Plant Resistance and Germplasm Enhancement for Managing Insect Pests of Southern Crops

Evaluate corn, sorghum, peanut, and forage germplasm for resistance to major pests. Determine the chemical/physical mechanism of resistance. Evaluate resistant plants with other control measures to develop sustainable systems that minimize use of pesticides. Establish CRADA to transfer resistance in corn silks to sweet corn using conventional and marker-assisted breeding procedures. Determine the relationship between insect damage to peanut and aflatoxin contamination. Evaluate field corn, sweet corn, and peanut for delta-endotoxin activity against the corn earworm, fall armyworm, lesser cornstalk borer, or velvetbean caterpillar. Select for resistance in the corn earworm to a specific gene for delta-endotoxin and determine susceptibility to other genes for delta-endotoxin.
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PROGRESS: 1999/10 TO 2000/09<BR>
1. What major problem or issue is being resolved and how are you resolving it? Insects are one of the major groups of pests of agricultural crops grown in the Southeastern U.S., reducing both yield and quality as a direct result of their damage. Plant resistance to insects offers the potential for development of control methods for major insect pests without the use of pesticides. Plant resistance has been shown to be an economically, socially, and environmentally acceptable means of controlling insects without the use of pesticides. Research is being conducted to identify sources of resistance to the corn earworm and fall armyworm on corn and sorghum, corn earworm, fall armyworm, tobacco thrips, potato leafhopper, and/or lesser cornstalk borer on peanut and/or forage grasses.<BR>
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2. How serious is the problem? Why does it matter? Loss due to damage to insect pests of agricultural crops in the southeast exceeds millions of dollars annually. In addition to their direct impact on the yield and quality of agricultural crops, they are often indirectly related to the introduction of plant pathogens such as Aspergillus flavus which produces aflatoxins, a group of potent carcinogens. Contamination of corn or peanut with aflatoxin may render the commodity unfit for interstate commerce, human consumption, or for animal feed. In addition, insect populations build on corn to tremendous numbers that, upon emergence as adults, migrate to lay eggs on other, high value crops. Thus, development of plant resistance will not only reduce damage to corn, but will reduce the potential for damage on other crops grown in the U.S. <BR>
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3. How does it relate to the National Program(s) and National Component(s)? National Program 304 Crop Protection and Quarantine 70%); National Program 305 Crop Production(30%): Research is being conducted on major insect pests of agricultural commodities grown in the Southeast such as field corn, sweet corn, sorghum, peanut and forage grasses. Germplasm is evaluated to identify sources of resistance to insects; bioassays and chemical extractions are made to determine the mechanism of resistance and identify the chemical(s) responsible for the resistance; and breeding studies are conducted to determine the genetics of the resistance. Improved germplasm with resistance to insects/aflatoxin producing fungi is then developed and released to private and public institutions for use in development of commercial germplasm to assist farmers in production of crops without use of pesticides. The germplasm is also evaluated for its effect on the population dynamics of these major insect pests. New molecular biology techniques have greatly enhanced transfer of resistant traits to more useful germplasm or to genetically engineered plants by transfer of a gene toxic to insects from one species to another. Molecular biology techniques are being used to identify the location of genes which confer resistance so that they may be used in marker assisted breeding that will greatly expedite the transfer of genes for resistance to insects. Several commercial companies have genetically engineered field corn or sweet corn to contain a Bt gene that produces an insect toxin. We have developed Cooperative Research and Development Agreements with several of these companies to assist them in evaluation of these genotypes for resistance to the corn earworm and fall armyworm. Our expertise in this area will expedite development of this germplasm so that it can be released for commercial production. <BR>
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4. What were the most significant accomplishments this past year? A. Single Most Significant Accomplishment during FY 2000 year: Alternate methods for controlling insects without the use of pesticides need to be developed. Working cooperatively with Dr. Peggy Ozias-Akins, University of Georgia, we conducted research at Tifton, GA, on peanut that was genetically modified to contain a CryIA(c) gene. Foliage from the transgenic peanuts containing the CryIA(c) toxin was highly resistant to the corn earworm, lesser cornstalk borer, and velvetbean caterpillar, but only moderately resistant to the fall armyworm. B. Other Significant Accomplishment(s), if any: Alternate methods for controlling insects without the use of pesticides need to be developed. Dow Agroscience developed a transgenic field corn hybrid that contained a modified construct for a Bt toxin. Field tests were