Free fatty acid contents in developing seed of three summer rape cultivars in Ontario

Field studies were conducted in 1989 and 1990 to determine the FFA levels during seed development of three Ontario-grown canola-quality summer rape (Brassica napus L.) cultivars, Global, Kristina and OAC Triton, to determine the relationship between FFA and brown seeds and to assess the effect of silique position within the raceme on FFA. Seed mass increased linearly until 44 DAF in 1989 and curvilinearly until 43 DAF in 1990. Seed oil increased until approximately 32 and 31 DAF in 1989 and 1990, respectively. The concentration of FFA in seeds declined in both years until oil concentration stopped increasing, suggesting that FFA were being incorporated into triacylglycerol. During oil synthesis total FFA per seed increased and, as oil synthesis slowed and stopped, FFA decreased. The individual cultivars decreased FFA to different levels as oil synthesis slowed, with Kristina having the lowest FFA. As the crop finished ripening the FFA levels increased in Global and OAC Triton in 1989 and in all cultivars in 1990. There was a strong positive correlation between FFA and percent brown seed in 1990 (r = 0.64) and in 1991 (r = 0.88). FFA and percent brown seed were 33 and 66%, respectively, higher in seed samples from siliques located on branches than in seed samples from siliques located on the main raceme. FFA and percent brown seed were higher in seed samples from siliques on tips than in seed samples from siliques located on the basal portion of the raceme by 137 and 142%, respectively. The results indicated that cultivars differed in their ability to decrease FFA during oil synthesis and a consistent rise in mg FFA kg−1 oil occurred at the end of the seed filling period. Key words: Free fatty acids, Brassica napus, seed development, brown seed, raceme position