Location: Crop Genetics and Breeding Research
2021 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
In cooperation with University of Georgia scientists, ARS scientists at Tifton, Georgia, completed a greenhouse evaluation of a new source of Meloidogyne arenaria resistance in the wild relative of peanut, Arachis stenosperma. A manuscript has been submitted to the agency for approval. (Objective 1).
In cooperation with University of Georgia scientists, ARS scientists completed one of two trials evaluating the resistance to M. hapla in wild species of peanut. (Objective 1).
ARS scientists collected a 4th year of data to determine if abundance of Pasteuria spores can be combined with root-knot nematode densities to better predict nematode damage to cotton. (Objective 2).
ARS scientists completed a field study to evaluate different combinations of treatments for management of root-knot nematodes in cotton. The treatments were winter cover crop (fallow, rye, and high residue rye), cotton cultivars with and without resistance to the nematode, and seed treatments with Avicta on susceptible cotton. A manuscript is in preparation by ARS scientists. (Objective 2).
ARS scientists initiated field studies to compare the economic value of growing root-knot nematode resistant cotton to growing nematode susceptible cotton with nematicides. (Objective 2).
ARS scientists initiated greenhouse studies to identify new sources of root-knot nematode resistance in sorghum, and we continued projects to breed root-knot nematode resistance into diverse sorghum lines. (Objective 2).
ARS scientists are currently collecting cotton germplasm for evaluation to identify new quantitative trait loci (QTLs) for resistance to root-knot nematodes. ARS scientists have so far been able to acquire about 20 germplasm lines previously identified as having some level of resistance. There are approximately 20 more germplasm lines, mostly from other countries, that we are still seeking. ARS scientists are seeking assistance from a collaborator in Brazil to acquire many of these lines. ARS scientists are trying to increase the amount of seed from the lines we have, but we have had significant difficulty with poor germination. (Objective 1).
Manuscripts are in preparation by ARS scientists for completed studies on 1) utilizing resistant varieties in a sweet sorghum-sugar beet-cotton cropping sequence (Objective 2), 2) utilizing marker-assisted selection to incorporate nematode resistance into sorghum lines (Objective 1), and 3) evaluating the effect of root system size on the ability of cotton to tolerate root-knot nematode parasitism (Objective 2).
ARS scientists initiated a project to evaluate the role of the innate defense mechanisms in cotton plants in the Fusarium wilt/root-knot nematode disease complex. (Objective 2).
Accomplishments
1. New sources of resistance to root-knot nematodes in peanut. ARS scientists at Tifton, Georgia, believe the peanut root-knot nematode (PRKN) causes substantial yield losses to peanut. Currently, there is only one available source of resistance to this nematode in peanut, thus additional sources are needed to improve the durability of resistance. Using marker-assisted selection, ARS scientists at Tifton, Georgia, in collaboration with scientists at the University of Georgia transferred two new genes conferring resistance to PRKN from the wild peanut species Arachis stenosperma into cultivated peanut. High levels of resistance to PRKN were confirmed in these advanced peanut breeding lines. These new sources of PRKN resistance can be used by peanut breeders to create durable resistance when combined with the previous resistance source.
2. Root-knot nematode resistance rapidly bred into diverse sorghum lines. ARS scientists at Tifton, Georgia, suggests the southern root-knot nematode (SRKN) has a wide host range and damages many crops in the southern United States. Host plant resistance is the most cost-effective means of reducing damage, and resistance can be combined with crop rotation to further improve nematode control. Sorghum is drought-tolerant and grows well in the southern United States; however, most varieties are susceptible to the SRKN, which makes sorghum a poor rotation choice for crops that are damaged by the SRKN. ARS scientists in Tifton, Georgia, successfully used marker-assisted selection (MAS) to rapidly incorporate a high level of SRKN 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. SRKN-resistant sorghum would be an effective rotation to minimize SRKN damage in crops such as cotton.
Review Publications
Timper, P., Strickland, T.C., Jagdale, G.B. 2021. Biological suppression of the root-knot nematode Meloidogyne incognita following winter cover crops in conservation tillage cotton. Biological Control. 155:104525. https://doi.org/10.1016/j.biocontrol.2020.104525.
Dasilva, M., Davis, R.F., Nichols, R., Kumar, P., Chee, P. 2021. The effect of two QTLs for resistance to Meloidogyne incognita in cotton on nematode egression from roots. Journal of Nematology. 52:e2020-122. https://doi.org/10.21307/jofnem-2020-122.
Liu, C., Timper, P. 2020. Effectiveness of Pasteura penetrans applied to seed or furrow. Nematropica. 50:229-232.
Khanal, C., Galbieri, R., Timper, P. 2021. Rotations with Crotalaria spp. do not suppress populations of Meloidogyne incognita in cotton. Nematology. 0:1-9. https://doi.org/10.1163/15685411-bja10086.
Ballen-Taborda, C., Chu, Y., Ozias-Akins, P., Timper, P., Jackson, S., Bertioli, D., Leal-Bertioli, S. 2021. Validation of resistance to root-knot nematode incorporated in peanut from the wild relative Arachis stenosperma. Agronomy Journal. 1-23. https://doi.org/10.1002/agj2.20654.
