Worm pheromones protect major crops
Protecting crops from pests and pathogens without using toxic pesticides has been a long-standing objective for farmers. Researchers at the Boyce Thompson Institute have discovered that compounds from an unlikely source - microscopic roundworms from the ground - could achieve this objective.
As described in research published in the May 2019 issue of the Journal of Phytopathology, these compounds have helped protect key crops from various pathogens, and therefore have the potential to save billions of dollars and increase agricultural sustainability around the world.
Led by Murli Manohar, BTI's Senior Research Associate, a team led by Professors Daniel Klessig and Frank Schroeder studied the effects of an ascaris metabolite called ascr#18 on plant health.
Ascr#18 is a member of the ascarosides family of pheromones, which are produced by many roundworm species living in the soil for chemical communication.
Researchers treated soybean (Glycine max), rice (Oryza sativa), wheat (Triticum aestivum) and corn (Zea mays) plants with small amounts of ascr#18, then infected the plants with a virus, bacteria, fungus or oocyte.
When examined several days later, plants treated with ascr#18 were significantly more resistant to pathogens than untreated plants.
"Plant roots are constantly exposed to roundworms in the soil, so it makes sense that plants have evolved to detect the pest and prime their immune systems in anticipation of attack," Schroeder explains.
Because they strengthen the plant's immune system instead of killing pests and pathogens, ascarosides are not pesticides. As a result, they are probably much safer than many current pest and pathogen control methods.
"Ascarosides are natural compounds that appear to be safe for plants, animals, humans and the environment," says Klessig. "I think they could thus offer plants more environmentally friendly protection against pests and pathogens."
In previous work, Klessig and Schroeder have demonstrated that ascr#18 and other ascarosides increase the resistance of tomatoes, potatoes, barley and Arabidopsis to parasites and pathogens.
"By extending the work to the main crops and focusing on their most important pathogens, this study establishes the potential of ascarosides to improve global agricultural production," says Klessig.
Indeed, rice is the most important staple food in the world for nearly half of the world's population. Ascr#18 provided protection against Xanthomonas oryzae pv. oryzae, a bacterium that causes 10-50% yield losses in Asian countries.
Wheat is just behind rice as a staple food, and ascr#18 has protected it against Zymoseptoria tritici, a fungus that is one of the most serious leaf diseases of the crop.
Maize is the most widespread cereal crop in the Americas, with great importance for food, biofuels and animal feed. Ascr#18 provided protection against Cochliobolus heterostrophus, a fungal pathogen that causes corn leaf blight.
Soya is an important seed crop rich in protein and oil, used as a food source for humans and animals. Ascr#18 protected soybeans against Phytophthora soya, an oomycete that can kill infected plants in a few days, as well as the bacterial pathogen Pseudomonas syringae pv glycineae and Soybean Mosaic Virus.
Extremely low concentrations of ascarosides are sufficient to provide plants with resistance to pathogens. It is interesting to note that the optimal concentration seems to depend on the plant species and not on the pathogen.
The researchers believe that the reason why different plant species have different optimal doses is probably related to the receptors of the plant cell for ascr#18. Different plant species may express different amounts of ascr#18 receptors, and receptors may have different affinities with ascarosides. Such differences would affect the amount of ascr#18 needed to trigger the plant's immune system.
The group is now working to determine the molecular mechanisms of how ascarosides initiate the plant's immune system.
These discoveries are being commercialized by Ascribe Bioscience, a start-up company of BTI and Cornell, as a family of plant protection products called PhytalixTM.
"This work is an excellent example of how the Institute is leveraging our technology through new start-up companies, an important strategic initiative at BTI," says Paul Debbie, Director of New Business Development at BTI. "The Institute is proud to have the opportunity to develop innovative technology in partnership with a new company that is having a positive economic impact here in our local community and in New York State.