conducted at Tifton, GA, to evaluate the hybrid for resistance to fall armyworm leaf feeding and corn earworm damage to the ear. The hybrid was highly resistant to fall armyworm leaf feeding and moderately resistant to ear damage. If released, this hybrid could provide another Bt transgenic corn with a novel new Bt gene construct. Many peanut producers in the southeast have switched to twin rows, i.e., two rows spaced approximately 9 inches apart. We conducted research at Tifton, GA, to evaluate recommended peanut lines for insect damage when planted at equal plant populations in single versus twin rows. No differences were noted in thrips, leafhopper, or corn earworm damage or in yield or grade of peanuts. Twin rows offer potential for reduced weed problems due to more rapid ground cover which shades weeds and often enhances yields. Sweet corn grown in the southeast is intensely sprayed with insecticide to eliminate insect damage to the ear. Collaborative research was continued to transfer resistance to the corn earworm due to maysin in silks from field corn to sweet corn. Research was conducted at Tifton, GA, and at the winter nursery at Homestead, FL, by backcrossing plants with high maysin content in the silk to the sweet corn parent. Successful completion of the transfer of the resistance mechanism to sweet corn could potentially reduce the usage of insecticides to prevent ear damage by 75-85 percent. C. Significant Accomplishments/Activities that Support Special Target Populations: None. <BR>
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5. Describe the major accomplishments over the life of the project including their predicted or actual impact. Resistance to the corn earworm and fall armyworm due to the presence of maysin in corn silks has been identified in the field, the mechanism of resistance determined, and the genetics of resistance studied. A CRADA was developed with Novartis Seeds, Inc. to transfer this resistance from field corn to sweet corn. We just completed the 5th year of the CRADA to transfer this resistance to sweet corn. Successful transfer of this resistance to sweet corn could reduce pesticide application to sweet corn by an estimated 75-85 percent. Plant resistance to insects via transgenic sweet corn containing a Bt gene could dramatically reduce the number of pesticide applications needed to prevent insect damage to the sweet corn ear. We evaluated 9 Bt sweet corn lines developed by Novartis, Seeds, Inc. in field and laboratory trials at Tifton, GA. Two of the lines were highly resistant to both the corn earworm and fall armyworm in that no larvae survived in the field in ears of the most resistant lines. These data were used to obtain EPA approval for commercial production of Bt sweet corn in the southeast.<BR>
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6. What do you expect to accomplish, year by year, over the next 3 years? This CRIS will be terminated since it was consolidated into new CRIS 6602-22000-031-00D in August 2000. The research for the next 3 years is shown below, but will be reported next year in the new CRIS project. <BR>
Year 1: Continue research to transfer resistance due to maysin in the silk to sweet corn using a backcross procedure, evaluate crosses for resistance to the corn earworm using germplasm generated from this research, and conduct evaluation of markers to identify resistance due to maysin. Continue the evaluation of Bt corn and peanut for resistance to insects. Continue evaluation of twin versus single rows with 6 recommended peanut cultivars to determine their impact on insect damage, yield, and grade. Study the preference of lesser cornstalk borer larvae for pods of different peanut lines. Evaluated fall armyworm collected from 4 geographical locations for susceptibility to the CryIA(b) toxin. <BR>
Year 2: Continue evaluation of sweet corn germplasm with high level of silk maysin for resistance to the corn earworm in both field and laboratory tests. Continue the evaluation of Bt corn and peanut for resistance to insects. Continue the evaluation of the effects of twin versus single rows with 6 recommended peanut cultivars to determine their impact on insect damage, yield, and grade. Continue evaluation of fall armyworm collected from 4 geographical locations for susceptibility to the CryIA(b) toxin. Initiate tests on minimum till peanut to determine impact on insects. <BR>
Year 3: Conclude evaluation of sweet corn germplasm with high level of silk maysin for resistance to the corn earworm in both field and laboratory tests. Continue the evaluation of Bt corn and peanut for resistance to insects. Continue the evaluation of the effects of twin versus single rows with 6 recommended peanut cultivars to determine their impact on insect damage, yield, and grade. Continue evaluation on minimum tilled peanuts. <BR>
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7. 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 germplasm lines with resistance to insects and/or aflatoxin contamination have been released and are currently being used by both public and private breeders around the world. Bt sweet corn was approved by EPA for commercial production in the southeastern U.S., based in large part on data collected by Unit scientists. Techniques for artificially infesting plants with insects and evaluation techniques have been transferred to numerous private companies and/or other governmental agencies and institutes worldwide for use in evaluation for resistance to insects.