Canola School: The science of heat blast and what you can do about it


It’s well-known that canola does not like heat during flowering. As soon as daytime highs rise beyond 30 degrees C — as we’re seeing through the current heat wave in Western Canada — the plant can become heat stressed, which leads to blasting and aborted pods.

High temperatures can essentially cause a breakdown in communication between the critical reproductive parts in each flower, explains Nate Ort, agronomy specialist with the Canola Council of Canada, in this Canola School episode.

The process of pod and seed formation in canola begins when pollen from the anther (part of the male part of the flower) falls onto the stigma (female part of the flower). As Ort describes in the video below, a combination of proteins and lipids on the pollen grain and stigma then tell the stigma to begin hydrating and nourishing the pollen, which leads to fertilization and hopefully a pod full of seeds.

However, when temperatures reach that 30 degree C range, those proteins and lipids on the pollen grain and stigma change, explains Ort. “They no longer communicate, and the stigma no longer recognizes that this is pollen that has fallen down onto it, so reproductive development then comes to a halt. That is why we see seed yield reductions under heat stress.”

Foliar-applied boron has been discussed as a treatment for mitigating heat stress. Research in Ontario showed applications in winter canola were economical about a third of the time, but Ort notes the Canola Council’s subsequent trials in Western Canada did not show a benefit. This could be due to the basic lack of water to transport the nutrient within the plant, as is discussed in this June 30 Canola Watch update. At least one company is also marketing a product that it says reduces the effects of heat stress in canola.

There are genetic differences in canola when it comes to tolerating that heat stress — life science companies and government researchers are screening for it. That might be information that canola growers in North America can use to make variety decisions in the future, notes Ort, but in the heat of the flowering period, on a hot day in June or July, there’s currently not much a grower can do that is proven to work.

For producers itching to do something to help the crop through the heat, Ort recommends doing your own on-farm research, with replicated check strips.

“This is a really good time to set up a field trial,” he says. “One thing I would strongly, strongly encourage is to leave not only one untreated check, but leave three. Now you have a replicated trial. The more reps, the better, but three is the bare bones.”

Watch as the Canola Council of Canada’s Nate Ort joins Kelvin Heppner to discuss the physiology of heat stress in canola, and how to evaluate products marketed for it:

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