Actinobacteria: Potential Candidate as Plant Growth Promoters

*Sumreen Hayat, Asma Ashraf, Bilal Aslam, Rizwan Asif, Saima Muzammil, Muhammad Asif Zahoor, Muhammad Waseem, Imran Riaz Malik, Mohsin Khurshid, Muhammad Afzal, Muhammad Saqalein, Muhammad Hussnain Siddique, Aqsa Muzammil and Sumera Sabir*

### **Abstract**

Plant growth enhancement using plant beneficial bacteria has been viewed in the sustainable agriculture as an alternative to chemical fertilizers. Actinobacteria, among the group of important plant-associated bacteria, have been widely studied for its plant growth promotion activities. Actinobacteria are considered as a limelight among agriculturists for their beneficial aspects toward plants. They are naturally occurring spore-forming bacteria inhabiting the soil and known for their plant growth-promoting and biocontrol properties. The mechanisms behind these activities include nitrogen fixation, phosphate solubilization, siderophore production, and other attributes such as antifungal production of metabolites, phytohormones, and volatile organic compound. All these activities not only enhance the plant growth but also provide resistance in plants to withstand unfavorable conditions of the environment. Hence, this chapter emphasizes on the plant growth traits of actinobacteria and how far it was studied for enhanced growth and bio-fortification.

**Keywords:** actinobacteria, rhizosphere, PGPR, growth promotion

### **1. Introduction**

Plant growth-promoting (PGP) microbes (epiphytic, endophytic, and rhizospheric) are likely to enhance the growth and productivity of crop by increasing the nutrient content. These plant microbiomes have been sorted out from diverse sources belonging to all three domains: archaea, bacteria, and fungi. The microbes associated with the plant rhizosphere are termed as rhizospheric microbes, and among them, actinobacteria are most dominant in nature [1]. As many researches stated actinobacteria as major microbial population present in the soil. The actinobacteria are known to have high G-C (57–75%) contents and comprise a broad

group of filamentous, spore-forming, gram-positive, and aerobic bacteria that form branching filaments or hyphae and play a fundamental function in ecology along with soil nutrient cycle. Actinobacteria resemble to unicellular bacteria, they are different by not having distinct cell wall; instead they produce mycelium, a nonseptate and more slender [2]. Actinobacteria are widely dispersed in both terrestrial ecosystem, as present in soil, and aquatic ecosystems as in fresh and marine water. The terrestrial actinobacteria contribute in recycling process and are essential to the decomposition of many complex mixtures of polymers and organic material, located in dead plants, animals, and fungal materials. The phylum actinobacteria is currently recognized as the largest taxonomic units within the bacterial domain and recognized for its economic importance because it produces various biological active substances like vitamins, antibiotics, and enzymes. It is estimated that almost 23,000 bioactive secondary metabolites are produced by many microorganisms and almost 45% (10,000 out of 23,000) of these bioactive microbial metabolites are produced by actinomycetes. Among these actinomycetes, *Streptomyces* are classified as most abundantly occurring *Actinomycete* in the soil, while *Nocardia*, *Micromonospora*, and *Streptosporangium* are the less abundant [3]. Streptomyces has established its importance in numerous sectors like health and agriculture, and it is also considered as most dominant actinobacteria, for root colonization and close association with plant roots. Actinomycetes are diversified organisms having various applications on many fields. Plant growth-promoting rhizobacteria (PGPR) actinobacteria promote the plant growth through a variety of mechanisms including production of phytohormones, antibiotics, siderophore, volatile organic compound, and different hydrolytic enzymes. These also promote nutrient fixation for easy


**389**

**Figure 1.**

*Mode of action of actinobacteria.*

*Actinobacteria: Potential Candidate as Plant Growth Promoters*

bacteria, its host plant, and targets are mentioned in **Table 1**.

are classified into direct and indirect method (**Figure 1**).

**2.1 Direct method for plant growth promoter by actinobacteria**

**2. Actinobacteria's role in PGPR activity**

competition for nutrients [18].

activities as shown in **Table 2**.

uptake by the plant and develop abiotic stress tolerance in plants. Actinobacteria are also considered to have the potential to be used as promising biocontrol agents because they produce spore which can resist environmental stress. The actinobacteria help plants by suppressing disease-causing microbes and enhancing nutrient availability and assimilation which subsequently have beneficial impact on the agricultural sector by accelerating plant growth [4]. Although actinomycetes have many applications in different sectors including health and agriculture, this chapter will only focus on actinomycetes' role as PGPR. Some commonly isolated actino-

Plant growth and development of important organs in plant are facilitated by plant hormones called plant growth regulators (PGR). These PGR can influence plant growth even at very low concentration. Actinobacteria act as PGPR, and its impact is determined by considering the effectiveness and ability to influence PGR in root system. Different mechanisms used for promoting PGR by actinobacteria

The direct method exhibits various activities including solubilization of phosphorus, nitrogen fixation, iron acquisition, and production of different phytohormones, for instance, indole acetic acid (IAA), cytokinins, and gibberellins. In indirect method, actinobacteria promote plant growth in many ways such as synthesizing extracellular enzymes for fungal cell wall degradation producing antibiotics, volatile compounds (VOCs), inducting systemic resistance, as well as

Actinobacteria promote the growth of plants by involving in various direct

*DOI: http://dx.doi.org/10.5772/intechopen.93272*

### **Table 1.**

*Biological activities of some isolated actinobacteria.*

*Actinobacteria: Potential Candidate as Plant Growth Promoters DOI: http://dx.doi.org/10.5772/intechopen.93272*

*Plant Stress Physiology*

*Streptomyces* sp. S30, *Streptomyces* sp. R18

*Streptomyces diastaticus*, *Streptomyces fradiae*,

*Leifsonia xyli*, BPSAC24, *Streptomyces* sp. BPSAC34

*Nocardiopsis* sp. ac 9, *Streptomyces* sp. ac19

*Streptomyces* sp. AzR-051, *Streptomyces* sp. AzR-010

*Streptomyces* sp. MBPu-75 *Cucumis* sp. and

*Mutabilis* CA-2 *Cleome arabica*,

*Biological activities of some isolated actinobacteria.*

*S. collinus*

group of filamentous, spore-forming, gram-positive, and aerobic bacteria that form branching filaments or hyphae and play a fundamental function in ecology along with soil nutrient cycle. Actinobacteria resemble to unicellular bacteria, they are different by not having distinct cell wall; instead they produce mycelium, a nonseptate and more slender [2]. Actinobacteria are widely dispersed in both terrestrial ecosystem, as present in soil, and aquatic ecosystems as in fresh and marine water. The terrestrial actinobacteria contribute in recycling process and are essential to the decomposition of many complex mixtures of polymers and organic material, located in dead plants, animals, and fungal materials. The phylum actinobacteria is currently recognized as the largest taxonomic units within the bacterial domain and recognized for its economic importance because it produces various biological active substances like vitamins, antibiotics, and enzymes. It is estimated that almost 23,000 bioactive secondary metabolites are produced by many microorganisms and almost 45% (10,000 out of 23,000) of these bioactive microbial metabolites are produced by actinomycetes. Among these actinomycetes, *Streptomyces* are classified as most abundantly occurring *Actinomycete* in the soil, while *Nocardia*, *Micromonospora*, and *Streptosporangium* are the less abundant [3]. Streptomyces has established its importance in numerous sectors like health and agriculture, and it is also considered as most dominant actinobacteria, for root colonization and close association with plant roots. Actinomycetes are diversified organisms having various applications on many fields. Plant growth-promoting rhizobacteria (PGPR) actinobacteria promote the plant growth through a variety of mechanisms including production of phytohormones, antibiotics, siderophore, volatile organic compound, and different hydrolytic enzymes. These also promote nutrient fixation for easy

**Actinobacteria Host plant Target pathogen References**

Medicinal plants *Fusarium oxysporum*,

*rolfsii*

*Actinoplanes Cucumis* sp. *Pythium aphanidermatum* [6]

*Streptomyces* sp. DBT204 *Solanum lycopersicum Fusarium proliferatum* [8]

*Microbispora* spp. *Solanum tuberosum* L. *Streptomyces scabies* [10] *Streptomyces* spp. R-5 *Rhododendron* sp. *Phytophthora cinnamomi* [11]

*Streptomyces* sp. RM 365 Leguminous plants *Xanthomonas campestris* [13] *Streptomyces* sp. PRY-2RB2 *Pseudowintera colorata Nocardia parvum* MM562 [14]

*Rhizoctonia solani* [5]

[7]

[9]

*Alternaria solani*, *Sclerotium* 

*Fusarium oxysporum* ciceri, *F. oxysporum*, *F. graminearum*,

*Colletotrichum orbiculare* [12]

*Rhizoctonia solani* [17]

*Rhizoctonia solani*

*Elaeis guineensis* Jacq. *Ganoderma boninense* [15]

*Azadirachta indica Alternaria alternate* [16]

*Lycopersicon esculentum*

*Curcuma longa*, *Eupatorium odoratum*, *Mirabilis jalapa*

*Cucurbita* sp.

