The productivity of plants is greatly affected by various environmental stresses such as drought, salinity and freezing. Among these, salinity is the most important factor limiting crop productivity. Nearly 20 % of worlds cultivated area and nearly half of worlds irrigated land is affected by salinity. The plants are classified as glycophytes or halophytes according to their capacity to grow on high salt medium. Most plants are glycophytes and cannot tolerate salt stress. High salt concentration affects plants by decreasing osmotic potential of soil solution creating water stress, cause severe ion toxicity and interact with other minerals resulting in nutrient imbalance and deficiencies.
Some of the species are employed in better understanding of salt tolerance mechanisms viz., homeostasis, detoxification and growth regulation and pathways, which regulate the expression of genes under salt stress for effective means to breed salt tolerant crops.1 Despite considerable research on salinity tolerance, a limited success has been achieved due to complexity of the trait both genetically and physiologically and lack of understanding of salinity tolerant mechanisms as well as lack of field and laboratory screening tests. Tolerance controlled by polygenes whose expression is influenced by various environmental factors.
Identification of quantitative trait loci (QTL) for salt tolerance is an effective tool for large scale screening of genotypes and identification of chromosomal regions associated with DNA markers. The QTL controlling various rice seedling traits conferring salt tolerance was mapped on molecular map of rice generated by using a doubled haploid population derived from cross between IR 64 X Azucena. A population of recombinant inbred lines (RILs) derived from cross Opata 85 X W7984 was used for genetic analysis in response to salt stress in wheat which resulted in identification of 47 QTLs mapping to all wheat chromosome except 1B, 1D, 4B, 5D and 7D at both germination and seedling stage. Understanding the salt tolerance mechanisms, which regulate gene expression and ability to transfer from other organisms to plants and use of novel approaches combining genetic, physiological and molecular techniques will provide excellent results in future.
1. Borsani, O., Valpuesta, V. and Botella, M. A., 2003, Developing salt tolerant plants in a new century: a molecular biology approach. Plant Cell, Tissue and Organ Culture, 73: 101-115.
2. Flowers, T. J. and Flower, S. A., 2005, Why does salinity pose such a difficult problem for plant breeders? Agricultural Water Management, 78: 15-24.
3. Liqing, M., Erfeng, Z., Naxing, H. and Ronghua, Z., 2007, Genetic analysis of salt tolerance in a recombinant inbred population of wheat (Triticum aestivum L.). Euphytica, 153: 109-117.
4. Raghavendra Prasad, S., Prashanth, G. B., Shailaja, H. and Shashidhar, H. E., 2000, Molecular mapping of Quantitative Trait loci associated with seedling tolerance to salt stress in rice (Oryza sativa L.) Current Science, 78: 162-164.
5. Sairam and Aruna Tyagi, 2004, Physiology and molecular biology of Salinity stress tolerance in plants. Current Science, 86: 407-421.
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