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Genetic Improvement of Corn and Sorghum for Resistance to Insects and Aflatoxin


<OL> <LI> Identify sources of resistance to insects/aflatoxin in corn/sorghum and transfer resistance to acceptable plant types.<LI> Develop germplasm with antibiosis/nonpreference resistance to insects. <LI> Determine genetics of resistance in different corn lines using conventional/molecular techniques. <LI> Transfer resistance to the corn earworm from field corn to sweet corn using conventional/marker-assisted breeding techniques.

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Conventional/molecular techniques will be used to study the genetics of resistance to insect pests/aflatoxin. Crosses between corn lines with high and low levels of resistance will be made and segregating generations will be used to determine if resistance is inherited simply or quantitatively. RFLP analyses will determine location of genes for resistance to the corn earworm and used for marker-assisted selection to transfer resistance. RFLP markers will also be used to determine the number of differing genes in germplasm lines with resistance to the corn earworm/aflatoxin. A CRADA will be established to transfer resistance to the corn earworm to elite sweet corn inbreds. Conventional backcrossing procedures, marker-assisted selection, maysin analyses, and bioassays with the corn earworm will be used to follow the transfer of the resistance to sweet corn. Chemicals associated with resistance will be isolated, identified, and assayed for activity.
PROGRESS: 2000/10 TO 2001/09<ol> <li>
What major problem or issue is being resolved and how are you resolving it? The corn crop in the Southeastern U.S. often sustains serious losses due to ear and leaf-feeding insects and to contamination of the grain with aflatoxin, a carcinogenic mycotoxin produced by several Aspergillus spp. of fungi. The losses are associated with one another in that damage to the ear exacerbates infection of the preharvest crop by A. flavus and A. parasiticus, and increases subsequent contamination by aflatoxin. Improving resistance of the host plant is being accomplished through selection for reduced ear damage by insects and selection for reduced ear infection by Aspergillus spp. and contamination by aflatoxin. The chronic problems of insect damage and aflatoxin contamination drastically reduce grain quality and often result in a product that is unusable. Sweet corn for both the fresh and processed sweet corn markets is extensively sprayed with pesticides to eliminate insect damage. Resistance to the corn earworm, the major insect pest of sweet corn in the southeast, has been identified and is being transferred to elite sweet corn inbreds. Successful completion of this research has the potential for reducing pesticide usage on sweet corn by an estimated 75-80%.
<li>How serious is the problem? Why does it matter? The prevention of damage by corn earworm to the sweet corn crop now requires the sustained application of insecticides (a range of 20-40 applications are commonly required) during the period of ear development until harvest. The cost to the grower and endangerment to the environment due to pollution are quite obvious. Contamination by aflatoxin in corn grain has been documented as a cause for increased evidence of cancer in humans and animals often resulting in death of pets and livestock when the contaminated grain is ingested. The aflatoxin problem has been established as a worldwide health hazard.
<li>How does it relate to the National Program(s) and National Component(s)? National Program: 301 Plant, Microbial and Insect Germplasm Conservation, and Development, 100%. Components: Germplasm Enhancement and Manipulation. The research allows scientists to work with commercial plant breeders to transfer antibiotic resistance in silks to sweet corn inbreds and hybrids. The research allows scientists to locate corn and sorghum germplasm resistant to insects and toxigenic fungi, improve it for release to public and private breeders, and develop and demonstrate ways to efficiently transfer that resistance to commercial hybrids. Research in this CRIS addresses Agency priorities of reduced usage of pesticides, improved food safety, and more sustainable agricultural production.
<li>What were the most significant accomplishments this past year? A. Single Most Significant Accomplishment during FY 2001 year: Corn ear worms (CEW) are one of the most serious pests on maize in the southern USA. Maysin, a plant chemical that gives resistance to CEW was transferred into adapted maize lines. An improved maize population with 10 times the normal level of maysin was developed and released. Corn breeders will have a source of high maysin germplasm that can be readily 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. First, we have been mapping the genes associated with insect resistance and genes that control/regulate resistance to aflatoxin production. Second, we are using mapping information to identify markers to apply marker-assisted