298
C. Pandey et al.
including plant growth-promoting bacteria, plant health-promoting bacteria, bioinoculant, biofertilizers, biocontrol agents, etc. PGPRs generally represent a wide
range of root colonizing bacteria belonging to Azotobacter, Azospirillum, Bacillus,
Burkholderia, Rhizobium, Pseudomonas, Serratia, etc. Along with plant growth
promotion, they reforest eroded areas, restore the contaminated sites, and thereby
render a positive effect on the degraded soil ecosystem (Gupta et al. 2015). It
seems inevitable that fewer agrochemicals with their low dosages will be used
in the coming time and more emphasis would be put on the use of environmentally and biologically safe alternatives including the use of beneficial microbes.
PGPRs have been found successful in getting established in the soil ecosystem
due to their high adaptability in a wide variety of environments, faster growth rate,
and biochemical versatility to metabolize a wide range of natural and xenobiotic
compounds. Successful studies using PGPRs including genera Acinetobacter, Alcaligenes, Arthrobacter, Azospirillum, Azotobacter, Bacillus, Burkholderia, Caulobacter,
Chromobacterium, Enterobacter, Erwinia, Flavobacterium, Micrococcus, Rhizobium, Serratia, Xanthomonas, Proteus, and Pseudomonas on the growth enhancement of various crops have been achieved in laboratory and field conditions (Glick
1995; Gray and Smith 2005; Verma et al. 2010; Negi et al. 2011; Maheshwari et al.
2015; Agarwal et al. 2017b) in Table 13.2.
PGPRs produce growth hormones, enzymes, and other metabolites that facilitate
solubilization of soil nutrients (phosphate, nitrogen, potassium, etc.) and thereby
enhance nutrient uptake with subsequent augmentation of the plant growth (Baligar
et al. 2001; Mishra et al. 2009). The interaction between plant, soil, and microbes is
influenced by abiotic (physical, chemical) and biotic (soil biota) factors (Jackson and
Prat 1996; Putten et al. 2013). Abiotic factors such as temperature (low and high),
high salt, pH, soil fertility, moisture content have been reported to influence enzyme
activities nutrient, concentration (Chapin 1980), and nutrient uptake (Gavito et al.
2001) which have shown to affect plant growth directly or indirectly (Heinze et al.
2017). Plant growth-promoting bacteria secrete various phytohormones such as GA
(Bottini et al. 2004; Hayat et al. 2010), IAA (Spaepen et al. 2007), Cytokinin, Salicylic
acid (Jochum et al. 2019), abscisic acid (Cohen et al. 2015). Phytohormones like
auxins, cytokinins, and gibberellin production have been observed for the significant
enhancement of seedling parameters (Melnykova et al. 2013; Talboys et al. 2014).
The broad spectrum antagonistic activities of PGPRs are executed by secretion of
several metabolites including antibiotics (Guo et al. 2014; Lee et al. 2016), volatile
compound HCN (Khabbaz et al. 2015), siderophores (Kesaulya et al. 2018), enzymes
chitinase and β-1, 3-glucanase, etc. (Huang et al. 2005). These beneficial microbes
can easily be applied in different crops by seed, root treatments, foliar sprays, mixing
in soil or organic manure, etc., to various crop plants (Fig. 13.1). The demerits include
(i) requirements for long-term storage, and (ii) generally crop-specific or site-specific.
C. Pandey et al.
including plant growth-promoting bacteria, plant health-promoting bacteria, bioinoculant, biofertilizers, biocontrol agents, etc. PGPRs generally represent a wide
range of root colonizing bacteria belonging to Azotobacter, Azospirillum, Bacillus,
Burkholderia, Rhizobium, Pseudomonas, Serratia, etc. Along with plant growth
promotion, they reforest eroded areas, restore the contaminated sites, and thereby
render a positive effect on the degraded soil ecosystem (Gupta et al. 2015). It
seems inevitable that fewer agrochemicals with their low dosages will be used
in the coming time and more emphasis would be put on the use of environmentally and biologically safe alternatives including the use of beneficial microbes.
PGPRs have been found successful in getting established in the soil ecosystem
due to their high adaptability in a wide variety of environments, faster growth rate,
and biochemical versatility to metabolize a wide range of natural and xenobiotic
compounds. Successful studies using PGPRs including genera Acinetobacter, Alcaligenes, Arthrobacter, Azospirillum, Azotobacter, Bacillus, Burkholderia, Caulobacter,
Chromobacterium, Enterobacter, Erwinia, Flavobacterium, Micrococcus, Rhizobium, Serratia, Xanthomonas, Proteus, and Pseudomonas on the growth enhancement of various crops have been achieved in laboratory and field conditions (Glick
1995; Gray and Smith 2005; Verma et al. 2010; Negi et al. 2011; Maheshwari et al.
2015; Agarwal et al. 2017b) in Table 13.2.
PGPRs produce growth hormones, enzymes, and other metabolites that facilitate
solubilization of soil nutrients (phosphate, nitrogen, potassium, etc.) and thereby
enhance nutrient uptake with subsequent augmentation of the plant growth (Baligar
et al. 2001; Mishra et al. 2009). The interaction between plant, soil, and microbes is
influenced by abiotic (physical, chemical) and biotic (soil biota) factors (Jackson and
Prat 1996; Putten et al. 2013). Abiotic factors such as temperature (low and high),
high salt, pH, soil fertility, moisture content have been reported to influence enzyme
activities nutrient, concentration (Chapin 1980), and nutrient uptake (Gavito et al.
2001) which have shown to affect plant growth directly or indirectly (Heinze et al.
2017). Plant growth-promoting bacteria secrete various phytohormones such as GA
(Bottini et al. 2004; Hayat et al. 2010), IAA (Spaepen et al. 2007), Cytokinin, Salicylic
acid (Jochum et al. 2019), abscisic acid (Cohen et al. 2015). Phytohormones like
auxins, cytokinins, and gibberellin production have been observed for the significant
enhancement of seedling parameters (Melnykova et al. 2013; Talboys et al. 2014).
The broad spectrum antagonistic activities of PGPRs are executed by secretion of
several metabolites including antibiotics (Guo et al. 2014; Lee et al. 2016), volatile
compound HCN (Khabbaz et al. 2015), siderophores (Kesaulya et al. 2018), enzymes
chitinase and β-1, 3-glucanase, etc. (Huang et al. 2005). These beneficial microbes
can easily be applied in different crops by seed, root treatments, foliar sprays, mixing
in soil or organic manure, etc., to various crop plants (Fig. 13.1). The demerits include
(i) requirements for long-term storage, and (ii) generally crop-specific or site-specific.