**3.2 Wheat**

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 plant metabolism [22].

## **3.3 Maize**

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


#### **Table 1.**

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

temperatures, resulting in significant crop yield losses [23]. Multiple abiotic stresses like salinity and drought can also affect the crop in semi-arid tropical regions [24]. Temperature increases above a threshold level have negative effects plant growth and development, that is, heat stress for an appropriate time span. Due to elevated temperature stress, the disruption in cellular homeostasis has the ability to cause retardation in plant growth, development and even death. High-temperature stress affects the phases of maize development differently. Drought stress resulted in maize yield loss ranging from 17 to 60% in Southern Africa. Sequential cycles of drought stress were subjected to maize inbred lines and their hybrid testcross progeny were at the seedling level. These cycles were done at diverse developmental stages of growth, that is, germination, survival and regeneration. The study revealed that the best parameter for secondary screening of maize under drought stress is seedling stage [23].

### **3.4 Soybean**

A wealthy source of protein and edible oil is soybean (*Glycine max* (L.) Merr). Soybean is the major cultivated crop of the world (approximately 6% world's territory). Drought stress affects the plant's rate of germination and seedling vigor. Underwater scarcity, the length of hypocotyl, germination, and dry and new weight of root and stem are reduced while the length of the root is increased. Growth occurs through differentiation of cells and division of cells, which is negatively affected by water scarcity. Cell elongation decreases under drought conditions due to decrease in turgor pressure [25].

### **3.5 Rice**

Rice (*Oryza sativa* L.) is a significant global staple food crop that provides food security and generates revenue, especially in developing countries. The anticipated global warming poses a severe danger to both rice manufacturing and the quality of the rice generated. In tropical and subtropical regions, temperature stress and drought are projected to increase to a greater degree, being the primary rice producing areas [26].

High temperature stress or drought conditions have adverse effects on plant development, including unalterable damage to plant growth and development, decreased photosynthesis [27], decreased amount of panicles in each plant and elongation of peduncle, limited pollen output, no pollen grain swelling, and reduced spikelet sterility. Low temperatures lead in inhibited growth of seedlings, decreased development of panicles, delay in heading, bad exertion in panicle, low fertility of spikelet and bad quality of grain. Water and temperature stresses, other than influencing development and grain yield, alter the chemical composition and quality of rice [28].

### **4. Effect of abiotic stress on crops**

A complex set of biotic and abiotic pressures includes the natural environment of crops. Abiotic stresses are of greater importance because they include different environmental factors that cannot be prevented, that is, drought, salinity, cold, heat, metal, etc. The impacts of abiotic stress on crop manufacturing are hard to predict correctly. Plant reactions to abiotic stress are both dynamic and complicated and can be either elastic (reversible) or plastic (irreversible) [29].

**9**

*Effect of Abiotic Stress on Crops*

**4.1 Drought effect on crops**

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

Drought stress affects the plants at all phenological developmental stages varying from morphological to molecular concentrations. In plants that determine yield, many physiological mechanisms are prone to drought [7]. Drought can trigger yield reductions in many plant species depending on their severity and period but the stress of drought after anthesis is detrimental to the output of grain regardless of its severity [30]. Prevailing drought stress limits the production of flowers and grain filling resulting in reduced quality and amount of grains. Micro and macronutrients like nitrogen (N), phosphorous (P) and potassium (K) are crucial for plant growth. Drought stress results in increased N significantly decreased P, in spite of this it has no definitive effects on K [31]. Overall, water deficit reduces nutrient accessibility in the root zone, absorption at root hair, translocation in xylem and phloem vessels leading to impaired metabolism of nutrients in cells and tissues [7]. The effectiveness of nutrient intake and utilization is also reduced due to less transpiration. Drought stress has significant on photosynthetic pigments like chlorophyll a, b, and carotenoid components and also impairs photosystem 1 and photosystem 2 [32]. It also reduces starch synthesis in plants by effecting Calvin cycle enzyme activity (Ribulose phosphatase). Plants can combat to drought stress by different mechanisms [33]. When the soil is scarce in water crops, their stomata tend to close, reducing CO2 input into the leaves and spare more electrons for active oxygen species growth [34]. Environmental circumstances that improve the rate of transpiration also increase leaf sap pH, encourage abscisic acid deposition and at the same moment reduce stomatal behaviour [35]. Failure in Rubisco's activity restricts photosynthesis under very serious drought conditions [36]. Some studies revealed that under drought conditions the activity of the photosynthetic electron transport chain is finely adjusted to chloroplast CO2 accessibility and photosystem II modifications [37]. The result of dehydration is a decrease in cell size. This improves the cellular content's viciousness. Protein-protein interaction increases outcomes in their aggregation and denaturation. An increased concentration of solutes may become toxic and may be detrimental to enzyme functioning, including photosyn-