selection and transfer of the resistant genes to elite germplasm. The implications of the newly improved germplasm are reduction of pesticide usage, a safer environment and safer food and feed. In 2001, we made the fifth selfs for four sweet corn inbreds in transferring antibiotic resistance to the silks of those inbreds to produce high maysin hybrids. Elucidation of detailed information on the inheritance of antibiotic compounds, maysin, apimaysin, 3'methoxymaysin, isoorientin and rhamnosyl isoorientin is a continuing process using molecular techniques, conventional quantitative procedures and translocation techniques. An efficient and less expensive technique for accomplishing the initial screening of genotypes for resistance to A. flavus infection and aflatoxin contamination was demonstrated and is being used in a continuing process. The technique utilizes the use of a color mutant of A parasiticus that causes a reddish stain of the aleurone layer in corn when infected with Aspergillus spp. Numerous germplasm releases with resistance to corn and sorghum insects have been made over the years resulting in hundreds of requests for the released material by seed companies and research scientists at state universities, USDA laboratories, and foreign research institutions.
<li>What do you expect to accomplish, year by year, over the next 3 years? FY2002. We plan to locate genes or markers linked to genes that are associated with agronomic traits and apply map-based cloning to clone new gene(s) that link to useful traits. Then, using marker-assisted selection methods, we plan to produce new germplasm that has better resistance to pests. In cooperation with other scientists, we will conduct multiple location performance tests for the resistance traits. Backcrossing of sweet corn inbreds to high silk maysin sources will be completed. FY2003. The process of combining resistance to insects and resistance to aflatoxin contamination will be accelerated using molecular markers and other mapping techniques in our pyramiding study to identify combined resistance in crosses. Funding has became available to incorporate economic parameters necessary for establishing an effective expert system, and extensive testing will continue. FY2004. Two high-maysin populations will be utilized as sources for inbred development and transfer to elite lines. A population released after nine cycles of selection for high in vitro dry matter digestibility, will be evaluated in feeding trials, and used as a source for development of inbred lines to be used in the formation of silage hybrids with excellent digestibility.
<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? Numerous seed requests for seed of germplasm releases were filled at the local, national and international level. Most requests are made by public and private plant breeders for introgression into their breeding programs. Corn performance data on commercially grown hybrids was published and distributed in a University of Georgia Bulletin. These data are used primarily to assist growers in making decisions about which hybrids they will grow. Georgia corn fields were surveyed for contamination with aflatoxin. This service is provided to assess the need to reduce losses due to toxigenic fungi and to determine the losses due to these fungi so that informed decisions can be made regarding the distribution of research funding. Two high-maysin corn populations and one high digestibility silage population have been released and have been registered as available germplasm sources in Crop Science. The publicity in the journal will result in wider distribution for use by state and federal breeders and scientists, and by commercial seed companies. The four sweet corn lines with silks, into which maysin has been transferred, under a CRADA will be released to be used by SynGenta in their sweet corn breeding program.
<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) Presented: Economic input for an 'Expert Management System' to minimize risk of aflatoxin contamination of maize, at the Aflatoxin/Fumonisin Workshop 2000, Oct.25-27, 2000, Yosemite, CA. Presented: 2000 evaluation of GEM crosses for yield and other agronomic traits, at cooperative meeting of Dec. 6-8, 2000, Chicago, IL. Presented: 2000 Research Progress Report, at SRIEG-51 meeting on January 23, 2001, Atlanta, GA. Coauthored presentations: Identification and pyramiding of genes/markers associated with corn ear resistance to insects and Aspergillus flavus for control of preharvest aflatoxin contamination in the Souther: A research report; Multi-location evaluation of single cross maize hybrids for aflatoxin contamination; Markers associated with silk antibiotic compounds, husk coverage, and aflatoxin concentrations in two maize mapping populations; and Evaluation of corn germplasm tolerance to drought stress and effects on aflatoxin production; at the Aflatoxin/Fumonisin Workshop 2000, Oct. 25-27, 2000, Yosemite, CA.</ol>

Widstrom, Neil
USDA - Agricultural Research Service
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