Genetics of Drought Stress Tolerance in Crop Plants

Ensuring stable crop yields in an era where climate change threatens traditional agricultural practices through altered rainfall patterns and increased urban con- sumption has become a vital concern in global food security. Projected freshwater availability for irrigation indicates that between 20 and 60 Mha of irrigated cropland may have to be reverted to rainfed management. Formerly irrigated crops would become entirely dependent on rainfall and vulnerable to yield loss due to drought. Biotechnology and mining of germplasm of numerous crop species has resulted in discovery of traits that control water use efficiency (WUE) and improve drought tolerance, but only a few of these traits have been implemented in the field. We need a Blue Revolution in agriculture that focuses on increasing productivity per unit of water more crop per drop, Secretary-General Kofi Annan called for a Blue Revolution in agriculture. The Green Revolution drastically increased agricultural productivity by remediating nutrient-poor soils with fertilizer, devel- oping irrigation methods and systems, instigating integrated control strategies for weeds and pests, and selected crops that responded to these changes with high yields. The Blue Revolution proposes to address decreasing water availability and climate change. This requires not just drought-tolerance traits, but a high level of control of WUE while still maintaining high yields required by both industrial agriculture and smallholders. An integrated research approach has emerged as a valuable strategy to tackle these necessities. One component of this approach is the mining and intro- duction of traits from landraces and wild relatives in order to improve drought tolerance and WUE in crop species. In some cases, this has been combined with modern biotechnology in an integrated approach. Recently, drought-tolerant maize hybrids have been released in the United States as a result of biotechnology and introduction of traits from distant relatives. This chapter gives a broad overview of the genetic basis of developmental and cellular responses known in crops to enhance drought tolerance. A number of key processes and genes have been discovered in model systems that show great promise for use in crop species. Furthermore, this chapter also addresses the potential for wild relatives of five major crop species (tomato, potato, wheat, rice, and corn) as sources for genetic improvement. These landraces and wild relatives are often remarkably well adapted to their environment through natural selection and traditional breeding. These relatives provide a resource for mining novel traits for the genetic improvement of cultivated crops that are vulnerable to environmental stress.