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Genetic diversity and antagonistic activity of plant growth promoting bacteria, isolated from tea-rhizosphere: a culture dependent study

Udaya Kumar Vandana, Ankita Chopra, Amarendranath Choudhury, Dattatreya Adapa, Pranab Behari Mazumder

Microbial activity in root environment is responsible for plant nutrition, growth and defence. The objective of this study is to analyse the plant growth promoting and antagonistic activity rendered by the rhizospheric bacteria of tea plant. In this study, 292 bacterial isolates were screened for indole acetic acid (IAA) production, phosphate solubilisation, ammonia production, chitinase production and protease production. Among all the bacterial isolates, 58 isolates were able to elicit minimum four plant growth promoting rhizobacteria (PGPR) traits, which were further analysed quantitatively for hydrogen cyanide (HCN), siderophore production and antagonistic activity. Based on the plant growth promoting potential scores and principle component analysis, 12 samples were further screened for the study of salt tolerance and antifungal activity profile against tea fungal pathogens (Rhizoctonia solani, Fomes lamenensis, Corticium invisum). The identity the isolates was revealed by 16s rDNA sequence analysis. Six isolates (n63, k32, n61, 31k, n57, n56) showing efficient PGPR traits were evaluated for growth promotion studies on rice seedlings. Isolate n61 (Bacillus cereus) induced significant increase in root length (9.85 mm), shoot length (7.86 mm), germination percentage (92.44) and vigour index (1566.42) in rice seedlings. Fresh bio mass was significantly higher in 31k (Pseudomonas putida) (81.33 mg) followed by n61 (Bacillus cereus) (80.84 mg) and dry mass was higher in n63 (Bacillus pseudomycoides) (15.84 mg) followed by n61 (Bacillus cereus ) (15.82 mg) while compared with control and the other isolates selected for in vitro growth experiments. ANOVA analysis showed significant (P<0.05) increase compared with control, indicating that, bacterial isolates are potent for plant growth promotion and productivity.