Abiotic stress tolerance in rice for Asia: progress and the future

Various abiotic stresses limit rice production in rainfed environments, which comprise about 45% of the global rice area. Important stresses include water deficit, submergence, salinity, and deficiencies of P and Zn. In recent years, advances in physiology, molecular biology, and genetics have greatly improved our understanding of how rice responds to these stresses and the basis of varietal differences in tolerance. Progress has relied on the application of rather specific phenotypic screens that allow the effects of stress to be distinguished from general differences in adaptation of diverse parents. QTLs have been identified that explain a considerable portion of observed variation, and in some cases, the genes underlying specific QTLs have been identified. Transformation has been used to assess the effects of altered expression of specific stress-related genes, allowing confirmation of the importance of particular metabolic pathways. Through expression profiling of many genes simultaneously, it has been possible to identify three types of stress-responsive gene networks: early signaling pathways, adaptive responses, and genes that reflect downstream results of damage. For crop improvement, the identification of useful allelic variation for genes in the second group may be the most promising approach. Once such genes or gene combinations are identified, either molecular approaches or trait-specific physiological screens can be used to search for these superior alleles. Marker-assisted backcrossing can then be applied to incorporate these alleles into agronomically superior germplasm. Media summary Abiotic stresses such as drought, salinity, submergence, and nutrient deficiencies limit rice production. Recent advances in our understanding of the physiology and molecular biology of stress tolerance in rice are being used to develop improved rice varieties.