Researchers have been generally unable to infect dogwood foliage (Cornus florida L.) with dogwood anthracnose (Discula destructiva Redlin) in artificial environments. We tested the influence of four factors on development of D. destructiva lesions in intact C. florida leaves wounded with a pin-prick device: (1) propagule (conidia or vegetative hyphae), (2) isolate origin (Catoctin Mountain, MD or Great Smoky Mountains National Park, TN), (3) controlled environment (growth room or air conditioned, humidified chamber in a greenhouse), and (4) period of time leaves were enclosed in humidified bags following inoculation. Of the manipulated factors, time spent in moistened bags and experimental environment were most important in determining lesion size. Lesions of similar size resulted from 0, 2 and 4 days in humidified bags, but leaves enclosed for 7 days had lesions over 5 times as large. Lesions that formed on trees in the greenhouse chamber were about 15 times larger than those in the growth room. Neither fungal propagule nor isolate origin affected lesion size. Based on this information, we have successfully infected both C. florida and Cornus kousa with D. destructiva in subsequent studies.
Special appreciation is extended to Dr. Arnold Saxton for statistical analysis and to Jenny Croker for assistance with graphics. This research was supported by special funding from the Tennessee Agricultural Experiment Station, a grant from The Horticultural Research Institute, Inc.,1250 I Street, N.W. Suite 500, Washington, DC 20005, and by USDA CSRS Special Grant No. 34241-5921.
2Graduate Research Assistant, Department of Entomology and Plant Pathology.
3Associate Professor, Department of Ornamental Horticulture and Landscape Design.
4Professor, Department of Plant Pathology, North Carolina State University.
5Associate Professor, Department of Entomology and Plant Pathology.