Abstract

A study to evaluate the antifungal activity of wood vinegar (pyrogenous acid) from maize cobs, acacia twigs, bean straw and an invasive tree species Prosopis juliflora against Ascochyta rabiei was conducted in vitro and at Egerton University Njoro, Kenya. The physicochemical characteristics of the different wood vinegar were also determined. Antifungal effects of wood vinegar were evaluated at different concentrations (0.5, 1, 1.5, 2, 2.5 and 3% v/v) using a Petri dish bioassay arranged in a completely randomized design. A fungicide (Metalaxy-M-40 g/kg) and water were used as positive and negative controls, respectively. All the wood vinegars had a smoky odor with brown/yellow coloration and an average density of 1.06 g/cm3. The wood vinegar from maize cobs showed a near acidic pH of 3.90 while bean straws showed a near neutral pH of 7.16. Prosopis and acacia showed moderate acidity of 5.10 and 5.43, respectively. The highest concentration of phenols was recorded in wood vinegar from maize cobs (4.56 mg/ml) followed by acacia (3.52 mg/ml). The results from the antifungal assay showed wood vinegar treatment significantly (P≤0.001) reduced A. rabiei mycelia growth at all tested concentrations when compared to the untreated control. The minimum inhibition concentration was 0.5% v/v for all the tested wood vinegars. The percent mycelia growth inhibition generally increased with increasing concentration except for maize cob which showed 99.33% and complete inhibition at 0.5 and 1.5 % v/v concentrations, respectively. Complete inhibition of the pathogen’s growth (100%) for all the wood vinegars tested was achieved at 2.5% v/v concentration. Plant-based wood vinegar has antifungal activity against A. rabiei.

Key words: Antifungal, Ascochyta rabiei, polyphenols, pyrogenous acid, wood vinegar.