Location: Corn Host Plant Resistance Research2013 Annual Report
1a. Objectives (from AD-416):
The objective of this project is to further validate new inbred lines displaying high and stable resistance to A. flavus and aflatoxin accumulation in new environments, and test which will be adapted to African growing conditions and disease pressures. Germplasm and genes will be sent to maize breeders in ongoing breeding programs to develop resistant varieties for developing world farmers within three years. In addition to adaptation, specific and general combining ability will be tested, and information on performance of the lines in hybrid combinations in different environments will be made publically available to maize breeders and small seed companies in Africa.
1b. Approach (from AD-416):
Considerable work has already been done in the mapping of aflatoxin and A. flavus resistance in maize, and breeding lines that show stable and consistent resistance are currently available for this project. Breeding lines from the CHPRRU will be field tested in various hybrid combinations and to form new synthetics to enhance resistance to aflatoxin accumulation in existing African maize germplasm. In the first year, a design II mating scheme will be used to generate hybrids with the CHPRRU donor lines. The resulting hybrids will be evaluated in multiple locations under naturally occurring A. flavus infection in the second growing season of the first year to generate information on combining ability of the lines for yield and resistance to aflatoxin production; ears from the hybrids will be tested for aflatoxin levels using an ELISA assay. The information will be useful to form synthetics, identify the best donor lines for African breeding programs, and select potential crosses that can be backcrossed to an adapted lines to generate source populations to develop new generation of inbred lines with much higher levels of resistance to aflatoxin accumulation. The hybrids will also be evaluated under controlled drought stress during the second year. Synthetics will be formed in the third year, which can be used directly as cultivars for farmers in parts of the world where aflatoxin poisoning has been an ongoing and serious problem, or can be used by breeders to extract new resistant inbred lines with good agronomic performance and local adaptation, via Marker Assisted Selection using markers linked to resistance genes from the CHPRRU. The synthetics will be field tested and varieties released after the third year.
3. Progress Report:
The primary objective of this project is to transfer corn germplasm with resistance to Aspergillus flavus infection and aflatoxin accumulation to plant breeders in developing countries and to facilitate integration of resistance into their breeding projects. New sources include new inbred lines displaying high and stable resistance to Aspergillus flavus and aflatoxin accumulation and also new genes and gene-based markers linked to these traits for the faster incorporation of resistance into ongoing breeding programs. Inbred lines displaying high and stable resistance to A. flavus and aflatoxin accumulation in the field tests conducted by ARS scientists at Mississippi State, Mississippi, will be evaluated for adaptation to African growing conditions and disease pressures. Identification of new resistant inbred lines was accomplished during the phenotypic characterization of an association mapping panel of 300 inbred lines of corn. The association mapping panel was created by ARS scientists at Mississippi State, Mississippi, and included 300 diverse inbred lines. Some lines were selected because of their known resistance to aflatoxin contamination; some were selected from environments where Aspergillus flavus is often epidemic; and others were selected to add genetic diversity to the panel. The lines were crossed with a susceptible inbred line that is adapted to the southern United States. The resulting testcrosses were grown in replicated field trials for two years. Grain samples collected from the field trials were analyzed to determine concentration of aflatoxin. The 30 most consistently resistant lines of the panel were identified; seed were increased in the ARS 2012-2013 winter nursery. Seed were sent to cooperators at the International Institute for Tropical Agriculture (IITA) in Nigeria where they are being grown for further seed increase and for production of testcrosses with two yellow and two white testers from different heterotic groups. The testcrosses will be evaluated for adaptation and resistance to aflatoxin contamination. General and specific combining ability for resistance to aflatoxin contamination and other important agronomic traits will be determined via the testcrosses. Information on performance of the lines in hybrid combinations in different environments will be made publically available to corn breeders and small seed companies in Africa. The information will also be used to generate synthetic corn varieties that will be further enhanced for resistance to aflatoxin contamination via Marker Assisted Reciprocal Recurrent Selection.