Nematodes are tiny pests with big impacts: parasitic cyst nematodes are quickly becoming a major economic concern for soybean, corn, sugar beet and potato producers.
Soybean cyst nematode (SCN) made its grand entrance in the U.S. in the 1950s, and since then has become soybean producers’ top pest, causing significant yield losses annually. In Canada, it has spread through Ontario and Quebec. Though it has not yet been detected in the Prairies, its arrival is impending.
But research is catching up to the miniature pests and offering hope for new, novel controls. Melissa Mitchum, an associate plant science professor at Missouri University, has discovered a mechanism by which cyst nematodes are able to feed on plants.
Over 10 years ago, Mitchum’s team discovered that these cyst nematodes produce and secrete “plant peptide mimics,” small molecules that look like and function like peptides, which provide chemical signals within the plant. In brief, the nematode finds a root and injects it with a chemical cocktail designed to look like the plant’s own chemical signals, and the plant is “tricked” into feeding the pest a steady stream of nutrients.
Recently, Mitchum proved that nematodes feed on cells near the plant’s vascular tissue. By using these “chemical mimics,” nematodes tap into a plant’s vascular stem cell pathway to form feeding cells that will last them the full 30 days of their life cycle.
“These parasites have been co-evolving with host plants for a long time. They’re highly adapted,” says Mitchum. “If we can identify the molecules and then mechanisms to block that process so the nematode can’t form feeding cells, we can create a novel form of resistance. If you shut down the feeding cell the nematode can’t survive.”
Mitchum’s project, which is funded by the National Science Foundation, aims to understand how plant peptides function.
Her lab has proven the mechanism in the model plant arabidopsis, as well as in soybean and potato; the next step is developing plants that are resistant to the nematode’s influence.
“In soybean we have the advantage because we can do peri-root transformation — we can make transgenic soybean roots for testing,” she says. “We’ve done that as a proof of concept. If we see promise we can move this to whole soybean transformation.”
But there’s a challenge to overcome: if breeders block the mechanism nematodes use to help themselves to plant nutrients, they might also block the plant from feeding itself.
Mitchum’s team has rich resources to do this in the form of new, precise gene editing technologies like CRISPR-Cas9, which can help them modify plants to resist nematodes without compromising growth.
It might take five to 10 years to develop new resistant soybean varieties. Mitchum’s team is in the market for an industry partner to make commercialization possible.
Like other pest controls, “this is not going to be a silver bullet,” Mitchum warns. “What we need is to have a diverse set of tools that we can use to try to keep the populations in the field below an economic threshold.
“We need to come together and develop different strategies.” GN