APS Abstract of Presentation

Identification and pathogenicity of Botryosphaeria species associated with avocado branch dieback and trunk canker in California
V. T. McDonald (1), S. C. Lynch (1), A. ESKALEN (1)
(1) University of California, Riverside, CA, USA
Phytopathology 99:S81

Species of Botryosphaeria are well known pathogens which cause canker and dieback in woody hosts. The objective of this study was to survey species diversity of Botryosphaeria associated with branch and trunk canker of avocado in California and to determine the pathogenicity of the species. Five symptomatic trees in each of six groves were chosen for study. Fungi were isolated from diseased tissues using potato dextrose agar amended with tetracycline (0.01%) (PDA-tet) from an average of 50 symptomatic branch and trunk canker samples per tree (250 samples per grove). Percent recovery of Botryosphaeria spp. based on morphological characters ranged from 40–100% in Riverside county, 42–53% inVentura county, 33% in Santa Barbara county and 60% in San Diego county. Molecular methods were used to identify species based on the analysis of the internal transcribed spacer region (ITS) of rDNA, and a partial sequence of the β-tubulin gene. Four different species of Botryosphaeria were identified: B. dothidea, B. lutea, B. parva and B. australis. Pathogenicity tests were performed by stem wound inoculations on 1-year-old cv. Hass seedlings. Plants were maintained in the greenhouse and, after six months, symptoms included internal vascular lesions extending from the wound site. Each species was consistently reisolated from inoculated plants. The results show that multiple species of Botryosphaeria are involved in the branch and trunk canker disease of California avocado.

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