First report of bleeding canker caused by Phytophthora cactorum on horse chestnut in Turkey

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Abstract:

Bleeding canker on horse chestnut (Aesculus sp.), caused by Phytophthora cactorum (Lebert and Cohn) Schröeter previously has been reported from the United States and Europe (1). In August 2000, it was found for the first time in a park in Ankara Province, Turkey. Symptoms included sparse yellowish brown foliage with abnormally small leaves, and dark-stained spots or dark brown necrosis of the bark on the trunk and main branches, with or without a reddish black gummy exudate. P. cactorum was isolated from tissues taken from the margins of necrotic bark. Pure cultures were slightly radiate, fluffy but not dense, and had short aerial hyphae when grown on carrot agar, potato dextrose agar, or V8 agar. Sporangia were ovoid, strongly papillate, and averaged 35.6 μm in length and 26.8 μm in width (range: 24 to 55 μm × 19 to 40 μm). The isolates were homothallic with smooth-walled paragynous oogonia ranging from 23.5 to 34.5 μm in diameter. To satisfy Koch's postulates, mycelium of P. cactorum was placed under the bark of six branches of healthy horse chestnut. Noninoculated wounds served as controls. Four months later a reddish black gummy exudate was observed oozing from the inoculated wounds, and the bark tissue was necrotic for 3 to 4 cm around each infection. P. cactorum was successfully reisolated from the necrotic bark tissue. Control wounds remained healthy. To our knowledge, this is the first report of this disease on horse chestnut in Asia Minor.

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