Isolation and Characterization of Pink Pigmented Facultative Methylotrophic Bacteria: An in-Vitro Evaluation of the Isolates for Plant Growth Promotion on Rice

Author: G. Violet Virginia Joel, P.C. Latha, A. Vijaya Gopal and B. Sreedevi

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Abstract

A total of 50 PPFM’s were isolated from rhizosphere soil and phyllosphere of Pink Pigmented Facultative Methylotrophic (PPFM) isolates (IIRRSV22-1 to IIRRSV22-18 and M1) obtained mostly from the phyllosphere of rice plants collected from Telangana were screened for plant growth promoting traits and for tolerance towards abiotic stresses. All isolates were observed to produce indole acetic acid (IAA), while gibberellic acid (GA) production was detected in nine isolates, with the isolate IIRRSV22-5 producing the highest IAA and GA of 10.88 and 10.20 µg/ml of culture filtrate, respectively. Seven and sixteen isolates possessed the ability to solubilise phosphorus and zinc respectively, whereas potassium solubilization was observed only in one isolate (IIRRSV22-8). Isolates IIRRSV22-9 and IIRRSV22-5 recorded the highest solubilization index of 3.12 and 3.50 for phosphorus and zinc respectively. Isolate IIRRSV22-1 possessed the highest siderophore production index (3.42), while isolate IIRRSV22-5 was observed to grow more luxuriantly using ACC as the sole N source compared to other isolates. HCN production was not observed in any of the isolates. All isolates were tolerant to 2% NaCl, while 8 isolates (IIRRSV22-1,3,4,5,11,13,14 and M1) tolerated 3% NaCl concentration. When screened for moisture stress tolerance using PEG 6000 with IIRRSV22-4 isolate recording the highest growth. An in vitro germination assay was performed using all the isolates, in which rice seeds (DRR Dhan 46) inoculated with IIRRSV22-5 showed the highest significant increase in seed germination (100%), root length (12.47cm), shoot length (6.49cm) and seedling vigour index (1896) compared to control. The bacterial isolates were scored based on their efficiency to act as PGPR and for their competence to induce a beneficial interaction during in-vitro studies with rice. The total score secured by each isolate was computed as the sum of scores across all traits and the isolates with the highest scores were selected as the most promising PPFM. The five isolates with the highest scores were identified as Methylobacterium aquaticum, Methylobacterium phyllosphaerae, Methylobacterium radiotolerans, Methylobacterium fujisawaense and Methylobacterium sp. Alleviating the negative effects of abiotic stresses like drought, heat and salinity that are responsible for sharp decline in rice yields is a major challenge in the present climate change scenario. A promising eco-friendly strategy for increasing rice yields is the use of microorganisms to reduce abiotic stress on rice. Therefore, the current study has identified PPFM strains that have ability to promote plant growth which can be further used for the betterment of production and productivity of rice.

Keywords

Rice, Phyllosphere, Cytokinins, Pink pigmented facultative methylobacteria (PPFM), Plant growth promotion, Abiotic stress tolerance

Conclusion

PPFM isolates were screened PGP traits like phytohormone production, insoluble mineral solubilization, ACC deaminase enzyme activity and siderophore production. In addition, the abiotic stress tolerance ability of PPFM isolates under drought and salt stress conditions were also investigated. The PPFM isolates were also assessed for their ability to improve germination and seedling vigour of rice. Based on these investigations, the most promising isolates were identified as Methylobacterium aquaticum, Methylobacterium radiotolerans, Methylobacterium sp, Methylobacterium fujisawaense. The strains identified in this study seem to be ideal candidates for promotion as bio-inoculants, due to their multiple PGP traits, abiotic stress tolerance and ability to promote rice seedling growth and vigour.

References

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How to cite this article

G. Violet Virginia Joel, P.C. Latha, A. Vijaya Gopal and B. Sreedevi (2023). Isolation and Characterization of Pink Pigmented Facultative Methylotrophic Bacteria: An in-Vitro Evaluation of the Isolates for Plant Growth Promotion on Rice. Biological Forum – An International Journal, 15(2): 1167-1179.