Drought Stress Tolerance
Drought stress severely limits plant growth and productivity. Traditional plant breeding strategies have made significant contributions to the generation of stress-tolerant plants. The problem in setting-up strategies for generating drought stress toleran
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Drought Stress Tolerance Dorothea Bartels and Jonathan Phillips
8.1
Introduction
Improving the drought tolerance of crops has been an important aim of plant breeders for a long time, and successful varieties have been developed. Despite this fact the issue of food security will become more serious due to the forecasted global climatic changes in combination with the increasing world population (FAO 2006). Many environmental factors are responsible for a reduced crop yield. Among them, drought is one of the major threats to agricultural production. Even in the most productive agricultural areas, periods of water deficiency are responsible for considerable reductions in biomass yield every year. This chapter focuses on drought, although exposure to drought often triggers reactions common to drought, salinity or low temperature. The consequence of all three environmental factors is cellular dehydration leading to osmotic stress, likewise the production of reactive oxygen species. Therefore plants often show tolerance to several stressors. Drought tolerance can be achieved by different mechanisms such as by taking up as much water as possible, high water-use efficiency, and by directing photosynthesis products into harvestable material like grains (Blum 1988). Three main approaches have been used in breeding for drought tolerant varieties: (i) select for high yield potential under optimal conditions, (ii) select for maximum yield in target environments, (iii) incorporate known morphological or physiological parameters of drought stress tolerance in the selection schemes. Drought stress tolerance is a complex phenomenon and involves many genes. The existence of differences in drought tolerance between genotypes indicates that there is a genetic basis for drought tolerance mechanisms. This is the justification for the analysis of genetic
D. Bartels and J. Phillips Institute of Molecular Biology and Biotechnology of Plants (IMBIO), University of Bonn, Kirschallee 1, 53115 Bonn, Germany e-mail: [email protected]
F. Kempken and C. Jung (eds.), Genetic Modification of Plants, Biotechnology in Agriculture and Forestry 64, DOI 10.1007/978-3-642-02391-0_8, # Springer-Verlag Berlin Heidelberg 2010
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variations through mapping quantitative trait loci (QTLs), which is often applied for crop plants. However, the time-frame from identification of QTLs to gene discovery is long, and success depends on the availability of a comprehensive genetic map. About two decades ago molecular approaches were started to dissect the gene network determining drought stress tolerance. Many genes have been identified which are responsive to drought stress (Seki et al. 2002). Molecular studies have preferentially used the genetic model plant Arabidopsis thaliana, because of its small genome size and the availability of the full genome sequence. Naturally desiccation-tolerant plants like the resurrection plant Craterostigma plantagineum have also been exploited in order to isolate genes which confer toleran
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