Zinc-Solubilizing Bacteria-Mediated Enzymatic and Physiological Regulations Confer Zinc Biofortification in Chickpea (Cicer arietinum L.)

Zinc (Zn) deficiency is a widespread micro-nutritional disorder in humans. The present research aimed at investigating the enzymatic and physiological roles of zinc solubilizing bacteria (ZnSB) to solubilize the insoluble form of Zn and in increasing Zn content in chickpea. Bacterial strains (50) were isolated from chickpea rhizosphere and were screened in vitro for their Zn solubilizing efficiency by culturing on Tris-minimal agar medium supplemented with insoluble Zn compounds (ZnO and ZnCO3). Initially, six potential ZnSB (ZnSB7, Paenibacillus polymyxa; ZnSB11, Ochrobactrum intermedium; ZnSB13, Bacillus cereus; ZnSB21, Streptomyces; ZnSB24, Stenotrophomonas maltophilia; and ZnSB25, Arthrobacter globiformi) were selected based on Zn solubilization halo, Zn solubilization efficiency, and quantitative solubilized Zn. These strains were further assayed for higher phosphate solubilizing index, available phosphorus, and IAA production, and characterized by 16S rRNA gene sequence analysis. A pot experiment was then conducted to assess the effects of six promising ZnSB as seed inoculation on growth traits and Zn contents in chickpea. Seed inoculation of ZnSB13 exhibited maximum phosphatase, dehydrogenase, and microbial activities in plant rhizosphere, thereby, caused a maximum availability of soil Zn. The positive effects of ZnSB13 inoculation were also revealed on maintained higher net photosynthetic rate, transpiration rate, and stomatal conductance and water use efficiency that responsible for considerable increase in dry biomass, nodulation, and yield of chickpea. Furthermore, inoculation of ZnSB13 exhibited maximum increase in grain N, grain P, and Zn contents in root, shoot, and grains of chickpea. Thus, ZnSB inoculation could be an effective approach to solubilize the unavailable soil Zn, and making them valuable for improving Zn biofortification in chickpea.