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.