Drought Predisposition to Cytospora Canker in Blue Spruce. Donald F. Schoeneweiss, Plant Pathologist, Illinois Natural History Survey, Champaign 61820. Plant Dis. 67:383-385. Accepted for publication 7 September 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-383.

Wound-inoculated stems of potted 5-yr-old Colorado blue spruce transplants subjected to drought stress became predisposed to attack by a conidial isolate of Cytospora kunzei. Bark cankers appeared on stems with a plant water potential of –20 and –30 bars. No cankers formed on unstressed stems or on stems of plants subjected to freezing stresses of –20 and –30 C. The pathogen colonized wood tissues of stressed and unstressed stems to the same extent but formed necrotic cankers only on the bark of drought-stressed plants. These results support the hypothesis that drought stress is the main factor in the predisposition of spruce to Cytospora canker. A selective medium was developed for isolation of C. kunzei.