*Aristida pungens*

**388**

**Table 1.**

uptake by the plant and develop abiotic stress tolerance in plants. Actinobacteria are also considered to have the potential to be used as promising biocontrol agents because they produce spore which can resist environmental stress. The actinobacteria help plants by suppressing disease-causing microbes and enhancing nutrient availability and assimilation which subsequently have beneficial impact on the agricultural sector by accelerating plant growth [4]. Although actinomycetes have many applications in different sectors including health and agriculture, this chapter will only focus on actinomycetes' role as PGPR. Some commonly isolated actinobacteria, its host plant, and targets are mentioned in **Table 1**.

### **2. Actinobacteria's role in PGPR activity**

Plant growth and development of important organs in plant are facilitated by plant hormones called plant growth regulators (PGR). These PGR can influence plant growth even at very low concentration. Actinobacteria act as PGPR, and its impact is determined by considering the effectiveness and ability to influence PGR in root system. Different mechanisms used for promoting PGR by actinobacteria are classified into direct and indirect method (**Figure 1**).

The direct method exhibits various activities including solubilization of phosphorus, nitrogen fixation, iron acquisition, and production of different phytohormones, for instance, indole acetic acid (IAA), cytokinins, and gibberellins. In indirect method, actinobacteria promote plant growth in many ways such as synthesizing extracellular enzymes for fungal cell wall degradation producing antibiotics, volatile compounds (VOCs), inducting systemic resistance, as well as competition for nutrients [18].

### **2.1 Direct method for plant growth promoter by actinobacteria**

Actinobacteria promote the growth of plants by involving in various direct activities as shown in **Table 2**.

**Figure 1.** *Mode of action of actinobacteria.*


### **Table 2.**

*Direct plant growth-promoting (PGP) properties of actinobacteria.*

### *2.1.1 Nitrogen fixation*

Nitrogen is a well-known and key element of nucleic acids and proteins, and it is also an indispensable nutrient for plant growth. Nitrogen gas is abundantly found in the air, constituting 78% of the atmosphere, but it is not directly available to plants for uptake unless it is converted into its soluble form [32]. Biological nitrogen fixer (BNF) used nitrogenase enzyme system which converts the atmospheric nitrogen required by plants into ammonium and nitrates [33]. Additionally, synthetic nitrogen fertilizers are also supplied to balance the limited availability of nitrogen provided by biological nitrogen fixer. But these fertilizers might be harmful to health and agricultural sustainability. Therefore, actinobacteria are good choice to be utilized as BNF to improve the plant growth for sustainable agriculture. *Frankia* is a versatile actinobacterium which enters in the root cell through different ways, such as intracellular using root-hair or intercellular by means of root invasion, and fixes nitrogen under both free-living and symbiotic conditions in nonlegume plants [34]. In addition to *Frankia*, many other endophytes like *Agromyces*, *Arthrobacter*, *Micromonospora*, *Corynebacterium*, *Propionibacterium*, *Mycobacterium*, and *Streptomyces* also demonstrated N-fixing ability [35].

### *2.1.2 Phosphorus solubilization*

After nitrogen, the second major element, for plant growth, is phosphorus [36]. Phosphorus exists in soil as both inorganic and organic forms [37], but 0.1% phosphorus is available as soluble form to be absorbed by plants. An immediate

**391**

**Figure 2.**

*Plant disease suppressing trait adopted by actinobacteria.*

*Actinobacteria: Potential Candidate as Plant Growth Promoters*

need of phosphorus is fulfilled by chemical fertilizers, like nitrogen, but the

and *Micromonospora* [39]. *Micromonospora endolithica* a non-streptomycete enhances the phosphate-solubilizing ability in bean plants which subsequently increase the growth of bean plants [40]. *Micromonospora aurantiaca*, *Streptomyces* sp., and *Streptomyces griseus* also showed similar results on wheat plants when grown under phosphorus-deficient soil. Many actinobacterial strains also aid in phosphorus solubilization by producing several organic acids such as citric acid, gluconic acid, oxalic acid, lactic acid, malic acid, succinic acid, and propionic acid. Therefore, it is more viable to utilize microorganisms like actinobacteria as biofertilizers economically. Some plant growth-promoting characteristic of actinobacteria

majority of these applied chemical fertilizers are not only expensive but also wasted because it retains in soil as an insoluble form just after the application [37]. In the past decades, many microbes have been described which can solubilize the insoluble phosphorus, and since then, numerous studies by many researchers have been carried out to investigate the phosphate-solubilizing potential of different microbes such as bacteria, fungi, and actinobacteria [38]. Different in vitro and in vivo studies have been executed, which highlight capability to solubilize soil phosphorus by PGP actinobacteria, for instance, *Streptomyces*, *Rhodococcus*, *Arthrobacter*, *Gordonia*,

*DOI: http://dx.doi.org/10.5772/intechopen.93272*

is shown in **Figure 2**.

### *Actinobacteria: Potential Candidate as Plant Growth Promoters DOI: http://dx.doi.org/10.5772/intechopen.93272*

*Plant Stress Physiology*

*Microbispora* spp.

spp.

*S. rochei*

RS15,

**Table 2.**

*Micromonospora* spp. *Nocardia*

*Streptomyces olivaceoviridis*,

*Brevibacterium epidermidis*

*Micrococcus yunnanensis* RS222

*Streptomyces* sp*.* IAA production

*2.1.1 Nitrogen fixation*

*Streptomyces* also demonstrated N-fixing ability [35].

*2.1.2 Phosphorus solubilization*

Nitrogen is a well-known and key element of nucleic acids and proteins, and it is also an indispensable nutrient for plant growth. Nitrogen gas is abundantly found in the air, constituting 78% of the atmosphere, but it is not directly available to plants for uptake unless it is converted into its soluble form [32]. Biological nitrogen fixer (BNF) used nitrogenase enzyme system which converts the atmospheric nitrogen required by plants into ammonium and nitrates [33]. Additionally, synthetic nitrogen fertilizers are also supplied to balance the limited availability of nitrogen provided by biological nitrogen fixer. But these fertilizers might be harmful to health and agricultural sustainability. Therefore, actinobacteria are good choice to be utilized as BNF to improve the plant growth for sustainable agriculture. *Frankia* is a versatile actinobacterium which enters in the root cell through different ways, such as intracellular using root-hair or intercellular by means of root invasion, and fixes nitrogen under both free-living and symbiotic conditions in nonlegume plants [34]. In addition to *Frankia*, many other endophytes like *Agromyces*, *Arthrobacter*, *Micromonospora*, *Corynebacterium*, *Propionibacterium*, *Mycobacterium*, and

**Actinobacteria PGP traits Host plant Reference** *Streptomyces* sp. GMKU 3100 Siderophore production Rice (*Oryza sativa L.)* [19]

Wheat [20]

Wheat [28]

Canola [29]

Soya bean [31]

[22]

[23]

[24]

*reticulata L*.)

*annuum* L.)

