An Evaluation of the Chemical Compositions and Antifungal Activity of Ocimum gratissimum (Nchuanwu) Leaves against Some Plant Pathogens

Aim: This work was carried out to determine the chemical compositions of Ocimum gratissimum leaf (Fig. 1) using GC-MS and its antifungal potential against some plant pathogenic fungi.

Study Design: The study was designed to determine its chemical compositions by GC-MS and to test the inhibitory ability of the plant extract on plant pathogens.

Place and Duration of Study: Department of Chemistry, Alvan Ikoku Federal College of Education, Owerri and Department of Plant Science and Biotechnology, Imo State University, Owerri, Nigeria, between February to July 2017.

Methodology: The ethanol extract of the leaf of Ocimum gratissimum was evaluated using GC-MS to determine the chemical compositions of the plant. The identification of compounds was done by comparing spectrum of the unknown component with the spectrum of the known components stored in the NIST library. The essential oil of the plant was used to analyze the antifungal potential of the plant. This was done against some plant pathogenic fungi using disc diffusion method and MIC using broth micro dilution method.

Results: The GC-MS analysis revealed eight compounds (Fig. 2) with n- Hexadecanoic acid constituting the bulk of the oil (37.21%), followed by Oleic acid (25.38%) and Octadecanoic acid (16.19%). Other compounds present in the plant are Glycyl alcohol (2.47%), Methyl alpha –D- Glucopyranoside (8.33%), Tetradecanoic acid (5.77%), Palmitic amide (2.72%) and d-Glucose, 2,3- diethyl-4,5-dithioacetyl (1.93%). Ocimum gratissimum exhibited different degrees of antifungal activity against the mycelial growth of Aspergillus niger, Botryodiploidia theobromae, Rhizopus stolonifer, Penicillium expansum and Colletotrichum spp and Fusarium oxysporium. The maximum percentage degree inhibition of Ocimum gratissimum oil was observed on A. niger at different concentrations while the least inhibition was observed in Colletotrichum spp at different concentrations.

Analysis of some of the compounds found in Ocimum gratissimum such as Methyl alpha.-d-glucopyranoside, Oleic acid etc, reveals the rich pharmacological potential of this medicinal plant and the inhibitory potential of the plant against fungi justify the use of Ocimum gratissimum as a medicine traditionally.