In 2012, scientists discovered that pea root rot caused by Aphanomyces was present on the Prairies. This project began to build a defensive toolkit for pea growers.

Pea growers in Western Canada have battled root rot in recent years. Until relatively recently, it was believed most of this disease was associated with the causal agent Fusarium.

According to Bruce Gossen, 2012 brought a game-changing development.

“At that time, there had been reports and observations indicating increasing problems associated with root rot in pea,” said Gossen, Principal Research Scientist with Agriculture and Agri-Food Canada in Saskatoon. “There was lots of Fusarium causing root rot but Dr. Sabine Banniza at the University of Saskatchewan demonstrated that we should also be looking at Aphanomyces.”

In 2013, with funding from Growing Forward 2, Gossen and a team of western Canadian plant disease specialists began a five-year project to build a knowledge base for root rot.

Start from the basics

When a pea or lentil plant shows signs of root rot, how do you know what caused it: Fusarium, Aphanomyces or another agent entirely? The project’s first order of business was coming up with reliable molecular assessments of the pathogen(s) causing the disease.

“We needed to develop identification techniques using molecular biology so we could go in and determine which species was causing problems in this pea field,” Gossen said. “Aphanomyces is hard to culture, so there was lots of effort just to do that.”

Next up, the team needed to determine just how widespread Aphanomyces root rot was. The news wasn’t good. Aphanomyces was found at high levels in virtually every region.

What about commercially available seed treatments and soil amendments as a way to manage Aphanomyces root rot? Gossen and team tested them all, but didn’t find the breakthrough that growers might hope for.

“There is a good mix of seed treatments that are useful on other pathogens,” Gossen said, “but we found nothing that was effective enough against Aphanomyces.”

Perhaps plant breeding offered a way forward. If some pea cultivars had some degree of genetic resistance to Aphanomyces, that could offer a long-term answer. Dr. Bob Conner (AAFC, Morden) and his group have had success identifying cultivars with less susceptibility to root rot in general than the rest of the available cultivars. They also identified lines with some specific resistance to Aphanomyces. The team developed molecular markers to give breeders a head start, which provides an avenue for the next stage of Aphanomyces research.

Once scientists learned of the widespread presence of Aphanomyces as a causal agent of root rot on pea and lentil, the push was on to find answers. This project established the foundation for a longer-term Aphanomyces defense. One thing’s for sure. Aphanomyces is now a fact of life for scientists, agronomists and pea growers.

“We were surprised by how widespread the Aphanomyces pathogen is,” Gossen said. “Recently, we’ve made progress on identifying fields at risk. Dr. Syama Chatterton (AAFC, Lethbridge) is developing a decision support system for growers that would recommend a break between susceptible crops for fields with a high risk of severe root rot.”

Project at a glance

Project title:                Pea root rot: distribution, genetic variability, resistance and management

Project lead:                Bruce Gossen, Agriculture and Agri-Food Canada

Total value of project: $1,757,400

Start date:                   April 1, 2013

Completion date:        March 30, 2018