3. Effects of salinity on field crops

Fulfill the food demand and livelihood of the increasing population by 2050, a remarkable increase about 50% more yield in the form of grain, fiber, sugar, etc. is required from major field crops such as wheat, rice, and maize sorghum, cotton, and sugarcane [28]. However, the purpose of competing for the demands of human beings on the globe while combating abiotic stresses, including salinity. The different crop has different responses against abiotic stresses such as salinity. Salinity suppresses the crop plants growth, development, and productivity. The sensitivity of the crops varies from low to high concentration of soluble salts or EC (Table 3). At low salt concentrations, yields are slightly affected or not affected at all in some crops [29]. Whereas the most plants, glycophytes, including the most crop plants, decrease yield towards zero or even plant death as soluble salt concentrations increase by 100–200 mM NaCl due to low resistance and tolerance capacity of plants [30] (Table 3).

#### 3.1 Salinity and rice (Oryza sativa L.)

Rice is monocot and belongs to a C3 plant with salinity responsive behavior as compared to other field crops [37]. Rice is vital to the lives of billions of people around the globe. Rice is grown in many parts of the world, especially in Asia, Latin America, and Africa, and taken as a chief food item for more than 50% population of the world [38]. Rice is among the first five major carbohydrate crops for the population of the world, particularly for Asian countries. Only Asia contributes 90% of total rice cultivation in the world. From this 90%, China contributes 30%, India

Salinity Stress in Arid and Semi-Arid Climates: Effects and Management in Field Crops DOI: http://dx.doi.org/10.5772/intechopen.87982


Where EC = electrical conductivity, FW = fresh weight, DW = dry weight, S = sensitive, MS = moderately sensitive, MT = moderately tolerant, and T = tolerant.

#### Table 3.

2.1.2 Salinity and nutrient imbalance in plant

antagonistic effect on potassium (K<sup>+</sup>

2.1.3 Salinity and oxidative stress in plant

2.1.4 Salinity and hormonal response in the plant

3. Effects of salinity on field crops

3.1 Salinity and rice (Oryza sativa L.)

plants [30] (Table 3).

202

development of rice and wheat spikelets, boll of cotton, etc.

has an antagonistic effect on P, K<sup>+</sup>

Climate Change and Agriculture

lation in plant tissues and soil [19]. High sodium ion (Na<sup>+</sup>

effect on N and Mg in field crops such as rice [23, 25].

Salinity has direct effects on nutrients imbalance between soil and plant. The most important harmful effect of salinity is the sodium and chloride ions accumu-

the plant has also been observed under high salt conditions [24]. Similarly, salinity

The production of reactive oxygen species (ROS), like oxygen radical (O2), superoxide (OH), and H2O2 under salinity is high [30]. These oxidative species can interrupt the routine functions of various cellular plant modules. For example,

The phytohormones are naturally produced in a chemical form called plant growth regulators. The phytohormones are active signal compounds which show response against salinity stress and reduce the plant growth [27]. Under salinity stress, the ethylene, cytokinin, and gibberellic acid concentration decreased, and abscisic acid contents increased. This alteration of hormones effects plant growth, such as germination, tiller formation, and reproductive growth. For example, poor

Fulfill the food demand and livelihood of the increasing population by 2050, a remarkable increase about 50% more yield in the form of grain, fiber, sugar, etc. is required from major field crops such as wheat, rice, and maize sorghum, cotton, and sugarcane [28]. However, the purpose of competing for the demands of human beings on the globe while combating abiotic stresses, including salinity. The different crop has different responses against abiotic stresses such as salinity. Salinity suppresses the crop plants growth, development, and productivity. The sensitivity of the crops varies from low to high concentration of soluble salts or EC (Table 3). At low salt concentrations, yields are slightly affected or not affected at all in some crops [29]. Whereas the most plants, glycophytes, including the most crop plants, decrease yield towards zero or even plant death as soluble salt concentrations increase by 100–200 mM NaCl due to low resistance and tolerance capacity of

Rice is monocot and belongs to a C3 plant with salinity responsive behavior as compared to other field crops [37]. Rice is vital to the lives of billions of people around the globe. Rice is grown in many parts of the world, especially in Asia, Latin America, and Africa, and taken as a chief food item for more than 50% population of the world [38]. Rice is among the first five major carbohydrate crops for the population of the world, particularly for Asian countries. Only Asia contributes 90% of total rice cultivation in the world. From this 90%, China contributes 30%, India

DNA, proteins, and lipids, are interfering metabolism of the plant [26].

) concentration has an

) ions [23]. Moreover, N uptake reduction by

, Zn, Fe, Ca2+, and Mn while it has a synergistic

Salt tolerance classification of major field crop.

(21%), and Pakistan (18%) respectively, while remaining 30% is contribution belongs to Japan, Thailand, Indonesia, and Burma [39]. Rice is a high yielding crop. However, the current average yield is 8–10 t/ha for indica rice, 10–15% yield is lower than its potential [40]. This rice production gap is due to many reasons, such as environmental stresses (biotic or abiotic), management strategies, and nutrients deficiencies.

Among the abiotic stresses, especially salinity is among the essential causes of this low yield. The morphological characteristics of rice are severely affected by salinity [41]. Rice plant responds differently against salinity compared to other field crops. The intent of salinity in rice plant life cycle varies from growth stages, and cultivar to cultivar, that is, the early seedling growth stage is more sensitive than the tillering stage in rice plant [14]. The threshold level of salt stress for rice is 3 dS m<sup>1</sup> [42]. However, a significant reduction in seedling growth and fresh weight were observed with increased salt stress from 1.9 to 6.1 dSm<sup>1</sup> and 5 to 7.5 dSm1, respectively [43]. Many studies also exposed that salinity stress decrease rice stand density and production of seedling biomass, which shows the high sensitivity against salinity [4, 44].