thetic equipment, leading in increased viscosity of cytoplasms [38].

The magnitude of agricultural estate affected by high salinity is increasing worldwide as a result of both natural and agricultural occurrences such as irrigation schemes. In plant growth, salinity presents two primary concerns: osmotic stress and ionic stress. It also manifests oxidizing stress. The detrimental effects of salinity alter different physiological and metabolic processes of plants. Often, the answers to these modifications are accompanied by various symptoms such as decreased leaf area, increased leaf density and succulence, leaf abscission, root and shoot necrosis, and decreased internode lengths. Salinity stress inhibits growth and increases cell senescence during extended exposure. Inhibition of growth is the major injury resulting in other symptoms, while programmed cell death may also happen under serious salinity shock [39]. Abscisic acid synthesis is induced under salt stress that closes stomata during transportation to guard cells. Due to stomatal closure and inhibition of photosynthesis and oxidative stress, photosynthesis reduces. Osmotic stress can directly or indirectly inhibit the development of cells through abscisic acid metabolism and translocation. Potassium is not received by plant root surface due to excessive sodium ions near the root zone. Due to the comparable biochemical behavior of sodium and potassium ions, sodium has a powerful repressive impact on root potassium

**4.2 Salinity effect on the crops**

## **4.1 Drought effect on crops**

Drought stress affects the plants at all phenological developmental stages varying from morphological to molecular concentrations. In plants that determine yield, many physiological mechanisms are prone to drought [7]. Drought can trigger yield reductions in many plant species depending on their severity and period but the stress of drought after anthesis is detrimental to the output of grain regardless of its severity [30]. Prevailing drought stress limits the production of flowers and grain filling resulting in reduced quality and amount of grains. Micro and macronutrients like nitrogen (N), phosphorous (P) and potassium (K) are crucial for plant growth. Drought stress results in increased N significantly decreased P, in spite of this it has no definitive effects on K [31]. Overall, water deficit reduces nutrient accessibility in the root zone, absorption at root hair, translocation in xylem and phloem vessels leading to impaired metabolism of nutrients in cells and tissues [7]. The effectiveness of nutrient intake and utilization is also reduced due to less transpiration. Drought stress has significant on photosynthetic pigments like chlorophyll a, b, and carotenoid components and also impairs photosystem 1 and photosystem 2 [32]. It also reduces starch synthesis in plants by effecting Calvin cycle enzyme activity (Ribulose phosphatase). Plants can combat to drought stress by different mechanisms [33]. When the soil is scarce in water crops, their stomata tend to close, reducing CO2 input into the leaves and spare more electrons for active oxygen species growth [34]. Environmental circumstances that improve the rate of transpiration also increase leaf sap pH, encourage abscisic acid deposition and at the same moment reduce stomatal behaviour [35]. Failure in Rubisco's activity restricts photosynthesis under very serious drought conditions [36]. Some studies revealed that under drought conditions the activity of the photosynthetic electron transport chain is finely adjusted to chloroplast CO2 accessibility and photosystem II modifications [37]. The result of dehydration is a decrease in cell size. This improves the cellular content's viciousness. Protein-protein interaction increases outcomes in their aggregation and denaturation. An increased concentration of solutes may become toxic and may be detrimental to enzyme functioning, including photosynthetic equipment, leading in increased viscosity of cytoplasms [38].
