*5.1.3 Role of PGPR as a sink for 1-aminocyclopropane-1-carboxylate (ACC)*

Increase in ACC levels can result in higher ethylene production under saline environment. It can also increase plant injuries [97, 98]. Cobalt ions and amino ethoxy vinyle glycine as chemical inhibitors of ethylene synthesis is often used to control salinity problems. These chemicals are expensive and have harmful effects on the environment. PGPR play a role of sink for ACC which can be hydrolyzed to generate a-ketobutyrate and ammonia to reduce the ethylene production.

## *5.1.4 PGPR-mediated ion homeostasis*

Plants inoculated with PGPR have showed high concentration of K<sup>+</sup> which led to high Na+ /K+ ratio and ultimately improved tolerance towards salt stress [99–101]. Salinity can damage the cell-membrane in plants which can enhance its permeability and electrolyte leakage. In maize, Lower the electrolyte leakage has been determined the inoculation with Rhizobium [102–104].

## *5.1.5 Accumulation of osmolytes*

The functioning of photosynthetic structures and maintaining water homeostasis are essential for reducing salinity impact on plants. Excessive production of various compatible organic solutes (such as glycine betaine and proline) has been

**123**

*Interactive Effect of Organic and Inorganic Amendments along with Plant Growth Promoting…*

observed as stress responses in plants [105]. Accumulation of proline is a physiological response of plants to saline conditions [106]. It also maintains high leaf water potential and protects the plants from negative effects of oxidative stress. Researchers have determined that PGPRs contribute to accumulation of osmolytes

Reactive oxygen species (ROS) damage the nucleic acids, proteins and lipids. Limited photosynthetic activity under salinity promotes the excessive production of ROS [107]. Antioxidants have been found to greatly reduce the oxidative damage. Under saline conditions, the activities of the enzymatic antioxidants such as guaicol peroxidase, catalase and superoxide dismutase increased [108]. Researchers determined that the application of PGPR caused a significant increase in polyphenol oxidase, superoxide dismutase and other enzymes involved in plant defense system. It also increases in enzymes such as peroxidase, phenyl alanine ammonialyase, catalase, phenolics and lipoxygenase [109–111]. These PGPR-stimulated enzymes are playing important role in removing hydrogen peroxide from stressed

*5.1.7 Ameliorating effects of bacterial extracellular polymeric substances (EPS)*

increasing the EPS-producing PGPR strains [114].

PGPR is the key role of PGPR in providing nutrients to plants.

*5.1.8 Enhancement of plant nutrient uptake*

*5.1.9 PGPR-mediated disease suppression*

plants grown under salt stress.

Researchers determined that inoculation with EPS-producing PGPR have significantly increased the volume of soil macropores, rhizospheric soil aggregation, improved fertilizer as well as water availability. This approach can help plants to survive in salt-stressed soils. Different studies have shown positive effects of EPSproducing PGPR on the rhizospheric soil aggregation [113]. As bacterial EPS can sequester the cations, there may be an opportunity to eliminate the salinity stress by

It is obvious that PGPR can regulate the availability of plant nutrients. So, employing PGPR can cut down the use of chemical fertilizers. Various PGPR strains are involved in solubilizing the inorganic phosphate and mineralization of organic phosphate, thus providing nutrients to plants [115]. However, the former activity of

Many rhizobacteria are known to produce antifungal metabolites like phenazines, HCN, pyrrolnitrin, tensin, pyoluteorin, 2,4-diacetylphloroglucinol, and viscosinamide [116]. However, various PGPR strains can control the pathogen of

An environment-friendly and cost-effective approach for lessening salinity in crop plants is the co-application of silicon and PGPR [117]. Different studies have shown that by improving photosynthetic efficiency, and scavenging enzyme

**6. Interactive techniques to ameliorate salinity stress in maize**

**6.1 Silicon and PGPR to mitigate salt stress in maize**

*DOI: http://dx.doi.org/10.5772/intechopen.99063*

to increase plant tolerance towards stress.

*5.1.6 Antioxidative enzymes*

roots [112].

#### *Interactive Effect of Organic and Inorganic Amendments along with Plant Growth Promoting… DOI: http://dx.doi.org/10.5772/intechopen.99063*

observed as stress responses in plants [105]. Accumulation of proline is a physiological response of plants to saline conditions [106]. It also maintains high leaf water potential and protects the plants from negative effects of oxidative stress. Researchers have determined that PGPRs contribute to accumulation of osmolytes to increase plant tolerance towards stress.

#### *5.1.6 Antioxidative enzymes*

*Landraces - Traditional Variety and Natural Breed*

**of salt stress in maize crop**

*5.1.1 Enhanced root proliferation and plant vigor*

*5.1.2 Phytohormones produced by bacteria*

observed to reduce salinity stress in plants.

