Effects of Ethylenediurea on Snap Bean at a Range of Ozone Concentrations

Ethylenediurea (EDU) [N-[2-(2-Oxo-1-imidazolidinyl)ethyl]-N'-phenylurea] often protects plants from visible foliar injury due to the air pollutant O₃ , and it has been used to demonstrate yield losses from O₃ under field conditions. A few studies, however, have indicated that EDU can suppress plant growth and yield. Because of the potential value of EDU as a research and assessment tool, controlled field experiments with snap bean (Phaseolus vulgaris L. 'BBL-290') were performed to test the effectiveness of different EDU application rates across a range of O₃ concentrations. Four O₃ concentrations were used in open-top chambers in each of two experiments [charcoal-filtered (CF) air, nonfiltered (NF) air, and nominal O₃ additions of 0.025 and 0.05 or 0.03 and 0.06 μL L^-1 O₃ to NF air]. Ethylenediurea was added biweekly to the potting medium (four applications per experiment) as a soil drench. The EDU treatment concentrations were 0, 14, 28, 56, and 120 and 0, 8, 16, and 32 mg EDU (active) L^-1 of potting medium in experiments one and two, respectively. Ethylenediurea provided some protection against O₃ -induced foliar injury and growth suppression in both experiments. Measurements of net carbon exchange rate (NCER) and carbohydrate status of the tissues reflected the protective effects of EDU. In the first experiment, however, EDU caused visible foliar injury at some growth stages and suppressed growth. In the second experiment, visible foliar injury was not caused by EDU at any concentration, but pod biomass (yield) was suppressed by EDU in CF chambers. The differences in response to EDU between the experiments may have been due to environmental conditions (i.e., hot and dry during the first experiment and cooler during the second). Ethylenediurea also affected biomass partitioning in the plants grown in CF air (relative biomass was increased in leaves and decreased in pods). The results indicate that although EDU does protect or partially protect snap bean against O₃ injury, it may also affect physiology and growth.