The first organ of the rice plant that keeps in contact with soluble salt is a root [45]. The root is responsible for the entrance of hydrogen peroxide (H2O2) and solutes by through different pathways such as symplastic, apoplastic, and transcellular, respectively. So, transport of water and solutes through the apoplastic pathway is vital in rice [46]. Mostly Na<sup>+</sup> transport in rice shoots via the apoplastic passage where Na+ transports by apoplast through Casparian tubes [47]. As a result of this Na<sup>+</sup> accumulation, a significant reduction in numbers of root per plant, root length, and shoot length occurred under increased salinity [48]. Based on these proofs, the reduced root and shoot lengths are considered two indicators of rice plant response to salinity.

Moreover, cell division and cell elongation in rice plant are severely affected by salinity, which results in a reduction of the root, leaf growth, and yield [16]. Rice plant shows response very soon after the exposure of salinity stress and affects plant growth. For example, rice leaf mortality boosted with increased salinity in almost all rice cultivars at early seedling stage [14]. Some rice cultivars showed leaf mortality up to 0–300% after 1 week of salinity exposure [16]. Salinity effect cause panicle sterility and poor development of inferior and superior spikelets, which result in the reduction of rice grain yield [4]. Many rice cultivars showed panicle sterility at pollination and fertilization stages due to some genetic mechanisms and nutrient

deficiencies resulting from salinity stress [49], which leads to a decrease in grain setting rate, pollen viability, and decline of the stigmatic surface.

and yield components of the plant, but depend on nature of cultivar. For example, at 125–200 mM NaCl and 12.5–16 dS m<sup>1</sup> salinity levels, germination time increased and decreased the GR and germination index [59–61]. During the germination process under salinity, seed faces the osmotic stress, which imbalance the enzymatic activities necessary for nucleic acid and protein metabolism, hormonal imbalance, and ultimate the disturb the seed reserves [62]. Along with these germination characteristics, salinity also affects the other agronomic parameters such as root length, shoot length, root and shoot dry weight, plant height, leaf area, tillering dynamics, and spikes numbers per plant at the early seedling stage. At the early growth stage of the wheat plant, plant shows high sensitivity at 120, 125,

Salinity Stress in Arid and Semi-Arid Climates: Effects and Management in Field Crops

wheat seedlings also reduce its growth; even exposure to salinity stress is for a few days (7–10 days) at 100 mM NaCl salt level. Similarly, yield components such as the number of spikes per plant, spikes length, and the number of spikelets per spike, above ground biomass, 1000-grain yield, harvest index, and grain yield per plant decreased with increased salinity stress [64]. However, when the wheat plant cross

7.1% with increasing salinity of per dS m<sup>1</sup> and significant yield reduction occurs at

Photosynthesis activities such as net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration, and water use efficiency (WUE) affected by salinity. The Pn badly influenced by the high accumulation of Na<sup>+</sup> and Cl in the chloroplast tissues [66]. These parameters (Pn, Tr, Gs, intercellular CO2 concentration) are reduced under 150 mM NaCl salinity level. Similarly, a decrease in photosynthesis pigments was observed at 320 mM NaCl concertation, and after 10 days exposure of NaCl, the chlorophyll contents (chl a, b, and carotenoids) decreased [67]. WUE and RWC also affect by osmotic stress caused by salinity. Water potential lower down with increased salinity levels and as a result relative RWC in the wheat plant decreased by 3.5% in the salt tolerant cultivar and 6.7% in salt-sensitive cultivar after 6 days exposure of NaCl (100 mM NaCl) [68]. Along with this leaf water potential and WUE also decrease in 150 mM NaCl and 16 dS m<sup>1</sup> salinity levels. For example, water content percentage in root reduced and increased in shoots and spike of wheat cultivar Banysoif 1. Similarly, at 320 mM NaCl, the RWChas decreased in leaves of wheat cultivar T. monococcum

3.2.3 Reactive oxygen species production and scavenging of antioxidants

closure. ROS such as H2O2, superoxide (O2•–), hydroxyl radical (OH•

Reactive oxygen species (ROS) increase under salinity in the plant. However, when plant faces high salinity, the production of ROS reduces the scavenging system and stops the oxidative stress. This change occurs in plants due to the reduction of CO2 availability in leaves and inhibits fixation of carbon, and excitation energy enhance which expose the chloroplast, all these happened due to stomatal

O2) are produced under increasing salinity stress in the plant [62, 65]. Osmotic stress caused by salinity is the leading cause of ROS production and results in the cellular damage by oxidation of lipids, proteins, and nucleic acid. The oxidative stress is caused by an imbalance in ROS production and scavenging of antioxidants in plant tissue. As a result of ROS production, phytotoxic reactions in plants occur such as lipid peroxidation, protein degradation, as well as DNA mutation [70]. For example, exposure of salinity levels 5.4 and 10.6 dS m<sup>1</sup> for about 2

, even seedlings death occurs [11, 63]. Furthermore,

), wheat grain yield reduces at the rate of

), and singlet

150 mM NaCl, and 16 dS m<sup>1</sup>

15 dS m<sup>1</sup> [65].

seedlings [69].

oxygen (<sup>1</sup>

205

the threshold level of salinity (6 dS m<sup>1</sup>

DOI: http://dx.doi.org/10.5772/intechopen.87982

3.2.2 Salinity and wheat physiological traits
