Isolation and Antifungal Susceptibilities of Phytopathogenic Fungi from Yam Leaves (Dioscorea Rotundata And Cayenesis) in Zaria, Nigeria

Isolation and Antifungal Susceptibilities of Phytopathogenic Fungi from Yam Leaves (Dioscorea Rotundata And Cayenesis) in Zaria, Nigeria.

ABSTRACT  

Fungal attack of yams leaves has been reported to substantially result in low yam tuber yield.

This study was designed to isolate phytopathogenic fungi from yam leaves in Zaria, Nigeria, and to evaluate their susceptibilities Minimum Inhibitory Concentration (MIC) and Minimun Inhibitory Concentration (MFC) to some antifungal agents (Terbinafine; Fluconazole; Flucytosine; Benomyl and Sodium propionate).

The fungistatic activities of these chemical compounds alone and in combinations at varying pH, temperature and different water sources used as diluents were investigated.

Fourteen fungi species namely Aspergillus niger, Cladosporium sp, Aspergillus ostianus, Scopolarium sp, Aspergillus flavus, Rhizopus sp, Penicillium citrinum, Aspergillus wentii, Penicillium oxalicum, Aspergillus cervinus, Penicillium sp, Aspergillus fumigatus, Aspergillus oryzae and Rhizopus stolonifer were isolated from infected yam leaves in eleven farms in Zaria, Nigeria.

The MIC values varied significantly from one organism to another. Generally, Aspergillus niger, Penicillium citrinum, Aspergillus cervinus, and Rhizopus stolonifer were the most resistant to the test antifungal agents.

The order of fungistatic activity (MIC) of the test antifungal agents against resistant Rhizopus stolonifer spores was Flucytosine (200.00µg/ml) > Terbinafine HCl (250.00µg/ml) > Benomyl (500.00µg/ml) > Fluconazole (1000. 00µg/ml) > Sodium propionate (2500. 00µg/ml).

However the lethal activity profile was not the same with the fungistatic activity and the order of lethal activity (MFC) was Terbinafine HCl (500.00µg/ml) > Flucytosine (1600.00µg/ml) > Benomyl (2000.00µg/ml) = Fluconazole (2000. 00µg/ml) > Sodium propionate (5000. 00µg/ml).

The effect of fungicidal concentration of the test antifungal agent against viable test fungal spores at different time interval showed rapid sporicidal effects.  

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INTRODUCTION  

Yams (Dioscorea spp) belong to the Family Dioscoreceae, order Liliales, subclass lilidae, class liliopsida (monocotyledons), division magnoliophyta (seed plants), sub-kingdom spermatophyte (flowering plants), sub kingdom tracheobionta (vascular plants) and finally kingdom plantae (plants) (Coursey, 1967a’b; Okigbo and Ikendiugwu, 2000; Okigbo and Nmeka, 2005 and USDA 2009).

The cultivated yam species in Nigeria are D. rotundata (white yam), D. cayenesis (yellow yam), and D. alata, (water yam).

There are also species of wild yam growing in Nigeria whose tubers are collected for eating in times of food shortage such as D. dumtorum (Cluster, or bitter yam), D. esculenta (Loir bark Chinese yam) and D. bulbifera L. (aeria yam) (Adeniji, 1970; Okigbo, 2004).

Yams are valuable source of carbohydrate, minerals (calcium, phosphorus, iron) and vitamins (riboflavin, thiamine and vitamin B and C) to the people of tropical and sub-tropical Africa, central and South America, parts of Asia including parts of China, Malaysia, Japan and Oceania and the Caribbean Islands (Coursey, 1967a’b; Okigbo and Ikediugwu, 2000; Okigbo and Nmeka, 2005; Panneerselvam et al., 2007).

Some species of yam are used as pharmaceutical bases and the toxic bye products have been used for hunting and as insecticides 20 (Degras, 1993; Panneerselvam et al., 2007; Jaleel et al., 2007).

In addition, there are numerous medicinal values from yams, which have been used medically to treat diseases such as diabetes mellitus, to increase coronary flow and prevent hypercholesterolemia.

Some yam bye products have also been used in dermatology, gastroenterology and traditional human and veterinary gynaecology in Asia, Africa and America (Coursey, 1967a).

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