Research improves understanding of pest resistance in sorghum

Husker scientists have identified a key plant hormone that strengthens sorghum’s defenses against the threat of sugarcane aphids. The project is part of the university’s multidisciplinary research to better understand sorghum’s natural defenses against pests.

Scientists from the University of Nebraska-Lincoln, in collaboration with the United States Department of Agriculture’s Agricultural Research Service, have pointed out the importance of auxin/IAA metabolism and the auxin complex IAA-Asp, which is involved in multiple aspects of plant growth and development.

Joe Lewis, the Harold W. Eberhardt Professor of Agricultural Entomology, said sorghum resistance was higher when the plants had higher levels of the hormone IAA-Asp, identified through a mutation in the gene Bmr12. Husker researchers are primarily focused on how mutations in this gene affect aphid populations and the mechanisms behind this, he said.

After identifying the importance of the IAA-Asp hormone, the researchers added different amounts of the hormone to the aphids’ food and found that this enhanced sorghum’s natural pest resistance.

The researchers’ findings were recently published in the journal New Phytologist.

Sorghum’s natural defenses are intended as a complement to other measures such as pesticides and genetically modified plants, and Louis added that the natural defenses may offer more durable and sustainable protection overall.

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

First, aphids use their needle-like mouthparts to pierce plants and suck out nutrients without initially causing any visible damage. Second, the pest’s waste, or honeydew, coats parts of the plant, preventing photosynthesis, which is essential for plant health. Finally, aphids can transmit viral diseases.

“If the plants survive and are ready to be harvested and there’s too much nectar, it will clog the harvesters,” Lewis said.

The Husker project is unique for its “holistic” interdisciplinary approach to this field of science, he said: Researchers are pursuing advanced studies of cells and tissues, as well as biochemistry, electrophysiology and computational analysis.

Lewis and his colleagues plan to continue studying whether the hormone is effective in boosting plants’ resistance to other types of aphids, and they also plan to look for additional biological factors that may affect sorghum’s natural level of defense.

The project showcased the university’s tradition of collaborating with USDA scientists, dating back to the late 1800s. One of the co-authors of the New Phytologist paper is Scott Sattler, adjunct professor of agronomy and horticulture and research leader in the USDA Agricultural Research Service’s Wheat, Sorghum and Forage Research Unit on East Campus.

In addition to Lewis, other co-authors are entomology doctoral graduates Sajjan Grover and Heena Puri, former entomology postdoctoral research associate Defen Mou, entomology postdoctoral research associate Kumar Shrestha, and entomology senior research associate Lise Pango.

This project was supported by a National Science Foundation CAREER grant to Louis and grants from the U.S. Department of Agriculture’s National Institute of Food and Agriculture to Louis and Sattler.

The project took an interesting twist, beginning with a study of lignin, a polymer that provides stability to cell walls and aids in water transport. Lewis and his colleagues initially thought that changes in lignin levels might be key to understanding resistance to aphids. But their findings didn’t match that hypothesis.

“To our surprise, we found that it had nothing to do with lignin,” Lewis says, “so it got us thinking, what else is going on? So we started looking at leveraging the different technologies available here.”

Through their multidisciplinary analysis, the scientists “were able to narrow down this compound – indole-3-acetic acid linked to the amino acid aspartic acid,” he said, “and then we tested it by administering it directly to the aphids’ food and found that this compound conferred resistance to the aphids.”

Such research developments are a natural part of complex scientific inquiry, Lui said.

“That’s the way science works,” he says, “we start somewhere and end up somewhere else, but that’s the fun part about doing science.”