Antifungal activity of plant extracts against Colletotrichum musae, the post harvest anthracnose pathogen of banana cv. Martaman

Purpose - The purpose of this paper was to determine the antifungal activities of different solvent extracts of common plants in vitro and in vivo against banana anthracnose fungus Colletotrichum musae (Berk& M.A. Curtis) Arx, and to investigate its effects on the pathogen and identify the bio active component(s). Design/methodology/approach - Extracts were obtained from leaves, tender shoots, rhizomes, bulbs, seeds and fruits of 42 naturally growing plant species following hot sequential extraction. Preliminary screening of the solvent extracts was done based on the inhibition of radial mycelial growth of C. musae following poison food technique and conidial germination inhibition by cavity slide technique. The selected extracts were assessed for their effect on harvested banana in reducing anthracnose during storage. The active components in the bio-active fractions of plant extract were identified by gas chromatography-mass spectroscopy. Findings - Methanol extracted a larger quantity of material (between 6.9 and 12.5 per cent) than hexane or chloroform, and all its extracts were active against the test pathogen with mycelial growth inhibition ranging from 13.70 to 88.89 per cent. Zingiber officinale rhizome extract as well as Polyalthia longifolia and Clerodendrum inerme leaf extracts exhibited more than 80 per cent inhibition of mycelial growth. Total inhibition of spore germination of C. musae was recorded in Z. officinale and P. longifolia extracts at 0.3 per cent w/v and 0.5 per cent w/v concentration, respectively, while only 68 per cent spore inhibition was recorded in C. inerme at 0.5 per cent w/v concentration. Of the three plant species, Z. officinale had the best antifungal activity (18.0 per cent disease incidence; 2.2 disease severity scale) when banana fruits were dipped in the extract at a concentration of 0.5 per cent w/v at 5 days of storage in ambient condition (80-82 per cent R.H., 27 +/- 1 degrees C). The bio-active compounds in the extract of Z. officinale were identified as alpha-curcumene and zingerone. Originality/value - Based on the antifungal activity, plant extract of Z. officinale can be used as an effective alternative to chemicals in controlling anthracnose pathogen in harvested banana.