The dry conditions in Illinois, Iowa, and Indiana for the past month have been reminiscent of 2012, causing many farmers making yield estimates to also look for potential mold damage from fungi that like dry conditions. Aflatoxin was a major revenue reducer last year for farmers and elevators, and it could disrupt the marketing of corn again if produced by mycotoxins thriving in the current weather. But some farmers, who might suspect the presence of molds, may not find it, thanks to the genetics in the Bt corn they have planted.
Bt corn is not a silver bullet for preventing mycotoxins and other molds in droughty corn, says Paul Vincelli at the University of Kentucky. However, some Bt hybrids will reduce the potential for mold development by preventing insect damage that fosters mold development.
Vincelli says kernels that are wounded by insect feeding make it easier for fungi to infect the kernel and produce mycotoxins, such as aflatoxin and fumonisin. Both can threaten the vitality of livestock that feed on infected corn and grain quality tests will frequently result in load rejection or severe elevator discounts for high levels of the toxin. Corn borers, ear worms, and other caterpillars that feed on corn will damage kernels and allow the introduction of contaminants.
Vincelli says research has shown that comparisons of two corn hybrids, different only by the presence of a Bt gene, indicates “meaningful mycotoxin reductions sometimes occur due to the Bt trait.” Research in both the US and Europe has shown reductions in fusarium ear rot and fumonisin contamination due to the Bt trait. In fact, some fumonisin reductions were as much as 90 percent, pushing the contamination level below the risk for humans and livestock. Similar findings occurred with aflatoxin, particularly when levels were moderate to high in the non-Bt hybrids
However, the use of Bt seed is not a cure-all, since sometimes there are no reductions in the amount of mycotoxins. Vincelli says it all depends on how and where the Bt gene is expressed in the corn plant. Bt genes which are expressed in corn roots, can control corn rootworm. But those Bt genes are not always expressed throughout the plant, particularly in the grain. Vincelli says, “The Bt toxin must be expressed in the corn kernel in order to reduce insect injury and, ultimately, mycotoxin levels. In some Bt corn hybrids, the Bt toxin is not expressed in the kernel. Such hybrids have no protection against wounds created by insect feeding, and therefore fumonisin contamination is not reduced in these hybrids.”
If the grain carries the Bt gene, many ear-feeding insects should be controlled and the chance for mycotoxin infection would be reduced. But Vincelli says success also depends on the insect. “The effectiveness of the Bt trait in reducing mycotoxin contamination depends on the insect pest present. For example, Bt corn is often effective at reducing feeding damage from the European corn borer, but not the corn earworm. Consequently, reductions in fumonisin contamination may occur if the European corn borer is the principal pest in a field, but not if the corn earworm is predominant.
But Vincelli also says not all hybrids will have the Bt genetics in the ear. “The Bt trait is not a “silver bullet”, eliminating all mycotoxin risk. However, reductions occur commonly enough, with no known “downside”, that the Bt trait is thought to contribute to food safety and livestock health in both developed and developing countries. While it is well-documented that the Bt trait can reduce mycotoxin contamination, it is best used wisely, and only in fields with a moderate to high risk of damage from the target insect pests.”
Some Bt hybrids will be able to shield themselves against mycotoxins that are produced in the fungus in droughty corn. The fungus typically attacks on the corn ear where insects have physically damaged the kernels. The Bt hybrid that carries the Bt gene into the grain will help prevent a mycotoxin infection, since it may be able to control ear-feeding insects. But not all Bt hybrids have that capability.
Source: FarmGate blog