“The big thing is that heat counts, but it also affects things that have happened before and will affect things for up to about a week later.”
Resisting heat stress might be the next item on canola breeders’ list to tackle, says Alberta Agriculture oilseed specialist Murray Hartman, who outlined research on the subject at a recent seminar here.
High temperatures can cause flowers to be destroyed and can cause blanks on the stems, Hartman said. Heat can also affect the flowers that are already fertilized and the pods that are developing up to a week after heat exposure. Plants that are affected by heat do recover, but never completely recover their full yield as there is damage to seeds, pods and flowers.
“The big thing is that heat counts, but it also affects things that have happened before and will affect things for up to about a week later. That’s why we see these long sections without pods,” Hartman said.
Another study revealed that heat distorted both the pods and the seeds. Late-bud to early-flower stages are the most sensitive to heat and cold. Hartman said that no one has really done any breeding to select for heat tolerance, and this might be a wise option.
A range of temperatures may cause damage to the plant, but researchers have been unable to pin it down to one specific temperature. Temperatures from about 27C to 30C will have an effect on the pods, said Hartman.
Heat stress affects both the male and female parts of the plants and the fertilization process, as well as flowers that are already fertilized. The heat seems to distort the hormone signals in the plants, Hartman said. Canola requires a double fertilization process which involves the fertilization of the pistil by a pollen grain to produce an embryo, while another pollen grain fertilizes the egg to produce an endosperm.
About 25 to 100,000 pollen grains per flower are released at one time over a period of four to five days while the flower is open. The pollen is usually released in clumps in warm, wet weather. “Mature pollen is actually semidessicated,” said Hartman. “It’s fairly resilient to heat and dry conditions once it’s mature.”
Canola generally uses about 50 per cent of the flowers produced for fertilization due to the activity of the hormones, said Hartman. Canola flowers are the most vulnerable from the green bud stage to about one week after flowering.