New Corn Lines Ward off Aflatoxin

Researchers are closing in on new corn lines whose kernels fend off harmful fungi with potent natural defenses. Commercial development of such resistant corn, possible within a few years, could help reduce aflatoxin contamination of the crop.

Since 1991, Agricultural Research Service scientists in New Orleans have been testing corn lines from all over the world for kernel resistance to Aspergillus flavus, the culprit behind aflatoxin. Aflatoxin contamination of crops by A. flavus is a serious problem during droughts. The fungus produces the toxin in corn seed as well as peanuts and cotton. Aflatoxin is so potent that no crop with more than 20 parts per billion can be sold for animal feed.

One promising corn line tested by ARS plant pathologist Robert Brown and colleagues is dubbed GT-MAS:gk. The researchers discovered that the line’s kernels “wear” a thick, waxy coat that inhibits the growth of A. flavus. They’re also trying to identify natural chemicals in the kernel wax that may foil the fungus.

Other resistant corn lines they examined have kernels with high levels of a protein called a trypsin inhibitor that keeps A. flavus and other fungi at bay. The New Orleans group and ARS colleagues based at Mississippi State University are testing the protein’s insecticidal properties against corn earworms. Chewing damage caused by this caterpillar pest helps virulent fungi gain easier entry to the plant.

Key to the scientists’ research is a kernel screening assay for measuring aflatoxin levels. It is fast and easy to use and requires only a few kernels. When used with a fungus equipped with a genetic fragment called a reporter gene, the assay allows researchers to pinpoint the microbe’s locale or concentration on seeds. This also helps reveal seed regions where resistant mechanisms might be at work. Plant breeders will also find the assay useful.

Scientific contact: Robert Brown, ARS Food and Feed Safety Research Unit, Southern Regional Research Center, New Orleans, La., phone (504) 286-4359, fax (504) 286-4419, Rbrown@nola.srrc.usda.gov.