The glucosinolate-free meal from rapeseed can be used as livestock feed, whereas glucosinolate-rich meal can be used as a pesticide. It has also been shown that glucosinolate content in Brassica (rapeseed) seeds can be manipulated by application of chemicals. However, the stage of seed development when potential chemical treatments could be applied has not been clearly identified. Thus, an experiment was conducted to evaluate accumulation of glucosinolate, oil, and erucic acid in developing seeds of rapeseed lines. These included lines that were classified as low or high for glucosinolate content. The florets of eight rapeseed lines were tagged at the 50% flowering stage and were sequentially harvested at 26, 28, 30, 33, 35, 37, 40, 42, 44, 47, 49, and 52 days after flowering (DAF). The oil content in both the high and low-glucosinolate lines increased approximately by a factor of four from 26 to 52 DAF. The oil content accumulation was not affected by glucosinolate content. Erucic acid content in the oil was significantly higher in low glucosinolate lines compared with high glucosinolate lines on 28 and 40 DAF. Developing seeds were most amenable to change in erucic acid content at approximately 37 DAF. The glucosinolate contents in high glucosinolate lines started to increase significantly at 26 DAF and continued up to 33 DAF. However, the glucosinolate content in the low glucosinolate lines increased only from 33 to 35 DAF. This indicates that the greatest accumulation of glucosinolate in developing rapeseed seeds may occur at approximately 26 DAF.
Rapeseed (Brassica sp.) is a potential alternative cash crop for US farmers. Industrial rapeseed oil contains high contents of erucic acid, whereas the meal contains high contents of total glucosino- lates. The erucic acid is a valuable raw material for manufacture of a wide array of industrial products such as plasticizers, surfactants, detergents, coatings, polyesters. The US industry annually uses approximately 18000 metric tons of erucic acid, which is mostly imported (US Congress, 1991). Thus, a potential exists for developing a domestic source of erucic acid (van Dyne et al., 1990). Glucosinolate, which consist of several forms of sulfur-containing organic anions with β-D -thioglucose moieties, are present in the meal residue of rapeseed after oil extraction (Brown et al., 1991). Glucosinolate restricts the feeding use of the protein-rich meal for ruminants. In contrast, the low glucosinolate meal from canola which was developed for low glucosinolate content can be used for livestock feed (Downey, 1990; Sovero, 1993). The high glucosinolate meal has been shown to have pesticidal properties (Bhardwaj et al., 1996). Therefore, either a reduction or an enhancement in glucosinolate content might be helpful in developing rapeseed as a domestic source of erucic acid. Doughty et al. (1995) have shown that the glucosinolate content can be controlled with jasmonic acid and its methyl ester.