Characterizing the Distribution of Aflatoxin and Fumonisin in corn Populations

Field experiments will be conducted for two seasons in conventional 38-inch row spacings on a Norwood silt loam soil at the Dean Lee Research Station in central Louisiana. The test includes two inbreds; 'B73' (susceptible) and 'Tex6' (resistant); and four treatments; 1=Open-pollinated noninoculated ears, 2=Open pollinated inoculated (Aspergillus flavus) ears, 3=Self-pollinated non-inoculated ears, and 4=Self-pollinated inoculated (Aspergillus flavus) ears. A split-plot design will be used with inbred as main plot and treatment as sub-plot. Each inbred-treatment combination is replicated 20 times. Plots are two-rows wide and 60 feet long. Sub-plots are 15-foot row increments of the main plot. Each plot will be separated by two rows of mixed corn to help ensure that foreign pollen is available during anthesis of both B73 and Tex6. Ten ears will be treated and tagged in each sub-plot, providing 200 ears to construct histograms for each inbred-treatment combination. A total of 1600 ears will be tested for aflatoxin and fumonisin. Self-pollinations will be made at anthesis. Inoculations will be made 10 to 14 days later using a hand-held 36-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 Aspergillus 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 coarse meal and sent to the USDA-ARS facility at Stoneville MS where they will be analyzed for aflatoxin and fumonisin using commercially available assay kits distributed by Neogen Corporation of Lansing, MI (Abbas et al, 1998). Histograms for each inbred and treatment will be constructed by plotting aflatoxin contamination on frequency of occurrence. Distribution and means will be calculated to determine how many ears are needed to confidently estimate the mean aflatoxin concentration in each population. To determine the effects of combining ears to measure aflatoxin, a small portion (Tablespoon) of finely ground meal will be taken out of individual sample bags for each ear within each subplot and combined (140 total additional samples). Aflatoxin readings from the combined samples will be compared to the mean of the 10 ears from which the sample was derived. A determination will be made at this point for additional combinations. In the second year of the study, 200 accessions will be screened using results (ear number and replications) from frequency distributions measured in the first year. Accessions will be planted on a Norwood silt loam soil in 38-inch rows.