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Postharvest Pathology and Mycotoxins

Growth Characteristics of Aspergillus flavus on Agar Infused With Maize Kernel Homogenates and Aflatoxin Contamination of Whole Kernel Samples. N. W. Widstrom, Research geneticist, Southern Grain Insects Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Tifton, GA 31793; W. W. McMillian(2), D. M. Wilson(3), D. L. Garwood(4), and D. V. Glover(5). (2)Research entomologist, Southern Grain Insects Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Tifton, GA 31793; (3)Professor, Department of Plant Pathology, University of Georgia College of Agriculture Experiment Stations, Coastal Plain Station, Tifton; (4)Owner, Garwood Seed Company, Stonington, IL 62567; (5)Professor, Department of Agronomy, Purdue University, W. LaFayette, IN 47907. Phytopathology 74:887-890. Accepted for publication 11 February 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-887.

Methods of measurement have been a major obstacle to the detection of maize (Zea mays L.) genotypes resistant to infection by Aspergillus flavus and aflatoxin production. Mature grain of field-inoculated hybrids was evaluated for preharvest aflatoxin contamination in 1977, 1978, and 1980, and laboratory-inoculated mature kernel samples were evaluated for aflatoxin production in 1981. In each year, ground grain of eight commercial hybrids sampled 25, 40, and 56 days after anthesis was infused in antibiotic-amended agar which was placed in petri plates and inoculated with the fungus. After incubation for 7 days at 30 C, evaluations were made for colony diameter, sporulation amount, and sporulation distribution. Colony diameter was a better criterion than sporulation characteristics for detecting differences among hybrids. Grain harvested 25 days after anthesis supported greater fungal growth than that harvested at 40 and 56 days. Various kernel genotypes having endosperms classified as amylose extender, brittle, dull, floury, normal, shrunken, soft starch, sugary, or waxy in B37 Oh43 (dent) and/or Ia453 Ia5125 (sweet) backgrounds were similarly tested. Colony diameters and amounts of sporulation were significantly different among endosperm genotypes within these backgrounds. Differences among hybrids and endosperm variants were more consistent for aflatoxin contamination than for colony characteristics. Mycelial growth was clearly enhanced by the presence of sugary endosperm. The more restricted growth on starchy types was consistent with that found for mature kernels of the commercial hybrids. Sugar content of the kernels was an overriding factor contributing to differences among genotypes for aflatoxin contamination of kernel samples in this study.