**Abstract**

Crop yield is mainly influenced by climatic factors, agronomic factors, pests and nutrient availability in the soil. Stress is any adverse environmental condition that hampers proper growth of plant. Abiotic stress creates adverse effect on multiple procedures of morphology, biochemistry and physiology that are directly connected with growth and yield of plant. Abiotic stress are quantitative trait hence genes linked to these traits can be identified and used to select desirable alleles responsible for tolerance in plant. Plants can initiate a number of molecular, cellular and physiological modifications to react to and adapt to abiotic stress. Crop productivity is significantly affected by drought, salinity and cold. Abiotic stress reduce water availability to plant roots by increasing water soluble salts in soil and plants suffer from increased osmotic pressure outside the root. Physiological changes include lowering of leaf osmotic potential, water potential and relative water content, creation of nutritional imbalance, enhancing relative stress injury or one or more combination of these factors. Morphological and biochemical changes include changes in root and shoot length, number of leaves, secondary metabolite (glycine betaine, proline, MDA, abscisic acid) accumulation in plant, source and sink ratio. Proposed chapter will concentrate on enhancing plant response to abiotic stress and contemporary breeding application to increasing stress tolerance.

**Keywords:** abiotic stress, drought, salinity, cold, heavy metals, morpho-physiological and biochemical changes

#### **1. Introduction**

Plants in their physical environment face several types of variation. Animals use techniques to prevent the impacts of this variation but plants fail because of the sessile nature of the growth habit. Plants therefore, rely on their internal processes to survive changes in the external environment. Plants are affected to function in an oscillating environment and normal external changes are countered by internal changes without any harm to growth or development. The possibility of abiotic or environmental stress is to cause physical harm to the plant due to serious or chronic adverse environmental circumstances. Any adverse influence of inanimate factors on living beings in a fixed setting is described as abiotic stress. To substantially impact the organism's demographic output or individual physiology, the non-living factor must alter the surrounding beyond its ordinary variation range. Due to the continuous climate change and environmental deterioration induced by human activity, physical surrounding stress has become a key threat to food security. Water deficit stress, salt stress, imbalances in nutrients (including mineral toxicity and

deficiencies) and temperature extremes are significant environmental limitations on productivity of crops all over the world [1].

Plant growth and crop yield are majorly affected by cold, drought, salt, and heavy metals. Abiotic stress impacts plants to molecular levels from morphological levels and is visible at all phases of plant development where drought occurs [1]. There are three significant stages of plant: vegetative development, pre-anthesis and terminal phase that are impacted by the drought [2]. Plant physiological reactions to stress include wilting of the leaf, abscission of the leaf, decreased leaf region and decreased water loss through transpiration [3]. Under drought stress, crop development facilitates the issue of extreme water use in agriculture to a big extent. Turgor pressure is decreased, which is one of the most delicate physiological mechanisms that cause cell growth. Drought stress creates water flow disruption in higher plants from xylem to the neighboring elongating cells, thereby suppressing cell elongation. In addition, decreased leaf area, plant height, and development of crop result from drought pressure owing to cell elongation, impaired mitosis and expansion [1]. Abiotic stress resistance contains escapeavoidance and tolerance mechanisms. Detrimental impacts of stress can be decreased by osmotic modification, which helps with an active accumulation of solutes in the cytoplasm to maintain cell water balance [4].

Survival and geographical spreading of plants are also greatly affected by low temperatures. Significant loss of crop due to reduced plant growth and crop efficiency is usually caused by cold stress [5]. Cell and tissue dehydration and cellular water crystallization are caused by cold stress, thereby reducing plant growth and productivity. Reduced membrane conductivity, increased water viscosity, and hydro active stomata closure is inhibited resulting in water stress and increased leakage of electrolytes at low temperatures [6]. It also delays metabolism, dissipates energy, and causes free radicals to form as a result of oxidative stress [7].

