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Flea Beetles Don’t Like Hairy Legs

In the future, farmers may be eliminating one pesticide application on their canola. Researchers at Agriculture and Agri-Food Canada’s Saskatoon Research Centre are developing “hairy” canola plants that prevent flea beetles from feeding on the leaf and stem surfaces of newly emerged canola seedlings.

This physical barrier means flea beetle resistance will be built into the plant, with little or no need for an insecticide application.

Margie Gruber, the research scientist leading the project, received funding from the Western Grains Research Foundation and various canola-funding agencies to develop germplasm that is flea beetle resistant.

TRICHOMES

“The trait we were looking at is trichomes, which are plant hairs,” says Gruber. “Lots of plants have trichomes. Canola has a few, but related species like mustards have a lot more. We’re interested in seeing if we can stimulate the plant to produce more on the seedling leaves and stems.”

Two types of trichomes are commonly found on plants. The first type is a bumpy protuberance on the plant surface that often releases various plant chemicals, like in the mint family. The other kind sticks out a bit further.

“We wanted to look at the ones that stick out. Those types of trichomes are in plant species related to canola, as well as in Arabidopsis – a model plant that has had a lot of research done on the genetic basis for the development of trichomes,” says Gruber.

The trichomes interfere with feeding patterns of the tiny flea beetles.

“It’s a specialized insect, with specific behaviours it undergoes when testing a plant surface before eating it. If a full series of behaviours are not completed, it starts over or moves off the plant,” she says.

GENE EXPRESSION

Overexpressing the genes in Arabidopsis increased trichome production by about 50 times, but overexpressing the same genes in canola produced about 1,000 times the number of trichomes.

“We were trying to put the hairs on any and all parts of the seedlings. What we achieved was to put them on the young leaves and stems. The cotyledons were still smooth, but they seemed to be more flea beetle resistant, even without the trichomes. So the genes that we used also modified the plants in some way to be more resistant,” she says.

Gruber already has lines developed with significantly reduced flea beetle feeding damage, but the trichomes don’t yet have any branches on them.

“We’re currently testing genes that would make branches on the trichomes. In Arabidopsis, they can have three to four branches depending on where they grow. In canola there are no branched trichomes at all,” she says.

“We feel branching will increase the density of the trichome mat, so flea beetles that can find a little bare spot and can burrow down wouldn’t be able to do that nearly as well. The average is three branches, but we can make mutants with six or seven. It’s just a matter of testing and isolating a number of different Arabidopsis trichome branching genes.”

BRANCHING

“We’re using Arabidopsis genes to promote trichomes in canola and also we’re trying to understand what’s going on with canola. That may lead to methods to develop trichomes in canola without genetic engineering.”

Gruber says it will still take some time to develop canola plants that are worthy of going into a plant-breeding program. Current breeding lines with the hairy characteristics mature about a week later than commercial canola varieties.

“We had these plants out in the field in generation three and four and they were small, but they gave good flea beetle resistance. They’re bigger now in generation seven, but we still want to improve the seedling vigour,” she says.

“When the agronomics of those lines are close to the agronomics of current varieties, then we’ll provide that material to plant-breeding companies. That might be in three years.”

She says this type of insect resistance will be a more robust resistance that won’t break down or have resistant insect populations develop, compared to things like Bt resistance. Because it’s a physical resistance rather than a biological system, insects will find adaptation more difficult.

Gruber says when the final developments are complete and the trichomes have branches, farmers shouldn’t have to use any chemical flea beetle control at all.

The Endowment Fund, the original core fund of WGRF, has supported more than 200 research projects since 1983. It funds projects on cereal grains, as well as oilseeds, pulse crops and other commodities. Research Reports on many of these projects are available on the WGRF website.

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