Prevalance of multifunctional Azospirillum formosense strains in the rhizosphere of pearl millet across diverse edaphoclimatic regions of India

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Research Articles | Published:

Print ISSN : 0970-4078.
Online ISSN : 2229-4473.
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Doi: 10.1007/s42535-022-00537-6
First Page: 1119
Last Page: 1129
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Keywords: Diazotrophs, Colonization, Root traits, Genus specific primers, Diversity


The present study aimed at selecting indigenous Azospirillum spp. strains exhibiting plant growth promoting traits and tolerance to osmotic stress, for their potential application as bioinoculants in rainfed pearl millet. Seventy-five putative Azospirillum spp. isolates were retrieved from the rhizosphere of pearl millet cultivated under diverse edaphoclimatic conditions of India using differential media. The isolates exhibited nitrogenase activity (range between 0.2 and 200 nmoles ethylene produced h− 1), indole acetic acid production (range between 2.5 and 28.3 µg ml− 1), siderophore production and mannitol tolerance (up to 1000 mM). The 16 S rRNA gene sequence (amplified using universal primers 8 F and 1492R) analysis with reference to NCBI nucleotide database revealed that majority of the isolates obtained from different locations exhibited maximum identity (93.31–99.32%) to A. formosense, whereas two isolates AIM1 and AIM45 exhibited maximum identity to A. soli (98.54% identity) and A. oryzae (93.86% identity), respectively. However, the homology below 97% indicated the possibility of novel strains/species among the isolates. Selected strains were evaluated by designing a vertical agar plate assembly (VAPA) for their effect on root traits and growth of pearl millet (RHB173) seedlings. Bacterial inoculation significantly improved plant biomass (shoot and root) and influenced root architecture (root branching and root hair density). Microscopic observations revealed extensive colonization on the root surface as well as in the endorhizosphere. The VAPA assay helped in selecting promising strains AIM19, AIM57, AIM80, AIM38 and AIM3 which were able to influence plant growth and root architecture, the trait helpful in survival under stressful conditions. The present study indicated the abundance of multifunctional A. formosense strains in the rhizosphere of pearl millet grown under diverse locations. Also, the VAPA assay demonstrated in the present study that it can be used for the screening of large number of isolates for early stage plant growth promotion studies.

Diazotrophs, Colonization, Root traits, Genus specific primers, Diversity

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Authors of this manuscript are thankful to ICAR-All India Coordinated Research Project on Pearl millet and Central Research Institute for Dryland Agriculture, Hyderabad for helping in the soil sample collection; and to Director, Indian Agricultural Research Institute for providing financial support to carry out the research work. Profuse thanks to Dr. Radha Prasanna, Dr. Sangeta Paul and especially Dr. Lata Nain of Division of Microbiology, Indian Agricultural Research Institute, for providing access to their lab facilities.

Author Information

Grover Minakshi
Division of Microbiology, Indian Agricultural Research Institute, New Delhi, India
Bana Ram Swaroop
Division of Agronomy, Indian Agricultural Research Institute, New Delhi, India

Bodhankar Shrey
Department of Agricultural Microbiology, Anurag University, Hyderabad, India