Assessing the in vitro zinc solubilization potential and improving sugarcane growth by inoculating Gluconacetobacter diazotrophicus

Abstract

Gluconacetobacter diazotrophicus is an endophytic diazotroph of sugarcane that has been reported to possess various plant growth-promoting characteristics. We have assessed the zinc (Zn) solubilization potential of G. diazotrophicus isolates under in vitro conditions (plate and broth assay) with different Zn compounds (ZnO, ZnCO3, and ZnSO4) and by the improvement of sugarcane growth following inoculation. The soluble Zn present in the culture broth by inductively coupled plasma–optical emission spectrophotometry. All five isolates solubilized the tested Zn compounds, although there were variations in the solubilization potentials, and effectively solubilized ZnO over ZnCO3 or ZnSO4. The solubilization might be due to the production of acids, since the pH of the culture broth shifted during the solubilization of Zn compounds. The nitrogenase activity of the G. diazotrophicus isolates ranged between 80.3 and 125.3 C2H4 h-1 vial-1 (ethylene), which was much more efficient than the nitrogenase activity in micropropagated plants. The GaD-1 isolate was found to be the most efficient isolate in terms of Zn compound solubilization and promotion of sugarcane plant growth when compared to other isolates. The application of G. diazotrophicus isolates with efficient nitrogenase activity in sugarcane production systems may possibly result in the reduction of chemical N fertilizer usage and the cost of sugarcane production; there may also be a considerable increase in production of sugarcane.