Plant-derived essential oils and extracts are known to be effective against many microorganisms. The essential oil obtained from fresh leaves of Ocimum gratissimum possessed promising antifungal activity against Penicillium digitatum. The antifungal potential of O. gratissimum essential oil can be markedly improved with the use of nanotechnology. O. gratissimum essential oil based nanoformulations were prepared using non-ionic surfactant and water by ultrasonication. The process was optimized for parameters such as surfactant concentration and sonication time to achieve minimum droplet diameter with high physical stability. Stable O. gratissimum essential oil nanoemulsions were obtained for 1:1 ratio (v/v) of essential oil and surfactant with mean droplet diameter of 259.4 nm for 10 min sonication time. Essential oil and all nanoemulsions were evaluated for their antifungal activity against P. digitatum of kinnow fruit by poisoned food technique. The nanoemulsion (1:1, 10 min) showed the highest growth inhibition (1 × 104 CFU ml−1, 96%) against P. digitatum followed by pure oil (13 × 104 CFU ml−1, 85%) on 15th day of incubation. Scanning electron and optical microscopy results further revealed stronger suppressive activity of O. gratissimum essential oil nanoemulsions for spore germination and hyphal elongation of P. digitatum than pure oil.

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