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 anti-fungal agents. The order of fungi-static activity (MIC) of the test anti-fungal 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 fungi-static 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. The cmbination of either Terbinafine HCl or Fluconazole or Benomyl with Sodium propionate displayed 8 synergistic anti-fungal activity with FICs of 0.098 to 0.140 against resistant Rhizomes stolonifer spores. The anti-fungal effects of the test anti-fungal agent and their combinations were shown to be more active at temperature of 450C. Combinations of the anti-fungal agents’ were effective at neutral pH with the exception of Terbinafine HCl and Sodium propionate that were only active at alkaline pH. The anti-fungal activities of the combined test anti-fungal agents were reduced when unboiled water sources were used as diluent. The in-vino anti fungal activity of the potential fungicides combination such as Benomyl/Fluconazole (1000/5,000μg/ml), Benomyl/Terbinafine HCl (1000/200μg/ml) and Benomyl/Sodium propionate (1000/15,000μg/ml) were observed to protect yam leaves from resistant Aspergillus Niger spores (2.0x108cfu/ml) on the farm in Zaria, Nigeria.

ISOLATION AND ANTIFUNGAL SUSCEPTIBILITIES OF PHYTOPATHOGENIC FUNGI FROM YAM LEAVES (Dioscorea rotundata and cayenesis) IN ZARIA, NIGERIA