GMOs and corn mycotoxins
Corn grain can be naturally contaminated by mycotoxins, natural toxins produced by fungi. Though most Kentucky corn crops are free of mycotoxins, fumonisins are the most common threat. These toxins affect a number of animal species, but horses and pigs are among the most sensitive. Aflatoxins are generally very uncommon in Kentucky, but when they occur, they can cause serious disruption to grain marketing. Both mycotoxin families pose health risks to humans.
Wounding of the kernel makes it easier for infection by the fungi that produce mycotoxins. European corn borer and other caterpillars commonly produce wounds that favor infection and mycotoxin contamination. That being the case, does the use of genetically modified Bt corn—genetically engineered to provide control of certain insect pests—result in reduced mycotoxin contamination?
To address this question, field studies have been conducted comparing Bt-hybrids to non-Bt hybrids that are otherwise genetically very similar. Thus far, the overall results are that meaningful mycotoxin reductions sometimes occur due to the Bt trait. A more detailed discussion follows.
Field studies in the USA and Europe have shown reduced Fusarium ear rot and reduced fumonisin contamination from Bt corn. These reductions have been associated with reduced insect feeding on kernels containing the Bt toxin.
In studies where reductions in fumonisin concentration occurred, these ranged from 20% to 90%, often bringing the grain below concentrations that pose risks to humans and the most sensitive animals. It is interesting to note that the application of synthetic insecticides to control kernel-feeding insects on non-Bt plants also sometimes reduces insect feeding and fumonisin contamination. This raises the question as to which is more sustainable: use of the Bt trait or application of insecticides. Either way, reductions in fumonisin contamination are highly desirable.
As with fumonisins, field studies have often documented reductions in aflatoxin contamination due to the Bt trait. Significant reductions were most common when aflatoxin levels were at moderate to high levels in the non-Bt corn.
In studies where reductions were documented, these commonly ranged from 50-90%. In some cases, aflatoxin reductions from the Bt trait were sufficient to bring the corn below 20 parts per billion, an important regulatory threshold for use of the grain in human foods. As with fumonisins, aflatoxin reductions from the Bt trait have generally been linked to reductions in kernel injury from insect feeding. In some cases, the Bt trait did not result in aflatoxin reductions. This may be due to several reasons:
- In those fields, drought stress may have been more important in promoting aflatoxin accumulation than insect damage to kernels;
- As noted below, the Bt trait isn’t effective against all kernel-feeding insects.