Location: Crop Protection and Management Research2012 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.
3. Progress Report:
This is the final report for project 6602-21220-013-00D, which terminated April 8, 2012 and has been replaced by new project 6602-21220-015-00D. Considerable progress was made in identifying and improving resistance to nematodes in cotton and peanut, and developing integrated strategies for management of plant-parasitic nematodes. DNA markers associated with nematode resistance genes will make selection of resistant plants faster and more accurate. In cotton, a simple sequence marker CIR316 linked to root-knot nematode resistance was found. In subsequent research, we more precisely defined the location of one resistance gene to a 3.6 cM region flanked by two DNA markers. There are two genes involved in nematode resistance in cotton. We have separated these genes into separate plants and will begin to study the individual effects of the two genes. In peanut, a genetic marker (197/909) linked with resistance to root-knot nematodes was identified. A peanut cultivar (Tifguard), which has a high level of resistance to both the tomato spotted wilt virus (TSWV) and root-knot nematodes, was developed and publicly released. This cultivar will enable growers to eliminate the use of nematicides, thus saving up to $100 per acre. We created a cotton germplasm line with a high level of resistance to root-knot nematodes, but which has yield and fiber quality similar to modern cotton varieties. This germplasm will be a valuable resource for cotton breeders in developing cultivars with resistance to root-knot nematodes. We showed that tropical spiderwort, an invasive weed, supported significant levels of reproduction by two wide-spread species of root-knot nematodes, the reniform nematode, and a major peanut disease (southern stem rot). Therefore, controlling tropical spiderwort is critical when managing nematodes and diseases with crop rotation. Cereal rye produces compounds that are toxic to nematodes; however, incorporating rye as a green manure did not suppress populations of root-knot nematodes or improve cotton yield. In cotton, we showed that root-knot nematodes can affect fiber quality by reducing fiber length, and the detrimental effects of nematode parasitism and drought stress are typically additive rather than synergistic. Therefore, nematodes must be managed to prevent loss of fiber quality, and irrigation does not compensate for nematode-induced yield loss. We showed that abundance of the nematode-parasitic bacterium Pasteuria penetrans was greater when peanut was rotated with another host (eggplant) for root-knot nematodes than when peanut was rotated with a nonhost. Our research indicated that root-knot nematodes could become resistant to this parasitic bacterium and that this could pose a problem for commercial products containing Pasteuria penetrans. We showed that use of the fumigant nematicide 1,3-dichloropropene in cotton reduced natural biological suppression of plant-parasitic nematodes (in part due to predatory nematodes), but that this negative effect did not persist into the next spring.
1. Systemic acquired resistance to nematodes in cotton was proven. ARS researchers in Tifton, Georgia, along with University of Georgia collaborators, demonstrated for the first time that the natural defense mechanisms in cotton plants could be activated to reduce the reproduction of plant-parasitic nematodes by 35 to 50%. This unique mechanism of resistance was effective against the two most widely distributed nematode species damaging cotton in the United States, and it could be elicited by prior infection by another nematode or by chemical application with salicylic acid analogs such as BTH. This novel means of nematode suppression could be used as a supplemental tactic to reduce nematode damage in cotton.
2. Nematode infection of peanut roots increases aflatoxin contaminatin of kernels. Aflatoxins are potent carcinogens produced by some fungi. It was thought that infection of the peanut pod by root-knot nematodes would create access points for the fungi to colonize the kernel. However, using a technique which physically separated pod set from root growth, ARS researchers in Tifton, Georgia demonstrated that infection of roots alone by root-knot nematodes (Meloidogyne arenaria) increased aflatoxin concentrations in kernels. Although root-knot nematodes are considered a secondary risk factor for aflatoxin contamination (drought and high temperatures are the primary), controlling these nematodes in fields where they are present should help mitigate aflatoxin contamination of peanut.
Aryal, S.K., Davis, R.F., Stevenson, K.L., Timper, P., Ji, P. 2011. Influence of infection of cotton by Rotylenchulus reniformis and Meloidogyne incognita on the production of enzymes involved in systemic acquired resistance. Journal of Nematology. 43(3-4):152-159.