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Ammonia, Siderophores, Ahemad et al., 2012a)

Exo-polysaccharides

Acinetobacter spp. IAA, Siderophores, (Rokhbakhsh-Zamin et al.,
Phosphate
2011)

Bradyrhizobium sp. IAA, Ammonia, HCN, (Ahemad et al., 2011;
Siderophores, Ahemad & Khan, 2011d,

Exo-polysaccharides 2011e; Ahemad et al.,

2012c)
Bacillus species PSB10 IAA, Siderophores, ( Wani et al., 2010)

Ammonia

HCN
Pseudomonas sp. Phoshate, IAA, HCN, (Tank et al., 2009)

Siderophore,

Through the direct mechanism, PGPR assist plants by providing the various compounds that

are generated by bacteria or enhancing the nutrients uptake from the ecosystem (Etesami et

al.,2020; Glick, 1995). The most frequent direct plant growth promotion mechanisms
comprise the nitrogen fixation (Machado et al., 2013), inorganic insoluble phosphate

solubilization (Goswami et al., 2019), production of siderophore (Yu et al., 2017) and

phytohormone secretion like gibberellins, auxins and cytokinin (Ghosh et al., 2015). Indirect
mechanisms of PGPR involve the induced systemic resistance against the phytopathogens

through the secretion of repressive substances and protect the host plant (Gupta et al., 2015).
Indirect mechanism of PGPR also includes the secretion of hydrolytic enzymes (chitinases,

proteases, cellulases, etc.) and antibiotics, production of EPS, production of volatiles
compound etc. (Bhattacharyya et al., 2012). Table 1.1 lists the various PGPR and their

mechanisms of action for plant growth promotion. Decent variety of microscopic organisms

have been utilized to improve the gracefully of supplements to crop plants like pulses, cereals
and oil seeds. For effective symbiotic nitrogen fixation with leguminous plants species of

Rhizobium (Rhizobium, Mesorhizobium, Sinorhizobium, Bradyrhizobium, Azorhizobium,
Burkholderia, Cupriavidas Ochrobacturm, Phyllobacterium, Herbspirillum, Shinella) have

been profitably used globaly (Bottomley et al., 1990). Non-symbiotic nitrogen fixing bacteria
such as Azatobactor, Bacillus, Clostridium, Enterobacter Alcaligenes, Azospirillum, and

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