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Xanthomonas campestris Associated with Avocado Canker in California. Donald A. Cooksey, Associate Professor, Department of Plant Pathology, University of California, Riverside 92521. Howard D. Ohr, Hamid R. Azad, John A. Menge, and Lise Korsten. Extension Plant Pathologist, Staff Research Associate, and Professor, Department of Plant Pathology, University of California, Riverside 92521; and Department of Microbiology and Plant Pathology, University of Pretoria, South Africa. Plant Dis. 77:95-99. Accepted for publication 25 August 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0095.

Canker symptoms were observed on avocado trees in several groves in southern California. The symptoms varied from small, sunken, dark areas with watery, reddish brown tissue beneath the bark to large, watery areas up to 10 cm in diameter, with the bark split open and a white powdery exudate on the surface. Multiple cankers on trunks and branches were usually connected by reddish brown necrotic streaks beneath the bark and often in the wood. Yellow mucoid bacteria, identified as Xanthomonas campestris, were isolated from 25 canker samples from five counties. Inoculation of the bacteria to stems of avocado plants resulted in a spreading internal reddish brown necrosis, accompanied by multiplication of the bacterium. No symptoms were produced by inoculation of avocado leaves.