ROS-mediated antifungal activity of Ocimum essential oil-loaded nanoemulsions against postharvest fungal pathogens of Kinnow

Abstract

Kinnow fruit is prone to fungal and microbial attacks, leading to significant postharvest losses during marketing and storage due to two most prominent fungal pathogens, Penicillium digitatum and P. italicum. Safer alternatives of synthetic fungicides are required for management of these pathogens. Essential oils (EO) with remarkable antimicrobial activities may offer an upcoming alternative, but the high volatility, thermal sensitivity, and hydrophobicity limit their commercial applications. In the current study, coarse and nanoemulsions (CEs and NEs) of the most potent Ocimum species were evaluated as novel coatings for Kinnow. In a screening in vitro study, the efficacy of Ocimum essential oil of three species against P. digitatum and P. italicum was assessed. The CEs and NEs (0.5%–0.3% concentrations) of Ocimum viride EO (OVEO, best screened EO) with three surfactants in 1:1 oil-surfactant proportion (OSP) were prepared. The NE formulated with 1% oil having OSP (1:1) sonicated for 10 min exhibited consistent stability till 1 month with mean droplet diameter of 180.2 nm, polydispersity index 0.328, ζ-potential (−22.58 mV) and pH of 7.84) exhibited complete inhibition of hyphal growth of test fungi at 500 mg L−1. The EO-NE treatment of the fungal hyphae led to enhanced generation of reactive oxygen species (ROS) manifested as hyphal distortion and suppression of spore germination as compared to EO. OVEO NEs may offer an ecofriendly alternate to synthetic analogues for postharvest management of Kinnow.