Abstract
Six microorganisms: four fungi—Aspergillus niger, Aspergillus flavus, Rhizopus stolonifera, Penicillium marneffei, two bacteria—Erwinia carotovora and Pseudomonas aeruginosa were isolated and identified from three rotten Dioscorea alata (water yam) varieties from two sites each in two local government areas of Benue State, Nigeria, in West Africa, between the months of May 2014 and May 2015. Pathogenicity test carried out using the microorganisms confirmed them to be the pathological agents of the rot. Antimicrobial activity test with aqueous extracts of nine plants: Terminalia catapa, Passiflora edulis, Daniella oliveri, Ceiba pentandra, Jatropha tanjorensis, Azadirachta indica, Carica papaya, Moringa oleifera, and Mangifera indica of fresh and dry material showed that three pathogens, Rhizopus stolonifera (fungi), Erwinia carotovora and Pseudomonas aeruginosa (bacteria) isolated were completely inhibited each by a plant. The result obtained shows that Passiflora edulis had the best antimicrobial activity for both fungi and bacteria; indeed it inhibited completely Rhizopus stolonifera which was stubborn with most of the other plants. Azadirachta indica, Carica papaya, Moringa oleifera, and Mangifera indica were also able to inhibit most of the fungi but not completely. Terminalia catapa and Jatropha tanjorensis were most effective against the bacteria. Erwinia carotovora was completely inhibited by Terminalia catapa and Pseudomonas aeruginosa was completely inhibited by Jatropha tanjorensis. Daniella oliveri and Ceiba pentandra had the least inhibition against the isolates. Generally, the fresh plant extract shows more activity as compared to the dry plant extract.
Highlights
Dioscorea alata (D. alata, water yam) belongs to the genus Dioscorea, family Dioscoreaceae [1] [2] and it ranks next to Dioscorea rotundata (D. rotundata, white yam) [2]-[5]
Four fungi; Aspergillus niger, Aspergillus flavus, Rhizopus stolonifera and Penicillium marneffei and two bacteria; Erwinia carotovora and Pseudomonas aeruginosa were isolated from the water yam samples (Table 1)
This study reveals the types of fungi and bacteria species associated with rot of water yam tubers in some parts of Benue State, Nigeria
Summary
Dioscorea alata (D. alata, water yam) belongs to the genus Dioscorea, family Dioscoreaceae [1] [2] and it ranks next to Dioscorea rotundata (D. rotundata, white yam) [2]-[5]. Harvested crops often show that the yield of the white yam is two thirds and water yam one third clearly showing that the yield of water yam is higher even though less fertilizer was applied. This fact has been verified by discussion with the local farmers and by personal farming experience. It is to be noted that some species of the family Dioscoreacea which D. alata belongs to have high phytochemicals which may be of great disease treatment value [11]; the phytochemicals in these species, like phytate, lectins, phenolic compounds, amylase inhibitors and saponins, are reported to reduce blood glucose, plasma cholesterol, triglycerides level and control cancer risks [11] [12]; others have a reasonable quantity of saponins and are used for medicinal purposes as a source of natural antibiotic used by the body to fight off infections and microbial invasion [13]
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