**3. The most effective environmental stress factors: salinity and drought**

#### **3.1. Salinity stress**

of mycorrhizae is the arbuscular mycorrhiza occurring in about 90% of plant species infected with mycorrhiza. The most common type of mycorrhizae is the arbuscular mycorrhiza occurring in about 90% of plant species infected with mycorrhiza, approximately 83% of dicotyledons, 79% of monocot, and 100% of gymosperms. Most crop plants form mycorrhizae with the exception of the Brassicaceae (e.g., mustard, cabbage, and canola) and Chenopodiaceae (e.g.,

AM fungi consists approximately 160 species belonging to three families. Glomaceae, Gigasporaceae, and Acaulosporaceae. More than 6000 fungal species can form mycorrhizae with about 240,000 plant species. AMF plants own bigger extraradical hyphae formation and soil aggregation. They enhance tilth and excrete hydrophobic protein called "glomalin." AMF produce more stress-resistant plants during production and for landscape, they reduce the pesticide usage, they increase the more drought and nutrient tolerant plants in landscape, and they potentially higher transplanting success and faster establishment. A symbiotic association formed by fungi with roots, exchanging for functioning as an extended root system, the

Arbuscular mycorrhizae fungi (AMF), which are useful organisms, have a significant role in performance and nutrition with plant mineral intake capacity [36]. AMF symbiosis is especially significant in improving the immobile uptake and indissoluble phosphate ions in soil with the interactions with bi/trivalent cations (especially Ca2+, Fe3+, and Al3+ [37, 38]. The main function in this mutualism is the capacity of AMF in developing external hyphae networks that may extend the surface area (up to 40 times) and the explorable soil volume for nutrient intake [39] by producing enzymes and/or excreting organic substances [40]. AMF can excrete phosphatases to hydrolyze phosphate from organic P-compounds [41–43], which enhance productivity under harsh conditions (deficiency of phosphorus; [44]). The extraradical hyphae are considered significant in terms of intake of ammonium, immobile

and Fe 3+) [45, 46]. It was demonstrated that AMF enhance plant nutrition (biofertilizers), and interferes with the phytohormone balance of the plants, which in turn affects development of plant (bioregulators) and alleviates the influence of the environmental stresses (bioprotectors). This increases the biomass and yield, and causes shifts in some quality

The horticultural products have high phytochemical elements (carotenoids, flavonoids, and polyphenols) and therefore meet the desires of consumers and authors with their health/benefit influences [48]. Furthermore, AMF also bring tolerance to drought [49, 50] and salinity [51, 52], nutrient deficiency, heavy metal contamination [53] and in adverse

The AMF life cycle begins with asymbiotic stage (germination of the asexual chlamydospores). This depends on several physical factors (temperature and humidity). AMF retract the cytoplasm without the presence of a plant and turn to the dormant phase because they are obligate biotrophs. However, near the roots of the plants, the presymbiotic phase begins with the ramification of the primary germ tube [56]. Root exudates [57] and specific metabolites (strigolactones) may also induce this [58]. When there is a physical contact with the surface of the root, the

, Ca2+, Mg2+,

micronutrients (Cu and Zn), and some mineral cations coming from the soil (K<sup>+</sup>

sugar beets and spinach).

parameters [47].

soil pH [54, 55].

fungi receives carbonhydrates from the host plant [35].

70 Physical Methods for Stimulation of Plant and Mushroom Development

Under saline conditions, the changes in soil-water potential cause that plant water intake is reduced as well as the nutritional and hormonal imbalance. In these conditions, proline, glycine betaine, trehalose, polyols, and similar organic solutes accumulate in the body of the plant to preserve the plant from the stress-induced effects with osmotic adjustment, with limiting water loss and diluting the toxic ion concentration [66, 68]. Such an accumulation makes it possible for the plant to maintain osmotic potential for improved water intake. For instance, proline accumulation preserves the plant by adjusting osmotic pressure and by stabilizing many functional units (e.g., complex II of the electron transport system, proteins, and enzymes [69, 70]. There are two mechanisms in which high-concentration soluble salts influence microbes: osmotic effect and specific ion effect. Osmotic potential (more negative) is increased by soluble salts and draws water out of the cells, which in turn, may kill microbes and roots via plasmolysis. Because of the low osmotic potential, it becomes more difficult for roots and microbes to eliminate water from the soil [71]. Plants, as well as microbes, can adapt to low osmotic potential through accumulating osmolytes. However, osmolyte synthesis necessitates large amounts of energy, which in turn, results in reduced growth and activity [72, 73]. Certain ions, including Na+ , Cl− , and HCO−3, are toxic for some plants when they are at high-concentrations [74]. In some previous studies, it was reported that salinity decreases microbial activity and microbial biomass and changes the structure of the microbial community [75–79]. The microbial biomass is decreased by salinity. The reason for this is that osmotic stress causes drying and cell lysis [80–86]. In previous studies, it was also reported that soil respiration was reduced with the increase in the soil EC [87–89]. Gerhardson [90] reported that soil respiration was decreased by more than 50% at EC1:5Z5.0 dS m1. However, according to Glick [91], soil respiration was not correlated at a statistically significant level with EC. However, they also reported that as EC increased, the metabolic quotient (respiration per unit biomass) also increased.

Microorganisms can adapt to/tolerate stress salinity stress by accumulating osmolytes [91–95]. Among the main organic osmolytes, there are proline and glycine betaine; and among the common inorganic solutes, there are potassium cations, which are used as osmolytes accumulated by saline-tolerant microbes [96]. However, high amount of energy is necessary for the synthesis of organic osmolytes [97, 98]. Inorganic salts accumulation (as osmolytes) may be toxic, and for this reason, it is limited to halophytic microbes which developed saline-tolerant enzymes to survive in highly saline medium. Fungi have a tendency for being more sensitive to salt stress than bacteria [99–102]. In this respect, the rate of bacteria/fungi may be increased in saline soils. When compared to nonsaline soils, salinity-tolerance differences among microbes cause those changes that appear in the structure of the community [103, 104].

