Location: Crop Genetics and Breeding Research
2020 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
ARS researchers at Tifton, Georgia, completed the final field trial evaluating whether the nematode resistance quantitative trait loci (QTLs) in cotton impart any deleterious effects (linkage drag) on yield or fiber quality. Analysis and interpretation are ongoing.
ARS researchers at Tifton, Georgia, are currently collecting cotton germplasm for evaluation to identify new QTLs for resistance to root-knot nematodes. ARS researchers at Tifton, Georgia, 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 ARS researchers at Tifton, Georgia, are still seeking. ARS researchers at Tifton, Georgia, are seeking assistance from a collaborator in Brazil to assist with acquiring many of these lines. ARS researchers at Tifton, Georgia, are trying to increase the amount of seed from the lines we have, but have had significant difficulty with poor germination.
ARS researchers at Tifton, Georgia, are completing the final cropping sequence in a multi-year crop rotation study (two cycles of a sorghum/sugar beet/cotton rotation). 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.
ARS researchers at Tifton, Georgia, are working collaboratively to identify sources of root-knot nematode resistance in corn and sweet sorghum. Related projects include identifying resistance QTLs (both crops) and developing improved germplasm with resistance (sweet sorghum).
ARS researchers at Tifton, Georgia, submitted 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.
ARS researchers at Tifton, Georgia, completed the 3rd 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.
ARS researchers at Tifton, Georgia, have 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. This project was planned to be completed after the 3rd year but we decided to add an additional year to obtain a stronger data set.
Accomplishments
1. In furrow treatments are more effective than seed treatments for biocontrol organism. 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 a graduate student from the University of Georgia showed in a greenhouse study that although applications of Pasteuria spores to the planting furrow or seed reduced root-knot nematode reproduction compared to the control, the furrow application was more effective than the seed treatment. While seed treatments of chemical and microbial pest control products are becoming more common, these results suggest that in the case of Pasteuria, they may be less effective than furrow treatments in managing root-knot nematodes.
2. Predatory nematodes are associated with reduced survival of root-knot nematodes. Scientists studying nematodes have long known that soils naturally harbor organisms able to suppress plant-parasitic nematodes but have largely ignored the role of predatory nematodes in this suppression. ARS researchers in Tifton, Georgia, in cooperation with a researcher at the University of Georgia demonstrated that predatory nematodes were abundant in two agricultural field sites and that survival of root-knot nematodes decreased with increasing proportions of predatory species in the nematode community. Contrary to their hypothesis, neither predators nor survival of root-knot nematodes were influenced by the presence or absence of cover-crop residue. These results suggest that predatory nematodes can play an important role in natural suppression of nematodes and more research on ways of increasing their abundance in soil is needed.
3. Resistance genes in cotton reduce eggs per egg mass but do affect gall size or egression. Two QTLs that impart resistance to the cotton root-knot nematode (Meloidogyne incognita) have been identified. ARS and University of Georgia researchers in Tifton, Georgia, demonstrated that despite having different modes of action, both QTLs equally reduce the number of nematode eggs per egg mass produced. 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 nematode infection. These findings advance our understanding of how the resistance QTLs affect the nematode and the plant’s response to infection.
4. Expression profiling narrows the list of potential nematode resistance genes in cotton. Although two QTLs imparting resistance to the cotton root-knot nematode (Meloidogyne incognita) are known, the specific genes within those QTLs involved in resistance are not known. By identifying differentially expressed genes within the two QTLs in susceptible and resistant cotton during nematode infection and development, ARS and University of Georgia scientists in Tifton, Georgia, identified genes possibly involved in the resistance response. These results greatly reduce the number of genes that must be evaluated to identify root-knot nematode resistance genes in cotton.
Review Publications
Kumar, P., Da Silva, M., Singh, R., Davis, R.F., Nichols, R., Chee, P. 2019. Transcriptome analysis of a nematode resistant and susceptible upland cotton line at two critical stages of Meloidogyne incognita infection and development. PLoS One. 14(9). https://doi.org/10.1371/journal.pone.0221328.
Hajihassani, A., Davis, R.F., Timper, P. 2019. Evaluation of selected nonfumigant nematicides on inoculation densities of Meloidogyne incognita on cucumber. Plant Disease. 103:3161-3165. https://doi.org/10.1094/PDIS-04-19-0836-RE.
Ballen-Taborda, C., Chu, Y., Ozias-Akins, P., Timper, P., Holbrook Jr, C.C., Jackson, S., Bertioli, D., Leal-Bertioli, S. 2019. A new source of root-knot nematode resistance from Arachis stenosperma incorporated into allotetraploid peanut (Arachis hypogaea). Scientific Reports. 9:17702. https://doi.org/10.1038/s41598-019-54183-1.
Galbieri, R., Davis, R.F., Scoz, L., Belot, J., Skantar, A.M. 2020. First report of Meloidogyne enterolobii on cotton in Brazil. Plant Disease. https://doi.org/10.1094/PDIS-02-20-0365-PDN.
Liu, C., Ji, P., Timper, P. 2019. Maternal stress reduces the susceptibility of root-knot nematodes to Pasteuria penetrans. Journal of Nematology. 51:E2019-40. https://doi.org/10.21307/jofnem-2019-040.
