Antifungal Activity of Cucumis metuliferus E.Mey. ex Naudin on Some Post-harvest Decay Fungi of String beans

Abstract

Crude aqueous and ethanolic extracts of Cucumis metuliferus fruit were screened for their phytochemical components which revealed the presence of alkaloids, tannins, flavonoids, saponins and cardiac glycosides. Steroids and anthraquinones were completely absent. The extracts were tested for their inhibitory effect on five fungal species (Aspergillus flavus, Fusarium oxysporum, Mucor sp., Penicillium citrinum and Rhizopus stolonifer) isolated from decayed Phaseolus vulgaris (String Bean). The different concentrations of the extract used ranged between 200-1000 mg/mL. Screening for antifungal activity using agar well diffusion method showed inhibition of all the test fungi especially at higher concentrations except for R. stolonifer that was not inhibited by the ethanolic extract. The highest effect of aqueous extract was observed in P. citrinum with inhibition zone of 34 mm at 1000 mg/mL, followed by Mucor sp. with inhibition zone of 32 mm, the least was recorded for F. oxysporum with zone diameter of 22 mm. The highest activity for ethanolic extract was recorded for A. niger with inhibition zone of 35 mm while the least was recorded for F. oxysporum with zone diameter of 18 mm. The Minimum Inhibitory Concentration (MIC) of the extracts was determined using agar dilution method. The MIC values of the extracts ranged between 12.5-25 mg/mL. The results showed A. niger and P. citrinum as the most sensitive and F. oxysporum as the least sensitive to the extract. The Minimum Fungicidal Concentration (MFC) of the extracts also ranged between 25-50 mg/mL indicating that the extracts are fungicidal at those concentrations.