#### *3.1.1. PGPR help plants tolerate salinity stress*

Salt stress enhances endogenous ethylene production in plants and mostly serves as a stress hormone. Probably decreasing the ethylene induced by salinity via any mechanism might reduce the negative effect of salt on the growth of plants. According to recent studies, plants inoculated with PGPR with ACC deaminase could cope with salinity stress with a normal growth pattern. According to Mayak et al. [105], *Achromobacter piechaudii*, which had ACC deaminase activity, increased fresh-dry weight of tomato seedlings at a great deal when grown in with NaCl salt (up to 172 mM). These bacteria decreased the ethylene production in tomato seedlings, and this situation would be stimulated if the seedlings were subjected to increased saline conditions. On the other hand, the sodium level in the plant could not be reduced, and phosphorus and potassium intake was increased. This situation may have enhanced the activation of the events that helped the relief of the side effects of the salt on the growth of the plants. In addition, these bacteria increased the water-use efficiency (WUE) under saline conditions. They also aided in relieving salt suppression of photosynthesis. According to Saravanakumar and Samiyappan [106], *Pseudomonas fluorescens* strain TDK1 that had ACC deaminase activity increased saline resistance of the groundnut plants. The strain also increased the yield when compared with *Pseudomonas* strain inoculation that lacked ACC deaminase activity. Glick et al. [107] verified that ACC deaminase bacteria provided plants with salt tolerance because they lower the salt-induced stress ethylene synthesis and enhance canola growth under saline conditions. We also saw similar results in maize under saline stress as a reaction to the inoculation with ACC deaminase PGPR. The results of research on the physiological effects of some vegetable species related to the benefits of PGPR in salt stress conditions are presented in **Table 1**.

regarding the saline sensitivity of the cultivar [117]. AM enhancement of saline resistance was generally related with AM-related increase in P acquisition and plant growth in cucumber [118]. *Gigaspora margarita* colonization enhanced stomatal conductance in sorghum in drought stress in saline soils and also improved the survival dual-stress rates. Evelin et al. [19] investigated whether tomato ("Zhongzha" 105) with *F. mosseae* could increase its salt tolerance. They reported that mycorrhization facilitated salt-related reduction of growth and fruit yield, and also determined that the P and K concentrations were higher and Na concentration was lower in AMF in non-AMF tomato in 0, 50, and 100 mM NaCl. They also claimed that an improvement of the ROS-scavenging enzymes (such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX)) in leaves of salt-affected and con-

**Table 1.** Summary of reported physiologic effects of plant growth promoting rhizobacteria (PGPR) under salinity stress

**Vegetable species**

**Stress factor**

Use of Some Bacteria and Mycorrhizae as Biofertilizers in Vegetable Growing and Beneficial…

**Result**

increased phenolic content, antioxidant activity, total sugar and

http://dx.doi.org/10.5772/intechopen.76186

73

the cuttings were treated with BA7, A16 and M3 compared to the other treatments. Mint cuttings inoculated with M3 had more dry matter content than control and the other treatments.

demonstrated positive results in practice. Both increased yield, nutrient element uptake and stem

soluble solid content.

Cucumber Salinity FE-43 increased yield 11%.

Carrot Salinity *Azotobacter* spp. significantly

Mint Salinity Root length was observed better in

Pepper Salinity 637 C and N 17/3 in bacteria have

diameter.

Compared to non-mycorrhizae plants, the bigger antioxidant enzyme activity in plants inoculated with AMF was related with the lower lipid peroxidation accumulation, which indicates lower oxidative harm in the mycorrhized plants. In a similar manner, Habibzadeh et al. [119] reported that enhancement in tolerance to saline stress ("Behta" and "Piazar") of the tomato inoculated with *R. intraradices* was associated with a higher P, K, and Ca intake and with lower Na toxicity. The net photosynthesis enhanced mycorrhization through increasing stomatal conductance and protecting PSII [120]. It was claimed that the increased sink strength of AMF roots was the reason for the mycorrhizae promotion of stomatal conductance [121]. Furthermore, in [122], it was reported that the P, Cu, Fe and Zn accumulation was high in inoculated (*F. mosseae*) than in non-inoculated tomato plants in control and medium salinity groups. However, the Na concentration in the shoot was low in mycorrhized plants, which confirms that the tolerance of the plant to salt stress is enhanced by AMF colonization. Authors [123–125] reported that mycorrhizae pepper ("11B 14" and "California Wonder

trol treatment accompanied AMF colonization.

**References Used plant growth promoting rhizobacteria (PGPR)**

[108] N-52/1, N-17/3, FE-43, F-21/3, 637 Ca, MfdCa1

*chroococum*, *Azotobacter vinelandii*,

*Burkholderia gladii (strain BA7), Pseudomonas putida (strain BA8), Bacillus subtilus (strain OSU142) Bacillus megatorium (strain M3)*

[109] *Azotobacter* spp., *Azotobacter* 

*Bacillus polymyxa*

[110] *Agrobacterium rubi (strain A16),* 

[111] N 52/1, N 17/3, Fe 43, F 21/3, 637

Ca

conditions on different vegetables.

