Zinc-Solubilization Potential of Putative Microorganisms Isolated from Tea [Camellia sinensis (L.) O. Kuntze] Rhizosphere

Background and Objective: Monocropping farming practice in North-eastern tea soils are major risk of zinc deficiency, leading to micronutrient malnutrition. Zinc solubilizing microorganisms (ZSMs) are important drivers in solubilization of insoluble Zn compounds, and consequently play an important role in soil fertility and nutrient allocation. The present study attemts to isolate, characterize and qualify the Zn-solubilizing microbes from tea rhizosphere. Materials and Methods: Using a culture-dependent approach, and dilution plate technique, the ZSMs were isolated and quantified in vitro from tea rhizosphere. Standard methodologies were used to determine the effectiveness of Zn solubilization. Results: 16 out of the 20 ZSM isolates were shown to have substantial halo zones. Bacteria accounted for 10 of the 16 ZSMs, whereas fungi for six. Modified Bunt and Rovira medium and 105 dilutions had the highest frequency of ZSM isolation (upto 6.9±0.7x105 cfu/g dry soil), followed by modified Pikovskaya agar (4.6±1.0x105 cfu/g dry soil). The Zn solubilisation index ranged from 125% to 325%. Several bacteria produced acids, as evidenced by a drop in the pH of the broth medium. When given ZnO as source of Zn, the strains produced indole-3-acetic acid (IAA) (up to 12.5 ppm by ZSB#09). The most common fungus genera were Aspergillus spp. and Trichoderma spp. Gram positive cocci were dominant among bacteria. Conclusion: As zinc deficiency is common in North-eastern tea soils, utilising the potential of ZSMs could lead to improve sustainability in Zn supplementation.