Studies on the Screening of some Ghanaian Plants for Fungitoxic Activity against Five Fungal Pathogens

Abstract

The effect of the aqueous and methanol extracts of 12 Ghanaian plants belonging to 10 families on some aspects of the physiology of Sclerotium rolfsii, Helminthosporium sp., Aspergillus niger, A. flavus and Fusarium oxysporium were investigated in vitro in either liquid broth or agar medium amended with varying dilutions (undiluted, 1:1 - 1:5 v/v) of the extracts. Comparatively higher fungistasis against Sclerotium rolfsii and Helminthosporium sp. were found in both aqueous and methanol extracts of the dry leaves of Cassia alata, Abrus precatorius~i. ajid Desmodium triflorum. The remaining plants (Azadirachta indica, Alternanthera pungens, Boerhavia diffusa, Catharanthus roseus, Clausena anisata, Sida acuta, Mitragyna inermis, Oxalis corniculata and Zanthoxylum xanthoxyloides exerted minimal inhibitory effect on the test fungi. In most instances, inhibitory effect was gradually removed with dilution of the extract and the minimal effects was even severer on Helminthosporium sp than S. rolfsii. Growth of test fungi in liquid medium did not differ significantly (P s 0.05) in liquid and on agar. The test plants significantly depressed sclerotia production in vitro especially at higher concentration (1:1 and 1:2 v/v dilution) and the inhibitory effect was gradually removed with increasing dilution of the extracts. In some instances, the methanol extracts were more effective than the aqueous extracts. It required a minimum contact period of 3 0 minutes with the extract of C. alata to permantly impair vegetative growth of S. rolfsii. The longer the immersion period in the extracts of C. alata the severer the depression in the dry matter accummulation by the fungus. Both vegetative growth and sclerotia production by S. rolfsii was completely prevented when the mycelium was buried in methanol extract of C. alata for 48 h prior to transfer into extract-free medium. Vegetative growth of Helminthosporium sp. similarly treated was depressed by 20.49 percent. Further studies with the extracts of C. alata and A. precatorius showed that they could also variably depress vegetative growth of Aspergillus niger, A. flavus and Fusarium oxysporium. Practical implication of these findings are discussed and sequel studies suggested.