Effect of high temperatures during seed development on oil composition of mid oleic canola and high erucic acid rapeseed

An experiment was undertaken to evaluate the effects of three-day periods of high and very high temperatures (32/24C and 37/25C day/night temperatures, respectively) at different stages of seed development (10, 20 and 30 days after flowering) on the fatty acid composition of a high erucic acid rapeseed (HEAR) and a mid oleic acid canola (MOAC) breeding line (“cultivar”). The earliest formed seed was analysed separately from the whole plant seed. The fatty acid composition of the MOAC cultivar in the control treatment included 71% oleic acid, 13% linoleic acid, 8% linolenic acid and 6% saturated fatty acids (palmitic and stearic acids). The control treatment of the HEAR cultivar contained 12% oleic acid, 14% linoleic acid, 10% linolenic acid, 7% arachidic and eicosenoic acids and 52% erucic acid. In contrast to earlier research on the effects of sustained high post-flowering temperatures, the fatty acid compositions of both cultivars were fairly tolerant of three days of high temperatures. The major exception was the large effect of very high temperatures in the later stages of seed development of the HEAR cultivar. The effect of very high temperatures (37/25C) on the oleic and linoleic acid levels of MOAC seeds from the whole plant was variable depending on the timing of the heat shock. However, the linolenic acid level decreased slightly while the saturated fatty acids increased slightly for most treatments. The high temperature treatment (32/24C) had less impact than the 37/25C treatment. In the earliest formed seed, the levels of the unsaturated fatty acids (oleic, linoleic and linolenic) were unaffected by all treatments. For the HEAR cultivar, the fatty acid composition was largely unchanged, except when the plants were exposed to very high temperatures (37/25C) in the late flowering stage which reduced erucic acid content from 52% to 44% in the whole plant seed sample. Linolenic acid also fell slightly, while all other fatty acid levels increased, particularly oleic acid (from 12 to 17%) and eicosenoic acid (from 7 to 11%). The high temperature treatment (32/24C) had almost no effect on fatty acid composition of the HEAR cultivar. The earliest-formed seeds followed a similar trend.