Full Thesis
INTRODUCTION
Genetic variations are the basic tools in the hands of breeders to develop new cultivars with better traits, like tolerance against various environmental stresses, resistance against pest and diseases and improved yield and quality. In field conditions, a number of abiotic stresses affect the crop plants. Abiotic factors generally disturb various cellular functions along with the complex metabolic pathways (Kassem et al., 2004; Lee et al., 2004; Popelka et al., 2004). Drought is one of the common environmental stresses affecting plant growth and productivity (Boyer, 1982). It has been estimated that 10% of the arable land can be classified under non-stress category, which implies that crops grown under 90% of the arable land experience different types of environmental stresses, like water stress. The prediction is that the water deficits will continue the major abiotic single abiotic factor likely to affect crop yield globally (Sharma and Lavanya, 2002).
Since abiotic stress is essentially unavoidable, many breeders are targeting many food crops, especially rice, and utilizing new technologies such as mutation induction and tissue culture techniques to produce crops that can maintain consistent yields in years when water is limiting. Simulation of drought stress under in vitro conditions during the regeneration process constitutes a conventional way to study the effects of drought on the morphogenic responses (Sakthivelu et al., 2008). Polyethylene glycol (PEG) of high molecular weights have been long used to simulate drought stress in plants as non-penetrating osmotic agents lowering the water potential in a way similar to soil drying (Larher et al., 1993). In this way, those individuals that will survive from PEG treatments carry mutations for drought resistance.
Many varieties of rice produced by tissue culture techniques and in vitro selection has improved some of the characteristics of shape, nutritional quality, pest resistance, and the
Genetic variations are the basic tools in the hands of breeders to develop new cultivars with better traits, like tolerance against various environmental stresses, resistance against pest and diseases and improved yield and quality. In field conditions, a number of abiotic stresses affect the crop plants. Abiotic factors generally disturb various cellular functions along with the complex metabolic pathways (Kassem et al., 2004; Lee et al., 2004; Popelka et al., 2004). Drought is one of the common environmental stresses affecting plant growth and productivity (Boyer, 1982). It has been estimated that 10% of the arable land can be classified under non-stress category, which implies that crops grown under 90% of the arable land experience different types of environmental stresses, like water stress. The prediction is that the water deficits will continue the major abiotic single abiotic factor likely to affect crop yield globally (Sharma and Lavanya, 2002).
Since abiotic stress is essentially unavoidable, many breeders are targeting many food crops, especially rice, and utilizing new technologies such as mutation induction and tissue culture techniques to produce crops that can maintain consistent yields in years when water is limiting. Simulation of drought stress under in vitro conditions during the regeneration process constitutes a conventional way to study the effects of drought on the morphogenic responses (Sakthivelu et al., 2008). Polyethylene glycol (PEG) of high molecular weights have been long used to simulate drought stress in plants as non-penetrating osmotic agents lowering the water potential in a way similar to soil drying (Larher et al., 1993). In this way, those individuals that will survive from PEG treatments carry mutations for drought resistance.
Many varieties of rice produced by tissue culture techniques and in vitro selection has improved some of the characteristics of shape, nutritional quality, pest resistance, and the
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