Adaptation of crops to warmer climates: Morphological and physiological mechanisms

Abstract

Increased surface temperature is one of the major reasons for reduced crop productivity in many parts of the world. Response to elevated temperature varies among crop species-a certain threshold temperature has been determined for each crop above which it suffers yield losses. Thus, some crop species, e.g. summer crops (cotton, rice, sorghum), are considered relatively more tolerant to high temperature than winter crops (wheat, barley, chickpeas, faba bean). Heat-induced yield penalties in crops are the result of inhibited vegetative growth or impaired reproductive development. High temperature can cause cellular injury, leading to catastrophic collapse of cellular organization and functioning and ultimately, growth inhibition. Similarly, reproductive structures, especially pollen are highly sensitive to elevated temperatures and a heat shock event at reproductive phase impairs fertilisation and consequently increases fruit or seed abortion. Tolerance to high temperature is associated with a range of physiological and morphological adaptations in plants. For example, plants can tolerate heat-induced damage through foliar orientation, stomatal regulation and stimulation of antioxidative defence systems. These adaptive mechanisms are regulated by stress responsive genes, encoding for specific proteins, e.g. heat shock proteins, which enable plants to survive under extreme environments. This chapter discusses various adaptive, avoidance and acclimation mechanisms of heat tolerance in plants. It also highlights the breeding and management techniques used for inducing heat stress tolerance in crop plants.