org/10.1079/9781789247541.0013.
