Wheat is the main crop in most countries and forms 15 to 18% of food consumption, which used for many purposes such as bread, different pastries, starch, and protein. Drought stress is still in the production of major limitation of crops. Morphological and physiological identification of drought resistance is of highly importance in the improvement of raised problems under drought stress. As a matter of fact, the genetic relationships of each of these processes and their exact relationship with grain yield are unknown. On the other hand, the heritability of drought resistant cultivars based on morphological and physiological component modification is proposed as an important solution. This study conducted to evaluation the drought stress effect on physiological and morphological traits of wheat.
Wheat bread (Triticum aestivum L.) cultivated in a vast range of environmental situations in the whole the world and has the widest mechanism among cereal species. Land allocated for wheat production in the world is more than any other plants. Much of wheat lands planted in Iran are in arid and semiarid regions. Due to lack of water resources and drought yield environment of wheat decreases significantly in these regions. 2015-16 wheat cultivation area is 2% decreased from 9199 thousand hectares to 9180 thousand hectares. Identification of factors influencing the reduction of grain yield is difficult in harsh environments.
What is stress:
Stress in the result of the abnormal physiological processes and can be obtained by the impact or influence of biological and environmental factors. Namely stress is exposure the organism under the influence of an environment factor and apparently makes a reduction in its output or value
What is drought:
Temporary climatic conditions in which unavailability of require water for crop productivity.
Study of form or shape.
Study of functions of living organisms and their parts.
Low rainfall and its irregular distribution causes drought stress during crop growth period Drought and the stress resulted by it is the most important and the most common environmental stress, which causes enormous damage to crops worldwide every year, especially in Iran as an arid and semiarid country. Drought stress has severe effects on the growth of three important stages. These steps are:
- Occurrence and formation of flower
- Pollination and fertilization
- Seed formation
In reproductive stage, the plant is particularly sensitive to water. There are many reasons that drought stress limitation prevents the rate of rise of flowering stem cells. Nevertheless, it has been proven that by removing the stress of cells it is formed faster than irrigated plants
Stress effect on photosynthesis respiration, materials transmission
Drought stress by reducing leaf area, pore blockage, reducing protoplasm activities and stabilization of carbon dioxide, reducing protein synthesis and chlorophyll reduces photosynthesis process. The conditions of severe respiratory stress, absorption of carbon, assimilate translocation, and transmission of raw materials in a wooden vessel, will rapidly decrease to a very low level, and while hydrolytic activity of the enzyme increases, reduction of assimilates saturates the levels from these substances and finally will lead to the photosynthesis reduction and hunger will happen. In terms of deficit, reduction in dry matter may be due to cell swelling pressure resulted from a reduction in the plant’s leaf area and a reduction in photosynthesis rate may be due area and a reduction in photosynthesis rate may be due to biochemical limitations resulting from water deficiency including reduction of photosynthetic pigments especially chlorophyll
Wheat production declined due to
- Water supply limited during initial stage
- Prolonged winter period
- During the April-May unexpected rainfall (GOP, 2015-16).
- In arid and semi-arid regions, salinity and water shortage are the major reasons cultivation and yield.
- Due to insufficient water supply drought is also causes problem in irrigated areas (Mirbahar et al., 2009).
Effects of drought on morphological traits:
Growth more sensitive to drought stress with reverence to the grain yield.
During the anthesis stage drought has severed impact on yield.
- Plant height decreases under drought conditions.
- Height decrease due to decrease cell size not in cell number.
- Height not as much effected by drought as other traits.
- Number of tillers decrease under drought stress. (Plaut et al., 2004).
1000 grain weight
- Grain weight decrease under the water deficit conditions because drought effect the grain filling. (Plaut et al., 2004).
Leaf area index (LAI)
- Leaf area index (LAI) is the ratio of leaf area to land area.
- Reduce under stress conditions.
Leaf area index (LAI):
- Decrease due to size of the cell (McCrea and Davis, 1974).
- Reduce in water status of plant due to increased abscission rate
- Leaf area index decreased due to water stress during vegetative stage of wheat (Qadir et al. 1999).
Number of productive tillers
- Chances of pollination reduced during the water stress at anthesis (Ashraf, 1998).
- Grain filling which leads to unproductivity of spikes.
Spike length and spikelets
- Drought effects the growth of spike
- Reduce the length of spike and spikelets per spike. (Ashraf, 1998).
- height and tillering
- productive tillers/plant
- length of the spike reduces
- Spikelets numbers/plants
- Number of grain/spike
- 1000 grain weight
So, ultimately drought reduces the yield. (Ashraf, 1998).
Effects of drought on physiological traits:
- Carbon dioxide (CO2) passage rate entering or water vapor leave out from the stomataof a leaf.
- CO2 enrichment reduced leaf stomatal conductance under different soil water status (Drake et al., 1997).
- Stomata partially close to save water (Drake et al., 1997).
- Concentration of CO2 increases which close stomata partially as the result transpiration also decrease: –
- Decrease in stomatal conductance
- (Kimball et al., 2002).
- Leaf temperature increase due CO2 concentration, which enhance the rate of transpiration (Kang et al., 2002).
- Under the stress photosynthesis rate decreases due to.
- Reduce in stomatal conductance
- Significant decrease in chlorophyll a, b and carotenoids.
- Chloroplast lipids are oxidizing
- Structure of pigments and proteins may have altered (Marcinska et al., 2013).
- Peroxidase and phenol oxidase activities in wheat leaves were negatively effects under drought conditions. (Iqbal, 2009).
- Peroxidaseenzymes play vital role in catalyzing the renovation of H2O from H2O2.
- phenol oxidase protect the plant from reactive phenolic compounds.
Membrane Integrity and proline
- stress membranes rupture or shriveled
- Proline believed to stabilize membrane phospholipids which overcome periods of drought stress. (Mujtaba et al.,2007).
Morpho and Physiological traits, genotypes of wheat are toughly effect during soil water scarcity. In water stress, wheat genotypes survive by adaptive variations in morphological characters and in the course of physiological and biochemical processes. Grain formation is sensitive to water shortage. Traits, such as best heading time, high RWC, rate of photosynthesis and chlorophyll contents can be use under rain fed situation, criteria of good selection for breeding of wheat genotypes.
- Interactions between breeders and soil scientists.
- Increase genetic diversity.
- Improve screening methodologies.
- Integration between molecular genetics & plant breeding
This article is collectively authored by Muhammad Umair Yasin*1, Arshad Ali1, Muhammad Yousaf Nadeem2 and Muhammad Umair Hassan1. 1Department of Agronomy, University of Agriculture, Faisalabad, Pakistan. 2Department of Agronomy, Nanjing Agriculture University, China.