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.