DOSE-RESPONSE STUDIES WITH THE ANTIOZONANT ETHYLENEDIUREA (EDU), APPLIED AS A SOIL DRENCH TO 2 GROWTH SUBSTRATES, ON GREENHOUSE-GROWN VARIETIES OF PHASEOLUS-VULGARIS L

To study plant growth and yield effects of the antiozonant ethylenediurea (EDU), which is frequently used for ozone crop loss assessments, dose-response studies were carried out with potted bean plants under greenhouse conditions in winter and spring. Two cultivars of Phaseolus vulgaris L., differing in sensitivity to ozone (O3), were grown in unfiltered air on a sandy loam rich in organic matter and on a vermiculite-clay mixture. Four treatments of EDU at concentrations from 300 to 800 mg liter-1 were given as a soil drench during plant development. Foliar symptoms of EDU phytotoxicity were observed at all doses, and plant biomass, particularly pod dry weight, was considerably reduced due to increasing doses of EDU Primary and first trifoliate leaf weight in EDU-treated plants increased as did the number of buds, indicating an extension of vegetative growth and a delay of reproductive processes. 'BBL 290' beans, which are O3-sensitive, were injured by EDU more than the O3-tolerant 'BBL 274'. The phytotoxic effects of EDU were more pronounced in the synthetic growth substrate than in field soil. In a second experiment, EDU was applied in concentrations from 100 to 400 mg liter-1 to 'BBL 290' plants, exposed to filtered air or simulated levels of O3 pollution. In field soil, plant growth and biomass partitioning in filtered air was only slightly altered by EDU, although leaf injury due to EDU occurred. In the vermiculite-clay mix, the biomass of most plant organs, particularly that of roots, was linearly reduced with increasing EDU doses. O3 did not cause any alteration in plant biomass in field soil-grown and EDU-treated plants. Ozone leaf injury, which affected 67% of primary leaf area in non-treated plants, was completely suppressed by EDU doses as low as 100 mg liter-1. This indicates that low concentrations of EDU, which do not affect plant growth in field soil, provide sufficient protection from O3 injury. The need for careful EDU dose-response studies prior to field assessments is emphasized.