Breeding for Drought Tolerance in Cereals: an Overview

Drought is among the most serious abiotic stresses in many parts of the world where cereal crops are essential human food source. Breeding cereals for such stress tolerance is strongly challenging the breeders’ efforts where difficulties are compounded by the complexity of crop yield on the genetic and physiological bases. For cereal plants, drought tends to develop slowly under field conditions as the soil dries. Plants that are subjected to drought stress in such gradual manner accumulate solutes that maintain cell hydration and undergo complex adjustments in their morphology and photosynthetic characteristics. Many investigators explained the plant response to drought through escape, avoidance, and/or tolerance mechanisms. Substantial cooperative efforts among physiologists and breeders have been devoted toward understanding and manipulating such complex of morpho-physiological traits for better sustainable crop performance under stress. Such cooperative efforts, beside advances in the field of stress physiology, resulted in many techniques of testing and selecting drought-tolerant plants. An effective screening tool in the hand of a plant breeder should be relatively simple, accurate, inexpensive, and dependable on physiological traits that are highly inherited and well correlated with crop performance under actual field-stressful conditions. Selection using such screening tools in many cases of well planned breeding programs resulted in sustainable cereals' yield under actual shifting dry field conditions. In recent years, more positive role of genomic-based approaches is expected toward improving drought tolerance of cereal crops. Several studies have been able to map J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.7 (1)2008 86 quantitative trait loci (QTL) for traits associated with drought tolerance in major cereal crops. Marker-assisted selection (MAS) has been employed as an integral component of breeding strategies to improve stress tolerance. Despite impressive technological breakthroughs, the results of such efforts are not always consistent due to the multi-genic nature of drought tolerance. Selection based on a comprehensive approach of testing might be more effective in breeding better drought-tolerant cultivars.