While improving management practices and reducing risk factors are still the best ways to avoid root rot in pulse crops, Agriculture and Agri-Food Canada (AAFC) researchers hope to find other tools. Syama Chatterton, an AAFC research scientist whose areas of expertise include diseases in pulse crops and soil borne diseases, is working on research projects that focus on minimizing root rot.
Currently, Chatterton has a number of research projects in the works, spanning from lab-based, fundamental research to field trials. In terms of field trials, she is looking at how the most common cultivars perform in high-risk fields. For this project, researchers chose 20 of the most prominently grown cultivars to see if some could stand up to root rot better than others.
“What we found is that all cultivars are equally susceptible to aphanomyces, but some of them still yielded better than others,” she said. “It tends to be the newer cultivars that have just been released that probably have a higher yield potential anyway.”
In another trial, Chatterton and her colleagues assessed seed treatments to see if available treatments have the ability to provide long-term protection.
“What we saw is that they do what the label claims, for the most part,” she said. “They give you early-season suppression or early-season control. But we didn’t see that that lent to any long-term growing season benefits.”
Chatterton is also involved in a cover crop project. The idea is that brassica cover crops, as they break down, produce bio-fumigants that may have the potential to speed up decay of the resting spores in the soil. There is good evidence to show that mustards produce bio-fumigants, but Chatterton and her team want to know if it’s cost-effective and feasible for growers. More importantly, they want to make sure that it will fit with their practices.
“It’s more of a feasibility research project,” she said. “We just want to look and see if it has potential for a solution.”
The project started in 2017, but already the researchers have run into a few snags. Typically, peas come off pretty early, leaving room for a cover crop to establish before winterkill sets in.
“This year was not a great year because we planted some of our mustard species in August, but we didn’t get any rain until it snowed in October,” she said. “So unfortunately, not the best year to embark on that research.”
“We ended up with really tiny plants, then it snowed and the ground froze,” she continued. “I’m not sure that anything’s going to survive that.”
Chatterton plans to try again in the spring, planting the peas into a living brassica cover crop, but says the crop’s success will depend on spring moisture levels.
In the future, Chatterton would like to look more closely at the impact of rotations. Until now, it has been assumed that the more peas and lentils you have in a rotation, the higher the likelihood of disease. “But it’s never actually been studied, and there are some questions coming up,” said Chatterton.
Growers want to know, for instance, how often you need to have peas and lentils in the rotation. They’d also like to know what happens if you replace peas and lentils with a non-host pulse crop, like fava beans or soybeans. Will that help to reduce the inoculant potential? Or will they still act as reservoirs for inoculant? Soybeans, explained Chatterton, are resistant to aphanomyces to the point where they would be considered a non-host. Information on fava beans, however, is somewhat conflicting.
“The ones we’ve tested seem to be very resistant,” said Chatterton. “But there’s older literature that says fava beans are susceptible. I suspect it has to do with different cultivars. There have been a lot of changes in fava bean cultivars over the past 10 years or so.”
Chickpea also shows resistance to aphanomyces. “We will maybe see a little bit of infection, but we don’t see new spores being produced in the root,” she said. “So that would say that it wouldn’t be increasing if you grow chickpea instead of a pea, but we want to verify that in the field.”
In the meantime, University of Saskatchewan breeders are working on new resistant cultivars. Some partially resistant germplasm lines have been jointly released by the U.S. and France and are now available for breeding programs. Researchers are trying to use rapid generation breeding to incorporate partial resistance into Canadian-adapted cultivars quickly and efficiently.
Breeding does take a while, said Chatterton, so it could be another five to six years before new cultivars are available to growers. And, even when these varieties do become available they will only offer partial, not full resistance. Improving management practices and reducing risk factors is still the best way to avoid root rot.
“If partially resistant varieties become available they will have to be managed quite closely, so that we don’t overcome that resistance that we have,” Chatterton concluded.