In vitro control of Mycosphaerella arachidis Deighton, the early leaf spot disease pathogen of groundnut, by extracts from six medicinal plants

Abstract

Ground nut (Arachis hypogaea) is one of the most popular commercial crops in Nigeria. Its successful production has been drastically affected by early leaf spot disease caused by Mycosphaerella arachidis Deighton. In vitro control of the pathogen by six medicinal plants (Entada africana, Vitex doniana, Lawsonia inermis, Azadirachta indica, Acalypha hispida and Nuaclea latifolia) was assessed in this study. The extracts of the plants were prepared using cold and hot water and alcohol. The pathogen was isolated from ground nut infected with early leaf spot disease. The results revealed a significant difference (P < 0.05) in yield of extracts between cold water, hot water and alcohol extracts. A significant difference (P < 0.05) was observed in percentage concentrations of the various phytochemical constituents present in the extracts. Flavonoids percentage concentration was the highest (0.68-1.95%) followed by saponin (0.09-1.53%) in N. latifolia extracts. Steroiods had the lowest percentage concentrations (0.00-0.09%) followed by terpenoids (0.02-0.71%) and proanthocyannin (0.05-0.86%). N. latifolia extracts produced the highest percentage concentrations (0.07-1.95%) of all the phytochemicals followed by A. indica (0.05-1.64%) and lowest concentrations were obtained in A. hispidia (0.09-0.87%) and V. doniana (0.00-0.88%). The extracts inhibited spore germination and growth of M. arachidis. The inhibition by alcohol extracts was high and significantly different (P > 0.05) from cold and hot water extracts. Alcohol extract of L. inermis gave 100% spore germination inhibition followed by N. latifolia and A.indica with 97.75% and 85.60% inhibition, respectively. Therefore, field trials with these six medicinal plants on the control of early leaf spot disease of ground nut are recommended.