2011 Annual Report
1a.Objectives (from AD-416)
New (additional) objectives per PDRAM memo #HQ01d dated July 5, 2007: .
1)Determine whether increased aflatoxin production in nematode-infected peanuts is due to a greater percentage of immature kernels, and the role of nematode infection of roots vs. pods. .
2)Determine whether nematode-resistant peanut genotypes reduced the risk of preharvest aflatoxin contamination in soil infected with root-knot nematodes.
Identify, characterize, and move genes for resistance to Meloidogyne spp. into cotton and peanut germplasm and cultivars. Utilization, mechanisms, and interactions of classical and contemporary methods in integrated nematode management. Enhance native and introduced antagonists of nematodes in cotton and peanut cropping systems.
1b.Approach (from AD-416)
Field and greenhouse experiments will be conducted to improve management of plant-parasitic nematodes in cotton and peanut. The approach will be multi-tactic including host-plant resistance, antagonistic crops, and biological control. Host-plant resistance to root-knot nematodes is the foundation of our nematode management strategy. Cooperative research will be conducted with plant breeders to develop cultivars and germplasm of peanut and cotton with desirable agronomic traits and a high level of nematode resistance. Plant material will be selected for resistance using traditional and marker-assisted selection. Durability of resistance genes is an important consideration in our research. Towards this end, we will search for new nematode resistance genes to deploy with previously identified resistance genes and determine the frequency and distribution of a species (the northern root-knot nematode) capable of reproducing on resistant peanut. 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 nematode pathogens. Specifically, we will determine the potential of Bt toxins, antagonistic cover crops, and antagonistic microorganisms to reduce root-knot and reniform nematode populations. Central to an effective management strategy is a thorough understanding of how nematodes interact with biotic and abiotic factors to reduce crop yield and quality; therefore, we will examine the interaction between root-knot nematodes and water stress, weeds, and fungi that produce aflatoxins. These studies will result in ecologically-based, cost-effective management options to reduce nematode populations, reduce damage from nematodes, and foster natural biological control.
We are cooperating with University of Georgia scientists to develop a high-throughput transformation system in peanut to identify the gene (Rma) responsible for resistance to the peanut root-knot nematode. The system involves Agrobacterium to induce hairy roots in plants and transfer DNA containing the transgenes to plant cells to produce transgenic roots while the shoots remain non-transgenic. We have shown that the transformed roots can support root galling and egg production by the nematode. In the upcoming year, we plan to evaluate the role of two candidate genes in nematode resistance using RNA interference (RNAi) to silence the gene in resistant plants and insertion of the gene in susceptible plants.
Predatory nematodes can feed on plant-parasitic nematodes, thereby reducing their numbers. We completed a study to evaluate whether tillage and fumigation with the nematicide 1,3-dichloropropene (Telone) has long-term detrimental effects on predatory nematodes. We showed that Telone dramatically reduced the abundance of predatory nematodes at planting time and into mid season. However, when we measured survival of the reniform nematode (a plant parasite) in the soil, we found that Telone reduced survival of the nematode at planting, but by mid season survival was similar in soil that had been treated with Telone and untreated soil. Tillage did not affect numbers of predatory nematodes. In the final year of a field study with the reniform nematode in cotton, we found that abundance of a nematode-parasitic bacterium, Pasteuria sp., was lower in plots treated with Telone and lower in areas of the field with higher sand content.
We completed a study evaluating the influence of a field’s physical characteristics (e.g., soil texture, elevation, and slope) on population levels of reniform nematode, the amount of damage caused by reniform nematode to cotton, and the effectiveness of chemical control measures (nematicides). Results indicate field characteristics can affect nematode levels so “nematode management zones” based on field physical characteristics can improve management of reniform nematodes by providing a logical way to divide a field for sampling prior to making management decisions. We also found that the range of field characteristics in this study did not influence the effectiveness of the nematicide treatments.
Soil suppressiveness against nematodes recovers after fumigation. Application of the fumigant nematicide 1,3-dichloropropene (Telone) could lead to pest resurgence if populations of predatory nematodes are slower to recover than their prey, plant-parasitic nematodes. ARS researchers in Tifton, GA demonstrated in a cotton field study that the fumigant reduced predatory nematodes and biological suppression of plant-parasitic nematodes, but only for a few months; by mid season, suppression of the plant parasites by the soil community was similar in fumigated and non-fumigated soil. This study provides the first evidence that predatory nematodes and other organisms antagonistic to plant-parasitic nematodes are more resilient following pesticide inputs than previously thought.
Induced resistance to nematodes in cotton. Infection of cotton by root-knot or reniform nematodes or certain chemicals (salicylic acid [SA] analogs) induce a plant defense response known as systemic acquired resistance (SAR) which is effective against nematodes. ARS and University of Georgia scientists in Tifton, GA showed that enzymes associated with SAR were significantly increased after nematode or chemical application, and reproduction of subsequently introduced nematodes was reduced significantly. This was the first documentation that infection of cotton by a nematode can elicit SAR to another nematode species, which has significant implications for nematode inter-species competition. This study also documents the potential benefit of the application of SA analogs for nematode management in cotton.
Cotton germplasm resistant to root-knot nematodes released. A cotton germplasm line, named GA 120R1B3, was jointly released by ARS and University of Georgia scientists in Tifton, GA. GA 120R1B3 is highly resistant to root-knot nematodes, suppressing nematode reproduction by 95%, and it has yield and fiber qualities that are superior to other resistant germplasm and are similar to many modern cultivars. GA 120R1B3 has good yield and excellent fiber quality in both the presence and absence of root-knot nematodes. Both public and commercial cotton breeding programs have begun to use GA 120R1B3 as a source of root-knot nematode resistance.
Timper, P. 2011. Utilization of biological control for managing plant-parasitic nematodes. In: Spiegel, I. and Davies, K., editors. Biological Control of Plant Parasitic Nematodes. New York, NY: Springer. p. 259-289.
Nagy, E.D., Chu, Y., Guo, Y., Khanal, S., Tang, S., Li, Y., Dong, W.B., Timper, P., Taylor, C., Ozias-Akins, P., Holbrook Jr, C.C., Beilinson, V., Nielsen, N.C., Stalker, H., Knapp, S.J. 2010. Recombination is suppressed in an alien introgression on chromosome 5A of peanut harboring Rma, a dominant root-knot nematode resistance gene. Molecular Breeding. 26:357-370.
Davis, R.F., Chee, P., Lubbers, E., May, O. 2011. Registration of GA 120R1B3 Germplasm Line of Cotton. Journal of Plant Registrations. 5:384-387.
Lu, P., Davis, R.F., Kemerait, R.C. 2010. Effect of mowing cotton stalks and preventing plant re-growth on post-harvest reproduction of Meloidogyne incognita. Journal of Nematology. 42:96-100.
Shen, X., He, Y., Lubbers, E.L., Davis, R.F., Nichols, R.L., Chee, P.W. 2010. Fine mapping QMi-C11 a major QTL controlling root-knot nematodes resistance in Upland cotton. Journal of Theoretical and Applied Genetics. 121:1623-1631.
Mueller, J.D., Khalilian, A., Monfort, W.S., Davis, R.F., Kirkpatrick, T.L., Ortiz, B.V., Henderson, W.G. 2010. Site-Specific Detection and Management of Nematodes. In: Oerke, E.C., Gerhards R., Menz G., Sikora, R.A., editors. Precision Crop Protection-the challenge and use of Heterogeneity. Berlin, Germany: Springer. p. 385-402.