Rice

Phosphate solubilization

*Streptomyces* spp. IAA production Sorghum

*Arthrobacter* sp. strain EZB4 ACC deaminase activity Pepper (*Capsicum* 

*Streptomyces griseoflavus* P4 Nitrogen fixation Soybean (*Glycine max*) [21]

*Micromonospora endolithica* Phosphate solubilization Carrot (*Daucus carota*) [25] *Streptomyces* sp. Nutrient uptake Clover [26] *Streptomyces* sp. Gibberellic acid, IAA, Marine environments [27]

*Streptomyces* spp. Phosphate solubilization — [30]

Auxin, gibberellin, and cytokinin synthesis

Nitrogen fixation IAA production ACC deaminase activity

Nitrogen fixation

Actinobacteria Phosphate solubilization,

*Direct plant growth-promoting (PGP) properties of actinobacteria.*

IAA production Mandarin (*Citrus* 

After nitrogen, the second major element, for plant growth, is phosphorus [36]. Phosphorus exists in soil as both inorganic and organic forms [37], but 0.1% phosphorus is available as soluble form to be absorbed by plants. An immediate

**390**

need of phosphorus is fulfilled by chemical fertilizers, like nitrogen, but the majority of these applied chemical fertilizers are not only expensive but also wasted because it retains in soil as an insoluble form just after the application [37]. In the past decades, many microbes have been described which can solubilize the insoluble phosphorus, and since then, numerous studies by many researchers have been carried out to investigate the phosphate-solubilizing potential of different microbes such as bacteria, fungi, and actinobacteria [38]. Different in vitro and in vivo studies have been executed, which highlight capability to solubilize soil phosphorus by PGP actinobacteria, for instance, *Streptomyces*, *Rhodococcus*, *Arthrobacter*, *Gordonia*, and *Micromonospora* [39]. *Micromonospora endolithica* a non-streptomycete enhances the phosphate-solubilizing ability in bean plants which subsequently increase the growth of bean plants [40]. *Micromonospora aurantiaca*, *Streptomyces* sp., and *Streptomyces griseus* also showed similar results on wheat plants when grown under phosphorus-deficient soil. Many actinobacterial strains also aid in phosphorus solubilization by producing several organic acids such as citric acid, gluconic acid, oxalic acid, lactic acid, malic acid, succinic acid, and propionic acid. Therefore, it is more viable to utilize microorganisms like actinobacteria as biofertilizers economically. Some plant growth-promoting characteristic of actinobacteria is shown in **Figure 2**.

**Figure 2.** *Plant disease suppressing trait adopted by actinobacteria.*

### *2.1.3 Siderophore production by actinobacteria*

Iron is an essential nutrient element for all organisms, which acts as a necessary co-factor for several enzymatic reactions. Many beneficial actinobacteria including *Streptomyces*, *Micrococcus*, *Microbacterium*, *Kocuria*, *Corynebacterium*, and *Arthrobacter* improve the plant growth through production of Fe-chelating compounds. Normally, soil iron resides in insoluble hydroxides and oxy-hydroxides forms that are not available for microbes and plants. For iron availability siderophore, a compound of high iron affinity and low molecular weight is needed to be synthesized [41]. Two major classes of siderophore are catechols and hydroxamate, produced by microbes and various actinobacterial strains that have been nominated as producers of siderophore [42]. Some well-known siderophores that are produced by the genus *Streptomyces* are hydroxamate, desferrioxamines, and coelichelin [43], and other members of actinobacteria like *Rhodococcus* and *Nocardia* produced heterobactin siderophore [44]. Siderophore also plays a role in plant protection from phytopathogens besides its role in plant nutrition. Both siderophore and pathogenic microbe require iron so a competitive environment creates between them in the root vicinity [45]. As actinobacteria produce high-affinity siderophore and fungal pathogen produces low-affinity siderophores, therefore actinobacteria can eliminate the fungal pathogen. *Streptomyces* produce siderophore that is also found to be effective against wilt disease on chickpea caused by *F. oxysporum* f. sp. *ciceri* [46].

### *2.1.4 Production of hormone*

Several rhizospheric and endophytic actinobacteria have been noticed to yield several phytohormones, namely, indole acetic acid (IAA), cytokinins, and gibberellins. These phytohormones show a significant role in the plant growth [47]. The most important phytohormone is indole-3-acetic acid, a principal form of auxin that shows the useful impact on plants by various cellular processes like cell division, elongation, and differentiation. Recently, endophytic actinobacteria are getting more attention because of their role in the production of phytohormones. It has been reported that *Nocardiopsis*, an endophytic actinobacterium, produces the highest percentage of IAA [22]. Many researchers studied that *Streptomyces* endophytes like *S. olivaceoviridis*, *S. rimosus*, *S. atrovirens*, *S. rochei*, and *S. viridis* also produce IAA that is responsible for improved seed germination, root elongation, and growth in different plants [48]. Hence, actinobacteria have the ability to boost the production and growth of plants by producing the phytohormone as shown in **Table 2**.

### **2.2 Indirect plant growth mechanism of actinobacteria**

In indirect plant growth mechanism, actinobacteria also enhance the growth of plants like direct mechanism which is mentioned in **Figure 3**.

### *2.2.1 Cell wall-degrading enzymes*

Actinobacteria synthesize many different extracellular enzymes that help to decompose material in soil. Some of these enzymes include xylanases, chitinases, hemicellulose, nucleases, amylases, lipases, glucanases, pectinase, proteinases, cellulases, ligninases, and keratinase. Mainly soil-living actinobacteria are saprophytic and play a central role in decomposition. Actinobacteria use this mixture of enzymes for decomposition against a variety of phytopathogens and majorly contribute to biocontrol potential by damaging cell wall of these pathogens. Cell wall of many bacteria and fungi is made up of polymers like glycan, cellulose,

**393**

**Table 3.**

**Figure 3.**

*Alleviation of abiotic stress in actinobacteria.*

*Production of hydrolytic enzymes by actinobacteria.*

*Actinobacteria: Potential Candidate as Plant Growth Promoters*

chitin, protein, and lipids [49]. Actinobacteria are regarded as the dominant organisms that decompose chitin in soil and also considered as promising antagonistic agents for biocontrol because of the hydrolytic reaction on mycelium of the fungi. Acctinobacteria are also observed to produced chitinase enzyme that inhibit fungal growth by cell wall chitin hydrolysis. Many species of *Streptomyces* genus have the potential to degrade the chitin polymer and are, therefore, known as a principal chitinolytic microbial group in soil [50, 51]. A list of some important enzyme secreted

**Enzymes Actinobacteria References**

Chitinase, glucanase *S. cavourensis* SY224 [53]

Ligase *Nocardia autotrophica* [25] Amylases, lipases, β-1-3-glucanase *Thermomonospora curvata*, *Streptomyces* spp. [55] Chitinase, glucanase and protease *Streptomyces* spp. 80 [56]

*S. albovinaceus*, *S. caviscabies*, *S. setonii*, *S. virginiae*

*A. missouriensis*, *Streptomyces clavuligerus*

[52]

[54]

Chitinase *Streptomyces viridificans*, *S. coelicolor*, *S. griseus*,

Cellulose *Thermomonospora* spp. *Actinoplanes philippinensis*,

*DOI: http://dx.doi.org/10.5772/intechopen.93272*

by actinobacteria is shown in **Table 3**.

### *Actinobacteria: Potential Candidate as Plant Growth Promoters DOI: http://dx.doi.org/10.5772/intechopen.93272*

chitin, protein, and lipids [49]. Actinobacteria are regarded as the dominant organisms that decompose chitin in soil and also considered as promising antagonistic agents for biocontrol because of the hydrolytic reaction on mycelium of the fungi. Acctinobacteria are also observed to produced chitinase enzyme that inhibit fungal growth by cell wall chitin hydrolysis. Many species of *Streptomyces* genus have the potential to degrade the chitin polymer and are, therefore, known as a principal chitinolytic microbial group in soil [50, 51]. A list of some important enzyme secreted by actinobacteria is shown in **Table 3**.

