Novel technology is now available to pinpoint when canola is most sensitive to heat stress, enabling breeding lines to be screened for heat-adaptive traits in field-scale experiments.
Under the GRDC-NSW Department of Primary Industries (DPI) Grains Agronomy and Pathology Partnership, NSW DPI crop physiologist Dr Rajneet Uppal and NSW DPI technical officer John Bromfield developed and tested eight portable heat chambers to apply and measure the impact of heat stress on one canola variety.
Previously, canola heat tolerance research was done in growth chambers where flowers were exposed to a constant high temperature at a similar growth stage.
However, Dr Uppal says in field conditions, all plants are not exposed to the same heat intensity, resulting in seed setting from non-stressed flowers.
In the field, she says, critical temperature is determined by the daily maximum temperature, which may only last for a short duration.
Dr Uppal's two-year pilot study investigated eight heat chambers (2.5 metres long by 1.8m wide by 1.2m high) positioned over replicated trial plots of the commercial variety ATR Stingray (PBR) to determine the reliability of the chambers in simulating heat stress in the field.
ATR Stingray (PBR) was chosen for the experiments because it is popular among growers in northern NSW and Western Australia.
The early maturing triazine-tolerant variety has a manageable canopy size, which Dr Uppal and her team considered important when optimising protocols for using the heat chambers.
Within each chamber, the researchers increased the temperature to 35 degrees Celsius for five hours over eight consecutive days from stem elongation until the end of podding.
Dr Uppal says ATR Stingray (PBR) was most sensitive to heat stress from mid-flowering to mid-pod formation.
"When heat stress was imposed at this growth stage, we saw a 63 per cent fall in yield under rain-fed conditions and a 52 per cent drop in yield when water was unlimited," she says.
"The oil fell by 5.7 per cent when heat stress was applied from mid-flowering to mid-podding."
Additionally, Dr Uppal says the stressed canola produced fewer grains that were larger in size; however, the larger grain did not compensate for the yield penalty.
Dr Uppal says only one variety was used because the experiment was about determining whether or not the portable heat chambers could simulate heat stress in field-grown canola.
"Our experiments were successful, which means we now have the opportunity to use these heat chambers to compare experimental breeding lines when researchers are searching for heat-tolerant germplasm," she says.
Using heat chambers, Dr Uppal says heat stress could be applied above the threshold temperature limit (29.5 degrees Celsius) for canola at flowering, which allowed heat stress to be simulated in the field.
She says the work confirms what growers and advisers already know regarding the importance of sowing canola so it flowers and develops pods when there is minimal risk of frost and heat stress.
"Even when the canola had access to unlimited water, there was a yield penalty of more than 50 per cent, which shows the value of developing heat-tolerant canola varieties," she says.
GRDC Research Code: BLG108-1
More information: Dr Rajneet Uppal, 0436 341 649, firstname.lastname@example.org
See also: GroundCover article and Dr Uppal's 2019 GRDC Grains Research Update Wagga Wagga paper