**2.1 Drought stress**

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.

#### **2.2 Salinity stress**

Salinity stress occurs due to an increase in salts contents in soil. Thus, an increase 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 Ca2+ while Na<sup>+</sup> 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

#### *Sustainable Crop Production*

such as reduced cell growth, reduced membrane function, and reduced cytosolic metabolism and ROS production. High soil salinity adversely impacts plant production quality and quantity by inhibiting seed germination, damaging growth and development phases as a consequence of the combined impacts of higher osmotic potential and particular ion toxicity [14].

#### **2.3 Extreme temperature stress (hot/cold)**

Extreme temperatures are one of the prime causes of different abiotic stresses like drought. Increases or decreases in temperature, both undesirably affect the plant's growth, development, and yield. Cold stress occurs when plants are subjected to very low temperatures. Cold stress is a major abiotic stresses that reduce productivity of crops by affecting quality and life after harvest. Cold stress impacts all cellular function characteristics in crops. Plants are categorized into three kinds in reaction to cold temperatures: chilling delicate plants: plants that are highly damaged by temperatures above 0°C and below 15°C, chilling resistant plants: crops capable of tolerating low temperatures and wounded when ice formation begins in tissues and frost resistant plants: plants capable of tolerating exposure to very low temperatures. Cold stress causes injury to plants by changes in the membrane structure and decrease in the protoplasmic streaming, electrolyte leakage and plasmolysis which leads to cellular damage. The metabolism of the cells is damaged by an increase or decrease in respiration rate and depending on the intensity of the stress, synthesis of abnormal metabolites occurs due to abnormal anaerobic respiration. Due to cellular damage and altered metabolism, there is reduced plant growth, abnormal ripening of fruits, internal discoloration (vascular browning), and increased susceptibility to decay and also cause the death of the plant [15].

If crops are subjected to very elevated temperatures, heat stress happens. For adequate moment to cause permanent injury to functioning or development of plant. Heat stress is defined as elevated temperatures. High temperatures boost the rate of sexual development, which reduces the time needed to add photosynthesis to the production of fruit or seed. Also, high temperatures can cause drought stress due to increased water loss by transpiration or evaporation. High soil temperatures can decrease the emergence of plants. High temperature stress can influence seed germination, plant growth and development, and can trigger irreversible drought stress that can lead to death as well [16].

#### **2.4 Metal stress**

Heavy metal stress (HM) belongs to a group of non-biodegradables, determined inorganic chemicals having atomic mass more than 20 and a density exceeding 5 g cm<sup>−</sup><sup>3</sup> with toxic effects on cells and genes, which causes mutagenic impacts on crops by influencing and contaminating irrigation, soil, drinkable water, food chains and the surrounding environment [17, 18]. There are two categories of metals discovered in soils that are mentioned as vital micronutrients for standard plant growth (Fe, Mg, Mo, Zn, Mn, Cu, and Ni) and non-essential elements with unknown physiological and biological function (Ag, Cr, Cd, Co, As, Sb, Pb, Se, and Hg) [19]. Plant surfaces both underwater and above ground can take HMs. In the enzyme and protein structure, the vital elements play a main role. Plants need them in minute quantities for their metabolism, growth, and development; yet, the concentration of vital and non-essential metals is an only essential factor in the increasing crop cycle so that their excessive presence can cause a decline and inhibition of plant growth. HMs at poisonous concentrations hinder ordinary functioning in plants and act as an barrier to metabolic procedures in different ways, comprising

**7**

**Table 1.**

*Effect of Abiotic Stress on Crops*

**3.1 Chickpea**

**3.2 Wheat**

plant metabolism [22].

**3.3 Maize**

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

**3. Major crops affected by abiotic stress**

the displacement or disturbance of protein structure construction blocks arising from the creation of blonds among HMs and sulfhydryl groups [20], interfering

After dry beans and dry peas, chickpea is the third most significant food legume worldwide. It is grown on 12.4 million hectares, generating 11.3 million tons at an average output of 910 kg/ha, according to FAOSTAT information in 2012–2013. In chickpea manufacturing and productivity, climate change is a significant challenge (**Table 1**). Climate change's negative impacts seem to result from drought effects [15].

Wheat is the major crop grown mainly in the Rabi season. Under various agroecological circumstances, it is commonly cultivated. Drought impacts vary from morphological to molecular. Many stages of plant development are influenced by drought. Drought has an impact on three major periods of plant developmentvegetative, pre-anthesis and terminal stage. Physiological responses of plants to drought comprise leaf wilting, reduced leaf area, leaf abscission and thus reducing water loss through transpiration. Higher plants cell elongation is suppressed under serious water deficit by interrupted water flow from the xylem to the neighboring elongating cells. Cell elongation, impaired mitosis and expansion lead under drought to lower height of plant, leaf area, and crop development. There is a conservative water loss resulting in stomatal closure and disruption in cell structure as well as

Maize (*Zea mays* L.) is one of the world's major staple food. It is used as cattle feed, meat supplement and also as biofuels. The crop is highly susceptible to elevated

> Cadmium (Cd) toxicity Copper (Cu) toxicity

Arsenic (As) metal stress

Heat

Heat

**Crops Stress** Chickpea (*Cicer arietinum* L.) Drought

Maize (*Zea mays* L.) Drought

Soybean (*Glycine max* L.) Drought Wheat (*Triticum aestivum* L.) Drought Rice (*Oryza sativa* L.) Drought

*List of some of the crops that are affected by various abiotic stresses.*

Black mustard (*Brassica juncea* L.) Cadmium (Cd) toxicity

with functional groups of significant cellular molecules [21].

the displacement or disturbance of protein structure construction blocks arising from the creation of blonds among HMs and sulfhydryl groups [20], interfering with functional groups of significant cellular molecules [21].