### **Figure 3.**

*Plant Stress Physiology*

*2.1.4 Production of hormone*

*2.2.1 Cell wall-degrading enzymes*

*2.1.3 Siderophore production by actinobacteria*

Iron is an essential nutrient element for all organisms, which acts as a necessary co-factor for several enzymatic reactions. Many beneficial actinobacteria including *Streptomyces*, *Micrococcus*, *Microbacterium*, *Kocuria*, *Corynebacterium*, and *Arthrobacter* improve the plant growth through production of Fe-chelating compounds. Normally, soil iron resides in insoluble hydroxides and oxy-hydroxides forms that are not available for microbes and plants. For iron availability siderophore, a compound of high iron affinity and low molecular weight is needed to be synthesized [41]. Two major classes of siderophore are catechols and hydroxamate, produced by microbes and various actinobacterial strains that have been nominated as producers of siderophore [42]. Some well-known siderophores that are produced by the genus *Streptomyces* are hydroxamate, desferrioxamines, and coelichelin [43], and other members of actinobacteria like *Rhodococcus* and *Nocardia* produced heterobactin siderophore [44]. Siderophore also plays a role in plant protection from phytopathogens besides its role in plant nutrition. Both siderophore and pathogenic microbe require iron so a competitive environment creates between them in the root vicinity [45]. As actinobacteria produce high-affinity siderophore and fungal pathogen produces low-affinity siderophores, therefore actinobacteria can eliminate the fungal pathogen. *Streptomyces* produce siderophore that is also found to be effective against wilt disease on chickpea caused by *F. oxysporum* f. sp. *ciceri* [46].

Several rhizospheric and endophytic actinobacteria have been noticed to yield several phytohormones, namely, indole acetic acid (IAA), cytokinins, and gibberellins. These phytohormones show a significant role in the plant growth [47]. The most important phytohormone is indole-3-acetic acid, a principal form of auxin that shows the useful impact on plants by various cellular processes like cell division, elongation, and differentiation. Recently, endophytic actinobacteria are getting more attention because of their role in the production of phytohormones. It has been reported that *Nocardiopsis*, an endophytic actinobacterium, produces the highest percentage of IAA [22]. Many researchers studied that *Streptomyces* endophytes like *S. olivaceoviridis*, *S. rimosus*, *S. atrovirens*, *S. rochei*, and *S. viridis* also produce IAA that is responsible for improved seed germination, root elongation, and growth in different plants [48]. Hence, actinobacteria have the ability to boost the production and growth of plants by producing the phytohormone as shown in **Table 2**.

In indirect plant growth mechanism, actinobacteria also enhance the growth of

Actinobacteria synthesize many different extracellular enzymes that help to decompose material in soil. Some of these enzymes include xylanases, chitinases, hemicellulose, nucleases, amylases, lipases, glucanases, pectinase, proteinases, cellulases, ligninases, and keratinase. Mainly soil-living actinobacteria are saprophytic and play a central role in decomposition. Actinobacteria use this mixture of enzymes for decomposition against a variety of phytopathogens and majorly contribute to biocontrol potential by damaging cell wall of these pathogens. Cell wall of many bacteria and fungi is made up of polymers like glycan, cellulose,

**2.2 Indirect plant growth mechanism of actinobacteria**

plants like direct mechanism which is mentioned in **Figure 3**.

**392**

*Alleviation of abiotic stress in actinobacteria.*


### **Table 3.**

*Production of hydrolytic enzymes by actinobacteria.*

### *2.2.2 Actinobacteria's role as nutrient promoter*

As PGP, actinobacteria also act to raise the soil fertility by exhibiting various activities; hence, it is acknowledged as a main natural nutrient enhancer. Besides siderophore producer and phosphate solubilizer, actinobacteria also produce many kinds of enzymes like lipase, amylase, peroxidase, xylanase, chitinase, keratinase, pectinase, cellulase, and protease. This cocktail of enzymes helps to convert nutrients into simple mineral forms, and due to this nutrient cycling ability of actinobacteria, it is considered as an optimal candidate for natural fertilizers [38]. These actinobacteria also promote the soil metal-mobilizing ability like Fe, Zn, and Se, which ultimately increase the germination of seeds and plant growth. Current research has exposed that the root colonization of arbuscular mycorrhizal fungi increases growth of crop and zinc and iron content of chickpea grains [57]. Under greenhouse and field conditions, two PGPR, namely, *Mesorhizobium* sp. and *Pseudomonas* sp., also enhance the production and acquisition of Fe in chickpea [58]. Some previous studies elaborated that actinobacteria enhance plant growth in various crops like cereals, oilseeds, and leguminous by mobilizing the minerals. PGP *Streptomyces* were also observed to increase Fe and Zn quantity by 38% and 30%, respectively, in grains of chickpea [59].

### *2.2.3 Actinobacteria in bioremediation of metals*

Anthropogenic activities are the main cause of metal pollution of agricultural lands which led to a decrease in the fruitful agricultural cropland. As reported by the Environmental Protection Agency (EPA), nearly more than 40,000 contaminated sites are present in the United States. Furthermore, due to heavy metal contamination, 50,000 hectare of forest, 55,000 hectare of pasture, and 100,000 hectare of cropland have vanished, and these need retrieval process [60]. PGP like actinobacteria stay in metal-contaminated soil and increase the bioremediation process by extracting and solubilizing mineral. Different reactions like oxidation, metal reduction, and biosorption as well as several substances like organic acids, siderophores, polymeric substances, glycoprotein, and bio-surfactants are released by the microbes which aid in the metal-mobilizing property of these microbes. Many studies have been performed by researchers which demonstrated the metalmobilizing mechanism [61].

### *2.2.4 Reduction of plant-pathogen stress by actinobacteria*

Primarily, plants use beneficial microorganisms and plant integrated defense mechanism to protect themselves from phytopathogens [62]. Beneficial microorganisms (pathogen antagonistic) alleviate the pathogen stress in plants through different mechanisms like secretion of anti-pathogenic metabolites, competition for space, and nutrients [8]. Actinobacteria also play vital role in plant protection against plant pathogens utilizing nutrients, required by pathogens for growth. Meanwhile, actinobacteria produce different volatile compounds, antibiotics and cell wall degrading enzymes against phytopathogens [63]. Actinobacteria have been reported to produce various antifungal volatile organic compounds against fungal disease [64]. *Streptomyces* actinobacteria also produce many kinds of volatile compounds which have antifungal activities against *Rhizoctonia solani* and *Botrytis cinerea* [65]. Actinobacteria have the ability to produce different hydrolytic enzymes that degrade fungal and bacteria pathogens cell wall, so protect the plants against phytopathogens [66]. A nonspecific (indirect) mechanism has also been developed by plants which

**395**

**Table 4.**

*Actinobacteria: Potential Candidate as Plant Growth Promoters*

*Kennedia nigriscans*

*discolor*

*Ferula sinkiangensis*

*Metabolites produced by actinobacteria used to suppress disease.*

*Rhynchotechum ellipticum*

provide the long-term protection against a wide range of phytopathogens. PGP actinobacteria have played an important role in developing disease resistance in plants by inducing gene expression related to defense pathway [67]. Plants display two types of indirect or nonspecific defensive mechanism: the one involves salicylic acid (SA) signaling pathway and pathogenesis-related (PR) protein genes, called systemic acquired resistance (SAR), and the other is induced systemic resistance (ISR) that involves two pathways, ethylene (ET) and jasmonic acid (JA) signaling pathways [68]. A study described that *Streptomyces bikiniensis* HD-087 produces metabolites which cause systemic resistance and suppress the *Fusarium* wilt in cucumber raised by *F. oxysporum* f. sp. *cucumerinum* [69]. Some important metabolites which are synthesized by actinobacteria against phytopathogens are shown in **Table 4**.

**Host plant Metabolite Target pathogen(s) Reference**

Potato Geldanamycin *Streptomyces scabiei* [71]

*Pythium ultimum*, *Rhizoctonia solani*, *Phytophthora cinnamomi*

*gloeosporioides*

*Fusarium solani*, *Rhizoctonia solani*

*Fusarium oxysporum*, *Fusarium proliferatum*

*F. oxysporum* f. sp. *lycopersici*

*Colletotrichum* sp. *Curvularia lunata*

*cubense*

Rice Bonactin *Pyricularia oryzae* [81]

Coumarin *Alternaria alternate* [77]

*P. oryzae* [72]

*Botrytis cinerea* [75]

[70]

[74]

[76]

[78]

[79]

[80]

[53]

Munumbicins A, B, C

acid, phenylacetic acid, cervinomycin A1

Pepper 2-Furancarboxaldehyde *Colletotrichum* 

*Monstera* sp. Coronamycin *Pythium ultimum*,

and D

Rice 2,3-Dihydroxybenzoic

and A2

*S. malaysiensis* Wheat Malayamycin *Stagonospora nodorum* [73]

Saadamycin/5,7- Dimethoxy-4 pmethoxylphenyl coumarin

Ketoconazole, fluconazole, miconazole

Tomato Filipin III (purified antibiotic)

*Streptomyces* sp. G10 Banana *F. oxysporum* f. sp.