#### *3.1.2. Inducing salinity stress tolerance through inoculation of mycorrhizae*

The symbiosis of AM has increased the resilience of the host plants to saline stress, maybe with bigger consistency than to drought stress. Compared to uninoculated controls, growth in saline soils was increased by the inoculation with *Glomus* spp., and with AM plants that had increased phosphate and decreased Na+ concentrations in shoots [112, 113]. AM colonization in maize enhanced the salt resistance [114], and in mung bean [115] and in clover [116]. The AM influence had a correlation with enhanced osmoregulation/accumulation of proline. The inoculation of AM also enhanced NaCl resistance in tomato with extent of enhancement


Microorganisms can adapt to/tolerate stress salinity stress by accumulating osmolytes [91–95]. Among the main organic osmolytes, there are proline and glycine betaine; and among the common inorganic solutes, there are potassium cations, which are used as osmolytes accumulated by saline-tolerant microbes [96]. However, high amount of energy is necessary for the synthesis of organic osmolytes [97, 98]. Inorganic salts accumulation (as osmolytes) may be toxic, and for this reason, it is limited to halophytic microbes which developed saline-tolerant enzymes to survive in highly saline medium. Fungi have a tendency for being more sensitive to salt stress than bacteria [99–102]. In this respect, the rate of bacteria/fungi may be increased in saline soils. When compared to nonsaline soils, salinity-tolerance differences among microbes cause those changes that appear in the structure of the community [103, 104].

Salt stress enhances endogenous ethylene production in plants and mostly serves as a stress hormone. Probably decreasing the ethylene induced by salinity via any mechanism might reduce the negative effect of salt on the growth of plants. According to recent studies, plants inoculated with PGPR with ACC deaminase could cope with salinity stress with a normal growth pattern. According to Mayak et al. [105], *Achromobacter piechaudii*, which had ACC deaminase activity, increased fresh-dry weight of tomato seedlings at a great deal when grown in with NaCl salt (up to 172 mM). These bacteria decreased the ethylene production in tomato seedlings, and this situation would be stimulated if the seedlings were subjected to increased saline conditions. On the other hand, the sodium level in the plant could not be reduced, and phosphorus and potassium intake was increased. This situation may have enhanced the activation of the events that helped the relief of the side effects of the salt on the growth of the plants. In addition, these bacteria increased the water-use efficiency (WUE) under saline conditions. They also aided in relieving salt suppression of photosynthesis. According to Saravanakumar and Samiyappan [106], *Pseudomonas fluorescens* strain TDK1 that had ACC deaminase activity increased saline resistance of the groundnut plants. The strain also increased the yield when compared with *Pseudomonas* strain inoculation that lacked ACC deaminase activity. Glick et al. [107] verified that ACC deaminase bacteria provided plants with salt tolerance because they lower the salt-induced stress ethylene synthesis and enhance canola growth under saline conditions. We also saw similar results in maize under saline stress as a reaction to the inoculation with ACC deaminase PGPR. The results of research on the physiological effects of some vegetable species related to the benefits of PGPR in salt stress

*3.1.1. PGPR help plants tolerate salinity stress*

72 Physical Methods for Stimulation of Plant and Mushroom Development

conditions are presented in **Table 1**.

had increased phosphate and decreased Na+

*3.1.2. Inducing salinity stress tolerance through inoculation of mycorrhizae*

The symbiosis of AM has increased the resilience of the host plants to saline stress, maybe with bigger consistency than to drought stress. Compared to uninoculated controls, growth in saline soils was increased by the inoculation with *Glomus* spp., and with AM plants that

tion in maize enhanced the salt resistance [114], and in mung bean [115] and in clover [116]. The AM influence had a correlation with enhanced osmoregulation/accumulation of proline. The inoculation of AM also enhanced NaCl resistance in tomato with extent of enhancement

concentrations in shoots [112, 113]. AM coloniza-

**Table 1.** Summary of reported physiologic effects of plant growth promoting rhizobacteria (PGPR) under salinity stress conditions on different vegetables.

regarding the saline sensitivity of the cultivar [117]. AM enhancement of saline resistance was generally related with AM-related increase in P acquisition and plant growth in cucumber [118]. *Gigaspora margarita* colonization enhanced stomatal conductance in sorghum in drought stress in saline soils and also improved the survival dual-stress rates. Evelin et al. [19] investigated whether tomato ("Zhongzha" 105) with *F. mosseae* could increase its salt tolerance. They reported that mycorrhization facilitated salt-related reduction of growth and fruit yield, and also determined that the P and K concentrations were higher and Na concentration was lower in AMF in non-AMF tomato in 0, 50, and 100 mM NaCl. They also claimed that an improvement of the ROS-scavenging enzymes (such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX)) in leaves of salt-affected and control treatment accompanied AMF colonization.

