IMPACT OF O-3 AND SO2 ON REPRODUCTIVE DEVELOPMENT IN OILSEED RAPE (BRASSICA-NAPUS L) .2. REPRODUCTIVE SITE LOSSES

The flowering racemes of Brassica napus L. cv. Tapidor were exposed in dependently from the vegetative component to 200 nl l(-1) SO2, 100 nl l(-1) O-3 or a mixture of 100 nl l(-1) O-3/30 nl l(-1) SO2. In all cas es, a single 6 h exposure significantly increased bud abortion and abs cission 2 and 5 d after treatment. Similar results were obtained using cv. Libravo, although the effect of 100 nl l(-1) O-3 was significant only after 2 d. Exposure to 30 nl l(-1) SO2 did not enhance bud aborti on and abscission in either variety. Longer term measurements for up t o 25 d revealed a trend towards sustained losses of fertile sites in t hose pollutant treatments which had exhibited demonstrable effects aft er 2 and/or 5 d. However, the number of fertile sites present was comp arable to or even higher than in the controls, indicating that compens ation for the initial losses must have occurred. Following exposure, p lants of cv. Tapidor tended to develop longer total raceme lengths and greater numbers of raceme branches, and those of cv. Libravo a greate r number of raceme branches, indicating possible methods by which new fertile sites may have been produced. The significance of these observ ations for the reproductive development of field-grown oilseed rape is discussed.