First Report of Stem Canker Caused by Botryosphaeria obtusa on Pistachio. Wijnand J. Swart, Senior Lecturer; Department of Plant Pathology, University of the Orange Free State, Bloemfontein 9300, South Africa . Wilma-Marie Botes, Graduate Student, Department of Plant Pathology, University of the Orange Free State, Bloemfontein 9300, South Africa. Plant Dis. 79:1036-1038. Accepted for publication 2 May 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1036.

Dieback of 3-year-old Pistacia vera L. trees, grafted onto P. atlantica rootstocks, was observed in trial plantings in the Prieska district of South Africa during the spring of 1992. Close examination of diseased trees revealed the presence of cankers on the lower part of the stem in the vicinity of the graft. Isolations from the margins of diseased tissue onto malt-extract agar consistently yielded black fungal colonies and pycnidia bearing mature conidia identified as belonging to the Sphaeropsis anamorph of Botryosphaeria obtusa. The fungus was shown to be highly virulent to three Pistacia species in pathogenicity tests in the field. Branches, measuring 5 mm in diameter, of P. atlantica, P. vera and P. integerrima developed mean cambial lesions measuring 53, 51, and 15 mm, respectively, 14 days after artificial inoculation with fungal mycelium. Wounding of branches prior to inoculation resulted in significantly larger cambial lesions. As far as we have been able to determine, there are no published reports of B. obtusa being associated with disease symptoms on cultivated pistachio trees.