Compared to non-mycorrhizae plants, the bigger antioxidant enzyme activity in plants inoculated with AMF was related with the lower lipid peroxidation accumulation, which indicates lower oxidative harm in the mycorrhized plants. In a similar manner, Habibzadeh et al. [119] reported that enhancement in tolerance to saline stress ("Behta" and "Piazar") of the tomato inoculated with *R. intraradices* was associated with a higher P, K, and Ca intake and with lower Na toxicity. The net photosynthesis enhanced mycorrhization through increasing stomatal conductance and protecting PSII [120]. It was claimed that the increased sink strength of AMF roots was the reason for the mycorrhizae promotion of stomatal conductance [121]. Furthermore, in [122], it was reported that the P, Cu, Fe and Zn accumulation was high in inoculated (*F. mosseae*) than in non-inoculated tomato plants in control and medium salinity groups. However, the Na concentration in the shoot was low in mycorrhized plants, which confirms that the tolerance of the plant to salt stress is enhanced by AMF colonization. Authors [123–125] reported that mycorrhizae pepper ("11B 14" and "California Wonder 300"), inoculated with *Rhizophagus clarum* and *R. intraradices*, had bigger biomass in shoots at different saline concentrations when compared to non-inoculated plants. In non-mycorrhizae plants, the lowest crop performance was reported to be associated with higher Na and lower N, P, K concentrations in leaf tissue and also with high leaf electrolyte leakage, but the effect of the saline stress on pepper shoot biomass varies among different fungi species at a significant level [126]. Cheng et al. [127] reported that inoculation with AMF (*R. intraradices*) might help to beat saline stress in zucchini-squash (*Cucurbita pepo* L. "Tempra"), which is a significant greenhouse vegetable. Enhanced nutrition (higher K and lower Na concentrations in leaf tissue) and the leaf water status might have helped plants to translocate minerals and assimilate to the sink, and alleviate the effects of saline stress on fruit production [128]. It was reported that onion (*Allium cepa* L.) and basil (*Ocimum basilicum* L.) inoculated with AMF could relieve deleterious influences of soil/water saline stress on the yield and growth of crop [129, 130]. About the leafy vegetables, in [131], it was reported that the DAOM 197198 isolate of *R. intraradices* might be accepted as a potential AMF candidate since it stimulated the growth of lettuce under two different saline concentrations. This influence was considered to be linked with higher leaf relative water content and lower ABA in roots, which show that AMF plants are less strained than nonmycorrhizal plants by saline conditions, which enables them to accumulate less ABA. Furthermore, in saline conditions, AM symbiosis improved the LsPIP1 expression, which involved in the transcellular water-flow regulation. A gene expression of this magnitude might contribute to regulate the root-water permeability to tolerate the osmotic stress caused by saline conditions better [132]. Hildebrandt et al. [133] reported in their study that AMF *R. irregularis* alleviated the deleterious influences of saline stress in lettuce ("Romana") by changing the hormonal profiles (higher strigolactone production) and affecting plant physiology in a positive manner, which allows lettuce to grow better under harsh conditions. Gadkar and Rillig [134] reported that AMF (*G. iranicum* var. tenuihypharum sp. nova) could alleviate the negative influence of irrigation with high saline water on physiological parameters (photosynthesis and stomatal conductance) in lettuce. The results of research on the physiological effects of some vegetable species related to the benefits of mycorrhizae in salt stress conditions are presented in **Table 2**.

#### **3.2. Drought**

Climate change is defined as the changes observed over many years in the average state of the climate regardless of its cause. Today's climate change depends on the greenhouse effect of gases released to the atmosphere due to fossil fuels, improper land use, deforestation, and industrial development, but it is not caused by natural factors, as it has been since the formation of the world. The primary effect of this change, in which the direct human factor plays a role, is the increase in mean surface temperatures, in other words global warming. Modeling efforts to understand global climate change predicts that the average global warming will increase by 1–3.5°C by 2100 and that there will be regional extreme temperatures, floods, and widespread and severe droughts all over the world. Drought is related to the amount of water that can be taken by the roots during the growth period of the plant which is added to the field rather than the total amount of rainfall that occurs throughout the year. Plants that are experiencing water deficiency during the growing period face with significant losses in terms of development and especially yield [143, 144]. Measures should be taken as soon as possible to mitigate the effects of agricultural drought, since the available water resources are limited and the occupancy rate of these reserves is predicted to decrease rapidly due to the global warming-related rainfall and especially the decrease in the amount of snowfall that feeds groundwater resources. Although plant varieties belong to the same species, they may differ

**Table 2.** Summary of reported physiologic effects of mycorrhizae under salinity stress conditions on different vegetables.

Plants can adapt their growth and development mechanisms in such a way that they are least likely to be affected from environmental changes, and even adapt to environmental conditions when they grow in the same climatic conditions for long periods of time. Drought is one of the abiotic stress conditions which mostly affects the growth and development of plants [145]. Water constitutes 50% of the fresh weight of the trees and 89–90% of the other plants [146]. Plant growth is affected considerably in arid conditions. This effect in growth depends on the length of time the water stress is experienced. In the early stages of arid conditions, the plant slows elongation and triggers root development to reach more water. On the other hand, if arid conditions last long enough to cause damage to the plant, both stem and root growth will stop, leaf area and number of leaves will decrease, and even some leaves turn yellow. The decline in plant growth is due to the division of cells in the shoot and root meristems and the arrest of expansion of the cells. The disruption of cell division or enlargement is directly related to the decrease in the rate of photosynthesis due to water insufficiency [147]. When

in their tolerance to drought.

**Reference type**

[137] *Glomus* 

[139] *Glomus* 

*fasciculatum*

*fasciculatum*

**Used mycorrhizae** 

**Vegetable species**

**Stress factor**

[135] *Glomus clarum* Pepper Salinity Activity of catalase (CAT), glutathione reductase

[136] *Glomus deserticola* Spinach Salinity *Glomus deserticola* increases K/Na ratio up to 54%.

[138] *Glomus occultum* Pepper Increase in hormone levels of pepper plants with

[140] *Glomus mosseae* Pepper *G. mosseae* significantly increased yield and nutrient

[141] *Glomus mosseae* Radish Caused important changes in the plant enzyme levels. [142] *Glomus mosseae* Mint More ACC deaminase has been detected in plants

**Result**

Use of Some Bacteria and Mycorrhizae as Biofertilizers in Vegetable Growing and Beneficial…

conductivity.

*G. occultum*

Tomato MDX levels have increased in plants treated with *G. fasciculatum*.

Cucumber *G. fasciculatum* caused important changes in the plant enzyme levels.

treated with *G. mosseae*.

element uptake according to control.

