Drought Resistance in Crops: Physiological and Genetic Basis of Traits for Crop Productivity

Drought is the most important environmental stress affecting agricultural productivity worldwide. Breeding of drought-tolerant crops is important in order to meet demands of food security in the face of an ever increasing world population, global warming and water shortage. Drought resistance (DR) is defined as the mechanism causing minimum loss of yield in a water deficit environment relative to the maximum yield in a water constraint free management of the crop. Plants have evolved several mechanisms to cope with water deficit stress which includes drought escape and drought tolerance. Plant breeders and physiologists have identified some important traits associated with DR in crop plants. Many of these traits relate to making appropriate use of water when it is available, often with the aim of ensuring reproductive success and grain yield. Traits associated with DR serve as important breeding tools in identifying stress-resistant genotypes and in introgressing the resistance traits into high yielding genotypes. Marker-assisted selection based around screening for desirable alleles at QTL for DR is an important approach for improving DR in crops. Dissecting these complex phenotypic traits into simpler heritable traits has led to the identification of genes associated with some QTLs for DR. Breeding for DR has met with limited success following either empirical or marker-assisted selection approach. It is essential to integrate crop physiology, functional genomics and breeding approaches to dissect complex DR traits, understand the molecular basis of DR and develop improved cultivars to adapt to the changing climate. This chapter focuses on the DR traits important for agricultural productivity in major crops, i.e. wheat and rice. The physiological and genetic basis of traits is discussed to highlight the complexity of the quantitative traits and the need to integrate this information in breeding drought-resistant crops.