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

Background and Objective: Monocropping farming practices in Northeastern tea soils are a major risk
of zinc deficiency, leading to micronutrient malnutrition. Zinc Solubilizing Microorganisms (ZSMs) are
important drivers in the solubilization of insoluble Zn compounds and consequently play an important
role in soil fertility and nutrient allocation. The present study attempts to isolate, characterize and qualify
the Zn-solubilizing microbes from the tea rhizosphere. Materials and Methods: Using a
culture-dependent approach and dilution plate technique, the ZSMs were isolated and quantified in vitro
from the tea rhizosphere. Standard methodologies were used to determine the effectiveness of Zn
solubilization. Results: The 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 (up to 6.9±0.7×105 CFU gG1 dry soil), followed
by modified Pikovskayas agar (4.6±1.0×105 CFU gG1 dry soil). The Zn solubilisation index ranged from
125-325%. Several bacteria-produced acids, as evidenced by a drop in the pH of the broth medium. When
given ZnO as the 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 Northeastern tea soils,
utilising the potential of ZSMs could lead to improve sustainability in Zn supplementation