(POD), and ascorbate peroxidase (APX) in leaves of plants treated with mycorrhizae increased. Leaf water potential and osmotic potential has increased. Pepper plants inoculated with mycorrhizal fungi showed the highest chlorophyll content and leaf area in saline conditions. The interaction between mycorrhizal fungi and plants occur higher photosynthesis activities and transpiration rates pursuing with stomatal

http://dx.doi.org/10.5772/intechopen.76186

75

**species**


300"), inoculated with *Rhizophagus clarum* and *R. intraradices*, had bigger biomass in shoots at different saline concentrations when compared to non-inoculated plants. In non-mycorrhizae plants, the lowest crop performance was reported to be associated with higher Na and lower N, P, K concentrations in leaf tissue and also with high leaf electrolyte leakage, but the effect of the saline stress on pepper shoot biomass varies among different fungi species at a significant level [126]. Cheng et al. [127] reported that inoculation with AMF (*R. intraradices*) might help to beat saline stress in zucchini-squash (*Cucurbita pepo* L. "Tempra"), which is a significant greenhouse vegetable. Enhanced nutrition (higher K and lower Na concentrations in leaf tissue) and the leaf water status might have helped plants to translocate minerals and assimilate to the sink, and alleviate the effects of saline stress on fruit production [128]. It was reported that onion (*Allium cepa* L.) and basil (*Ocimum basilicum* L.) inoculated with AMF could relieve deleterious influences of soil/water saline stress on the yield and growth of crop [129, 130]. About the leafy vegetables, in [131], it was reported that the DAOM 197198 isolate of *R. intraradices* might be accepted as a potential AMF candidate since it stimulated the growth of lettuce under two different saline concentrations. This influence was considered to be linked with higher leaf relative water content and lower ABA in roots, which show that AMF plants are less strained than nonmycorrhizal plants by saline conditions, which enables them to accumulate less ABA. Furthermore, in saline conditions, AM symbiosis improved the LsPIP1 expression, which involved in the transcellular water-flow regulation. A gene expression of this magnitude might contribute to regulate the root-water permeability to tolerate the osmotic stress caused by saline conditions better [132]. Hildebrandt et al. [133] reported in their study that AMF *R. irregularis* alleviated the deleterious influences of saline stress in lettuce ("Romana") by changing the hormonal profiles (higher strigolactone production) and affecting plant physiology in a positive manner, which allows lettuce to grow better under harsh conditions. Gadkar and Rillig [134] reported that AMF (*G. iranicum* var. tenuihypharum sp. nova) could alleviate the negative influence of irrigation with high saline water on physiological parameters (photosynthesis and stomatal conductance) in lettuce. The results of research on the physiological effects of some vegetable species related to the benefits

74 Physical Methods for Stimulation of Plant and Mushroom Development

of mycorrhizae in salt stress conditions are presented in **Table 2**.

Climate change is defined as the changes observed over many years in the average state of the climate regardless of its cause. Today's climate change depends on the greenhouse effect of gases released to the atmosphere due to fossil fuels, improper land use, deforestation, and industrial development, but it is not caused by natural factors, as it has been since the formation of the world. The primary effect of this change, in which the direct human factor plays a role, is the increase in mean surface temperatures, in other words global warming. Modeling efforts to understand global climate change predicts that the average global warming will increase by 1–3.5°C by 2100 and that there will be regional extreme temperatures, floods, and widespread and severe droughts all over the world. Drought is related to the amount of water that can be taken by the roots during the growth period of the plant which is added to the field rather than the total amount of rainfall that occurs throughout the year. Plants that are experiencing water deficiency during the growing period face with significant losses in terms of development and especially yield [143, 144]. Measures should be taken as soon as possible

**3.2. Drought**

**Table 2.** Summary of reported physiologic effects of mycorrhizae under salinity stress conditions on different vegetables.

to mitigate the effects of agricultural drought, since the available water resources are limited and the occupancy rate of these reserves is predicted to decrease rapidly due to the global warming-related rainfall and especially the decrease in the amount of snowfall that feeds groundwater resources. Although plant varieties belong to the same species, they may differ in their tolerance to drought.

Plants can adapt their growth and development mechanisms in such a way that they are least likely to be affected from environmental changes, and even adapt to environmental conditions when they grow in the same climatic conditions for long periods of time. Drought is one of the abiotic stress conditions which mostly affects the growth and development of plants [145]. Water constitutes 50% of the fresh weight of the trees and 89–90% of the other plants [146]. Plant growth is affected considerably in arid conditions. This effect in growth depends on the length of time the water stress is experienced. In the early stages of arid conditions, the plant slows elongation and triggers root development to reach more water. On the other hand, if arid conditions last long enough to cause damage to the plant, both stem and root growth will stop, leaf area and number of leaves will decrease, and even some leaves turn yellow. The decline in plant growth is due to the division of cells in the shoot and root meristems and the arrest of expansion of the cells. The disruption of cell division or enlargement is directly related to the decrease in the rate of photosynthesis due to water insufficiency [147]. When the plants are exposed to drought stress, the water balance between the tissues is disturbed. In case of stress, cell growth is negatively affected by the loss of turgor, so the cells remain small. The decrease in cell growth also affects the synthesis of the cell wall. While protein and chlorophyll are adversely affected, it is observed that the seeds lose their germination ability [148–150]. Photosynthesis and respiration slow down and stop. Decrease in cell growth causes the leaves to shrink and the production of photosynthesis to decrease further [151]. Water deficiency causes the formation of various reactive oxygen derivatives (ROD) such as superoxide radical (O<sup>2</sup> − ), hydrogen peroxide (H<sup>2</sup> O2 ), hydroxyl radicals (OH) and superoxide radical (O<sup>2</sup> − ) [152]. ROD damages membrane lipids, nucleic acids, proteins, chlorophyll, and macromolecules in the cell. The effect of free oxygen radicals on the cell membrane depends on lipid peroxidation. Lipid peroxidation, which leads to cell membrane destruction, produces malondialdehyde (MDA) as a result of several reaction steps. Drought stress also has an important effect on enzyme activity and enzyme amount in plants. In addition, the amount of abscisic acid is 40 times higher in the leaves, while in other organs including the root, this increase is less. Abscisic acid prevents the transpiration of water by closing the stomata [153].

