Worm pheromones protect major crops, BTI scientists find

Protecting crops from pests and pathogens without using toxic pesticides has been a longtime goal of farmers. Researchers at the Boyce Thompson Institute have found that compounds from an unlikely source – microscopic soil roundworms – could achieve this aim.

Soybean plants treated with the pheromone ascr#18, right, were healthier and had higher survival rates than untreated seeds, left, when infected with the deadly fungus-like pathogen Phytophthora sojae.

As described in research published in May in the Journal of Phytopathology, these compounds helped protect major crops from various pathogens, and have the potential to save billions of dollars and increase global agricultural sustainability.

The research team – led by Murli Manohar, BTI senior research associate; Daniel Klessig, adjunct professor in the School of Integrative Plant Science and BTI faculty member; and Frank Schroeder, professor of chemistry and chemical biology and BTI faculty member – investigated the effects of a roundworm metabolite called ascr#18 on plant health. Ascr#18, from the ascaroside family of pheromones, is produced by many soil-dwelling species of roundworms for chemical communication.

The researchers treated soybean, rice, wheat and maize plants with small amounts of ascr#18, and then infected the plants with a virus, bacteria, fungus or oomycete (a form of mold).

When examined several days later, the ascr#18-treated plants were significantly more resistant to the pathogens compared with untreated plants.

“Plant roots are constantly exposed to roundworms in the soil, so it makes sense that plants have evolved to sense the pest and prime their immune systems in anticipation of being attacked,” Schroeder said.

Ascarosides are not pesticides. Instead of killing pests and pathogens, they boost plants’ immune systems. As a result, they are likely to be much safer than many current means of pest and pathogen control.

“Ascarosides are natural compounds that appear to be safe to plants, animals, humans and the environment,” Klessig said. “I believe they could thus provide plants more environmentally friendly protection against pests and pathogens.”

In previous work, Klessig and Schroeder demonstrated that ascr#18 and other ascarosides increased resistance against pests and pathogens in tomato, potato, barley and Arabidopsis, a small flowering plant.

“By expanding the work to major crops, and concentrating on their most significant pathogens, this study establishes the potential for ascarosides to enhance agriculture production worldwide,” Klessig said.

Extremely small concentrations of ascarosides can provide plants with resistance against pathogens. The optimal concentration appears to be dependent on the plant species and its immune system, rather than the pathogen.

The group is now working to determine the molecular mechanisms of how ascarosides prime the plant’s immune systems.

These discoveries are being commercialized by a BTI and Cornell-based startup company, Ascribe Bioscience, as a family of crop protection products called Phytalix.

Collaborators included researchers from Cornell; the University of Kentucky; Justus Liebig University in Germany; the University of California, Davis; and Colorado State University.

The research was partially funded by the U.S. Department of Agriculture (USDA) National Institute for Food and Agriculture, the USDA Agricultural Food and Research Initiative, the Colorado Agricultural Experiment Station, the Kentucky Soybean Promotion Board and the German Minister of Education and Research.

Aaron J. Bouchie is a science writer for Boyce Thompson Institute.

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