Author: Okonkwo-Chukwuemeka Chidinma Juliana
Department: Botany
Affiliation: Nnamdi Azikiwe University Awka

Toxic effects of extracts of Zingiber officinale, Occimum gratissimum and Azadirachta indica on four rot fungi (Sclerotia rolfsii, Fusarium solani, Aspergillus niger and Penicillium oxalicum) of stored sweet potato tubers were studied in vitro using aqueous and ethanol extraction methods. Pathogenicity tests revealed that Fusarium solani, Aspergillus niger, Penicillum oxalicum and Sclerotia rolfsii induced rot in healthy sweet potato tubers 14 days after inoculation, with Aspergillus niger being the most virulent. Even though all the extracts showed varying degrees of antifungal activiy, ethanol extract proved to be more potent. The efficacy of the extract varied with the solvent of extraction, extract concentration and the test pathogens. Four different extract concentrations were obtained from each plant part by blending 0.5, 1.0, 1.5 and 2.0g in 10 ml of the solvents. Phytochemical screening of the plants was conducted using different standard methods. This revealed the presence of alkaloid, saponin, tannin, flavonoid, phenol and steroid in all the plants but at different concentrations. The antimycotic effect of the extracts showed that ethanol extract of Z. officinale and O. gratissimum had effective inhibition range (29.87 – 82.03%) on mycelial growth of all the test fungi, while ethanol extract of A. indica showed slight to moderate effective inhibition range (22.13% – 66.93%). Their corresponding aqueous extracts showed slight to moderate inhibition range (18.77 – 74.07%). Inhibition of fungal growth increased with increase in extract concentration. The inference of this study showed the potential antifungi activity of extracts of Z. officinale, A. indica and O. gratissimum on stored potato rot fungi.

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