#### *3.2.1. Inducing drought stress tolerance through inoculation of PGPR*

Drought affects almost every climatic region in the world and more than half of it is prone to drought each year. Drought limits the growth and the production of crops as one of the most important stresses. The response to drought by plants is at cellular and molecular level. Drought stimulates the ethylene production in the tissues of plants as it is the case in some other environmental factors and also causes abnormal growth in plants. According to [154], ACC deaminase PGPR *Achromobacter piechaudii* ARV8 increases the fresh-dry weights in tomato and pepper seedlings at a great deal under transient water stress. Also, these bacteria decreased the ethylene production in tomato seedlings under water stress. In water stress, the bacteria had no effects on the water content of plants, and enhanced the recovery of plants if irrigation was started again. It is interesting that when bacteria were given to the tomato plants, the plant growth continued under water stress and also when irrigation was started again. Giri et al. [155] investigated the physiological response of peas (*Pisum sativum* L.) to inoculation with ACC deaminase bacteria *Variovorax paradoxus* 5C-2 in moisture stress and watering conditions. Bacterial effects were more obvious and consistent in controlled soil drying process (moisture stress conditions). In trials that had short time periods, it was seen that ACC deaminase bacteria had positive influences on root-shoot biomass, leaf area, and plant transpiration. In trials that had long time periods, it was seen that the plants that were inoculated with ACC deaminase bacteria produced more seed yields (25–41%), seed numbers, and seed nitrogen accumulations than the plants that were uninoculated. In addition to these, the inoculation caused that the nodulation in pea plants under drought was restored to uninoculated plant levels that were well-watered. In recent years, similar results were reported. According to the recent reports, the inoculation with ACC deaminase bacteria eliminated the influences of water stress on growth, yield, and ripening of *Pisum sativum* L.—although partly—pot and field experiments. The results of the physiological effects of some studies related to the benefits of PGPRs on vegetables in drought stress are given in **Table 3**.

*3.2.2. Drought stress tolerance through mycorrhizae*

**References Used plant growth promoting rhizobacteria (PGPR)**

[157] *Agrobacterium rubi, Pseudomonas* 

[158] *Bacillus megaterium* TV-3D,

[159] *Bacillus megaterium var. phosphaticum*

conditions on different vegetables.

E43 F, 637Ca, MFD Ca1, 52/1, 21/3 + 637Ca, 52/1 Zeatin

*putida, Pseudomonas fluorescens, Pantoea agglomerans, Bacillus subtilis, Bacillus megaterium*

*Bacillus megaterium* TV-91C, *Pantoea agglomerans* RK- 92 and *Bacillus megaterium* KBA-10

[156] 52/1 and E43, 21/3F, 17/3 N,

Arbuscular mycorrhizae (AM) symbiosis is associated with enhancing the resistance to water and drought stress despite the change of plant physiology and the expression of plant genes [120, 160]. It was reported in previous studies that AM-related increase in drought tolerance involved increased dehydration and dehydration tolerance [161]. AM fungi inoculation was able to reduce the leaf content of malondialdehyde and soluble protein and improve the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), which resulted in enhanced osmotic adjustment and drought tolerance of mycorrhizae citrus-grafting seedlings [162]. Inoculation of *Glomus versiforme* in citrus plants enhanced the osmotic adjustment of the

**Table 3.** Summary of reported physiologic effects of plant growth promoting rhizobacteria (PGPR) under drought stress

**Vegetable species**

**Stress factor**

Use of Some Bacteria and Mycorrhizae as Biofertilizers in Vegetable Growing and Beneficial…

**Result**

Tomato Drought 21/3F, 21/3 + 637 Ca and 17/3 N bacteria

Garlic Drought *Bacillus subtilis* caused important changes

Broccoli Drought PGPR treatments increased seedling

Tomato Drought Plant growth, total and marketable yield

*phosphaticum*.

in the plant enzyme levels.

races applications had positive effects on yield and yield components of tomato.

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77

length, stem diameter, leaf area, and leaf dry matter at ratios of 7.85%, 42.56%, 18.12% and 41.98%, respectively, compared to the control. Except for Na, the mineral element content was also increased with PGPR treatments.

increased by *Bacillus megaterium var.* 

It was reported that the role of abscisic acid (ABA) was behind the AM-related stress response in plants [164]. When exogenous ABA was added, the ABA content was improved in shoots of non-AM plants, concomitant with the expression of the stress marker genes Lsp5cs and Ls1ea and the gene Lsnced. However, when exogenous ABA was added, the ABA content in AM shoots decreased, and this addition did not cause more improvement of the expression. Co-inoculation of lettuce with PGPR *Pseudomonas mendocina* and *G. intraradices* or *G. mosseae* improved an antioxidative catalase in serious drought, which shows that they might be used in inoculants to relieve the oxidative harm [165]. A 14-3-3 protein encoding gene from *Glomus intraradices* growing in vitro and subjected to drought stress was identified [166]. The role of these proteins regulating the signaling pathways and effector proteins was claimed to impart

), Ca(<sup>+</sup>

), and

plant in drought stress via improved levels of non-structural carbohydrates, K(<sup>+</sup>

Mg(2+), which resulted in improvement of drought tolerance [163].


**Table 3.** Summary of reported physiologic effects of plant growth promoting rhizobacteria (PGPR) under drought stress conditions on different vegetables.

