Black Dead Arm and Basal Canker of Vitis vinifera cv. Red Globe Caused by Botryosphaeria obtusa in Chile.

Several years ago, Vitis vinifera cv. Red Globe vines (over 6 years old), started to show disease symptoms approximately 10 weeks after bud break. Symptoms first appeared on the leaves at the base of the shoots and then spread to other leaves, continuing to appear throughout the growing season. Two forms of the disease (severe and mild) were observed, each case leading to premature leaf fall. The severe form was characterized by dieback of one or more shoots accompanied by leaf drop and shriveling and drying of fruit clusters. The mild form was characterized by wine-red spots on the leaf margins or the leaf blade, which coalesced to form large zones of necrosis between the veins and the margins of the leaf. Fruit clusters may wither. If the bark is scraped off, a brown streak, 1 to 2 cm wide, was often seen in the wood. The streaking began at the base of the affected shoot and extended upward to the ground level, eventually resulting in a basal canker. Botryosphaeria obtusa (Schwein.) Shoemaker (anamorph = Sphaeropsis malorum Berk.) was isolated from 86% of samples from vines that were 6 to 10 years old from 12 locations in IV, V, VI, and metropolitan regions of Chile. Isolations were made from brownstreaked wood. Isolates were identified on the basis of a previous description (1,2) and internal transcribed spacer (ITSI-5.8S-ITS2) rDNA sequences identical to those of B. obtusa (culture KJ9356, GenBank Accession No. AF027759). B. obtusa is established as one of the main fungi associated with black dead arm of grapevine (2,3). Pathogenicity tests were completed by inoculating approximately 20 μl of mycelial suspension via injection into the pith of 16 single-node, rooted cuttings of V. vinifera cv. Red Globe. Sixteen control cuttings were injected with an equal volume of sterile distilled water. Twenty weeks after inoculation, all B. obtusa-inoculated cuttings exhibited brown streaks in the wood extending 50 to 60 mm from the point of inoculation. The wood streaking observed in inoculated plants was identical to symptoms observed in naturally infected black dead arm vines in the vineyard. No symptoms were observed in the controls. B.obtusa was reisolated from the region of brown streaking in all the inoculated cuttings. B. obtusa was not isolated from the water-treated controls. To our knowledge, this is the first report of B. obtusa causing black dead arm and basal canker on Red Globe grapevine in Chile. The fungal isolates have been deposited in the plant pathology laboratory of the Sanidad Vegetal Department of Agronomy Faculty of the University of Chile under the name V. vinifera/B. obtusa from N 1 to 16. References: (1) G. Cristinzio. Inf. Fitopatol. 28:21, 1978. (2) P. Larignon and B. Dubos. Phytoma 538:26, 2001. (3) A. J. L. Phillips. J. Phytopathol. 146:327, 1998.