Screening Buddleia Cultivars for Acute Ozone Sensitivity

Eight cultivars of buddleia were exposed to ozone (O₃) concentrations up to 375 ppb for two 4-hour periods on consecutive days in 1995. Visible injury to all cultivars consisted of small, discrete spots, reddish purple in color, on the adaxial leaf surface. Cultivars differed in sensitivity to acute O₃ exposure with ‘Empire Blue’ and ‘Opera’ being the most tolerant and ‘Black Knight’, ‘Nanho Blue’, ‘Pink Delight’, and ‘Royal Red’ the most sensitive. Severe injury occurred on the most sensitive cultivars with O₃ exposures of 250 or 375 ppb. At the highest O₃ concentration, the severity index (SI), an indicator of foliar injury, ranged from 1.3 (less injury) for ‘Opera’ to 4.6 (more injury) for ‘Pink Delight’. An exposure-response study with ‘Black Knight’ resulted in visible injury increasing as both concentration and number of exposures increased, with the most severe injury to plants given the most exposures (5 days) to the highest concentration (375 ppb, SI of 6.3).