#### *3.2.2. Drought stress tolerance through mycorrhizae*

the plants are exposed to drought stress, the water balance between the tissues is disturbed. In case of stress, cell growth is negatively affected by the loss of turgor, so the cells remain small. The decrease in cell growth also affects the synthesis of the cell wall. While protein and chlorophyll are adversely affected, it is observed that the seeds lose their germination ability [148–150]. Photosynthesis and respiration slow down and stop. Decrease in cell growth causes the leaves to shrink and the production of photosynthesis to decrease further [151]. Water deficiency causes the formation of various reactive oxygen derivatives (ROD) such as

O2

macromolecules in the cell. The effect of free oxygen radicals on the cell membrane depends on lipid peroxidation. Lipid peroxidation, which leads to cell membrane destruction, produces malondialdehyde (MDA) as a result of several reaction steps. Drought stress also has an important effect on enzyme activity and enzyme amount in plants. In addition, the amount of abscisic acid is 40 times higher in the leaves, while in other organs including the root, this increase is less. Abscisic acid prevents the transpiration of water by closing the stomata [153].

Drought affects almost every climatic region in the world and more than half of it is prone to drought each year. Drought limits the growth and the production of crops as one of the most important stresses. The response to drought by plants is at cellular and molecular level. Drought stimulates the ethylene production in the tissues of plants as it is the case in some other environmental factors and also causes abnormal growth in plants. According to [154], ACC deaminase PGPR *Achromobacter piechaudii* ARV8 increases the fresh-dry weights in tomato and pepper seedlings at a great deal under transient water stress. Also, these bacteria decreased the ethylene production in tomato seedlings under water stress. In water stress, the bacteria had no effects on the water content of plants, and enhanced the recovery of plants if irrigation was started again. It is interesting that when bacteria were given to the tomato plants, the plant growth continued under water stress and also when irrigation was started again. Giri et al. [155] investigated the physiological response of peas (*Pisum sativum* L.) to inoculation with ACC deaminase bacteria *Variovorax paradoxus* 5C-2 in moisture stress and watering conditions. Bacterial effects were more obvious and consistent in controlled soil drying process (moisture stress conditions). In trials that had short time periods, it was seen that ACC deaminase bacteria had positive influences on root-shoot biomass, leaf area, and plant transpiration. In trials that had long time periods, it was seen that the plants that were inoculated with ACC deaminase bacteria produced more seed yields (25–41%), seed numbers, and seed nitrogen accumulations than the plants that were uninoculated. In addition to these, the inoculation caused that the nodulation in pea plants under drought was restored to uninoculated plant levels that were well-watered. In recent years, similar results were reported. According to the recent reports, the inoculation with ACC deaminase bacteria eliminated the influences of water stress on growth, yield, and ripening of *Pisum sativum* L.—although partly—pot and field experiments. The results of the physiological effects of some studies

related to the benefits of PGPRs on vegetables in drought stress are given in **Table 3**.

) [152]. ROD damages membrane lipids, nucleic acids, proteins, chlorophyll, and

), hydroxyl radicals (OH) and superoxide

superoxide radical (O<sup>2</sup>

−

radical (O<sup>2</sup>

−

76 Physical Methods for Stimulation of Plant and Mushroom Development

), hydrogen peroxide (H<sup>2</sup>

*3.2.1. Inducing drought stress tolerance through inoculation of PGPR*

Arbuscular mycorrhizae (AM) symbiosis is associated with enhancing the resistance to water and drought stress despite the change of plant physiology and the expression of plant genes [120, 160]. It was reported in previous studies that AM-related increase in drought tolerance involved increased dehydration and dehydration tolerance [161]. AM fungi inoculation was able to reduce the leaf content of malondialdehyde and soluble protein and improve the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), which resulted in enhanced osmotic adjustment and drought tolerance of mycorrhizae citrus-grafting seedlings [162]. Inoculation of *Glomus versiforme* in citrus plants enhanced the osmotic adjustment of the plant in drought stress via improved levels of non-structural carbohydrates, K(<sup>+</sup> ), Ca(<sup>+</sup> ), and Mg(2+), which resulted in improvement of drought tolerance [163].

It was reported that the role of abscisic acid (ABA) was behind the AM-related stress response in plants [164]. When exogenous ABA was added, the ABA content was improved in shoots of non-AM plants, concomitant with the expression of the stress marker genes Lsp5cs and Ls1ea and the gene Lsnced. However, when exogenous ABA was added, the ABA content in AM shoots decreased, and this addition did not cause more improvement of the expression. Co-inoculation of lettuce with PGPR *Pseudomonas mendocina* and *G. intraradices* or *G. mosseae* improved an antioxidative catalase in serious drought, which shows that they might be used in inoculants to relieve the oxidative harm [165]. A 14-3-3 protein encoding gene from *Glomus intraradices* growing in vitro and subjected to drought stress was identified [166]. The role of these proteins regulating the signaling pathways and effector proteins was claimed to impart the protection to the host plants against drought stress. Glutathione and ascorbate have a significant effect in conferring the protection and maintaining metabolic function of plants in water deficit conditions.

AMF are known to have an efficacious and sustainable mechanism. With this mechanism, tolerance to drought is enhanced in vegetables [167, 168]. AMF cause changes in the roots of plants, especially in length, density, diameter, and number of lateral roots [169]. Improved root structure in mycorrhizae plants allows the extraradical hyphae to extend beyond depletion zones of plant rhizosphere, which makes the water and low-mobile nutrient intake (P, Zn, and Cu) more efficiently under water stress [170].

