Morphological and physiological traits to improve wheat for drought tolerance
In the cereal crops, wheat is most important crop with annual production 718 million tons and one-fifth world population depends on it. Wheat production increased by two ways, increase the cultivated area or high productivity per unit area. First option is not suitable because of population rapidly increase and build new colonies, towns, building etc. Second option is suitable for increase productivity to fulfill the demand of growing population. Different abiotic factors affect heavily on crop growth and yield, water shortage is a big factor. Drought prolonged because of little rain and high temperature. In Pakistan, drought is one of most important disaster which could result in high wheat yield loss. Different morphological and physiological traits can be used to improve the wheat under drought environment. Wheat should be able to drought escape. In drought, wheat should be able to complete their life cycle before drought occurs. It should be grown in that cropping pattern which is drought escape. Increase the root density from surface to depth and with greater radial hydraulic conductivity at depth may lead to high yield under drought environment. Drought avoidance can be done by improvement in roots architecture. Stomata’s should be on lower side because it does not directly expose to the sun and reduce the transpiration. Leaves size less or narrow there will be less number of stomata. Stomata should be done work more efficiently in drought environment. In wheat during grain development, water use efficiency positively correlated with stay green duration of flag leaf and harvesting index. During grain filling 30%-50% photosynthates needed and contributed by flag leaf photosynthesis. In selection parameters use that trait to improve the wheat under drought condition. Drought resistant in wheat can be done by sustained ability for grain filling. Photosynthesis takes place in leaves and store in vegetative organs and later transport to growing grains. Cells should be maintained the water balance by osmotic adjustment because of osmolytes (glycine betaine, proline, polyamines). It is major component of drought resistant. In water shortage condition, oxidative stress promote because over generation of ROS. Antioxidative defense mechanism enzymatic (catalase (CAT), peroxidase (POX), superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR)) and non-enzymatic (ascorbic acid, α-tocopherol, reduced glutathione, β-carotene) accumulation in plant cell prevent from oxidative damage. Plant growth by modulating leaf expansion, elongation, tissue water conductance through stomatal oscillations, control cellular dehydration and improving root growth regulate by abscisic acid (ABA) in drought environment. Drought rapidly increases because of climate change. Breeder should be produced the varieties which is more responsive in drought environment and give maximum yield. Breeders should be aware about morphological and physiological traits which make plant more efficiently use water.