Assessment of the Antifungal Activity and Phytochemical Composition of Hyptis Suaveolens L. (Bush Mint) Against Fungi Causing Watermelon Fruit Rot

Abstract

Watermelon (Citrullus lanatus) is an economically important fruit crop susceptible to post harvest fungal diseases. Hyptis suaveolens L. (Bush Mint) is a medicinal aromatic shrub renowned for its diverse bioactive secondary metabolites, and the present study investigated the phytochemical composition and antifungal potential of its aqueous and ethanolic leaf extracts against Aspergillus flavus, Aspergillus niger, Fusarium oxysporum, and Rhizopus oligosporus — major causative agents of watermelon fruit rot. Extraction was performed by the cold maceration method of Harborne (1998) with slight modifications; qualitative and quantitative phytochemical analyses were conducted using standard procedures; Gas Chromatography–Mass Spectrometry (GC-MS) was employed to characterize bioactive components; antifungal activity was evaluated by the agar well diffusion method (50–400 mg/mL); and the Minimum Inhibitory Concentration (MIC) was determined by broth microdilution in Sabouraud Dextrose Broth across serial two-fold dilutions of 6.25–400 mg/mL. Phytochemical screening confirmed alkaloids, flavonoids, saponins, tannins, terpenoids, and phenols, with the ethanolic extract showing significantly higher concentrations; GC-MS identified 45 compounds, with resorcinol (15.05%), squalene (13.72%), d,α-tocopherol (12.13%), 2,4-di-tert-butylphenol (5.49%), and phytol isomer (4.17%) as the most abundant; the ethanolic extract exhibited superior antifungal efficacy with larger inhibition zones, particularly against A. flavus, followed by A. niger, F. oxysporum, and R. oligosporus, with the lowest MIC (12.5 mg/mL) recorded against A. flavus, while the aqueous extract required up to 50 mg/mL. These findings underscore the significant antifungal potential of H. suaveolens and support its application as a natural botanical fungicide for managing post-harvest fungal diseases in watermelon fruits.