Drought stress and tolerance mechanisms in crops What

Drought stress and tolerance mechanisms in crops: • What is drought: A period or conduction of unusually dry weather with a geographic area where there is a lack of precipitation. • Drought stress accounts for more production losses than all other factors combined. • Fraction of world arable land subjected to drought (abiotic stress) 26%. • Drought is caverned by various factors, the most prominent are: Ø Extreme of temp Ø Photon irradiance Ø Paucity of water

• The characteristic features of drought stress is low water potential due to high solute concentration. • Low water supply causes soil mineral toxicities and can make a plant more susceptible to damage from high irradiance

Major reasons of drought • Atmospheric factors: Ø High temp Ø High wind Ø Air pollution • Soil factors: Ø Low temp Ø Excessive soil salinity Ø Receding water content

Different type of drought • Meteorological drought: Due to prolonged period with less than average precipitation. • Agricultural drought: Which affect crop production or ecology of range. • Hydrological drought: When the water reserves available in sources such as lack and reservoirs fall be low statistical avrerage.

• Effect drought stress on plants �Effect on growth: Reduction of turgor pressure, due to cell size will be smaller. �Effect on photosynthesis: Photosynthesis decreases due to distruption of PS II (photo system II), stomatal closure and decrease in electron transport. �Decrease in nuclear acid and proteins

• Mechanism of drought tolerance: �Drought scape: It is defined as ability of a plant to complete its life cycle before supply of water in soil is depleted. These plant known as drought scapers. �Drought avoidance: It is ability of plant to maintain relatively water balance despite a shortage of soil moisture.

• �Drought tolerance: It is ability of plant to withstand water deficit with low tissue water potential.

Mechanisms of resistance to drought Morphological response to drought: Ø Increase in water absorption and transportation, declination of transpiration. Ø Developed root system and higher ratio of root to shoot. Ø Thick leaf Ø Small leaf area Ø Thick cuticle Ø Developed veins and bundle Ø Smaller and more stomata

Physiological and biochemical basis of drought stress tolerance in plants: Ø Increase in capacity of resistance to dehydration of cytoplasm: rapid accumulation of proline, glycinebetaine, and ion etc. Ø Synthesis of specific proteins like LEA. Ø Reduced ROS accumulation. Ø Increase in antioxidative enzymes. Ø Decreased efficiency of Rubisco.

Ø Phytohormone play vital role in drought tolerance in plants. Ø Under drought condition, endogenous contents of auxins, gibberellins, cytokine, usually decrease while those of abscisic acid and ethylene increase. Ø There are many signals that induce stomatal closure among these the best known signal is ABA.

Summary • In the days of global warming, the effect of drought stress on crop productivity is expected to increase. • The crop plant have involved certain resistance mechanism against drought stress. We should identify these mechanism and traits and introgress these into succeptable genotypes • Only conventional breeding is not sufficient in development of drought tolerant varieties. • Non conventional approaches i. e. molecular breeding can play a significant role in the sphere of abiotic stress mainly drought tolerance. • Genomic regions carrying drought tolerant gene can contribute for abiotic stress tolerance.