Evaluation of in vitro antifungal activity of selected plant extracts and antagonistic bacteria against butt rot disease of pineapple / Nurnadirah Mat Nawi

Butt rot disease caused by Thielaviopsis paradoxa is an important disease of pineapple planting material in Malaysia. Plant extracts and antagonistic bacteria are potential biocontrol agents as they are effective and safer than chemical controls. In this study, five groups of antagonistic bacteria were isolated from soil sampled from pineapple plants infected with butt rot disease and non-infected plants and four species of plant extracts, namely Leucaena leucocephala (leaf, bark) Eucalyptus camaldulensis (leaf), Alpinia galanga (rhizome) and Cinnamomum iners (bark) were tested against fungal pathogen. In vitro antifungal potential of both biocontrol agents were evaluated against T. paradoxa. Well diffusion method was used to evaluate antifungal activity of plant extracts, while dual culture method was used to test the antifungal activity of antagonistic bacteria. The result indicated that, among all the tested extracts, three ethanol extracts of L. leucocephala bark, E. camaldulensis leaf and A. galangdl rhizome and two chloroform extracts of L. leucocephala leaf and C. iners bark have showed their antifungal activities with 1.25%, 1.5%, 1.5%, 2.25% and 42.75% radial growth inhibition. Antagonistic bacteria, Bl showed the highest radial growth inhibition with 75%. Results also showed that B2, B3, B4 and B5 bacteria exhibited positive inhibition towards the pathogen with 70.75%, 57.25%, 56.25% and 47.50% radial growth inhibition, respectively. Microscopic observation of antifungal activities by plant extracts and antagonistic bacteria showed that the antifungal activities were via degradation, retardation, malformation, swelling, coagulation and breakage of the hyphae of T. paradoxa