ECODA project number: B.2.5, B.2.6 and B.2.7
Principal investigator: Hugh J. Earl
Elevated levels of free fatty acids (FFAs) in the seed has historically been the most important quality defect threatening marketability of the Ontario canola crop. Accordingly, variety recommendations for Ontario place a large weighting on this quality factor, and varieties that show high FFA levels in public Ontario variety trials will not be recommended for production in the province. Historical experience with the Ontario crop indicates that high FFAs are more likely to become an important quality issue in seasons where temperatures are high.
In this project, it was proposed to develop a controlled environment stress protocol that would provide a mechanism to pre-screen candidate canola varieties for susceptibility to elevated FFAs under heat stress. However, it was found that in controlled environment growth cabinets, heat stress or combined
heat / drought stress that was sufficient to reduce pod set and seed yield by up to 50% had no effect on FFA levels, which were extremely low in all cases. While disappointing, this result points out the need to reconsider current ideas about the causes of elevated FFAs and the reasons why this problem is more prevalent in Ontario than in the major canola-growing regions of Western Canada.
This project also investigated the hypothesis that applications of foliar boron (B) to canola during early flowering could result in significant yield increases, and that these increases would be greatest when the crop was under high temperature stress during flowering. A further objective was to elucidate the physiological basis of foliar boron’s effect on the canola crop.
A series of field trials demonstrated conclusively that foliar B applications can produce a change in the pod and seed distribution of the crop (with relatively more yield on the main raceme and less on the branches), due to a reduction in abortion of pods on the main raceme. In one third of the trials a
significant yield increase resulted, but the increases were generally small (approximately 5%). In two of the trials, foliar B treatment also produced a significant reduction in seed content of FFAs.
A controlled environment study corroborated the field results, with B treatments significantly increasing main raceme pod counts and decreasing main raceme pod abortions. However, importantly, this effect was observed only when the plants were exposed to heat stress during the flowering period; plants grown under control conditions (no temperature stress) showed no response to B.
In summary, the results indicate that foliar B applications can increase canola yields, but that these benefits are more likely to be realized when there is significant heat stress during flowering. The conventional wisdom regarding the connection between heat stress and FFAs was not supported by the controlled environment studies; additional research should be directed towards identifying the true causes of this important quality defect.