Even when enough moisture is available, canola yields have been found to decline by as much as 50 per cent if heat wave conditions occur during flowering and mid-podding.
These findings were among those from an in-field pilot project conducted by NSW Department of Primary Industries crop physiologist Rajneet Uppal, Wagga Wagga, who developed a methodology to study plant response to extended periods of daytime temperatures at 32 to 35 degrees.
The two-year project was a step towards attracting funding for a five-year follow-up nationwide project, "Improving canola heat tolerance - a coordinated multidisciplinary approach", to develop heat tolerant varieties, which kicks off this year and includes a team of pre-breeders, physiologists and agronomists.
"We all know that climates are changing - there's already shifts happening in Australia," Dr Uppal said at September's Henty Machinery Field Days where she was a guest speaker at the Grains Research and Development research forum session.
"High spring temperatures can slash yield potential of canola, a serious threat to our $2.67 billion canola industry, so it's important we have some solutions for assessing the heat tolerance in the field so there is a wider application of the experimental results.
"There is already a three degree shift in August and September temperature, which is a lot, and it is particularly important to the winter season crops that they adapt to the hotter climates."
So far though, research into canola heat tolerance had mostly been undertaken in glasshouses or in controlled environment rooms with the work done on a single plant or maximum five plants.
"So therefore when we want to extrapolate those results at a plot scale, generally the plants that are considered heat tolerant from the glasshouse experiments are usually not the heat tolerant ones," Dr Uppal said.
It was therefore crucial to develop a method that could test heat tolerance in a natural field environment.
For this project Dr Uppal's team created its own climate chambers from scratch - a challenge in itself which had to be overcome before the pilot project, a co-investment between NSW DPI and GRDC, could even get off the ground.
She said these chambers were portable and were made with clear polycarbonate sheets which allowed 90 per cent of the sun's radiation to penetrate.
Each chamber contained two heaters which allowed the team to raise the temperature as much as 10 degrees compared to the ambient temperature.
"Inside the chamber there is also a ceiling fan, which allows heat to evenly distribute," Dr Uppal said.
"You park these chambers over the plants (one person can push them around) and simulate, or apply heat for five hours for 35 degrees each day and the idea is to simulate a heat wave which lasts for say six to eight days.
"We found that canola is most sensitive to heat stress during 50pc flowering to 50pc podding, so that's the phase when canola starts developing young grain."
The team also set up different in-crop water regimes simulating a low rainfall environment (250 millimetres), as well as a medium rainfall environment (370mm) to allow them to distinguish whether yield was effected by available moisture, heat, or both.
"So what we find, when there was enough moisture available, still there was a 50pc yield reduction when there was a heat wave for eight days," she said.
"So the implication for the grower is they can sometimes grow a nice crop, but still it's not hitting the yield potential because pods are developing but the seed number is impacted.
"We also found there was only a 6pc reduction on the oil quality when there was heat stress during mid flowering to mid podding.
"(So) the same stage is sensitive to grain yield, as well as quality."
Dr Uppal said their portable chamber design generated a lot of requests worldwide, so her team has developed a manual on how to build the chambers.
The ensuing five-year plant breeding project will assess different germplasm from around the world to identify genes for heat tolerance and they have also received an international collaboration request on the research, as there is no known commercial heat tolerant varieties anywhere in the world.
