Using these diverse varieties of corn allowed the researchers to zero in on the regions of the genome responsible for conferring resistance to the three diseases — and thus to varieties that are very resistant to disease.

“We tested the lines for resistance to these three diseases and found that if a line is resistant to one disease, chances are it’s also resistant to the other two,” Balint-Kurti says.

The researchers then delved into the question of why this multiple resistance occurs.

“One hypothesis was that if a corn variety has resistance genes for one disease, it is likely to also have resistance genes for the others,” Balint-Kurti says.

“The other hypothesis was that the same genes conferred resistance to multiple pathogens. Our evidence suggests that the latter hypothesis is more likely. In particular, we have developed good evidence that a specific gene, a member of a gene family called glutathione-S-tranferases, is associated with resistance to all three diseases.”

Southern corn leaf blight is a moderate problem in the Southeastern United States, Balint-Kurti says, and can be a significant problem in Southeast Asia, southern Europe and parts of Africa.

Prevalent in hot, humid climates across the globe, it causes small brown spots on leaves. The spots get larger and eventually spread to the whole plant. Severe infections can cause major corn yield losses.

Northern leaf blight can be found in the Midwestern corn belt; it causes cigar-shaped lesions on leaves.

Gray leaf spot — which produces an eponymous effect — is found both in the Midwest and Southeast. All three pathogens are so-called necrotrophic fungi, or fungi that kill what they eat.

Balint-Kurti says the study provides “one of the most comprehensive analyses of multiple disease resistance in plants.”

The research was funded by USDA-ARS, the National Science Foundation, CGIAR Generation Challenge Program, the North Carolina Corn Growers Association, and USDA-National Institute of Food and Agriculture.