Comparison of Fumonisin Concentrations in Kernels of Transgenic Bt Maize Hybrids and Nontransgenic Hybrids

Fungi in the genus Fusarium are very common associates of maize (Zea mays L.) plants. These fungi can cause disease at all developmental stages of the plant, but also may infect plants without causing symptoms (24). Certain Fusarium species, particularly F. verticillioides (Sacc.) Nirenberg (synonym = F. moniliforme J. Sheld.) and F. proliferatum (T. Matsushima) Nirenberg, often infect maize plants through wounds caused by insects such as the European corn borer (Ostrinia nubilalis) (3,24). The same two species are capable of producing fumonisins, a class of mycotoxins that can cause fatal leucoencephalomalacia in horses, pulmonary edema in swine, and cancer in laboratory rats (13). Esophageal cancer in humans has been associated with consumption of maize with high concentrations of the fumonisins. The compounds are now classified as Class 2B, probable human carcinogens (10,20). Fumonisins can be found in maize grown throughout most of the world, and they are the most commonly occurring mycotoxins in maize grown in the midwestern United States (16,27). This class of toxins includes several homologs, but fumonisin B1 is typically found in the highest concentrations (16). Fumonisin-producing Fusarium species cause Fusarium ear or kernel rot, but fumonisins also can be detected in symptomless infected maize kernels (16). The European corn borer (ECB) is a major pest of maize. The larvae of this insect tunnel into the stalks and ears of the plants, causing yield reduction and loss of grain quality (14). In the north central United States, two generations of ECB larvae typically occur per year; the first generation attacks plants during the midto late-vegetative stages (V8-V10 [22]), and the second generation attacks during the reproductive stages (R1 to maturity). Adult moths lay masses of eggs on leaf surfaces, and the larvae migrate to protected sites, where they feed on leaves, stalks, and ears (14). These larvae cause physical injury to the plants, where Fusarium infection can occur (3), and the larvae also can carry Fusarium spores from the leaf surface, transmitting them to the infection court (feeding site) (25). A new strategy for the management of O. nubilalis is the use of transgenic maize hybrids (Bt maize). Now commercially available, these hybrids contain cry genes originating from the bacterium Bacillus thuringiensis; gene expression results in the production of insecticidal crystalline proteins in plant tissue (8). Currently available commercial hybrids express one of three Cry proteins: CryIA(b), CryIA(c), or Cry9C. Maize hybrids expressing Cry proteins have demonstrated a high level of resistance to feeding by ECB larvae (2,11). Expression of Cry proteins in specific maize tissues can be manipulated through the use of different gene promoters (11). Specific combinations of transgenes and gene promoters are often called “transformation events,” and each combination must be approved separately by the U.S. Environmental Protection Agency. The use of these genetically engineered maize hybrids has been widely accepted in the United States but has met opposition elsewhere in the world because of concerns about food safety, environmental protection, and ethical issues. Transgenic maize hybrids expressing CryIA(b) in kernels can experience less Fusarium infection in kernels because of the association between Fusarium infection and insect feeding (17). We hypothesized these hybrids also might contain lower concentrations of fumonisins than nontransgenic hybrids that are susceptible to the ECB. The objective of this study was to test this hypothesis through field experiments using near-isogenic maize hybrids with and without cry genes. Fusarium infection data from two of ABSTRACT Munkvold, G. P., Hellmich, R. L., and Rice, L. G. 1999. Comparison of fumonisin concentrations in kernels of transgenic Bt maize hybrids and nontransgenic hybrids. Plant Dis. 83:130138.