Antifungal potentials of some botanicals on Sclerotium rolfsii schum., the causal pathogen of damping-off of Gmelina arborea Roxb. in Ibadan, Southwestern Nigeria

Abstract

Gmelina arborea (Gmelina) is a drought-tolerant tree species with rapid growth. It has excellent wood properties, and these have made this tree an emerging important plantation species. Pest and diseases are the major threats to plantations of this tree, especially at the nursery stage. Antifungal effects of some plant extracts, namely bitter leaf (Vernonia amygdalina L.) and neem (Azadirachta indica A. Juss) on the mycelia growth and sclerotium production of Athelia rolfsii, causal agent of damping-off and collar rot of Gmelina, were evaluated. Infected root samples were collected from 2-week-old G. arborea seedlings raised from seeds in a screenhouse. Isolations and identification of pathogens were performed following standard procedures. Pathogenicity screening of the isolate was carried out on G. arborea following Koch’s postulate. The test pathogen was inoculated on PDA (potato dextrose agar) medium containing extract on Petri plates and incubated at (28–32 °C) for 14 days. Soil treatment using the botanicals was used for the screenhouse examination. Observations on the mycelia growth and sclerotia production of A. rolfsii were recorded from 3 days after inoculation. Incidence of damping-off was recorded at 2 and 4 weeks after transplanting. A. rolfsii was pathogenic on G. arborea. The botanicals used in this study reduced the incidence of damping-off on Gmelina seedlings, mycelia growth and sclerotia production at both full- and half-strength concentrations. Neem seed extract gave a 100% mycelia inhibition. Bitter leaf extract reduced the radial growth significantly at both concentrations: half strength (72%) and full strength (80%). Sustainable approaches to plant pest and disease management will boost plant production and reduce environmental hazards due to misuse of synthetic agrochemicals. Intensive investigations into the use of botanicals such as neem and bitter leaf are recommended.