Ozone dose-response relationships for tropical crops reveal potential threat to legume and wheat production, but not to millets

The tropical-grown crops common bean (Phaseolus vulgaris), mung bean (Vigna radiate), cowpea (Vigna unguiculata), pearl millet (Pennisetum glaucum), finger millet (Eleusine coracana), amaranth (Amaranthus hypochonriacus), sorghum (Sorghum bicolour) and wheat (Triticum aestivum) were exposed to different concentrations of the air pollutant ozone in experimental Solardome facilities. The plants were exposed to ozone treatments for between one and four months, depending on the species. There was a large decrease in yield of protein-rich beans and cowpeas with increasing ozone exposure, partly attributable to a reduction in individual bean/pea weight. Size of individual grains was also reduced with increasing ozone for African varieties of wheat. In contrast, the yield of amaranth, pearl millet and finger millet (all C4 species) was not sensitive to increasing ozone concentrations and there was some evidence of an increase in weight of individual seedheads with increasing ozone for finger millet. Sorghum did not reach yield, but was not sensitive to ozone based on changes in biomass. Dose-response relationships for these crop species demonstrate that tropospheric ozone pollution could reduce yield of important crops, particularly legumes, in tropical regions such as sub-Saharan Africa.