Screening the World Corn Collection to Find New Genes with Resistance to Aflatoxin and Fumonisin

Approach: Three major steps are outlined to improve resistance of commercial hybrids to aflatoxin biosynthesis. The first is large scale screening of corn germplasm (accessions) to identify new resistance. The second is to stabilize newfound resistance into improved populations. The third is to transfer resistance into commercial inbreds. Step one: Screen Corn Germplasm for Improved Resistance. Our screening procedure requires two seasons. In season one corn accessions are hybridized with B73 to produce F1 seed. Mr. Mark Millard, Maize Curator at the North American Plant Introduction Center in Ames, Iowa, will share responsibility to select accessions for screening and provide seed. Initial priority will be given to accessions originating from hot and dry climates where active or passive selection for resistance might have occurred. Accessions will be hybridized B73 to produce F1 seed in summer nurseries at Alexandria, Louisiana. B73 has been perhaps the most widely recognized corn inbred and represents one side of the most common heterozygous hybrid combination. Accessions hybridized with B73 produce F1 seed with improved vigor and ear size. Resistance in F1 seed also provides a better indicator of useful resistance than in the original accession. In season two, F1 ears are inoculated with Aspergillus flavus and screened for aflatoxin and fumonisin contamination. Screening nurseries are conducted in conventional 38-inch row spacings on a Norwood silt loam soil at the Dean Lee Research Station in central Louisiana by Dr. Steven Moore, LSU Ag Center corn breeder. A randomized complete block design is used with two replications. Each replication will include resistant checks of B73:Mp313e and B73:Tex6. The experimental unit is ten ears from a single row. Ears will be inoculated with A. flavus spores after anthesis using a hand-held pin bar apparatus dipped in a container containing spores in liquid suspension (about or equal to 90 million spores/ml). Ears will be harvested after physiological maturity, dried, ground to a fine meal and sent to the USDA-ARS facility at Stoneville, Mississippi, for aflatoxin and fumonisin analyses by Dr. Hamed Abbas, USDA Research Pathologist. Dr. Abbas will also maintain inoculum and provide spore suspensions at the time of anthesis. Resistance will be assessed by Dr. Moore. To date, 1600 lines from the North American Plant Intoduction Center have been planted in nurseries at Alexandria, LA, although many have not been successfully pollinated and screened. Step two: Develop Breeding Populations - Seed from accessions showing the lowest aflatoxin will be screened again to confirm resistance. Selected accessions crossed to B73 will be selfed to the F4 generation. Resistant and non-resistant populations will be identified and planned for use in commercial marker-assisted programs where resistance can be transferred into elite inbreds. Eleven lines with potentially improved resistance are now being advanced (Nigerian Composite B. Manio-PI490411, Haiti 33-PI483902, Saint Croix1-PI484036, TZI18-PI506253, Tx81, Tx807 and CML43-PI595535). Step three: Transfer Improved Resistance into Commerical Inbreds.