ANTIFUNGAL ACTIVITY OF AQUEOUS AND ETHANOL EXTRACTS OF TROPICAL PLANTS AGAINST TOMATO FUNGAL PATHOGENES.

Several plant extracts may have a strong antifungal activity that can be exploited in the management of fungal diseases as an alternative to synthetic fungicides, the abuse of which may have consequences on the environment and health. Ethanol extracts (EE) and water extracts (WE) of three tropical plants, Stachytarpheta cayennensis (Verbenaceae), Oxalis barrelieri (Oxalidaceae) and Euphorbia hirta (Euphorbiaceae) were obtained and screened for their antifungal activity against three major phytopathogenic fungi of tomato: Fusarium sp., Alternaria sp. and Colletotrichum sp. The phytopathogenic fungi used across the experiments were isolated in Cameroon on severely affected tomatoes and their molecular identification and characterization is ongoing. The antifungal activity was checked in vitro on different media supplemented with different concentrations of the extracts. O. barrelieri EE, at the concentration of 25 mg/ml, inhibited the mycelium growth of Fusarium sp. by 26.8% and remarkably modified its morphology. WE and EE of the same O. barrelieri inhibited the mycelium growth of Colletotrichum sp. by 43.7% and 50.3% respectively, but showed no inhibition on Alternaria sp. The phytochemical analysis of these plant extracts revealed that EE of S. cayennensis was the richest in polyphenols and flavonoids. EE from O. barrelieri was particularly rich in alkaloids. The inhibitory effects on the phytopathogenic fungi were possibly related to the amount of polyphenols and alkaloids obtained through the extraction. Field experiments are being conducted on tomato to confirm the action of such extracts in vivo. These findings may contribute to develop new biofungicides to protect tomato from some fungal pathogens.