Bacillus mediated synthesis of nano silver aqua formulations and their effect on rice crop (Oryza sativa L.)

This study aims to biosynthesize PGPR (Plant Growth Promoting Rhizobacteria) mediated Silver Nanoparticles for further preparation of aqueous formulations and ultimately to check the impact of prepared formulations on Rice (Oryza sativa L.) through morphological, physiological and biochemical parameters. Antifungal activity of extract of PGPR strains was performed against phytopathogenic fungi: Magnoporthe grisea, Trychophyton ajelloi, Aspergillus niger, Alternaria solani, Rhizoctonia solani and Sclerotium rolfsii. We have procured five PGPR strains Bacillus subtilis, Bacillus siamensis, Bacillus amyloliquefaciens, Bacillus velezensis and Bacillus atrophaeus and the two most potent PGPR strains were selected based on the antifungal activity. B. amyloliquefaciens showed very strong inhibition activity against four pathogens (11.5 ± 0.95 mm against S. rolfsii, 9.5 ± 0.86 mm against A. niger, 9 ± 0.91 mm against M. grisea and 8.75 ± 1.31 mm against A. solani) whereas, B. velezensis showed very strong inhibition activity against three pathogens (12.25 ± 094 mm against S. rolfsii, 11.5 ± 0.28 mm against A. solani and 10 ± 0.28 mm against A. niger). Characterization of the nanoparticles by different techniques like UV-Vis (Ultraviolet–visible) Spectrometry, Fluorescence spectrometry, DLS (Dynamic Light Scattering), FESEM (Field Emission Scanning Electron Microscopy), FTIR (Fourier-transform infrared), XRD (X-Ray Diffraction), Raman spectrometry, EDX (Energy-dispersive X-ray Spectroscopy), XPS (X-ray photoelectron spectroscopy), TGA (Thermogravimetric analysis) and DSC (Differential Scanning Calorimetry) were performed to confirm the synthesis of spherical dispersed nanoparticles. Size of the Nanoparticles were 14.69 nm and 16.54 nm for B. amyloliquefaciens and B. velezensis respectively. Rice seeds were primed with different sets of prepared formulation and their effect was studied on morphological, physiological and biochemical traits of thirty days old plants. Consortium of Nano formulations took the lowest time to initiate seed germination (2.66 days), enhanced root length (4.8 cm), leaf length (12.16 cm), tiller no. (3), protein (603.52 µg/mL), and chlorophyll content (44.67 mg/g) in the plants, which were higher than all the other formulations. Highest antioxidant activity was shown in B. velezensis Nano treated plants (160.97 ± 18.21 µg/mL). At the applied concentration, the silver nanoparticles exerted no detectable toxicological effect on the bacterial strains and on the rice plants.