*5.1.4 PGPR-mediated ion homeostasis*

*5.1.5 Accumulation of osmolytes*

stability has important for improvement of soil properties. The soil microbial communities such as free-living or symbiotic organisms play an immense role to improve soil structure. It is proved that the activities which microbes performed to soil aggregate stability are very advantageous [88]. It can efficient solution for saline soil and make it fit for agricultural practices. PGPRs can help in inducing plant tolerance to various abiotic stresses including salt stress. In saline environments, PGPR-crop interactions improved the plant growth. It can also promote plant survival in adverse conditions [89]. PGPR promote the growth and development of plants by providing nitrogen, phytohormones soluble phosphates, and iron [90]. The plant is being protected against various soil-borne diseases, and it is known that

most of these diseases are caused by pathogenic fungi [91].

**5.1 Various attributes of PGPsRs in mitigating negative effects** 

PGPRs can promote the growth of the plants by means of PGPRs which colonize

The physiological response in plants is increased by phytohormones produced by microbes in root zone. Production of indoleacetic acid and gibberellins promote the root length. It also increases number of tips, surface area of roots and uptake of nutrients thus promoting the plant vigor exposed to saline conditions [93–96]. Indole acetic acid production is a common characteristic of PGPR. This bacterium is

Increase in ACC levels can result in higher ethylene production under saline environment. It can also increase plant injuries [97, 98]. Cobalt ions and amino ethoxy vinyle glycine as chemical inhibitors of ethylene synthesis is often used to control salinity problems. These chemicals are expensive and have harmful effects on the environment. PGPR play a role of sink for ACC which can be hydrolyzed to

the rhizosphere [92]. The co-inoculation of seeds of different PGPR species is a beneficial strategy to remediate salt-stressed soil. This approach has improved the

plant tolerance towards abiotic stresses and the structure of root hairs.

*5.1.3 Role of PGPR as a sink for 1-aminocyclopropane-1-carboxylate (ACC)*

generate a-ketobutyrate and ammonia to reduce the ethylene production.

Plants inoculated with PGPR have showed high concentration of K<sup>+</sup>

determined the inoculation with Rhizobium [102–104].

Salinity can damage the cell-membrane in plants which can enhance its permeability and electrolyte leakage. In maize, Lower the electrolyte leakage has been

The functioning of photosynthetic structures and maintaining water homeostasis are essential for reducing salinity impact on plants. Excessive production of various compatible organic solutes (such as glycine betaine and proline) has been

ratio and ultimately improved tolerance towards salt stress [99–101].

which led to

**122**

high Na+

/K+

Reactive oxygen species (ROS) damage the nucleic acids, proteins and lipids. Limited photosynthetic activity under salinity promotes the excessive production of ROS [107]. Antioxidants have been found to greatly reduce the oxidative damage. Under saline conditions, the activities of the enzymatic antioxidants such as guaicol peroxidase, catalase and superoxide dismutase increased [108]. Researchers determined that the application of PGPR caused a significant increase in polyphenol oxidase, superoxide dismutase and other enzymes involved in plant defense system. It also increases in enzymes such as peroxidase, phenyl alanine ammonialyase, catalase, phenolics and lipoxygenase [109–111]. These PGPR-stimulated enzymes are playing important role in removing hydrogen peroxide from stressed roots [112].

#### *5.1.7 Ameliorating effects of bacterial extracellular polymeric substances (EPS)*

Researchers determined that inoculation with EPS-producing PGPR have significantly increased the volume of soil macropores, rhizospheric soil aggregation, improved fertilizer as well as water availability. This approach can help plants to survive in salt-stressed soils. Different studies have shown positive effects of EPSproducing PGPR on the rhizospheric soil aggregation [113]. As bacterial EPS can sequester the cations, there may be an opportunity to eliminate the salinity stress by increasing the EPS-producing PGPR strains [114].

#### *5.1.8 Enhancement of plant nutrient uptake*

It is obvious that PGPR can regulate the availability of plant nutrients. So, employing PGPR can cut down the use of chemical fertilizers. Various PGPR strains are involved in solubilizing the inorganic phosphate and mineralization of organic phosphate, thus providing nutrients to plants [115]. However, the former activity of PGPR is the key role of PGPR in providing nutrients to plants.

#### *5.1.9 PGPR-mediated disease suppression*

Many rhizobacteria are known to produce antifungal metabolites like phenazines, HCN, pyrrolnitrin, tensin, pyoluteorin, 2,4-diacetylphloroglucinol, and viscosinamide [116]. However, various PGPR strains can control the pathogen of plants grown under salt stress.

#### **6. Interactive techniques to ameliorate salinity stress in maize**

#### **6.1 Silicon and PGPR to mitigate salt stress in maize**

An environment-friendly and cost-effective approach for lessening salinity in crop plants is the co-application of silicon and PGPR [117]. Different studies have shown that by improving photosynthetic efficiency, and scavenging enzyme activity soil salinity tolerance can be enhanced. It also determined that this approach can improve the plant tolerance towards salinity, ROS and Na<sup>+</sup> /K+ ratio [118]. PGPR promote the growth of plants via synthesis of phytohormones, exopolysaccharides, volatile organic compounds and different other mechanisms [118]. Recently, it has been found that both Si and PGPR can enhance plants tolerance to saline environment to improve growth and yield of plants [118].
