EFFICACY OF EXTRACTS OF WATER YAM (Dioscorea alata) AND AERIAL YAM (Dioscorea bulbifera) PEELS IN THE CONTROL OF WHITE YAM(Dioscorearotundata) ROT

Author: Opara Paschal Uche
Department: Botany
Affiliation: Nnamdi Azikiwe University Awka

The efficacy of ethanol and aqueous extracts of the peels of Dioscorea alata and Dioscorea bulbifera on the growth of pathogenic fungi of rotten white yam (Dioscorea rotundata) were investigated. Two different extract concentrations were derived from each yam peels used by blending 10g to 40g in 100ml of sterile distilled water and 70% ethanol. Standard fungicide was used as positive control. Pathogenicity test revealed that Sclerotia rolfsii, Botryodiplodia theobromae and Fusarium oxysporum induced rot in healthy white yams after seven days of inoculation with Botryodiplodia theobromae being the most virulent. Even though all the extracts showed varying degrees of antifungal effect, ethanol extract proved to be more potent. The efficacy of the extract varied with the extract concentration, solvent used for extraction and the test pathogenic fungi. Inhibition of fungal growth increased with a corresponding increase in concentration of the extracts. Dioscorea alata extracts had slightly, moderate and effective inhibition on mycelial growth of all the test fungi ranging from 13.04% to 94.44% while the extracts of Dioscorea bulbifera showed slightly, moderate and effective inhibition on the mycelia of the test fungi ranging from 6.66% to 88.88%. The most fungitoxic of all the extracts was observed with the 10% ethanol extract of Dioscorea alata which showed significant (P<0.01) inhibition on all the test fungal pathogens. Phytochemical screening of the extracts were conducted using different standard methods, this revealed the presence of saponins, alkaloids, tannins, phenols and flavonoids in both extracts but at different concentrations. The fungitoxic potentials of these extracts on white yam rots can proffer the need for genetical modification of the white yam which is more prone to rot and can also provide an alternative to synthetic fungicides since it is less expensive, environmental friendly and easy to prepare.

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