Effect of harvest date and pod position on glucosinolates in oilseed rape (Brassica napus)

Pod samples from four varieties of winter oilseed rape (Brassica napus L) were taken twice weekly from 26 to 3 days before harvest from upper, middle and lower third portions of the main raceme. Seeds were analysed for individual glucosinolate concentration by HPLC. Total glucosinolate content increased suddenly during the sampling period. The timing of the increase depended on variety but occurred before harvest would have been practical. Proportions of individual glucosinolates in Rafal, the only “high” glucosinolate variety examined, did not change over the sampling period. In the other varieties, the proportion of 2‐hydroxy‐but‐3‐enyl (progoitrin) increased and the proportion of 2‐hydroxy‐pent‐4‐enyl decreased as sampling progressed, so that the concentration of individual glucosinolates could not be predicted from total glucosinolate content. The ‘low’ glucosinolate varieties contained a significantly smaller concentration of progoitrin and summed aromatic glucosinolates than Rafal. Variations in glucosinolate content with pod position were smaller than those due to sampling date, but there was a greater concentration of glucosinolates in seeds from pods lower on the terminal raceme. The results would indicate that care should be taken if seed samples from the plant are taken.