Characterization of fungal pathogens of yam (Dioscorea sp.) From seka chekoressa district, Jimma Zone, Southwestern Ethiopia

Abstract

In the present study, characterization of different fungal pathogens (Fusarium isolate (AUF1), Alternaria isolates (AUA1 and AUA2) and Verticillium isolates (AUV1 and AUV2) was done from infected yam leaves and tubers grown in Seka Chekoressa district, Jimma Zone, southwestern Ethiopia. The fungal isolates were identified to the genus level based on cultural and microscopic characteristics. Pathogenicity test was performed by inoculating apparently healthy yam leaves and tubers of which Fusarium AUF1 strain, Alternaria AUA1 strain and Verticillium AUV1 strain were the most virulent ones with 100% infection of leaves and tubers evident from the development of disease symptoms. Among the isolates, Fusarium AUF1 and Verticillium AUV1 displayed the maximum mycelial growth diameter of 90 mm on potato dextrose agar medium (PDA). All fungal pathogens showed maximum growth at 25°C with the exception of Alternaria AUA1 that achieved the same growth at 30°C. With regard to pH, the maximum dry mycelial weight was recorded at pH 6.0 from Alternaria AUF1 (624.5±4.0 mg), Alternaria AUA1 (693.9±3.3 mg) and Verticillium AUV2 (697.6±1.6 mg). However, Alternaria AUA2 and Verticillium AUV1 gave maximum dry mycelial weight of 356.4±1.1 mg and 693.4±4.9 mg at pH 7.0 and 5.0, respectively. Likewise, Fusarium AUF1 and Verticillium AUV1 grew best on dextrose containing medium; whereas Alternaria AUA1, Alternaria AUA2 and Verticillium AUV2 preferred maltose as the best carbon source for growth. Potassium nitrate was the best nitrogen source for all fungal isolates with the exception of Alternaria AUA2 which grew better on ammonium nitrate.

Keywords/phrases: Dioscorea species, Fungal isolates, Growth parameters, In vitro.

Ethiop. J. Biol. Sci. 16(2): 205–225, 2017