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

Five steps are proposed for identifying and using new resistant genes. Step One - Select corn accessions for screening. Mr. Mark Millard, Maize Curator at the North American Plant Introduction Center in Ames, Iowa has primary responsibility to select accessions for choosing and securing seed, and for making quarantine arrangements where needed. Initial priority will be given to accessions originating from hot and dry climates where active or passive selection for resistance might have occurred. Three-hundred lines will be screened in 2003, including lines originating from the Carribean, Ethiopia, Guinea, Ghana, Mexico, South Africa, West Texas and Zimbabwe. The intent is to screen 2000 lines in subsequent years. Step Two - Inoculate corn lines in a field nursery. Dr. Steven Moore, LSU corn breeder, will conduct a field nursery at the Dean Lee Research Station in central Louisiana. A randomized complete block design will be used with two replications. Each replication will include resistant checks, including Gt-MAS:gk, Mp313e, Mp420, Mp715, and Tex6. Ears will be inoculated with A. flavus spores 10 to 14 days after anthesis using a hand-held pin bar apparatus dipped in a container containing spores in liquid suspension (90 million spores/ml). Ears will be harvested after physiological maturity and dried below 12% moisture. Harvested ears will be rated for A. flavus growth on a 0 to 9 scale, shelled, and then ground to a coarse meal and rated for bright greenish-yellow fluorescence (BGYF) on a 0 to 9 scale. Samples will then be ground to a fine meal and sent to the USDA-ARS facility at Stoneville, Mississippi for aflatoxin and fumonisin analyses. Step Three - Analyze corn lines for aflatoxin and fumonisin. Dr. Hamed Abbas, USDA Research Pathologist, will analyze corn meal samples for aflatoxin and fumonisin using commercially available assay kits distributed by Neogen Corporation of Lansing, MI (Abbas et al, 1998). Dr. Abbas will also maintain inoculum and provide spore suspensions at the time of anthesis. Resistance will be assessed by Dr. Moore. Step Four - Hybridize resistant lines. Lines showing superior resistance will be hybridized with "B73' or `Mo17' inbreds in a winter nursery to produce F1 hybrid seed to determine breeding value the subsequent year. Approximately 10 ears will be selfed and 10 ears will be cross-pollinated. Step Five - Incorporate resistant lines into breeding programs. Seed from resistant lines and hybrid seed from the same lines crossed to B73 or Mo17 will be sent to Dr, Bazou Guo at Tipton, Georgia, to Dr. Xavier Bertrand at College Station, Texas, and to Dr. Steven Moore at Alexandria, Louisiana. Seed will be tested further for resistance and incorporated into the respective breeding programs. This procedure allows for the most rapid evaluation.