Agronomic and Physiological Responses to High Temperature, Drought, and Elevated CO2 Interactions in Cereals

Cereals such as rice, wheat, maize, and barley account for major proportion of global food grain production. High temperature, drought, and other climate change drivers are predicted to increase in frequency and magnitude, posing serious challenges to sustain global food production under changing climate. These climate change drivers often interact with each other under realistic field conditions resulting in impacts that are notably different compared to individual stress exposure. Till date, there has been no systematic synthesis comparing the impacts of different combinations of high temperature, drought, and elevated CO2 [eCO2], across cereals. Hence, the major objective of this chapter is to capture the overall agronomic and physiological impact of different combinations of these three factors compared with their independent exposure. High temperature or drought affects almost all growth and developmental phases during crop cycle leading to significant decline in photosynthesis, floral abnormalities, spikelet/kernel sterility, grain yield, and quality losses. Combined high temperature and drought stress can result in additive detrimental effect on growth physiology and productivity. On the other hand, interactive effect of [eCO2] with either high temperature or drought varies with species (C3 and C4), and also depends on other factors such as phenological stage, intensity and duration of stress, etc. Constraints and available avenues for breeding multiple abiotic stress tolerant cereals, role of modern genomic tools, precision phenotyping, and trait-based breeding program are highlighted. Finally, the chapter summarizes future research direction, in addressing combined stress resilience to ensure sustained global food security under warmer and drier climate.