Rhizosphere associated bacteria and soil physicochemical properties of tea garden.

In the rhizosphere, plant-microbe associations play critical part in major ecosystem processes. The pHs of the collected rhizosphere soil were acidic (4.24 - 4.77) and favorable for the established tea orchards. Soil texture was either sandy clay loam or sandy loam in nature. Organic carbon of the samples ranged from 0.91 - 1.19%, depicting the soil falling in very low to low category due to monoculture of tea for a long time. Total nitrogen content of the soil samples ranged in between 0.10 and 0.13%. Moreover, Phosphorus and important metal ions viz. potassium, calcium and magnesium were measured. Mean heterotrophic bacterial load of the soil samples ranged from 1.59 ± 0.22 × 106 to 10.88 ± 2.31 × 106 cfu/g and from 1.58 ± 0.29 × 106 to 6.93 ± 0.79 × 106 cfu/g on NA and PYG, respectively. Maximum bacterial count on both media was observed in samples of Saloon Section Area plot while the lowest counts were found in samples of D1 Section plot. Sixteen bacterial isolates were selected and purified for identification, which was conducted by amplifying ∼ 600 bp fragments of 16S rDNA. All the isolates were Gram positive and rod shaped. Bacillus was found to be the dominant genus (63%) in the tea rhizosphere soil. Other isolates were identified as varied species of Lysinibacillus (19%), Paenibacillus (12%) and Brevibacterium (6%). A phylogenetic tree was generated which showed only one major cluster comprising of two sub-clusters grouping Paenibacillus sp. in one and Lysinibacillus along with Bacillus sp. in another. Present observation indicated that Bacillus sp. is a major organism and has a strong role in evolution among the tea rhizospheric bacteria.