Location: Crop Genetics and Breeding Research
2019 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
Completed greenhouse tests evaluating the effects of two root-knot nematode resistance quantitative trait loci (QTLs) in cotton on the interactions between the nematode and the Fusarium wilt pathogen. In our study, the QTLs had little effect on the interaction of the nematodes and Fusarium wilt.
The first field trial evaluating whether the nematode resistance QTLs in cotton impart any deleterious effects (linkage drag) on yield or fiber quality was not harvested due to wet weather in the fall followed by the government shutdown. The trial has been reestablished and should be completed one year later than originally planned.
Currently collecting cotton germplasm for evaluation to identify new QTLs for resistance to root-knot nematodes. We 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. We are seeking assistance from a collaborator in Brazil to assist with acquiring many of these lines. We are trying to increase the amount of seed from the lines we have, but we have had significant difficulty with poor germination.
Completed the first cropping sequence in a multi-year crop rotation study and have begun to repeat the sequence. The first summer crop (sweet sorghum), the first winter crop (sugar beet), and the second summer crop (cotton) were successfully completed. The second summer crop (sweet sorghum) is being completed.
Preparing a manuscript from a recently completed field study showing that in one of two field sites, organic residue from a winter cover crop of rye led to lower reproduction of root-knot nematodes in cotton.
Manuscript in press on the effect of crowding on the susceptibility of root-knot nematodes to infection by the parasitic bacterium Pasteuria.
Completed the 1st year of a study to determine if we can predict root-knot nematode (RKN) damage to cotton based on the abundance of Pasteuria spores (a parasite of RKN) from the previous fall. Unfortunately, we were unable to harvest our cotton because of the government shutdown.
Completed the 3rd year and established the 4th year of a field study to evaluate different combinations of treatments for management of root-knot nematodes in cotton. The treatments are winter cover crop for nematode suppression (fallow, rye, and high residue rye), cotton cultivars with and without resistance to root-knot nematodes, and seed treatments with Avicta on the susceptible cotton.
Accomplishments
1. Sting nematodes greatly increase Fusarium wilt in cotton. Although the potential for sting nematodes to interact with the fungal pathogen Fusarium oxysporum f.sp. vasinfectum (Fov) to cause Fusarium wilt (FW) in cotton was suggested in the 1950s, virtually all cases of FW were believed to result from the interaction of Fov with root-knot nematodes (RKN) or from very high levels of Fov. By sampling individual plants, ARS researchers and University of Georgia researchers in Tifton, Georgia, demonstrated that many plants with FW symptoms were associated with sting nematodes and not RKN, thereby providing the most conclusive evidence to date for a sting nematode-Fov interaction. It was previously believed that controlling RKN was the most effective method of reducing FW in cotton, but this work proved that sting nematode also must be controlled.
2. Crowding leads to more resistant nematodes. Root-knot nematodes, which are major agricultural pests worldwide, can be effectively controlled by the parasitic bacterium Pasteuria. An ARS researcher in Tifton, Georgia, in cooperation with researchers from the University of Georgia showed that female root-knot nematodes raised under crowded conditions produce offspring that are more resistant to infection by Pasteuria than females raised under non-crowded conditions. This discovery has important ramifications for biological control of root-knot nematodes: 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.
Review Publications
Liu, C., Gibson, A., Timper, P., Morran, L.T., Tubbs, S. 2018. Rapid change in host specificity in a field population of the biological control organism Pasteuria penetrans. Evolutionary Applications. 12:744-756. https://doi.org/10.1111/eva.12750.
Hua, G., Timper, P., Ji, P. 2019. Meloidogyne incognita intensifies the severity of Fusarium wilt on watermelon caused by Fusarium oxysporum f. sp. niveum. Canadian Journal of Plant Pathology. https://doi.org/10.1080/07060661.2018.1564939.
Snider, J.L., Davis, R.F., Earl, H.J., Timper, P. 2019. Water availability and root-knot nematode management alter seedcotton yield through similar effects on fruit distribution patterns. Field Crops Research. 233:88-95. https://doi.org/19.1016/j.fcr.2019.01.008.
Galbieri, R., Davis, R.F., Kobayasti, L., Albuquerque, M., Belot, J., Echer, F., Boldt, A. 2018. Influenece of cotton root system size on tolerance to Rotylenchulus reniformis. Plant Disease. 102:2473-2479. https://doi.org/10.1094/PDIS-09-17-1424-RE.
Dasilva, M.B., Davis, R.F., Kumar, P., Nichols, R.L., Chee, P.W. 2019. Resistance Quantitative Trait Loci qMi-C11 and qMi-C14 in cotton have different effects on the development of Meloidogyne incognita, the Southern root-knot nematode. Plant Disease. 103:853-858.
Da Silva, M., Davis, R.F., Doan, H., Nichols, R., Kemerait, R., Halpern, H., Brewer, M., Jagdale, G., Chee, P. 2019. Fusarium wilt of cotton may commonly result from the interaction of Fusarium oxysporum f. sp. vasinfectum with Belonolaimus longicaudatus. Journal of Nematology. 51:10. https://doi.org/10.21307/jofnem-2019-015.
Harris-Shultz, K.R., Davis, R.F., Wallace, J., Knoll, J.E., Wang, H. 2019. A novel QTL for root-knot nematode resistance is identified from a South African sweet sorghum line. Phytopathology. 109(6):1011-1017. https://doi.org/10.1094/PHYTO-11-18-0433-R.
Dasilva, M., Davis, R.F., Paterson, A.H., Smith, S.M., Suassuna, N.D., Chee, P.W. 2019. Host-pathogen wars: New weapons from biotechnology and genomics. American Journal of Plant Sciences. 10:402-416. https://doi.org/10.4236/ajps.2019.103029.
Davis, R.F., Galbieri, R., Asmus, G. 2018. Nematode parasites of cotton and other tropical fibre crops. In: Sikora, R.A., Coyne, D., Hallmann, J., Timper, P., Editor(s). Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. 3rd Edition. Wallingford, UK: C.A.B. International. p. 738-754.
