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Morphological and Cultural Characterization of Phytophthora colocasiae Isolates Collected from Taro Growing Areas of Southern Ethiopia

Zerhun Tomas, Elfinesh Shikur, Alemar Said

Leaf blight of taro caused by Phytophthora colocasiae has been responsible for the serious decline in yield of taro. In Ethiopia it has contributed to the decline in taro production but still farmers have not recognized taro leaf blight as a disease associating its symptom with a maturity stage of the crop and impact of heavy rain fall. Survey was carried out to isolate the pathogen from different taro growing areas of Southern Ethiopia to study if there is variation in morphological and cultural characteristics among isolates. Totally 27 farmers’ fields were surveyed and 15 P.colocasiae isolates were isolated and designated as A-O. The fifteen isolates were characterized based on morphological and cultural characteristics by observing under simple light microscope at a magnification of 40X. Studies on morphological characteristics of different isolates of Phytophthora colocasiae revealed that the mycelium was aseptate and stalked sporangia. Sporangia type for isolate A, B, D, E, G, I, L and M were Semi papillate whereas isolate C, F, H, J, K, N and O have papillate. Sporangia shape for isolate A, G, H, J, L, M and N were lemon, isolate B, C, F and O were Globose where as isolate D, E, I and K have Ovoid shaped sporangia. The color of colony is ranging from white to dull white, cottony to moderately cottony in texture and abundance of mycelium is profuse to slightly sparse growth on PDA plates. Differences were observed among the isolates with respect to growth rate per day, cardinal growth temperature response and virulence level. Growth rate of the isolates was between 5and 14 mm/day in diameter. The isolates responded well to the growth temperatures they exposed. There were significant differences among isolates in their growth temperature responses at 20°C, 28°C and 38°C.