Growth and physiological responses of two sugarcane cultivars exposed to elevatedsurface ozone

Surface ozone (O3) pollution is known to have a detrimental effect on agriculture whilst rising carbon dioxide (CO2) concentrations are sometimes found to offer plants protection against O3 effects. Considering the important role of sugarcane (Saccharum spp. hybrids) as a major food crop in South Africa and its contribution to the national economy, the tolerance of this crop to O3 damage must be established. A pilot study using open-top chambers was conducted whereby two local commercial sugarcane cultivars (NCo376 and N31) were fumigated during the summer growth season to explore the effects of elevated O3 as well as the interacting effects of O3 and CO2 on various stress and crop quality indicators. Statistical significance of differences in treatment means was analysed by hierarchical linear modelling to account for variability between chamber and pots in explaining changes across individual plants. The results revealed a significant reduction in the number of dead leaves (senescing) for the N31 cultivar exposed to elevated O3 compared with the other treatments. There was also a statistically significant decrease in chlorophyll fluorescence (used to assess photosynthetic performance) in the O3-treated NCo376 plants. This pilot study shows limited effects of O3 fumigation on growth and physiology, with preliminary indications that sugarcane is less sensitive to O3 than other crops. An increase in O3 concentrations associated with future climate change is expected, which will have implications for cultivar selection as a possible adaptation strategy to reduce susceptibility of this crop to O3.