Impact of tropospheric ozone pollution on wheat production in Southeast Asia

The drastic changes in the amount of significant secondary air pollutant tropospheric ozone (O3) severely damage the crop productivity worldwide directly by generating oxidative stress in cellular compartments. Apart from that being the third major greenhouse gas, Dobson unit advancement in production of O3 causes elevation of temperature by 0.02 K uphold its contribution toward the global warming indirectly. The past few decades have seen a noteworthy increase in concentration of air pollutants, especially the secondary one (e.g., O3), which are produced in the air by the photooxidation of precursor gases such as carbon monoxide (CO), methane (CH4), and volatile oxygen compounds in the availability of nitrogen oxides (NOx), considered to be the responsive action for the O3 generation in ground level. Besides the continuous production, O3 also gets transported across urban to rural region or even continents beyond national boundaries apparently ensuring the increase in background O3 amount, thus rendering threat toward regional and global food security. O3 is indeed pernicious to plant kind as it introduces reactive oxygen species (ROS) in plant cell after entering into the substomatal cavity of the leaves. The oxidative stress owing to generation of ROS subsequently alters the plant cell ultrastructure, biochemical, physiological, and metabolic processes, thereby reducing photosynthesis, chlorophyll content, and stomatal closure, accelerating senescence, weakening defense upon pathogen attack, and suppressing economic yield, biomass, and productivity. Throughout the world, wheat is considered as one of the most severely damaged O3-sensitive crops. In general, reports depicted a loss of 15%–35% in wheat production under ambient O3 pollution, which may get worse under its elevated concentration. Different researches depicted that modern cultivars are more sensitive than older ones. Scientists believe that higher sensitivity of modern wheat cultivars might be because, while developing new varieties, breeders try to maximize the photosynthetic rates of crops. But to make more food, plants need to absorb more carbon dioxide. So they open their stomatal pores for longer periods of time. Ozone present in the environment also gains easy entry into the plants through their stomata and damage the cells. This chapter mainly focuses on reviewing the available reports on responses of different popularly grown Indian wheat cultivars from different regions of India, under ambient and higher levels of O3. We believe that this chapter provides a comprehensive update of interregional as well as intercultivar responses of Indian wheat cultivars under O3 pollution and paves a way for researchers for future study.