Seasonal Variation in Glucosinolate Composition of Rutabaga and Turnip

Glucosinolates, determined by quantifying their hydrolysis products, were studied in seeds and in roots of two cultuvars of rutabaga (Brassica napobrassica Mill.) and of turnip (Brassica rapa L.) sampled at 2-wk intervals during growth on both loam and organic soils. The glucosinolates generally were higher in roots of rutabaga than in those of turnip. Accumulation of different glucosinolates in roots of both species occurred at different times during the growing season in the sequence after seeding: indolyl glucosinolates yielding ionic thiocyanate at the 2-wk stage; glucosinolates yielding volatile isothiocyanate hydrolysis products at the 4-wk stage; and 2-hydroxy-3-butenyl glucosinolate (progoitrin) yielding 5-vinyl-oxazolidine-2-thione (goitrin) at the 6- or 8-wk stage. Mean total glucosinolate content of rutabaga and turnip grown on organic soil was 15 and 38% higher than those grown on loam soil, respectively. The contents of goitrin and volatile isothiocyanates were inversely correlated in the seed of both species.