Glucosinolate Content in Rapeseed in Relation to Suppression of Subsequent Crop

In crop rotations that include rapeseed (Brassica napus L.), the growth of the crops following rapeseed is sometimes inhibited. The aim of this study was to assess the role of glucosinolates (GSLs) in the inhibitory effect. Three cultivars with zero erucic acid content (Asakano-natane, Kizakino-natane, Nanashikibu: single-low cultivars) and one cultivar with zero erucic acid and low GSL contents (Kirariboshi: double-low cultivar) were grown. The GSL contents differed greatly depending on plant part, stage of development, and cultivar. Progoitrin and gluconapin were detected mainly in the seeds of the single-low cultivars. Their contents either did not change or increased slightly during the reproductive stage. The double-low cultivar Kirariboshi contained almost none of either progoitrin or gluconapin in any part during the reproductive stage. Glucobrassicanapin, glucobrassicin, and gluconasturtiin were detected, mainly in the roots, of all four cultivars, and tended either to decrease or to remain steady as plants matured. Dense stands of rapeseed seedlings that had germinated from seeds dropped at harvest grew together with the subsequent crop. The GSL contents in the leaves and roots of these seedlings were high. These results suggest that the GSLs in the seeds of single-low cultivars, in the roots of both types at harvest, and in the leaves and roots of volunteer seedlings are the candidate cause of the generally observed phenomenon of inhibited growth of the crop following rapeseed.