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Histology of Botryosphaeria Canker of Susceptible and Resistant Highbush Blueberries. R. D. Milholland, Associate Professor of Plant Pathology, North Carolina State University, Raleigh 27607. Phytopathology 60:70-74. Accepted for publication 28 July 1969. DOI: 10.1094/Phyto-60-70.

Botryosphaeria corticis penetrated highbush blueberry stems through open stomates 6 hr after inoculation. No evidence of direct penetration was obtained. Enlargement of the stem canker is due to increased cell numbers, and not to increased cell size. Hyphae were both intra- and intercellular, and ranged from 2-12 µ in diam. Mature perithecia were observed 1 year after infection. The cortex and phloem were completely disorganized in susceptible blueberry stems, but no disorganization of these tissues was observed in resistant stems. Xylem invasion was associated with the proliferation of the cortical parenchyma into xylem rays. Rays were larger in infected than in normal wood. Lesions in highly resistant cultivars result from cell division in the epidermis. No fruiting structures, pycnidia, or perithecia were observed in cankers of resistant stems 18 months after inoculation.