Researcher studies flea beetle-blackleg link

Agriculture Canada scientist wonders if wounds from 
beetle feeding allow infection to take hold in canola plants

It’s a scientific fact — a cut on the skin, anywhere on a person’s body, increases the risk of infection.

And before the invention of antibiotics, that infection could be deadly.

Given the connection between a wound and disease, an Agriculture Canada scientist is wondering if there’s a similar relationship for canola plants.

If a flea beetle chews a hole in the leaf of a canola plant, does that increase the risk of a disease like blackleg?

“It’s a gut feeling, it’s a hypothesis,” said Gary Peng, a plant pathologist with Agriculture Canada in Saskatoon.

Peng, who spoke at the Manitoba Agronomists Conference last month in Winnipeg, visited a farm near Portage la Prairie a couple of years ago. The grower had a large operation, about 10,000 acres, and had applied a foliar insecticide to all of his canola fields to control flea beetles.

Meanwhile, there was a canola field across the road from the large-acreage farmer where the grower didn’t spray for flea beetles.

Both fields had the same variety of canola, but the crop across the road had much higher levels of blackleg.

“They had about 50 percent (of plants) with blackleg,” Peng said.

Meanwhile, in the nearby canola fields that were sprayed for flea beetles, the incidence of blackleg was basically zero.

“I had a hard time finding a single plant (with blackleg)…. I thought, ‘what’s going on?’ ”

Blackleg is a fungal disease that infects plant stems, restricting nutrient and water flow to developing canola plants. It’s one of the major canola diseases in Western Canada, but fortunately for growers, there are canola varieties with genetic resistance to blackleg.

However, blackleg is evolving and new races of the disease are emerging, so genetic resistance is not a silver bullet.

Canola Council of Canada data has shown that R-rated (resistant) varieties have zero to 30 percent of the disease severity of susceptible varieties. MR (moderately resistant) varieties have 30 to 50 percent of the disease severity.

Following his visit to Portage la Prairie, Peng had an “ah ha” moment. He realized that certain blackleg spores need a wound, or opening on the plant tissue, in order to infect the plant.

“If there is no wounding, it wouldn’t be able to infect the plants,” Peng said.

“That gives a sense that the wounding is relevant.”

Because flea beetles cause wounds early in the growing season when they chew on canola cotyledons, Peng concluded there could be a relationship between flea beetles and blackleg.

“It seems to be anecdotal,” he said. “It’s something we don’t quite know for sure yet.”

To test out his hypothesis, Peng is planning an experiment that will look at the blackleg-flea beetle connection.

The idea is to cause different levels of flea beetle damage on canola plants by using or not using a foliar insecticide on the beetles.

Peng and his colleagues will measure the relationship between plant damage and blackleg incidence and severity.

He hopes to have results in a couple of years.

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