The efficacy of four potential phosphate solubilizing Enterobacter isolated from non-rhizospheric soil in Western ghat forest in India. Plant growth promoting ability of these isolates was evaluated in cowpea. All are gram negative, rod shaped, 0.8-1.6 mm in size, and psychrotrophic in nature, grow from 5 to 40°C (optimum temp. 28 ± 2°C). All isolates exhibits growth at a wide range of pH 6-12, optimum at pH 7.0 and tolerates up to 7% (w/v) salt concentration. 16S rRNA gene sequencing reveals the confirmation of isolates to Enterobacter aerogenes sp. (NII-0907 and NII-0929), Enterobacter cloacae subsp. cloacae sp. (NII-0931) and Enterobacter asburiae sp. (NII-0934) with which they share >99% sequence similarity. Under in vitro conditions, all the four isolates were found to produce indole acetic acid, P-solubilization and hydrogen cyanide. The P-solubilizing activity coincided with a concomitant decrease in pH of the medium (pH 7.0-<3.0). The plant growth promotion properties were demonstrated through a cow pea (Vigna unguiculata (L.) walp) based bioassay under greenhouse conditions. Although the bacterial inoculation was found to result in significant increment in root, shoot and biomass and it stimulated bacterial counts in the rhizosphere. Hence, these isolates can further formulated and used for field application.

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Aims:  To isolate plant growth‐promoting bacterium from Western Ghat forests in India. Methods and Results:  A Gram‐negative, rod shaped, cream white coloured strain Pantoea NII‐186 isolated from Western Ghat soil sample. The taxonomic position of the bacterium was confirmed by sequencing of 16S rRNA and phylogenetic analysis. A strain grew at a wide range of temperature ranging from 5–40°C, but optimum growth was observed at 28–30°C. It showed multiple plant growth‐promoting attributes such as phosphate solubilization activity, indole acetic acid (IAA) production, siderophore production and HCN production. It was able to solubilize (28 μg of Ca3PO4 ml−1 day−1), and produce IAA (59 μg) at 28°C. The solubilization of insoluble phosphate was associates with a drop in the pH of the culture medium. Pantoea sp. NII‐186 tolerate to different environmental stresses like 5–40°C, 0–7% salt concentration and 4–12 pH range. Conclusions:  The 16S rRNA gene sequence confirmed that the isolate NII‐186 was belongs to Pantoea genus and showed considerable differences in physiological properties with previously reported species of this genus. Isolate NII‐186 possessed multiple attributes of plant growth‐promoting activity. Significance and Impact of the Study:  Hence in the context it is proposed that Pantoea sp. NII‐186, could be deployed as an inoculant to attain the desired plant growth‐promoting activity in agricultural environment.

A potential bacterial strain designated as NII-0928 isolated from Western ghat forest soil with multiple plant growth promoting attributes, and it has been identified and characterized. Plant growth promoting traits were analyzed by determining the P-solubilization efficiency, Indole acetic acid production, HCN, siderophore production and growth in nitrogen free medium. It was able to solubilize phosphate (76.6 lg ml -1 ), and produce indole acetic acid (58.9 lg ml -1 ) at 28 ± 2°C. Qualitative detection of siderophore production and HCN were also observed. At 5°C it was found to express all the plant growth promotion attributes except HCN production. The ability to colonize roots is a sine qua non condition for a rhizobacteria to be considered a true plant growth-promoting rhizobacteria (PGPR). 16S rRNA gene sequencing reveals the identity of the isolate as Serratia nematodiphila with which it shares highest sequence similarity (99.4%). Seed bacterization with black pepper cuttings in greenhouse trials using Sand: Soil: FYM with three individual experimental sets with their respective control showed clearly the growth promoting activity. Hence, Serratia nematodiphila NII-0928 is a promising plant growth promoting isolate showing multiple PGPR attributes that can significantly influence black pepper cuttings. The result of this study provides a strong basis for further development of this strain as a bioinoculants to attain the desired plant growth promoting activity in black pepper growing fields.

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