*Brassica rapa* Benzaldehyde, butanoic acid

*DOI: http://dx.doi.org/10.5772/intechopen.93272*

**Endophytic actinobacteria**

*Streptomyces* sp. NRRL 3052

*S. melanosporofaciens* EF-76 and FP-54

*Micromonospora* sp.

*S. cavourensis* subsp. *cavourensis* SY224

*Streptomyces* sp. MSU-2110

*Microbacterium* sp.

S4S17

*Streptomyces olivaceus*, *Streptomyces* sp. BPSA 121

*S. miharaensis* 100%

*Streptomyces* sp. AMA49

*Streptomyces angustmyceticus* NR8–2

*Streptomyces chryseus Potentilla* 

M39

### *Actinobacteria: Potential Candidate as Plant Growth Promoters DOI: http://dx.doi.org/10.5772/intechopen.93272*

*Plant Stress Physiology*

*2.2.2 Actinobacteria's role as nutrient promoter*

30%, respectively, in grains of chickpea [59].

*2.2.3 Actinobacteria in bioremediation of metals*

*2.2.4 Reduction of plant-pathogen stress by actinobacteria*

mobilizing mechanism [61].

As PGP, actinobacteria also act to raise the soil fertility by exhibiting various activities; hence, it is acknowledged as a main natural nutrient enhancer. Besides siderophore producer and phosphate solubilizer, actinobacteria also produce many kinds of enzymes like lipase, amylase, peroxidase, xylanase, chitinase, keratinase, pectinase, cellulase, and protease. This cocktail of enzymes helps to convert nutrients into simple mineral forms, and due to this nutrient cycling ability of actinobacteria, it is considered as an optimal candidate for natural fertilizers [38]. These actinobacteria also promote the soil metal-mobilizing ability like Fe, Zn, and Se, which ultimately increase the germination of seeds and plant growth. Current research has exposed that the root colonization of arbuscular mycorrhizal fungi increases growth of crop and zinc and iron content of chickpea grains [57]. Under greenhouse and field conditions, two PGPR, namely, *Mesorhizobium* sp. and *Pseudomonas* sp., also enhance the production and acquisition of Fe in chickpea [58]. Some previous studies elaborated that actinobacteria enhance plant growth in various crops like cereals, oilseeds, and leguminous by mobilizing the minerals. PGP *Streptomyces* were also observed to increase Fe and Zn quantity by 38% and

Anthropogenic activities are the main cause of metal pollution of agricultural lands which led to a decrease in the fruitful agricultural cropland. As reported by the Environmental Protection Agency (EPA), nearly more than 40,000 contaminated sites are present in the United States. Furthermore, due to heavy metal contamination, 50,000 hectare of forest, 55,000 hectare of pasture, and 100,000 hectare of cropland have vanished, and these need retrieval process [60]. PGP like actinobacteria stay in metal-contaminated soil and increase the bioremediation process by extracting and solubilizing mineral. Different reactions like oxidation, metal reduction, and biosorption as well as several substances like organic acids, siderophores, polymeric substances, glycoprotein, and bio-surfactants are released by the microbes which aid in the metal-mobilizing property of these microbes. Many studies have been performed by researchers which demonstrated the metal-

Primarily, plants use beneficial microorganisms and plant integrated defense mechanism to protect themselves from phytopathogens [62]. Beneficial microorganisms (pathogen antagonistic) alleviate the pathogen stress in plants through different mechanisms like secretion of anti-pathogenic metabolites, competition for space, and nutrients [8]. Actinobacteria also play vital role in plant protection against plant pathogens utilizing nutrients, required by pathogens for growth. Meanwhile, actinobacteria produce different volatile compounds, antibiotics and cell wall degrading enzymes against phytopathogens [63]. Actinobacteria have been reported to produce various antifungal volatile organic compounds against fungal disease [64]. *Streptomyces* actinobacteria also produce many kinds of volatile compounds which have antifungal activities against *Rhizoctonia solani* and *Botrytis cinerea* [65]. Actinobacteria have the ability to produce different hydrolytic enzymes that degrade fungal and bacteria pathogens cell wall, so protect the plants against phytopathogens [66]. A nonspecific (indirect) mechanism has also been developed by plants which

**394**

provide the long-term protection against a wide range of phytopathogens. PGP actinobacteria have played an important role in developing disease resistance in plants by inducing gene expression related to defense pathway [67]. Plants display two types of indirect or nonspecific defensive mechanism: the one involves salicylic acid (SA) signaling pathway and pathogenesis-related (PR) protein genes, called systemic acquired resistance (SAR), and the other is induced systemic resistance (ISR) that involves two pathways, ethylene (ET) and jasmonic acid (JA) signaling pathways [68]. A study described that *Streptomyces bikiniensis* HD-087 produces metabolites which cause systemic resistance and suppress the *Fusarium* wilt in cucumber raised by *F. oxysporum* f. sp. *cucumerinum* [69]. Some important metabolites which are synthesized by actinobacteria against phytopathogens are shown in **Table 4**.


### **Table 4.**

*Metabolites produced by actinobacteria used to suppress disease.*

### *2.2.5 Actinobacteria's role against stress*

Several abiotic stress factors including flooding, extreme temperatures, salinity, nutrient stress, drought, and metal stress impose a harmful impact on yields of the crop, as well as it also severally damaged the soil. As described by the Food and Agriculture Organization (FAO), if precautionary steps are not implemented, in the next 25 years 30% land degradation will happen due to abiotic stress factors, and this will rise to 50% in 2050 [16]. Strains of actinobacteria have better tolerance against abiotic stress factors like temperature, salinity, and metal stress, and inoculation of tolerant actinobacteria strain was noticed to encourage the plant growth. Useful effects of PGP *Streptomyces* sp. were observed on maize and wheat under saline conditions [82]. In another in vitro study, *Streptomyces* sp. PGPA39 inoculation showed similar results under saline conditions and ultimately increase the biomass and secondary growth of *Arabidopsis* seedlings (Palaniyandi et al. 2014). Actinobacteria stress tolerance potential was also studied in chickpea [49]. Treatment with *Streptomyces rochei* SM3 in chickpea under stress salt condition decreases mortality (48%) toward *Sclerotinia sclerotiorum* infection and increases biomass (20%). Physiological studies of SM3-treated plants showed increased accumulation of phenolics and proline along with increased catalase and phenylalanine ammonia lyase activities. Further genetic level investigation showed that ET-responsive ERF transcription factor (CaTF2) is triggered by strain SM3 under challenging conditions. Moreover, *Streptomyces padanus* tolerate drought situations by induction of increased osmotic pressure of plant cells and cell wall lignification. Co-inoculation of drought-tolerant *Streptomyces olivaceus* DE10 and *Streptomyces geysiriensis* DE27 endophytic actinobacteria verified the highest yield in wheat [83]. In response to stress, plants produce stress ethylene also known as ET which leads to premature plant death [84]. Microbes synthesize an enzyme known as 1-aminocyclopropane-1-carboxylate (ACC) deaminase that prevents the effect of ethylene due to ethylene precursor ACC conversion to ammonia and a-ketobutyrate which is shown in **Figure 3**. Currently effects of this enzyme on stress management are considered as a central phenomenon of PGP traits and are studied for the past two decades [85]. Some famous actinobacteria that are known to produce ACC deaminase include *Amycolatopsis*, *Streptomyces*, *Nocardia*, *Rhodococcus*, and *Mycobacterium* [86]. Many halo-tolerant actinobacteria having ACC deaminase are isolated from rhizosphere of naturally growing halophytic plants and soil of barren land [29].

