In vitro assessment of fungicidal activity of Ageratum conyzoides and Cybopogon flexuosus weed extracts against some phytopathogenic fungi associated with fruit rot of water melon (Citrullus lunatus (Thunb.))

Abstract

The ethanolic extracts of Cybopogon flexuosus and Ageratum conyzoides were tested at concentrations of 20, 40, 60, 80, 100 and 120 mg/ml for their in vitro fungicidal activities against five phytopathogenic fungi isolated from diseased watermelon fruits. The pathogens were Fusarium verticillioides, Aspergillus flavus, Botryodiplodia theobromae, Curvularia lunata and Alternaria cucumeria – Amans as confirmed by pathogenicity tests. All isolated pathogenic fungi were significantly (p ≥ 0.05) highly pathogenic with the exception of A. cucumeria which had the least significant (p ≥ 0.05) pathogenicity. The inhibitory effects of the extracts increased significantly (p ≥ 0.05) with increase in concentrations. Some of the concentrations reduced the mycelial growth of the pathogens to a significant (p ≥ 0.05) level. Very strong fungicidal activity was produced by extracts of A. conyzoides at 100 mg/ml against all the fungi. The inhibitory effects of C. flexuosus extracts at 20, 40 and 60 mg/ml were greater than those of C. flexuosus on A. flavus, F. verticillioides and A. cucumeria. The results of the investigation indicated that plant extracts possess antifungal activity that can be exploited as an ideal treatment for future plant disease management in the control of rot of water melon.