The AM symbiosis effectiveness in improving drought tolerance was also investigated in vegetables. Open-field tomato (*Solanum lycopersicum* L.) inoculated with AMF (*R. intraradices*) influenced the agronomical and physiological responses of exposure in different drought intensities [171]. Compared to non-inoculated ones, the fruit yield of inoculated plants in severe-moderate-mild drought stresses was high at a statistically significant level by 25, 23, and 16%, respectively. It was reported in this study that high crop performance in inoculated plants was associated with better nutritional status (higher N and P) in connection with the maintenance of leaf water status. Ikiz et al. [172] confirmed this effect on tomato. They showed that the colonization of processing tomato "Regal 87-5" plants by *F. mosseae* and *G. versiforme* might increase marketable yield by 20% and 32%, respectively, when compared with those of non-inoculated plants under mild-heavy drought stress. Greenhouse melon (*Cucumis melo* L. "Zhongmi 3") plants (inoculated with three *Glomus* species: *G. versiforme* and *R. intraradices* and, especially, *F. mosseae*) showed higher tolerance to drought stress than non-inoculated plants. This situation was determined in plant heights, root lengths, biomass production, and net photosynthetic rates [173]. They claimed that the increase in drought tolerance and better crop performance might be associated with the antioxidant enzyme production (SOD, POD, and CAT) and the soluble sugar accumulation by AM symbiosis. Lucy et al. [174] examined the mechanisms which affected the relief of drought by a mixture of *Glomus* spp. from Mexico ZAC-19 (*G. albidium*, *G. claroides*, and *G. diaphanum*) in Chile ancho pepper (*C. annuum* L. San Luis). They reported that ZAC-19 had the potential to be incorporated into Chile pepper transplant systems to relieve the harmful effect of drought in open-field production in Mexico, which was shown by high root-to-shoot rate and leaf water potential. In a similar manner, in [175] it was reported that drought enhanced bigger extraradical hyphae development of *G. deserticola* in bell pepper, and as a result, a high water intake, when compared to non-mycorrhizae plants. It was also reported that AMF symbiosis enhanced lettuce (*Lactuca sativa* L. "Romana") tolerance to drought and recovery. This enhancement was achieved via the modification of the plant physiology and the expression of plants genes [176, 177]. Lettuce, which was inoculated with the AMF *R. intraradices*, gave high root hydraulic conductivity and low transpiration in drought, when it was compared with non-inoculated plants. Authors [178, 179] also emphasized that the plants inoculated with AMF could regulate their abscisic acid (ABA) concentrations in a better and quicker manner than non-inoculated plants, which allows a better balance between leaf transpiration-root water movement in drought stress and recovery [180, 181]. It was reported that inoculation with AMF enhanced WUE in watermelon [182], which shows that AMF improved water intake and resulted in the host plant making

use of water in a more efficacious manner [183]. This was associated with the mechanisms that could increase transpiration and stomatal conductance [184], and also improve the availability of the nutrients [183]. The results of the physiological effects of some studies related to the

**Table 4.** Summary of reported physiologic effects of mycorrhizae under drought stress conditions on different vegetables.

Today, the utilization of natural resources in agriculture comes to the forefront because of improving environmental awareness. The evaluation of the use of natural resources, such as mycorrhiza and a cleaner environment, is important both for economic reasons. Resources are often used as a source of plant nutrition in hydroponics. Given the chemical, the use of mycorrhiza in agriculture is very important in soil. Particularly with the use of mycorrhiza, the use of chemical fertilizers especially consisting phosphorus, can be reduced. As a conclusion, mycorrhizae are important for the growth of agricultural crops as well as healthy ecosystem functions. Many benefits of mycorrhizal symbiosis can be enhanced by changing agricultural

Hydraheaded stress caused by biotic and abiotic reasons is threatening modern agriculture. Several stress types explained in this chapter emphasize ethylene biosynthesis, which prevents plant growth by some tools at molecular level. In this chapter, for the purpose of regulating

benefits of mycorrhizae on vegetables in drought stress are given in **Table 4**.

**Vegetable species Stress** 

**factor**

[185] *Glomus mosseae* Muskmelon Drought K/Na ratio has increased in several plant

[186] *Glomus mosseae* Watermelon Water use efficiency, Leaf water content and

[187, 188] *Glomus mosseae* Lettuce Endogenous auxin and cytokinin levels are

[189] *Glomus occultum* Cabbage Yield and quality increased with mycorrhizae. [190] *Glomus fasciculatum* Lettuce L-arabinose (L Ara), ribose (Rib); D-xylose (D

[191] *Glomus mosseae* Aubergine Water use efficiency, Leaf water content and

[193] *Glomus mosseae* Melon Water-use efficiency, leaf water content, and

[192] *Glomus caledonium* Pepper Activity of superoxide dismutase (SOD),

**Result**

Use of Some Bacteria and Mycorrhizae as Biofertilizers in Vegetable Growing and Beneficial…

tissues.

leaf osmotic potential has increased.

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79

increased in the presence of *G. mosseae.*

Xyl), L-xylose (L Xyl), adonitol (Ado), betamethyl-D-xyloside (Mdx) levels increased.

leaf osmotic potential has increased.

catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in leaves of plants

leaf osmotic potential has increased.

treated with *Glomus* increased.

practices which may decrease colonization and mycorrhizal abundance [194].

**4. Conclusion**

**Reference type**

**Used mycorrhizae** 

**species**

Use of Some Bacteria and Mycorrhizae as Biofertilizers in Vegetable Growing and Beneficial… http://dx.doi.org/10.5772/intechopen.76186 79


**Table 4.** Summary of reported physiologic effects of mycorrhizae under drought stress conditions on different vegetables.

use of water in a more efficacious manner [183]. This was associated with the mechanisms that could increase transpiration and stomatal conductance [184], and also improve the availability of the nutrients [183]. The results of the physiological effects of some studies related to the benefits of mycorrhizae on vegetables in drought stress are given in **Table 4**.