### **3. Conclusion**

Production of food to fulfill the need of an increasing population and mimic the reliance on nonrenewable resources and also environmental effect is the greatest challenge of this century. To complete this challenge, the use of plant growth microbes such as actinobacteria is a good choice as an alternative tool for sustainable agriculture. Various studies highlight the abilities of actinobacteria as a plant growth promoter and their additive impact on plant growth and protection. Actinobacteria isolates have shown the multidimensional way to be effective on plant growth. They promote plant growth by involving various activities like production of phytohormones, siderophore production, solubilization of phosphate, fixation of nitrogen, complementing mycorrhizal fungi, and also balancing the ecology of the soil system. Additionally, many studies also have proven the potential of actinobacteria as a biocontrol agent. These characteristics of the actinobacteria group have proved them as inevitable tools for increasing productivity and quality in agriculture. Keeping in mind all these aspects, it is a need of time that we focus

**397**

**Author details**

Mohsin Khurshid1

Pakistan

Sumreen Hayat1,3, Asma Ashraf2

Muhammad Hussnain Siddique4

University, Faisalabad, Pakistan

provided the original work is properly cited.

Muhammad Asif Zahoor1

, Bilal Aslam1

, Aqsa Muzammil4

, Muhammad Waseem1

1 Department of Microbiology, Government College University, Faisalabad,

2 Department of Zoology, Government College University, Faisalabad, Pakistan

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

3 Department of Biotechnology, University of Sargodha, Sargodha, Pakistan

4 Department of Bioinformatics and Biotechnology, Government College

\*Address all correspondence to: saimamuzammil83@gmail.com

, Muhammad Afzal4

, Rizwan Asif<sup>1</sup>

, Muhammad Saqalein1

, Imran Riaz Malik<sup>3</sup>

,

and Sumera Sabir1

, Saima Muzammil1

,

\*,

*Actinobacteria: Potential Candidate as Plant Growth Promoters*

microbe might contribute to plant growth improvement.

on the use of actinobacteria as an alternative tool and reduce the use of harmful chemicals. The studies referred in this chapter also support the belief that the use of eco-friendly microorganisms and designing new formulations with cooperative

*DOI: http://dx.doi.org/10.5772/intechopen.93272*

*Actinobacteria: Potential Candidate as Plant Growth Promoters DOI: http://dx.doi.org/10.5772/intechopen.93272*

on the use of actinobacteria as an alternative tool and reduce the use of harmful chemicals. The studies referred in this chapter also support the belief that the use of eco-friendly microorganisms and designing new formulations with cooperative microbe might contribute to plant growth improvement.

## **Author details**

*Plant Stress Physiology*

*2.2.5 Actinobacteria's role against stress*

Several abiotic stress factors including flooding, extreme temperatures, salinity,

nutrient stress, drought, and metal stress impose a harmful impact on yields of the crop, as well as it also severally damaged the soil. As described by the Food and Agriculture Organization (FAO), if precautionary steps are not implemented, in the next 25 years 30% land degradation will happen due to abiotic stress factors, and this will rise to 50% in 2050 [16]. Strains of actinobacteria have better tolerance against abiotic stress factors like temperature, salinity, and metal stress, and inoculation of tolerant actinobacteria strain was noticed to encourage the plant growth. Useful effects of PGP *Streptomyces* sp. were observed on maize and wheat under saline conditions [82]. In another in vitro study, *Streptomyces* sp. PGPA39 inoculation showed similar results under saline conditions and ultimately increase the biomass and secondary growth of *Arabidopsis* seedlings (Palaniyandi et al. 2014). Actinobacteria stress tolerance potential was also studied in chickpea [49]. Treatment with *Streptomyces rochei* SM3 in chickpea under stress salt condition decreases mortality (48%) toward *Sclerotinia sclerotiorum* infection and increases biomass (20%). Physiological studies of SM3-treated plants showed increased accumulation of phenolics and proline along with increased catalase and phenylalanine ammonia lyase activities. Further genetic level investigation showed that ET-responsive ERF transcription factor (CaTF2) is triggered by strain SM3 under challenging conditions. Moreover, *Streptomyces padanus* tolerate drought situations by induction of increased osmotic pressure of plant cells and cell wall lignification. Co-inoculation of drought-tolerant *Streptomyces olivaceus* DE10 and *Streptomyces geysiriensis* DE27 endophytic actinobacteria verified the highest yield in wheat [83]. In response to stress, plants produce stress ethylene also known as ET which leads to premature plant death [84]. Microbes synthesize an enzyme known as 1-aminocyclopropane-1-carboxylate (ACC) deaminase that prevents the effect of ethylene due to ethylene precursor ACC conversion to ammonia and a-ketobutyrate which is shown in **Figure 3**. Currently effects of this enzyme on stress management are considered as a central phenomenon of PGP traits and are studied for the past two decades [85]. Some famous actinobacteria that are known to produce ACC deaminase include *Amycolatopsis*, *Streptomyces*, *Nocardia*, *Rhodococcus*, and *Mycobacterium* [86]. Many halo-tolerant actinobacteria having ACC deaminase are isolated from rhizosphere of naturally growing halophytic plants and soil of barren land [29].

Production of food to fulfill the need of an increasing population and mimic the reliance on nonrenewable resources and also environmental effect is the greatest challenge of this century. To complete this challenge, the use of plant growth microbes such as actinobacteria is a good choice as an alternative tool for sustainable agriculture. Various studies highlight the abilities of actinobacteria as a plant growth promoter and their additive impact on plant growth and protection. Actinobacteria isolates have shown the multidimensional way to be effective on plant growth. They promote plant growth by involving various activities like production of phytohormones, siderophore production, solubilization of phosphate, fixation of nitrogen, complementing mycorrhizal fungi, and also balancing the ecology of the soil system. Additionally, many studies also have proven the potential of actinobacteria as a biocontrol agent. These characteristics of the actinobacteria group have proved them as inevitable tools for increasing productivity and quality in agriculture. Keeping in mind all these aspects, it is a need of time that we focus

**396**

**3. Conclusion**

Sumreen Hayat1,3, Asma Ashraf2 , Bilal Aslam1 , Rizwan Asif<sup>1</sup> , Saima Muzammil1 \*, Muhammad Asif Zahoor1 , Muhammad Waseem1 , Imran Riaz Malik<sup>3</sup> , Mohsin Khurshid1 , Muhammad Afzal4 , Muhammad Saqalein1 , Muhammad Hussnain Siddique4 , Aqsa Muzammil4 and Sumera Sabir1

1 Department of Microbiology, Government College University, Faisalabad, Pakistan

2 Department of Zoology, Government College University, Faisalabad, Pakistan

3 Department of Biotechnology, University of Sargodha, Sargodha, Pakistan

4 Department of Bioinformatics and Biotechnology, Government College University, Faisalabad, Pakistan

\*Address all correspondence to: saimamuzammil83@gmail.com

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[17] Goudjal Y et al. Biocontrol of *Rhizoctonia solani* damping-off and promotion of tomato plant growth by endophytic actinomycetes isolated from native plants of *Algerian Sahara*. Microbiological Research. 2014;**169**(1):59-65

[18] Majeed A et al. Isolation and characterization of plant growthpromoting rhizobacteria from wheat rhizosphere and their effect on plant growth promotion. Frontiers in Microbiology. 2015;**6**:198

[19] Rungin S et al. Plant growth enhancing effects by a siderophoreproducing endophytic streptomycete isolated from a Thai jasmine rice plant (*Oryza sativa* L. cv. KDML105). Antonie Van Leeuwenhoek. 2012;**102**(3):463-472

[20] Aly MM, El Sayed H, Jastaniah SD. Synergistic effect between *Azotobacter vinelandii* and *Streptomyces* sp. isolated from saline soil on seed germination and growth of wheat plant. Journal of American Science. 2012;**8**(5):667-676

[21] Soe KM, Yamakawa T. Lowdensity co-inoculation of *Myanmar Bradyrhizobium yuanmingense* MAS34 and *Streptomyces griseoflavus* P4 to enhance symbiosis and seed yield in soybean varieties. American Journal of Plant Sciences. 2013;**4**(09):1879

[22] Shutsrirung A et al. Diversity of endophytic actinomycetes in mandarin grown in northern Thailand, their phytohormone production potential and plant growth promoting activity. Soil Science and Plant Nutrition. 2013;**59**(3):322-330

[23] Gopalakrishnan S et al. Plant growth-promoting activities of *Streptomyces* spp. in sorghum and rice. Springerplus. 2013;**2**(1):574

[24] Sziderics A et al. Bacterial endophytes contribute to abiotic stress adaptation in pepper plants (*Capsicum annuum* L.). Canadian Journal of Microbiology. 2007;**53**(11):1195-1202

