Inhibitory Effect of Aqueous and Ethanolic Extracts of Neem Parts on Fungal Rot Disease of Solanum tuberosum.

Abstract

The processing and preservation of Irish potato tubers like many other crops has been affected by various pathogens like fungi (particularly storage rot) which causes a major constraint to Irish potato production in Nigeria resulting to enormous post-harvest spoilage. The inhibitory effect of aqueous and ethanolic extracts of neem leaves, stem bark and seeds on fungal rot disease of Solanum tuberosum (Irish potato) as an alternative treatment for fungal storage disease on Irish potato tubers cultivated in Nigeria has been determined in this study. Neem parts were harvested from Wukari, Nigeria and were processed for the experiment. Isolation of fungi and sub-culturing of the isolates was carried out to obtain pure culture. Pathogenicity study was carried out and effect of the plant extracts on mycelia growth of the test fungi was studied using the food poisoning techniques. The qualitative and quantitative phytochemical studies of the neem parts were carried out using standard methods. Qualitative phytochemical screening of the selected parts of neem plant showed the presence of alkaloids, glycoside, flavonoids, carbohydrates, reducing sugar, steroids, tannins and saponins. The quantitative test revealed that the percentage quantity of phytochemicals in these plant parts ranged from 10.17-23.88%. Effect of the extracts on the test organisms was significant (p<0.05). Ethanolic extract of the seed (ESE) exhibited the highest inhibitory effect on Aspergillus niger (88.37%) followed by aqueous extract of stem bark (ABE) (87.21%), while aqueous seed extract (ASE), ethanolic leaves extract (ELE), aqueous leaves extract (ALE) and ethanolic stem bark extract (EBE) exhibited inhibition of 81.78, 77.52, 72.87 and 39.53%, respectively. The inhibitory effect of EBE was significantly (p<0.05) lower than that of other extracts, while there was no significant difference in the inhibitory effects of ESE, ASE and ABE compared to ketoconazole on Aspergillus niger. The ethanolic extracts of the seed and leaves had 100% inhibitory effect on Fusarium oxyporium with 87.60% inhibition by aqueous extract of the leaves. The seed and the leaves ethanolic extracts exhibited the highest inhibitory effects on Pythium spp. and Fusarium oxyporium, while the aqueous leaves extract showed the least inhibition on Fusarium oxyporium. The plant extracts in this study were found to be very effective in inhibiting fungal mycelia growth and hence can be potentially effective for preservation during storage of Irish potatoes to minimize post-harvest lost.