DIFFERENTIAL RESPONSE OF BUDDLEIA (BUDDLEIA-DAVIDII FRANCH.) TO OZONE

Five cultivars of buddleia, Buddleia davidii Franch., were exposed to sub-ambient, ambient, and twice-ambient levels of ozone in open-top ch ambers for 8 weeks (June-August) during 1995. Plants were evaluated fo r foliar injury, growth index, and inflorescence characteristics durin g and following exposure. Destructive harvests were conducted at the e nd of the exposure period to determine dry weights of both above-and b elow-ground plant components. All cultivars had symptoms of visible in jury in the twice-ambient treatment at both three and eight weeks afte r exposures began. No visible symptoms were observed at ambient ozone concentrations. At three weeks of exposure, 'Pink Delight' had the hig hest percentage of the leaves injured (PLI), 46.2%, followed by 'Opera ' with a PLI of 23.3%. The other three cultivars had similar PLIs of l ess than 15%. After eight weeks of exposure, visible injury was equall y severe on all cultivars with a mean PLI of 50.2% and mean Horsfall-B arratt rating of 5.4, indicating 12 to 25% of the leaf area was injure d. No ozone x cultivar interaction was found for any growth variable m easured. Across cultivars, growth index was reduced by 6%, total dry w eight by 35%, and the number of developing floral buds and inflorescen ces by 29% for plants in twice-ambient ozone concentrations compared t o ambient ozone concentrations. Percent biomass allocated to infloresc ences was significantly greater for plants exposed to sub-ambient leve ls compared to those exposed to ozone at either ambient or twice-ambie nt concentrations. Results indicate that ozone levels similar to those in large urban areas in the southeastern United States have the poten tial to reduce growth and flowering of this important landscape plant. (C) 1998 Elsevier Science Ltd. All rights reserved.