Wild Poinsettia, African Ebony and Ashanti Pepper: Potential Biofungicides Against Phytophthora colocasiae Raciborski

Abstract

Plant extracts could be used as substitutes to synthetic pesticides in the management of fungi and other plant pathogens. The biofungicidal potential of aqueous extracts of wild poinsettia (Euphorbia heterophylla L., a weed) and African ebony (Diospyros crassiflora Hiern, a tree) leaves, and Ashanti pepper (Piper guineense Schumach., a spice) seeds was assessed against Phythophthora colocasiae in vitro. The plants were screened at the rates of 0 (control), 45 and 90%. The synthetic fungicide, mancozeb was included. Results indicated that all the plant extracts were fungitoxic and there was a variation in their potency. Also, the level of inhibition was higher at 90% concentration than at 45%. At 24-120 hours after exposure (HAE), a concentration of 90% Ashanti pepper consistently gave complete inhibition of the fungus similar to mancozeb. Complete inhibition of the fungus was also recorded for 45% Ashanti pepper at 24–48 HAE. At 45% concentration, the inhibitory levels of the extracts were Ashanti pepper: 89.6–100.0%, African ebony: 29.6–33.1 and wild poinsettia: <20.0%. At a concentration of 90%, the levels were Ashanti pepper: 100%, African ebony: 36.7–39.1% and wild poinsettia: 17.1–26.9%. The plant extracts showed promising activity against P. colocasiae and should be exploited for incorporation in management programmes for the fungus.