EFFECTS OF AMBIENT OZONE ON INJURY AND YIELD OF PHASEOLUS-VULGARIS AT4 RURAL SITES IN THE NETHERLANDS AS ASSESSED BY USING ETHYLENEDIUREA (EDU)

To assess adverse effects of ambient ozone on injury and yield, EDU (e thylenediurea) and non-EDU-treated plants of bean (Phaseolus vulgaris L. cv. Lit) were exposed to ambient air at four rural sites in the Net herlands in 1994. After 6 wk of exposure, the proportion of leaves inj ured in non-EDU-treated plants was higher than that in plants treated with the antioxidant. A maximal degree of 35% injury was observed. The highest ozone levels accumulated at each site for three consecutive d ays before injury clearly exceeded the proposed short-term critical le vel for injury development. Both injury in untreated plants and the pr otective effect of EDU differed between sites and were not related to the measured ozone levels. EDU increased the d. wt of dry (mature) pod s after 11 wk of exposure but not of green (marketable) pods after 6 w k. The effect of EDU in enhancing dry pod yield did not differ between sites and was 20% on average. The proportional yield increases in EDU -treated plants compared with those of non-EDU-treated plants at the s ites were not correlated with the measured ozone levels known to adver sely affect bean yield. The available evidence, however, suggests that ambient ozone was involved in the observed yield increase by EDU. Whe n the dry pods were harvested, EDU-treated plants had more leaves than non-EDU-treated ones. The effect of EDU in delaying senescence appear s to be an important factor to consider when attempting to evaluate th e effect of ambient ozone on pod weight in beans using the EDU approac h.