Includes bibliographical references.

Rhizoctonia solani Kühn is ubiquitous in its distribution worldwide and in India causing 8-50% yield losses to the farmers. It is very difficult to control both the mycelia and sclerotia of the pathogen with traditional chemical fungicides. The use of nano zinc loaded bioactive formulation provides an alternative way to manage the pathogen. Zinc is the fourth most important yield limiting nutrient and Indian soils are generally deficient in zinc content. Zinc oxide nanoparticles (ZnO NPs) are generally regarded as Generally Recognised as Safe (GRAS) materials due to their safe application and antimicrobial activity. The present study focused on the synthesis of nano zinc loaded bioactive formulation, study on the physiochemical properties by exploring the enzymatic activity, biosafety and phytotoxicity properties against rice cell suspension culture and the release efficiency against R. solani at different concentrations of microbe synthesized (green engineered) nano zinc loaded bioactive formulation ranging from 1, 5, 10, 20, 50, 100, 150 and 200 ppm. ZnO NPs was synthesized from Bacillus subtilis by adding zinc acetate dihydrate as a precursor and sodium borohydride as a reducing agent. Iturin A was extracted from PGPR species and purified. Gum arabic was used as a stable encapsulating agent of both ZnO NPs and iturin A. The resulting product was named as nano zinc loaded bioactive formulation and coded as En-ZnO-NP-PGPR-BF. The synthesized En-ZnO-NP-PGPR-BF has shown the best enzymatic activity at 200 ppm on superoxide dismutase (1.61 U/ml), catalase (2.97 U/ml) and malondialdehyde content (55.26 nmol/mg) and lowest in the control (-0.12 U/ml, 0.04 U/ml and -1.65 nmol/mg) respectively. The uptake rate of En-ZnO-NP-PGPR-BF was more in 200 ppm (96.79%) as compared to other concentrations. There was no effect of En-ZnO-NP-PGPR-BF on the morphology of rice cell suspension culture when observed under the compound microscope and SEM. The rice cells were actively proliferating and remained viable up to 200 ppm (98.05%) after confirming it with the MTT test. LDH test revealed negligible cytotoxicity of En-ZnO-NP-PGPR-BF on rice plant cells even in 200 ppm (3.14%). The anti-oxidant potential of En-ZnO-NP-PGPR-BF was similar in 200 ppm (93.43, 69.69%) in both DPPH and NO radical scavenging activity with the standard potential anti-oxidant L-Ascorbic acid (98.71, 62.33%) respectively. The release efficiency was found to be increasing after treating the rice seeds with En-ZnO-NP-PGPR-BF and placed in MS media. 200 ppm possessed the highest release efficiency after 2 hrs, 6 hrs, 12 hrs, 18 hrs and 24 hrs with 42.64, 53.64, 67.31, 79.33 and 91.50% lowest in the control with 1.36, 2.36, 3.16, 4.4 and 6.39%.