Study of the inhibitory effects of hydro–alcoholic extract and nanoemulsion essential oil of Khuzistani savory on local lesion induction by cucumber mosaic virus (CMV) on cowpea

Plant viruses are a limiting factor in agriculture. Natural compounds, especially herbal plant metabolites, have been considered to control viruses. In this regard, the effect of aqueous–ethanolic extract (50% water) and essential oil nanoemulsion of Satureja khuzistanica were investigated to reduce the infection of cucumber mosaic virus on the local lesion test plant of cowpea (Vigna unguiculata) in greenhouse conditions. The extract and essential oil nanoemulsion were applied in four concentrations of 0.5, 1, 2 and 4 percent (g/100 mL) and three different times including simultaneously, two hours before, and after inoculation of plant leaves with virus inoculum (concentration 2 mg/ml). The lowest number of local lesions was obtained by using 2 and 4% of hydro–ethanolic extract (by 66–78% disease reduction) and nanoemulsion of essential oil with a concentration of 2% (by 59% disease reduction), and two hours after inoculation with virus inoculum. The particle size of the nanoemulsion after preparation was 119.4 nm, which reached 232.8 nm after 60 days of storage, which indicates the good physical stability of the nanoemulsion. According to GC–MS analysis, the main constituents of essential oil were carvacrol (91.5%), para–cymene (1.5%), beta–caryophyllene (1.1%) and beta–pinene (1.1%). Nanoemulsion of this essential oil improved its efficiency to inhibit the cucumber mosaic virus on cowpea. This study is the first report of the antiviral effect of phytochemical compounds of Khuzistani savory to inhibit a plant virus.