Development of Improved Peanut Germplasm with Resistance to Disease and Nematode Pests

The best sources of resistance to aflatoxin contamination, along with susceptible checks, will be examined under varying levels of drought duration to define the optimal length of drought stress for differentiating levels of resistance. These genotypes will also be examined for morphological and chemical attributes to attempt to define mechanisms of resistance and possible indirect selection tools. Segregating population will be examined to define genetic control for resistance to the peanut root-knot nematode and to identify selections for possible germplasm release. Data for pest resistance and morphological characteristics will be used to develop a smaller and more effective core collection for peanut.
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<ol> <li>What major problem or issue is being resolved and how are you resolving it? Breeding and genetic research is being conducted to address three major problems in peanut. The first problem is preharvest aflatoxin contamination (PAC). It is being resolved by the development of peanut germplasm with resistance to PAC. The second problem is yield and quality losses caused by the peanut root-knot nematode. This problem is also being resolved by the development of peanut germplasm with resistance to this pathogen. The third problem is a lack of utilization of valuable genes contained in the U.S. germplasm collection of peanut. This problem is being resolved by the development and refinement of a peanut core collection to improve the efficiency of germplasm evaluations.
<li>How serious is the problem? Why does it matter? The American Peanut Council, representing all segments of the U.S. peanut industry, has identified PAC as the most serious challenge facing the industry. Progress in developing resistant cultivars would represent a major advance for the U.S. peanut industry. The root-knot nematode is a microscopic worm that feeds on the roots, pegs, and pods of peanut plants. This nematode can greatly reduce yield and quality and costs U.S. peanut farmers over 30 million dollars annually. Development of resistant cultivars would be economically beneficial to growers, and would reduce use of agricultural chemicals. The size of germplasm collections for all crops increases over time, which in turn increases the costs of collection maintenance and the evaluation expenses needed to identify particular genes. The testing and refinement of the core collection theory is expected to reduce these expenses for all crop species.
<li>How does it relate to the National Program(s) and National Component(s)? The control of mycotoxins to prevent their presence, and potential for their presence, in crops is one of the three major objectives listed in the National Program Statement for Food Safety (301). The development of peanut cultivars with resistance to PAC would directly address this objective. Host plant resistance is a major objective of the National Program Statement for Plant Diseases (303) because it can be highly effective, is environmentally benign, and requires little or no additional expense to producers. The development of peanut cultivars with resistance to the peanut root-knot nematode would directly address this objective. The development and refinement of a core collection also addresses this objective since it has resulted in the identification of sources of resistance to several pathogens within the germplasm collection of peanut. All the research conducted by this CRIS addresses objectives outlined in the National Program Statement for Plant Germplasm Resources, Conservation, and Development (301).
<li>What were the most significant accomplishments this past year? A. Single Most Significant Accomplishment during FY 2001: The objective of this research was to identify countries of origin that are rich sources of resistance to important peanut diseases. Accessions in the peanut core collection were evaluated for resistance to five economically significant pathogens. Several geographical areas that appear to be rich sources for disease resistant genes were identified. This information should enable plant breeders to more efficiently utilize the genes for disease resistance that are available in the U.S. germplasm collection. B. Other Significant Accomplishment(s), if any: None C. Significant Accomplishments/Activities that Support Special Target Populations: None D. Progress Report: None
<li>Describe the major accomplishments over the life of the project including their predicted or actual impact. Fourteen plant introductions were observed to have on average, a 70% reduction in PAC in multiple years of testing. Six of these accessions exhibited a 90% reduction in PAC in multiple years of testing. These genotypes have been entered into a hybridization program to combine the resistance with acceptable agronomic performance. We conducted research to evaluate preharvest aflatoxin contamination in genotypes known to have drought tolerance. Drought tolerant genotypes had significantly less aflatoxin contamination. Significant positive correlations were observed between aflatoxin contamination and leaf temperature and between aflatoxin contamination and visual stress ratings. Leaf temperature and visual stress ratings are less variable and less expensive to measure than aflatoxin contamination. Leaf temperature and visual stress ratings may be useful in indirectly selecting for reduced aflatoxin contamination in breeding populations. We examined the peanut core collection for resistance to the peanut root-knot nematode (PRN). We identified 54 resistant accessions representing 21 countries of origin. There were relatively large numbers of resistant accessions from China and Cuba. Peanut cultivars are available that have resistance to PRN or tomato spotted wilt virus (TSWV), however, no cultivars are available that have resistance to both pathogens. Using a field screening nursery for resistance to TSWV and a greenhouse screening technique for resistance to , we have selected advanced generation breeding lines with resistance to both PRN and TSWV. Agronomic evaluations are ongoing to determine if this material would be an acceptable cultivar. We have developed a core collection for peanut. A major benefit of having a core collection has been a great increase in evaluation of peanut germplasm. Work by several groups of researchers has resulted in the evaluation of core accessions for 24 characteristics. This has resulted in the identification of numerous sources of resistance to several economically significant pathogens. Research was also conducted to test the core collection concept. Data for resistance to late leaf spot and data for resistance to the peanut root knot nematode were used to evaluate the effectiveness of a two-stage core screening approach in identifying resistance in the entire collection. Both studies clearly demonstrated that the core collection approach can be used to improve the efficiency of germplasm evaluation.
<li>What do you expect to accomplish, year by year, over the next 3 years? FY2002. We will evaluate hundreds of progenies from breeding populations to search for material that has resistance to PAC and acceptable yield and grade. We will evaluate thousands of progenies from breeding populations to search for material that has resistance to the peanut root-knot nematode and acceptable yield and grade. Germplasm with a very high level of resistance to Tomato Spotted Wilt Virus will be released. FY2003. We will evaluate hundreds of progenies from breeding populations to search for material that has resistance to PAC and acceptable yield and grade. We will evaluate thousands of progenies from breeding populations to search for material that has resistance to the peanut root-knot nematode and acceptable yield and grade. Germplasm with a very high level of resistance to Tomato Spotted Wilt Virus and the Peanut Root-knot Nematode will be released. FY2004. We will evaluate hundreds of progenies from breeding populations to search for material that has resistance to PAC and acceptable yield and grade. We will evaluate thousands of progenies from breeding populations to search for material that has resistance to the peanut root-knot nematode and acceptable yield and grade. Germplasm with a very high level of resistance to Preharvest Aflatoxin Contamination will be released.
<li>What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end user (industry, farmer, other scientists)? What are the constraints if known, to the adoption & durability of the technology product? At present the technologies developed by this project have been transferred to other scientist. Information has been published on the development of screening techniques and on the identification of sources of resistance. These are available for use by other scientist involved in peanut breeding and genetics. It appears likely that technology will be transferred to farmers in the form of improved cultivars within the next five years.
<li>List your most important publications in the popular press (no abstracts) and presentations to non-scientific organizations and articles written about your work (NOTE: this does not replace your peer-reviewed publications which are listed below) Mullen, M. Breeding for resistance. 2001. The Peanut Farmer. June p.8.</ol>