Antifungal activity of nano emulsions of neem and citronella oils against phytopathogenic fungi, Rhizoctonia solani and Sclerotium rolfsii

Abstract Biopesticides are considered to be safe, target specific, biodegradable and eco-friendly. These, especially Azadirachta indica A. Juss. (neem) based biopesticides, are mainly used as emulsified concentrate (EC). There is growing interest in nano emulsions based on phytochemical mixtures due to their better efficacy compared to conventional biopesticides. A. indica seed oil and Cymbopogon nardus (L.) Rendle (Citronella) oil are known to have pest control properties. However, their utilization is often restricted due to relatively low water solubility. This drawback can be overcome by encapsulating oils in oil-in-water (O/W) emulsions or nano emulsions using low or high energy methods. In this study, various nano emulsions of crude neem and citronella oils with surfactants were developed and characterised by Dynamic Light Scattering (DLS) and Transmission Electron Microscope (TEM). Composition of various ingredients of nano emulsions was standardised. TEM study showed the spherical shape of neem and citronella oil nano emulsions. The average size of droplets of neem nano emulsion (NNE) with different percentage of citronella oil ranged from 11.23 ± 3.86 nm to 17.80 ± 4.52 nm while that of citronella nano emulsion (CNE) with different percentage of neem oil ranged from 8.12 ± 2.80 nm to 12.04 ± 3.74 nm. It was found that increase in surfactant ratio to neem oil or citronella oil decreases the size of droplets in nano emulsions. Further, in vitro antifungal study of against Rhizoctonia solani and Sclerotium rolfsii was carried out by poisoned food technique. Results showed that neem nano emulsion 10 (NNE10) and citronella nano emulsion 10 (CNE10) were most active against R. solani (ED 50 13.67 mg L −1 and 25.64 mg L −1 ) and S. rolfsii (ED 50 14.71 mg L −1 and 20.88 mg L −1 ). The standardization of the composition and development of citronella essential oil and neem oil based nano emulsions and their antifungal activity against these two fungi has been reported for the first time.