Effectiveness of Massep (Ocimum gratissimum L.) essential oil and its nanoemulsion toward Sclerotium rolfsii, Phytophthora infestans and Alternaria solani, pathogens associated with tomato rot diseases

Abstract

This study aimed to evaluate the antimicrobial potential of Massep essential oil and its nanoemulsion against Sclerotium rolfsii, Phytophtora infestans and Alternaria solani, the main pathogens of tomato. Essential oil (EO) was extracted by hydrodistillation and their chemical composition analyzed by gas chromatography coupled with mass spectrometry (GC-MS). The nanoemulsion of EO was prepared by emulsification with Tween 80 as surfactant. The antimicrobial activity of EO and its nanoemulsion was evaluated in vitro on mycelial growth. In situ tests were performed with the pure EO and the formulation on tomato fruits by direct inoculation as preventive and curative tests. Results showed that, the yield of Massep EO was 0.40%. GC-SM analysis revealed 29 compounds with Thymol (35.15%), 3,7,7-trimethyl-1,2,3-Cycloheptatriene (13.09%), γ-Terpinene (10.08%), Eugenol (9.89%) and β –Thujene (3.43%) as major components. The Massep EO formulation was "milky-white" in appearance, stable, had pH 7.4, and the average particle size of 199 nm. In vitro, Massep EO nanoemulsion significantly inhibited the mycelial growth of Sclerotium rolfsii, Phytophtora infestans and Alternaria solani, more than pure Massep EO, based on minimal inhibitory concentration (MIC). In situ, Massep EO nanoemulsion was more active than pure EO. It reduced necrosis diameter at a rate of 100%, 100% and 71.81% (curative test) respectively, against S. rolfsii, P. infestans and A. solani, at concentrations of 1000 μl/l, 1200 μl/l and 2400 μl/l. Statistical analysis revealed that, EO nanoemulsion was significantly efficiency than Pure EO.