For instance, up to 45% of the world's farming based land is encountered to frequent periods of time when there is scanty of rainfall in which 38% of the world's population resides and the world's mapped area is affected by salinity in more than 3106 km2 area or about 6% of the entire area of land [8]. In addition, 19.5% of irrigated agricultural land is classified as saline. In addition, about 1% of world agricultural land is deteriorated by salinity (2 million ha) each year, resulting in decreased or no crop productivity [9]. Major abiotic stress affects the plants during their growth and development arises due to water limitation caused by inadequate rainfall, cold condition, and salinity. The worldwide land region impacted by drought, cold and salinity is 64, 57, and 6%, respectively, according to the FAO World Soil Resources Report, 2000. Comprehension of crop plant abiotic stress reactions has thus become component of plant studies to protect food security [10]. Abiotic stresses are interrelated and influence the relationships of plant water on the cellular and also the entire plant level, affecting certain and uncertain reactions resulting in a series of morphological, physiological, biochemical and molecular changes that affects the growth and development of plants adversely.

These abiotic stresses characterize the main cause of crop fiasco globally, introducing more than 50% of the average returns for significant crops [10]. Improving cultivation is therefore vital to fill the gap between population growth and food production, which is widening by initiating stress tolerance. Plants can introduce some molecular, cellular and physiological modifications to react to and acclimatize such stresses in order to deal with abiotic stress. Better knowledge of plant responsiveness to abiotic stress in both traditional and modern breeding application will assist to enhance stress tolerance. Studies with high stress tolerance on some wild plant species also make a significant contribution to our understanding of stress tolerance.

**5**

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*Effect of Abiotic Stress on Crops*

**2.1 Drought stress**

**2.2 Salinity stress**

**2. Types of abiotic stresses**

cantly reduce the crop's productivity.

*DOI: http://dx.doi.org/10.5772/intechopen.88434*

Different abiotic stresses affect the plants due to global warming and fluctuations in the environmental conditions. Abiotic stresses like water scarcity, high salinity, extreme temperatures, and mineral deficiencies or metal toxicities signifi-

Drought is described as stress related to the water deficit. Drought is a climate word described as a period of moment with less rainfall. Drought stress in plants happens when environmental conditions result in a decrease in the quantity of water in the soil, leading in a constant loss of water through transpiration or evaporation. Water is a crucial element of plant survival and essentially needed for transportation of nutrients. Hence, deficiency of water leads to drought stress, which results in reduced vitality of plants [11]. Water stress may occur in plants due to high salt conditions. The soil water potential reduces because of elevated salt circumstances, because the osmotic potential of salt is smaller than water, which makes it hard for roots to absorb the soil's water. Also, owing to enhanced water loss via transpiration or evaporation, elevated temperatures can trigger drought stress. Not only greater temperatures, but reduced temperatures can also trigger stress from the water deficit. Lower freezing temperatures result in ice crystals being created in the extracellular spaces of plant cells, decreasing the water potential and leading to intracellular water efflux. Thus, in general, drought stress occurs due to various causes which further leads to the efflux of cellular water, leading to plasmolysis and thus causing cell death. Water deficit stress is damaging because it inhibits photosynthesis by affecting the thylakoid membranes. An increase in the toxic ions in all the cells of plants is the potential damage caused to the plants due to drought stress. Drought stress is therefore complicated abiotic stress that directly

affects plant growth and advancement and leads to decrease in plant output.

in salt content in soil is referred to as soil salinity or salinization [12]. It mainly occurs in arid as well as semi-arid environments where the plants have higher evaporation and transpiration rates compared to precipitation volume throughout the year. Salts in the soil may increase in the subsoil naturally which is referred to as primary soil salinity or it may be introduced due to anthropogenic conditions like environmental pollution which is called secondary soil salinity. Secondary soil salinity arises due to modification in soil content, an increase in fertilizers or due to the use of saline water in irrigation purposes [13]. Soil salinity is a global problem and a severe risk to the entire agricultural world as it reduces the output of plants. High salt concentration limits growth and development of crops in multiple ways. Two significant impacts in crops result from higher salt content: ionic toxicity and osmotic stress. The osmotic stress in plant cells is greater in ordinary circumstances than in soil. This increased osmotic pressure is used by plant cells to absorb water and the necessary minerals from the soil into the root cells. However, under circumstances of salt stress, the soils osmotic pressure solution surpasses the plant cells osmotic pressure owing to an increase in the salt content in the soil, thereby

restricting plants 'ability to absorb water and minerals such as K+

 and Cl<sup>−</sup> ions move in the cells and have damaging effects on the cell membrane and metabolism in cytosol. Stress with salinity creates some adverse effects

Salinity stress occurs due to an increase in salts contents in soil. Thus, an increase

and Ca2+ while
