In vitro and in Situ Biofilm Formation and Plant Growth Promoting Potential of Rhizobia on Wheat Plant

Inthis study forty five isolates of rhizobia were isolated from root nodules of chickpea, pea, lentil and berseem. Thirty three percent isolates solubilized phosphate on Pikovskaya's medium. Quantitative analysis revealed solubilization in the range of 263–544 μg ml⁻¹. Indole acetic acid (IAA) production in the presence of 500 μg ml⁻¹ tryptophan was recorded in all isolates which varied from 98–280 μg ml⁻¹. Similarly, siderophore production was recorded in 22.2% isolates which ranged from 12.5–17.5 μg ml¹. Production of ammonia, hydrogen cyanide, exopolysaccharide and exoprotease activity was recorded in fair number of isolates. In vitro biofilm screening on 96 well microtiter plate and glass coverslip was performed. Twelve isolates form strong biofilm. Further inoculation of test isolates enhances seed germination and seedling growth of wheat and showed better rhizosphere colonization compared to control. Isolate showing enhanced rhizosphere colonization was subjected to biofilm formation assay on wheat seedling roots and visualized by scanning electron microscopy (SEM). The data revealed that isolate form biofilm on root of wheat seedlings. However, variation in seedling growth indicated that both biofilm formation and PGP traits of isolates influence the plant growth. Further experimentation is needed to know the mechanism of biofilm formation in promoting plant growth.