Husker findings boost understanding of sorghum’s pest resistance

Husker scientists have identified a key plant hormone that strengthens sorghum self-protection against the threat of the sugarcane aphid. The federally funded project is part of the university’s wide-ranging, multidisciplinary work to advance understanding of sorghum’s natural defenses against the pest. 

University of Nebraska–Lincoln scientists, in collaboration with the U.S. Department of Agriculture’s Agricultural Research Service, pointed to the significance of auxin/IAA metabolism and auxin conjugate IAA-Asp, which are involved in various aspects of plant growth and development. 

Sorghum resistance was greater when the plants had a higher level of the identified IAA-Asp hormone due to a mutation in the gene Bmr12, said Joe Louis, Harold W. Eberhard Professor of Agricultural Entomology. Husker researchers are primarily focused on how the mutation of this gene affects the aphid population and the mechanism behind it, he said. 

After identifying the importance of the IAA-Asp hormone, researchers added varying amounts of it to the aphid diet and found it boosted sorghum’s natural pest resistance. 

The researchers’ findings recently appeared in the journal New Phytologist. 

Natural defenses for sorghum are intended as a supplement to other measures such as pesticides and genetically modified plants. Adding that natural protection may provide more durable and sustainable protection overall, Louis said. 

The sugarcane aphid has been a serious pest for sorghum in the United States since 2013, causing damage in multiple ways. 

First, aphids use their needle-like mouthpart to pierce the plant and suck out nutrients without any visible damage initially to the plant. Second, the pests’ excretions, or honeydew, cover parts of the plant and disrupt photosynthesis crucial to the plant’s well-being. Third, aphids can transmit viral diseases. 

“If the plants survive and are ready for harvest and there is a lot of honeydew, the harvester gets clogged,” Louis said. 

The Husker project is unique for its a “holistic” multidisciplinary approach to this area of science, he said. The researchers pursue high-level study of cells and tissues, as well as biochemical, electrophysiological and computational analysis. 

Louis and his colleagues will follow up by studying whether the hormone is effective in boosting plant resistance to other types of aphids. They also will look for additional biological factors possibly affecting sorghum’s level of natural self-protection. 

The project illustrated the university’s tradition, extending back to the late 1800s, of research collaboration with U.S. Department of Agriculture scientists. A co-author of the New Phytologist paper is Scott Sattler, adjunct professor of agronomy and horticulture and research leader with the USDA Agricultural Research Service Wheat, Sorghum and Forage Research Unit on East Campus. 

In addition to Louis, the other co-authors are Sajjan Grover and Heena Puri, doctoral alumni in entomology; De-Fen Mou, former postdoctoral research associate in entomology; Kumar Shrestha, postdoctoral research associate in entomology, and Lise Pingault, senior research associate in entomology. 

A National Science Foundation CAREER grant to Louis supported the project, as did a grant from USDA’s National Institute of Food and Agriculture to Louis and Sattler.

The project took interesting twists and turns, beginning with study of lignin, a polymer providing cell wall stability and aiding water transport. Louis and his colleagues initially thought changes in lignin levels were central to understanding resistance to the aphid. But the findings didn’t square with that hypothesis.

“To our surprise, we found it has nothing to do with lignin,” Louis said. “That made us think, what else is going on? So we started looking at using all these different technologies available here.”

The scientists’ multidisciplinary analysis “helped us narrow down to this compound, the indole-3-acetic acid, conjugated with the amino acid aspartate,” he said. “Then, we tested it directly into the aphid diet, and we found this compound is providing resistance to the aphid.”

Such perambulations of research are an expected part of complex scientific inquiry, Louis said. 

“This is the way science works,” he said. “We started somewhere, and we ended somewhere else. But that's the fun part of doing science.”