Location: Crop Protection and Management Research2010 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
A germplasm release is being submitted for a germplasm line which is highly resistant to root-knot nematodes and has yield and fiber qualities that are superior to other resistant germplasm and are similar to many modern cultivars. By utilizing the cotton isolines we created which are genetically the same except for nematode resistance, we were able to conduct the first year of a field study to evaluate whether incorporation of nematode resistance imparts any negative effects on yield or fiber quality. We have identified a gene for resistance to root-knot nematodes in cotton that is different from previously described resistance genes, and a manuscript is in preparation. A backcross breeding program was started to incorporate resistance to reniform nematodes into an elite germplasm line created in our research program. We completed a study showing that a field population of root-knot nematodes is heterogenous for susceptibility to the parasitic bacterium Pasteuria penetrans. We also provide evidence for reciprocal selection between the nematode and bacterium in which the nematode developed resistance to the bacterium leading to selection of a subpopulation of the bacterium virulent to the nematode. A manuscript on this study is in press. In an ongoing field study, populations of predatory nematodes were dramatically reduced following application of the fumigant nematicide Telone. The impact of Telone on the suppressive service of the soil was also determined; bioassays revealed that after Telone application, the survival and reproductive potential of plant-parasitic nematodes was greater than in control plots. However, by mid season, suppression of plant-parasitic nematodes by the soil community was similar in the Telone and control plots. In a field study, we found that densities of Pasteuria sp. attacking the reniform nematode were lower in plots treated with Telone and lower in areas of the field with higher sand content. A greenhouse study is underway to determine whether Pasteuria sp. is significantly suppressing reniform nematode populations. We began the third year of a study to evaluate 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). Preliminary results indicate that “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.
1. Fine mapping a root-knot nematode resistance gene in cotton. Host plant resistance is the most effective and economical approach to control the root-knot nematode, which is the most significant pathogen of cotton in the US, and identifying DNA markers that are tightly linked to resistance genes is a crucial step toward marker assisted selection in breeding cotton for nematode resistance. We previously had identified a section of DNA measuring 12.9 cM containing a quantitative trait locus (a QTL we named Mi-C11) which was responsible for a significant amount of the resistance to root-knot nematode. In this study, ARS and University of Georgia scientists in Tifton, GA more precisely defined the location of the resistance QTL to a 3.6 cM region flanked by two DNA markers. These results provide a critical tool for marker assisted selection of root-knot nematode resistance in cotton and also provide the foundation for map-based isolation of the nematode resistance gene.
2. Parasitic bacterium in an arms race with its host nematode. Root-knot nematodes (RKN) cause severe yield losses in a number of crops throughout the southern US. The bacterium Pasteuria penetrans is an obligate parasite of these nematodes and can substantially reduce populations of these pests. ARS research in Tifton, GA showed that individuals within a population of RKN differed in their susceptibility to Pasteuria, and that the Pasteuria in the field had changed over time, presumably to adapt to changes in susceptibility of the nematode. These results indicate that, to avoid resistance development in the nematode population, formulations of Pasteuria should include diverse biotypes.
Timper, P.N., Kone, D., Yin, J., Ji, P., McSpadden Gardener, B.B. 2009. Evaluation of an antibiotic producing strain of Pseudomonas flourescens for suppression of plant-parasitic nematodes. Journal of Nematology. 41:234-240.