Chemical composition and antifungal activity of essential oils of Tagetes minuta (Asteraceae) against selected phytopathogenic fungi

Citation:
Gakuubi M, Wagacha J, Dossaji S, Wanzala W. "Chemical composition and antifungal activity of essential oils of Tagetes minuta (Asteraceae) against selected phytopathogenic fungi." American Journal of Essential Oils and Natural Products. 2016;4(3):16-26.

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.

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