Coleus cultivars (Solenostemon scutellarioides (L.) Codd.) as potential bioindicators of chronic ozone exposure

Abstract

Sensitivity of plant under ozone exposure can indicate its potency of being important bioindicator. Early studies have found that coleus plant (Solenostemon scutellarioides (L.) Codd.) has a potency to be ozone bio-indicator. This study aims to investigate the effect of chronic ozone exposure on root and leaf biomass and to quantify any change based on the plant appearance. Four different cultivars of coleus plant with different colour namely fully green (FG), green purple (GP), yellow purple (YP), and reddish (RD) had been selected. These four cultivars were fumigated with three different concentrations of ozone gas (≤ 10 ppb, 40 ppb, and 150 ppb) for 8 hours fumigation during 30-day period of experiment. All cultivars showed a stable leaf biomass after 30-day period of ozone exposure. Similarly, root biomass of all cultivars was not significant changed after fumigation period. Nonetheless, magnitude of ozone symptoms on leaf showed variation in certain cultivars. FG cultivar showed a significant number of chlorosis leaves under 40 and 150 ppb ozone exposure. The exposure of 150 ppb ozone also caused a noticeable percentage of curling leaves on RD cultivar. Moreover, the purple area in YP and GP showed a larger ratio under exposure of 150 ppb ozone. Consequently, coleus plants displayed resistance responds in terms of biomass. On the other hand, the plants also revealed variation in leaf symptom magnitudes and colour patterns under ozone exposure. However, these cultivars are potential to be bio-indicator due to their sensitivity in terms of appearance.