Corn's resistance to insects may potentially be enhanced by transplanting beneficial microbes found in teosinte, corn’s ancestor. By focusing on beneficial microbes from teosinte, a Texas A&M AgriLife research team aims to create an environmentally friendly insect-control method.
The work is needed because fall armyworm, western corn rootworm and other insects are becoming increasingly resistant to existing control methods. In the United States alone, western corn rootworm causes more than $1 billion in damage to corn crops each year. Insect resistance to pesticides can lead to more pesticide use.
Leading the project is Julio Bernal, a professor in the entomology department at Texas A&M University. Bernal is collaborating with Sanjay Antony-Babu, an assistant professor in the department of plant pathology and microbiology, and Thomas Isakeit, a Texas A&M AgriLife Extension Service specialist, and also a professor in the department of plant pathology and microbiology.
A series of clues in the past decade gave the team the idea for the project. Bernal’s previous work showed that teosinte is much less hospitable to insects than corn. Studies also showed that the corn microbiome has greatly changed in the past century, diverging from teosinte. Most all of the studies to date have focused on microbes living on and around the roots of corn and teosinte. In contrast few studies have focused on microbes living inside corn tissues, especially in the leaves, Bernal said.
“Studies have shown that the rhizosphere affects insect resistance in corn and can improve it,” he said. “But no one had looked at the microbiome inside corn tissues so we began looking into that.”
If teosinte’s microbiome holds answers for insect resistance in corn, seeking answers in teosinte’s internal microbiome has several advantages to looking at root surfaces or the soil. Teosinte’s internal microbiome must be compatible with the plant’s innate immune system. So the microbial community is less likely to contain pathogens and more likely to contain species that would thrive in corn.
The team collected dead teosinte leaves at the end of the growing season. The researchers then added those leaves to the soil where they grew corn seedlings.
“We saw effects on growth and insect resistance,” Bernal said.
In corn seedlings grown in soil treated with teosinte leaves, resistance was much better. Next the team worked to establish whether the leaves’ internal microbes rather than those on the leaves were a key factor in resistance to fall armyworm.
Antony-Babu separated the bacteria from green teosinte leaves and applied the microbes to corn seeds. Bernal’s team then grew the seeds into seedlings.
“We ran the experiment, and it gave us different results than before,” Bernal said.
Antony-Babu suggested that both fungi and bacteria from the teosinte microbiome may be involved in enhancing insect resistance. So the researchers applied a fungal-bacterial mixture to the corn seeds. After that the seedlings grew better and had better insect resistance than the controls.
In the next three years, the team plans to refine the method. The researchers will optimize culturing techniques and the way they apply the seed treatment. They also will look for effects against important pests other than fall armyworm, such as western corn rootworm. The team will identify the species composing the microbiome and determine a combination of species that are key for insect resistance.
“Maybe only 10 of the species create the effect,” Bernal said. “Once we know what species make it work, we can create a treatment from cultures in the lab. We wouldn’t have to return every time to teosinte leaves.”
The study’s third year will involve growing a small set of treated crops in the field as proof of concept. If the team’s efforts eventually lead to a commercial product, pests would be less likely to evolve resistance to a mixture of microbes than to a single chemical treatment. And corn growers could obtain an alternative treatment against insects.
Olga Kuchment is a communication specialist for Texas A&M AgriLife Communications in College Station, Texas.