The influence of stages of development, soil types, dates of seeding, cultivars, and boron nutrition on glucosinolate composition and variation in rutabaga (Brassica napobrassica Mill.) and turnip (B, rapa L.) cultivars was studied by quantifying the glucosinolate hydrolysis products in these species. While in seeds of both species contents of goitrin and volatile isothiocyanates were inversely correlated, there was little variation in thiocyanate ion and total glucosinolate contents. Major synthesis or accumulation of different glucosinolates occurred at different times during the growing season in the sequence after seeding: indolyl glucosinolates yielding thiocyanate ion at the 2-week stage; glucosinolates yielding volatile isothiocyanate hydrolysis products at the 4-week stage; and progoitrin yielding goitrin at the 6- or 8-week stage. These glucosinolates were generally higher in roots of both species grown on organic soil than on loam soil. During ontogeny of both species, the content of volatile isothiocyanates generally were positively correlated with top/root ratio, while growth rate was positively correlated with thiocyanate ion content. While the contents of goitrin and volatile isothiocyanate tended to be higher in early-seeded (May 27) crops, the thiocyanate ion contents tended to be higher in late-seeded (June 21) crops. The occurrence of boron deficiency symptoms in roots of hydroponically-grown Snow Ball turnip (0.1 ppm boron treatment) was associated with an accumulation of high quantities of glucosinolates and reducing sugars.

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