INDUCED CHANGES IN THE INDOLE GLUCOSINOLATE CONTENT OF OILSEED AND FORAGE RAPE (BRASSICA-NAPUS) PLANTS IN RESPONSE TO EITHER TURNIP-ROOT-FLY (DELIA-FLORALIS) LARVAL FEEDING OR ARTIFICIAL ROOT DAMAGE

Plants from two cultivars of forage rape and one cultivar of oilseed r ape were inoculated with turnip root fly (Delia floralis) eggs at eith er 4 or 6 weeks prior to harvest, or, alternatively, were artificially damaged by mechanically removing approximately one-third of the root volume. Larval damage increased the total glucosinolate content of the roots. In contrast, artificial damage reduced the total glucosinolate content of the roots, with the levels decreasing as the time interval between damage and harvest lengthened. Turnip root fly larval damage also modified the glucosinolate composition of the roots, with the pro portion of indole glucosinolates increasing significantly. No such cha nges were observed in the artificially damaged roots. Neither type of damage appeared to affect the total glucosinolate content of foliar sa mples significantly, when averaged over all cultivars, but if was of i nterest to note that the proportion of glucobrassicin present in the l eaves of the oilseed rape cultivar, Ariana, was consistently greater i n both the larval and artificially root damaged plants compared with u ndamaged plants of the same cultivar. These results are discussed in r elation to sulphur availability and the validity of root trimming as a simulation for turnip root fly damage.