Antifungal effect of aqueous and ethanolic extracts of neem leaves, stem bark and seeds on fungal rot diseases of yam and cocoyam

• Published in: Chemical and biological technologies in agriculture Vol. 5; no. 1; pp. 1 - 9
• Main Authors: Ezeonu, Chukwuma S., Imo, Chinedu, Agwaranze, Dawn I., Iruka, Assumpta, Joseph, Abraham
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 11.09.2018; Springer Nature B.V; SpringerOpen
• Subjects: Agriculture; Antifungal; Antifungal activity; Antiviral activity; Bark; Biomedical and Life Sciences; Dextrose; Fungi; Fungicides; Inhibition; Inoculation; Ketoconazole; Leaves; Life Sciences; Neem; Organic Chemistry; Pathogenicity; Pathogens; Plant Biochemistry; Plant extracts; Plant Physiology; Plants (botany); Post-harvest decay; Potatoes; Rhizopus stolonifer; Rot; Seeds; Soil Science & Conservation; Tubers; Fungi; Pathogenicity; Antifungal; Inhibition; Neem
• ISSN: 2196-5641; 2196-5641
• DOI: 10.1186/s40538-018-0130-3

Background Fungal rot diseases of white yam ( Discorea rotundata ) tubers and cocoyam ( Colocasia esculenta ) are the major post-harvest challenges in the availability of these root tubers. The use of biological extract of plants will prevent post-harvest losses without any negative health challenge. Methods Microwave-assisted method of extraction was used for both aqueous and ethanolic extracts of neem samples. Fungal-rotted yam and fungal-rotted cocoyam samples were collected, and fungi from them were cultured on potato dextrose agar (PDA). The same medium was used for subculturing until pure fungal isolates were obtained. Pathogenicity tests were carried out on the yam and cocoyam tubers by inoculating with isolated fungi. The neem extracts were integrated into the PDA and their antifungal effects examined. Results and discussion From the yam, Aspergillus ochareus , Sclerotium rolfsii and Lasidiodiplodia theobromae were isolated, while Aspergillus niger , Aspergillus oryzae and Rhizopus stolonifer were isolated from cocoyam samples. After 14 days of inoculation, isolated fungi were shown to be highly pathogenic except R. stolonifer and A. ochareus , which showed moderate pathogenicity. All the plant extracts showed antifungal activities at varied percentage mean zones of inhibition. The inhibition against fungal growth from the isolates of the rotted cocoyam gave mean inhibition between 39.53 ± 8.39% and 96.76 ± 1.60%. Except for ethanolic stem bark extract which gave 39.53 ± 8.39% limited zone of inhibition against A. niger growth, the rest of the extract exhibited good zones of inhibition against cocoyam-isolated fungi ranging between 72.87 ± 3.55 and 96.79 ± 1.60%. On fungal isolates from yam, the mean percentage zones of inhibition of all extracts of the neem plant parts showed more effectiveness than the positive control (Ketoconazole) against L. theobromae growth. Aqueous stem bark extract with 93.80 ± 1.78% zone of inhibition showed comparable effectiveness to the control (100% inhibition) against A. ochareus growth, while against S. rolfii growth, there was good inhibition by all the extracts though not to the extent as that of the control. Conclusion The fungitoxic potential of these plant extracts on rot-inducing fungi of stored yam and cocoyam suggests that the above extracts used in this study can be put to use by farmers as alternative to commercial/synthetic fungicides.