First Report of Botryosphaeria dothidea and B. obtusa on Apple in Bolivia.

Abstract

Gala and Winter Banana apples are important commercial crops in Azurduy and Lima Bamba, which are located in the Department (state) of Chuquisaca, Bolivia. White or bot rot (causal agent Botryosphaeria dothidea (Moug.:Fr.) Ces. De. Not. [anamorph Fusicoccum aesculi Corda]) and black rot (causal agent B. obtusa (Schwein.) Shoemaker [anamorph Sphaeropsis malorum Berk.]) have not been reported previously from Bolivia. Both fungi were isolated from apple fruit and branch cankers in Azurduy, but only B. dothidea was isolated from rotted fruit and limb cankers in Lima Bamba. Both fungi also were isolated from rotted Gala and Winter Banana fruit purchased in the markets in Sucre, Bolivia. Symptoms on fruit consisted of light-to-dark brown lesions that ranged from 3- to 8-cm in diameter. Cankers on limbs were sunken and reddish brown and ranged from 2 to 25+ cm in length and 0.5 to 3 cm in diameter. Neither pathogen produced pycnidia in lesions on rotted fruit, but they often developed in branch cankers. Pseudothecia of B. dothidea and B. obtusa were not observed. Identification of both pathogens was based on descriptions of their anamorphic stages (1). To fulfill Koch's postulates, four healthy Gala apple fruit were inoculated with two isolates of each pathogen by wounding the opposite faces of surface-disinfected fruit with a 5-mm-diameter cork borer and inserting mycelial plugs of the pathogens. Plugs were obtained from the margins of cultures growing on potato dextrose agar (PDA). Wounds were made on the opposite sides of each fruit, a mycelial plug of one of the pathogens was inserted in one wound, and on the opposite side, a plug of sterile PDA was inserted as a control. Each plug containing fungal mycelium or sterile PDA was covered with a plug of trimmed apple tissue, and the apple fruit were incubated in a moist chamber at 17 to 20°C for 10 days. Six branches on two young apple trees growing outdoors in a nursery were inoculated in a similar manner with one isolate of each pathogen: bark was wounded with a 5-mm-diameter cork borer, and the wounded area was inoculated with a plug of PDA containing the pathogen or a plug of sterile PDA for the control. The inoculated sites were wrapped with masking tape to prevent dehydration. Within 10 days, all fruit wounds inoculated with isolates of each pathogen developed brown lesions up to 5 cm in diameter. Each pathogen was reisolated from tissues in which it had been inoculated, but not from any of the noninoculated control sites. Within 6 to 8 weeks, all but one wound on branches inoculated with each pathogen developed depressed canker lesions up to 2 cm in length. Each pathogen was reisolated from the canker produced by inoculation with that pathogen, but not from any of the control sites. Reference: (1) T. B. Sutton. White rot and black rot. Pages 16-20 in: Compendium of Apple and Pear Diseases, A. L. Jones and H. S. Aldwinckle, eds. The American Phytopathological Society, St. Paul, MN, 1991.