[25] El-Tarabily KA, Nassar AH, Sivasithamparam K. Promotion of growth of bean (*Phaseolus vulgaris* L.) in a calcareous soil by a phosphatesolubilizing, rhizosphere-competent isolate of *Micromonospora endolithica*. Applied Soil Ecology. 2008;**39**(2):161-171

[26] Franco-Correa M et al. Evaluation of actinomycete strains for key traits related with plant growth promotion and mycorrhiza helping activities. Applied Soil Ecology. 2010;**45**(3):209-217

[27] Rashad FM et al. Isolation and characterization of multifunctional *Streptomyces* species with antimicrobial, nematicidal and phytohormone activities from marine environments in Egypt. Microbiological Research. 2015;**175**:34-47

[28] Aldesuquy H, Mansour F, Abo-Hamed S. Effect of the culture filtrates of *Streptomyces* on growth and productivity of wheat plants. Folia Microbiologica. 1998;**43**(5):465-470

[29] Siddikee MA et al. Isolation, characterization, and use for plant growth promotion under salt stress, of ACC deaminase-producing halotolerant bacteria derived from coastal soil. Journal of Microbiology and Biotechnology. 2010;**20**(11):1577-1584

[30] Nafis A et al. Actinobacteria from extreme niches in Morocco and their plant growth-promoting potentials. Diversity. 2019;**11**(8):139

[31] Amule F et al. Effect of actinobacterial, rhizobium and plant growth promoting rhizobacteria consortium inoculation on rhizosphere soil properties in soybean in

**398**

*Plant Stress Physiology*

Medical Ltd; 2017

Antibiotics. 2018;**7**(2):36

Research. 2016;**33**:299-306

[5] Cao L et al. Isolation and characterization of endophytic *Streptomyces* strains from surfacesterilized tomato *(Lycopersicon esculentum)* roots. Letters in Applied Microbiology. 2004;**39**(5):425-430

[6] El-Tarabily KA, Hardy GESJ, Sivasithamparam K. Performance of three endophytic actinomycetes in relation to plant growth promotion and biological control of *Pythium aphanidermatum*, a pathogen of cucumber under commercial field production conditions in the United Arab Emirates. European Journal of Plant Pathology. 2010;**128**(4):527-539

[7] Singh S, Gaur R. Evaluation of antagonistic and plant growth promoting activities of chitinolytic endophytic actinomycetes associated with medicinal plants against *Sclerotium rolfsii* in chickpea. Journal of Applied Microbiology. 2016;**121**(2):506-518

[8] Passari AK et al. Detection of biosynthetic gene and phytohormone

production by endophytic actinobacteria associated with

[4] Stamenov D et al. The use of *Streptomyces* isolate with plant growth promoting traits in the production of English ryegrass. Romanian Agricultural

[1] Lata RK, Divjot K, Nath YA.

ecological significance and

Endophytic microbiomes: Biodiversity,

*Solanum lycopersicum* and their plantgrowth-promoting effect. Research in Microbiology. 2016;**167**(8):692-705

[9] Passari AK et al. In vitro and in vivo plant growth promoting activities and DNA fingerprinting of antagonistic endophytic actinomycetes associates with medicinal plants. PLoS One.

2015;**10**(9):e0139468

Master's Theses; 2014

2004;**70**(1):66-68

[10] Goodman AA. Endophytic Actinomycetes as Potential Agents to Control Common Scab of Potatoes. Nothern Michigan University: NMU

[11] Shimizu M et al. Identification of endophytic *Streptomyces* sp. R-5 and analysis of its antimicrobial metabolites. Journal of General Plant Pathology.

[12] Shimizu M, Yazawa S, Ushijima Y. A promising strain of endophytic *Streptomyces* sp. for biological control of cucumber anthracnose. Journal of General

Plant Pathology. 2009;**75**(1):27-36

[13] Shivlata L, Satyanarayana T. Actinobacteria in agricultural and environmental sustainability. In: Agro-Environmental Sustainability. New Delhi, India: Springer; 2017. pp. 173-218

[14] Purushotham N et al. Community structure of endophytic actinobacteria in a New Zealand native medicinal plant *Pseudowintera colorata* (Horopito) and their influence on plant growth. Microbial Ecology. 2018;**76**(3):729-740

[15] Ting ASY, Hermanto A, Peh KL. Indigenous actinomycetes from empty fruit bunch compost of oil palm:

Evaluation on enzymatic and antagonistic properties. Biocatalysis and Agricultural Biotechnology. 2014;**3**(4):310-315

[16] Verma V, Singh S, Prakash S. Biocontrol and plant growth promotion

biotechnological applications. Research Journal of Biotechnology. 2019;**14**:10

[3] Binda E et al. Specificity of induction of glycopeptide antibiotic resistance in the producing actinomycetes.

[2] Chander J. Textbook of Medical Mycology. Chandigarh, India: JP

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[51] Yandigeri MS et al. Chitinolytic *Streptomyces* vinaceusdrappus S5MW2 isolated from Chilika lake, India enhances plant growth and biocontrol efficacy through chitin supplementation against *Rhizoctonia solani*. World Journal of Microbiology and Biotechnology. 2015;**31**(8):1217-1225

[52] Liotti RG, da Silva Figueiredo MI, Soares MA. *Streptomyces griseocarneus* R132 controls phytopathogens and promotes growth of pepper *(Capsicum annuum)*. Biological Control. 2019;**138**:104065

[53] Wonglom P et al. Streptomyces angustmyceticus NR8-2 as a potential microorganism for the biological control of leaf spots of Brassica rapa subsp. pekinensis caused by *Colletotrichum* sp. and *Curvularia lunata*. Biological Control. 2019;**138**:104046

[54] Saito A, Fujii T, Miyashita K. Distribution and evolution of chitinase genes in *Streptomyces* species: Involvement of gene-duplication and domain-deletion. Antonie Van Leeuwenhoek. 2003;**84**(1):7

[55] Khamna S, Yokota A, Peberdy JF, Lumyong S. Indole-3-acetic acid production by *Streptomyces* sp. isolated from some Thai medicinal plant rhizosphere soils. EurAsian Journal of BioSciences. 2010;**4**(1):23-32

[56] Marsh P, Wellington EMH. Molecular ecology of filamentous actinomycetes in soil. Molecular Ecology of Rhizosphere Microorganisms. Wellington, New Zealand: Wiley-VCH Verlag GmbH; 2007. pp. 133-149

[57] Pellegrino E, Bedini S. Enhancing ecosystem services in sustainable agriculture: Biofertilization and biofortification of chickpea (*Cicer arietinum* L.) by arbuscular mycorrhizal fungi. Soil Biology and Biochemistry. 2014;**68**:429-439

[58] Kaur N, Sharma P. Screening and characterization of native *Pseudomonas* sp. as plant growth promoting rhizobacteria in chickpea (*Cicer arietinum* L.) rhizosphere. African Journal of Microbiology Research. 2013;**7**(16):1465-1474

[59] Sathya A et al. Plant growthpromoting actinobacteria on chickpea seed mineral density: An upcoming complementary tool for sustainable biofortification strategy. Biotech. 2016;**6**(2):138

[60] Mahmood T. Phytoextraction of heavy metals-the process and scope for remediation of contaminated soils. Soil and Environment. 2010;**29**(2):91-109

[61] Sessitsch A et al. The role of plantassociated bacteria in the mobilization and phytoextraction of trace elements in contaminated soils. Soil Biology and Biochemistry. 2013;**60**:182-194

[62] Dangl JL, Jones JD. Plant pathogens and integrated defence responses to infection. Nature. 2001;**411**(6839):826

[63] de Jesus Sousa JA, Olivares FL. Plant growth promotion by streptomycetes: Ecophysiology, mechanisms and applications. Chemical and Biological Technologies in Agriculture. 2016;**3**(1):24

[64] Wang Z et al. Fumigant activity of volatiles from Streptomyces alboflavus TD-1 against *Fusarium moniliforme* Sheldon. Journal of Microbiology. 2013;**51**(4):477-483

[65] Wan M et al. Effect of volatile substances of Streptomyces platensis F-1 on control of plant fungal diseases. Biological Control. 2008;**46**(3):552-559

[66] Pal KK, Gardener BM. Biological Control of Plant Pathogens. Gujarat, India: The Plant Health Instructor; 2006

