Chemical Composition And Antifungal Activity Of Essential Oils Of Tagetes Minuta (Asteraceae) Against Selected Phytopathogenic Fungi

Abstract

Over the years, management of plant pathogenic fungi has primarily relied on the use of synthetic chemical fungicides. However, in the recent past, exploration for biologically active compounds from plants with the aim of discovery and development of novel and eco-friendly biopesticides to combat current and emerging plant pathogenic fungi has received increased interest. This study aimed at extraction and characterization of Tagetes minuta essential oils (EOs) as well as evaluation of their antifungal activity against selected phytopathogenic fungi namely: Fusarium oxysporum, F. solani, Aspergillus flavus, A. parasiticus and A. niger. Essential oils were extracted using the steam distillation method in a modified Clevenger-type apparatus. The antifungal activity of the EOs was assessed by disc diffusion method while gas chromatography - mass spectrometry (GC/MS) was used for characterization of the chemical components of the EOs. Twenty compounds corresponding to 96% of the total essential oils and constituting a mixture of monoterpenes (70%) and sesquiterpenes (30%) were identified in the Eos. They included elixene and silphiperfol-6-ene, which are being reported for the first time in essential oils of Tagetes minuta. The EOs of T. minuta exhibited potent antifungal activity against the studied fungi with the highest growth inhibition observed in F. oxysporum and A. niger with mean inhibition zones of 28.7mm after five days of incubation. Four out of the five test fungi fell within the category of extremely sensitive (inhibition zone diameters ≥ 20mm) when subjected to the crude EOs. The minimum inhibitory concentrations (MICs) and minimum fungicidal concentrations (MFCs) of the EOs against the fungi were in the ranges of 24 - 95mg/mL and 24 - 190mg/mL, respectively. This study thus lays down significant groundwork for a more comprehensive study on the practical feasibility of using T. minuta EOs as possible alternative to synthetic fungicides in the management of economically important phytopathogenic fungi.