Heat Stress Alone Is Not Sufficient to Increase Free Fatty Acid Content in Spring Canola.

The most important quality issue affecting the Ontario canola industry is the risk of high levels of free-fatty acids (FFAs), which has historically been a problem under hot, dry growing conditions.  The objective of this project was to develop a simple controlled environment protocol for evaluating canola varieties for FFA levels under heat stress.  In one experiment, a single commercial spring canola variety was grown under low stress conditions (24⁰C daytime high temperature / 14⁰C nighttime low) and then exposed to stressful temperatures (32/20⁰C). The stress treatment was applied for two different durations (1 week or 2 weeks) beginning at one of four different growth stages (1,2,3 or 4 weeks after first flower) for a total of nine different stress treatments. The 32/20°C temperature regime proved to be a relatively mild stress, with only a minor effect on pod counts, and none of the stress treatments had any effect on seed FFA levels.  A second experiment was conducted using more severe stress treatments. At two weeks after first flower, plant were either i) maintained at 24/14⁰C or transferred to a growth cabinet set for ii) 35/20⁰C or iii) 38/22⁰C, and maintained there until physiological maturity. Also, in each of these groups, plants were either kept well watered or were allowed to wilt in between watering in order to induce drought stress in addition to the heat stress.  In this experiment the most severe stress treatment reduced seed yield by approximately 50%. Despite this, none of the stress treatments had any effect on FFA levels. In general, FFA levels in this experiment were extremely low, averaging just 0.04% of total oil. We conclude that heat stress alone, or heat stress in combination with drought stress applied during the seed-fill period, are not sufficient to induce high FFA levels in canola.