First Report of Botryosphaeria dothidea Causing Shoot Blight of Kiwifruit (Actinidia deliciosa) in Greece

In the spring of 2010, in commercial orchards located in the Prefecture of Pieria in northern Greece, wilted shoots of kiwifruit cv. Hayward were observed. Blighted shoots took on a distinct dark color. Isolations from the lower margins of the cankers were made by plating sodium-hypochlorite-treated shoot tissue sections of approximately 3 mm on acidified (2.5 ml of 85% lactic acid per liter of nutrient medium to create a pH = 3.5 after autoclaving) potato dextrose agar. Plates were incubated at 23°C for 5 days, and a fast-growing, mouse-gray colored fungus was consistently isolated from diseased stems. Identification of the pathogen was based on morphological characteristics and confirmed by using the four random amplified polymorphic DNA primers (K19 [CAC AGG CGG A], K20 [GTG TCG CGA G], R13 [GGA CGA CAA G], and R15 [GGA CAA CGA G], suggested by Ma et al. (2). This fungus formed darkly pigmented pycnidia (170 × 155 μm), while the conidia observed in these bodies were one-celled, hyaline, ellipsoidal to fusoid with distinctly truncate bases, and measured 10.9 to 21.55 × 3.25 to 10.10 μm. The pycnidia exuded conidia in white tendrils. Koch's postulates were completed in the laboratory by inoculating 20 segments (6 cm long and 1.5 to 2 cm in diameter) of 1-year-old woody shoots of kiwifruit cv. Hayward. Using a cork borer, a 7-mm-diameter wound was created in the middle of each shoot segment by removing the bark and a 6-mm-diameter agar plug bearing mycelia from a 15-day-old culture of B. dothidea was inserted into the wound. The wound was covered with petroleum jelly and wrapped with adhesive tape to prevent desiccation. Ten control segments were similarly wounded and inoculated with an agar disk without fungal mycelium. All inoculated and noninoculated shoot segments were incubated at 25°C in moist chambers, after which the resulting necrosis was recorded. Koch's postulates were satisfied after reisolating the fungus from inoculated shoots that developed symptoms similar to those observed on shoots collected from orchards. Although B. dothidea has been previously reported to cause dieback on kiwifruit in Japan (1), to our knowledge, this is the first report of the occurrence of B. dothidea on kiwifruit in Greece. This pathogen can cause a high level of shoot blights in diseased plants and presents a significant threat to the commercial kiwifruit production in Greece. References: (1) M. Kinugawa and T. Sato. Ann. Phytopathol. Soc. Jpn. 69:373, 2003. (2) Z. Ma et al. Phytopathology 91:665, 2001.