Effects of ambient ozone on injury and yield of Phaseolus vulgaris at four rural sites in the Netherlands as assessed by using ethylenediurea (EDU)

To assess adverse effects of ambient ozone on injury and yield, EDU (ethylenediurea) and non-EDU-treated plants of bean (Phaseolus vulgaris L. cv. Lit) were exposed to ambient air at four rural sites in the Netherlands in 1994. After 6 wk of exposure, the proportion of leaves injured 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 days before injury clearly exceeded the proposed short-term critical level for injury development. Both injury in untreated plants and the protective effect of EDU differed between sites and were not related to the measured ozone levels. EDU increased the d. wt of dry (mature) pods after 11 wk of exposure but not of green (marketable) pods after 6 wk. 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 sites were not correlated with the measured ozone levels known to adversely affect bean yield. The available evidence, however, suggests that ambient ozone was involved in the observed yield increase by EDU. When the dry pods were harvested, EDU-treated plants had more leaves than non-EDU-treated ones. The effect of EDU in delaying senescence appears to be an important factor to consider when attempting to evaluate the effect of ambient ozone on pod weight in beans using the EDU approach.