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[69] Zhao S, Du C-M, Tian C-Y. Suppression of *Fusarium oxysporum* and induced resistance of plants involved in the biocontrol of *Cucumber Fusarium* Wilt by *Streptomyces bikiniensis* HD-087. World Journal of Microbiology and Biotechnology. 2012;**28**(9):2919-2927

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[72] Ismet A et al. Production and chemical characterization of antifungal metabolites from *Micromonospora* sp. M39 isolated from mangrove Rhizosphere soil. World Journal of Microbiology and Biotechnology. 2004;**20**(5):523-528

[73] Li W et al. Malayamycin, a new streptomycete antifungal compound, specifically inhibits sporulation of *Stagonospora nodorum* (Berk) castell and Germano, the cause of wheat glume blotch disease. Pest Management Science. 2008;**64**(12):1294-1302

[74] Park S et al. Determination of polyphenol levels variation in *Capsicum annuum* L. cv. Chelsea (yellow bell pepper) infected by anthracnose (*Colletotrichum gloeosporioides*) using liquid chromatography-tandem mass spectrometry. Food Chemistry. 2012;**130**(4):981-985

[75] Zhao K et al. The diversity and anti-microbial activity of endophytic actinomycetes isolated from medicinal plants in *Panxi plateau*, China. Current Microbiology. 2011;**62**(1):182-190

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[79] Kim JD et al. Identification and biocontrol efficacy of *Streptomyces miharaensis* producing filipin III against *Fusarium* wilt. Journal of Basic Microbiology. 2012;**52**(2):150-159

[80] Getha K et al. Evaluation of *Streptomyces* sp. strain g10 for suppression of *Fusarium* wilt and rhizosphere colonization in pot-grown banana plantlets. Journal of Industrial

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*DOI: http://dx.doi.org/10.5772/intechopen.93272*

Microbiology and Biotechnology.

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[82] Sadeghi A et al. Plant growth promoting activity of an auxin and siderophore producing isolate of *Streptomyces* under saline soil conditions. World Journal of Microbiology and Biotechnology.

[83] Yandigeri MS et al. Drought-tolerant endophytic actinobacteria promote growth of wheat (*Triticum aestivum*) under water stress conditions. Plant Growth Regulation. 2012;**68**(3):411-420

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biosynthesis of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole-3-acetic acid (IAA) as endophytic preferential selection traits by rice plant seedlings. Journal of Plant Growth Regulation. 2014;**33**(3):654-670

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ecological significance. PLoS One.

2014;**9**(6):e99168

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2019;**13**(2):653-665

2012;**28**(4):1503-1509

pp. 365-385

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Microbiology and Biotechnology. 2005;**32**(1):24-32

*Plant Stress Physiology*

[67] Conn V, Walker A,

Springer; 2016. pp. 193-202

[69] Zhao S, Du C-M, Tian C-Y.

[65] Wan M et al. Effect of volatile substances of Streptomyces platensis F-1 on control of plant fungal diseases. Biological Control. 2008;**46**(3):552-559

specifically inhibits sporulation of *Stagonospora nodorum* (Berk) castell and Germano, the cause of wheat glume blotch disease. Pest Management

Science. 2008;**64**(12):1294-1302

[74] Park S et al. Determination of polyphenol levels variation in *Capsicum annuum* L. cv. Chelsea (yellow bell pepper) infected by anthracnose (*Colletotrichum gloeosporioides*) using liquid chromatography-tandem mass spectrometry. Food Chemistry.

[75] Zhao K et al. The diversity and anti-microbial activity of endophytic actinomycetes isolated from medicinal plants in *Panxi* 

on *Monstera* sp. Microbiology.

[77] Liu Y et al. Endophytic bacteria associated with endangered plant *Ferula sinkiangensis* KM Shen in an arid land: Diversity and plant growthpromoting traits. Journal of Arid Land.

[78] Passari AK et al. Insights into the functionality of endophytic actinobacteria with a focus on their biosynthetic potential and secondary metabolites production. Scientific

[79] Kim JD et al. Identification and biocontrol efficacy of *Streptomyces miharaensis* producing filipin III against *Fusarium* wilt. Journal of Basic Microbiology. 2012;**52**(2):150-159

[80] Getha K et al. Evaluation of *Streptomyces* sp. strain g10 for suppression of *Fusarium* wilt and rhizosphere colonization in pot-grown banana plantlets. Journal of Industrial

*plateau*, China. Current Microbiology.

[76] Ezra D et al. Coronamycins, peptide antibiotics produced by a verticillate *Streptomyces* sp.(MSU-2110) endophytic

2012;**130**(4):981-985

2011;**62**(1):182-190

2004;**150**(4):785-793

2017;**9**(3):432-445

Reports. 2017;**7**(1):11809

[66] Pal KK, Gardener BM. Biological Control of Plant Pathogens. Gujarat, India: The Plant Health Instructor; 2006

Franco C. Endophytic actinobacteria induce defense pathways in *Arabidopsis thaliana*. Molecular Plant-Microbe Interactions. 2008;**21**(2):208-218

[68] Senthilraja G. Induction of systemic resistance in crop plants against plant pathogens by plant growth-promoting actinomycetes. In: Plant Growth Promoting Actinobacteria. Singapore:

Suppression of *Fusarium oxysporum* and induced resistance of plants involved in the biocontrol of *Cucumber Fusarium* Wilt by *Streptomyces bikiniensis* HD-087. World Journal of Microbiology and Biotechnology. 2012;**28**(9):2919-2927

[70] Castillo UF et al. Munumbicins E-4 and E-5: Novel broad-spectrum antibiotics from *Streptomyces* NRRL 3052. FEMS Microbiology Letters.

[71] Clermont N et al. Effect of biopolymers on geldanamycin production and biocontrol ability of *Streptomyces melanosporofaciens* strain EF-76. Canadian Journal of Plant Pathology. 2010;**32**(4):481-489

[72] Ismet A et al. Production and chemical characterization of antifungal metabolites from *Micromonospora* sp. M39 isolated from mangrove Rhizosphere soil. World Journal of Microbiology and Biotechnology.

[73] Li W et al. Malayamycin, a new streptomycete antifungal compound,

2006;**255**(2):296-300

2004;**20**(5):523-528

**402**

[81] Buatong J et al. Antifungal metabolites from marine-derived *Streptomyces* sp. AMA49 against *Pyricularia oryzae*. Journal of Pure and Applied Microbiology. 2019;**13**(2):653-665

[82] Sadeghi A et al. Plant growth promoting activity of an auxin and siderophore producing isolate of *Streptomyces* under saline soil conditions. World Journal of Microbiology and Biotechnology. 2012;**28**(4):1503-1509

[83] Yandigeri MS et al. Drought-tolerant endophytic actinobacteria promote growth of wheat (*Triticum aestivum*) under water stress conditions. Plant Growth Regulation. 2012;**68**(3):411-420

[84] Saraf M, Jha CK, Patel D. The role of ACC deaminase producing PGPR in sustainable agriculture. In: Plant Growth and Health Promoting Bacteria. Berlin, Heidelberg: Springer; 2010. pp. 365-385

[85] Etesami H et al. Bacterial biosynthesis of 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indole-3-acetic acid (IAA) as endophytic preferential selection traits by rice plant seedlings. Journal of Plant Growth Regulation. 2014;**33**(3):654-670

[86] Nascimento FX et al. New insights into 1-aminocyclopropane-1-carboxylate (ACC) deaminase phylogeny, evolution and ecological significance. PLoS One. 2014;**9**(6):e99168

## *Edited by Akbar Hossain*

Due to the changing climate, food security for the increasing population has raised a great threat globally. Therefore, it is imperative to find alternate solutions for enhancing agricultural sustainability through plant stress physiology. The concept of plant stress physiology has been well-established over the past 60 years due to the increasing trends of environmental stress. Researchers have found that crop stress physiology has an association with two main areas, one is concerned with agronomy, the other concerned with plant breeding. The contents of the current book emphasize the integration of both breeding and agronomy strategies to ensure agricultural productivity and environmental safety under changing climate.

Published in London, UK © 2021 IntechOpen © Yousef Espanioly / Unsplash

Plant Stress Physiology

Plant Stress Physiology

*Edited by Akbar Hossain*