Corn Wax Makes Toxin Wane

Waxy build-up may be bad on floors, but it could be good news if you’re growing corn, scientists with USDA’s Agricultural Research Service say.

They report that kernels of a corn line called GT:MAS:gk seem to have unusually thick waxy outer layers. This waxy coating helps protect the corn against attacks by Aspergillus flavus, a fungus that produces a dangerous contaminant on corn kernels called aflatoxin.

Federal law prohibits use of any crop as a food source or as dairy feed if it contains more than 20 parts per billion of aflatoxin. One part per billion is equal to an inch in 16,000 miles. Farmers sometimes have to destroy crops if aflatoxin levels are too high.

Years ago, an ARS scientist reported GT:MAS:gk corn had resistance to aflatoxin. This thick waxy coating on its kernels could explain, at least in part, the higher resistance.

Scientists say one important factor is the sheer bulk of the GT:MAS:gk wax. It averages 25 percent more than in corn lines vulnerable to A. flavus, but can climb to 60 percent more.

But the aflatoxin barrier may be more than just physical. Research done in collaboration with Louisiana State University scientists suggests the waxy outer layer may chemically fend off the fungus as well. In studies, GT:MAS:gk wax inhibited growth of A. flavus colonies by 35 percent. Wax from susceptible corn did nothing to stem fungal growth.

Scientists say the wax formula might be duplicated in the lab. They’re studying the wax structure and looking for ways to breed or genetically engineer commercial corn lines to express this waxy trait.

Scientific contact: Robert Brown, USDA-ARS Southern Regional Research Center, New Orleans, La., phone (504) 286-4531, e-mail rbrown@nola.srrc.usda.gov; Neil Widstrom, USDA-ARS Insect Biology and Population Management Research Laboratory, Tifton, Ga., phone (912) 387-2320, e-mail nwidstro@tifton.cpes.peachnet.edu