Preharvest contamination of com (Zea mays L.) with aflatoxin, a metabolite produced by the fungus Aspergillus flavus Link: Fr., is a recurrent problem in the southeastern United States, but occasional serious outbreaks also occur in the Midwest Com Belt (21). Aflatoxins are recognized as potent hepatotoxins and carcinogens, causing mortality or reducing the productivity of farm animals (89). Aflatoxin-contaminated foodstuffs also have been associated with increased incidence of liver cancer in humans (39). In com-producing regions, the economic impact from yield loss is not very large, but A. flavus contaminates the grain with aflatoxin. Fungal toxins reduce the value of grain as an animal feed and devalue it as an export commodity (74).

Any strategy that reduces the extent of aflatoxin contamination of com will result in a safer and more valuable food supply for humans and animals. Plant pathologists and com breeders have thus far been unable to identify com genotypes with substantial resistance to aflatoxin contamination. On ears in the field, A. flavus grows saprophytically on the remains of kernels damaged by insects or birds. These damaged kernels can become contaminated with substantial quantities of aflatoxin (i.e., to as much as 300,000-600,000 ppb). Aflatoxin also accumulates (to as much as 4,000 ppb) in many of the adjacent intact kernels. It does not take a large quantity of these aflatoxin-contaminated kernels to contaminate bulk grain with >20 ppb aflatoxin. At present, the only reliable method for preventing aflatoxin from entering the food chain has been the detection and segregation of aflatoxin-contaminated produce.