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Infection of Juniperus virginiana and J. scopulorum by Phomopsis juniperovora. Glenn W. Peterson, Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, Forest Service, USDA, Lincoln, Nebraska 68503; Phytopathology 63:246-251. Accepted for publication 20 August 1972. DOI: 10.1094/Phyto-63-246.

Nonwounded new foliage of Juniperus virginiana and J. scopulorum was highly susceptible to infection by Phomopsis juniperovora; lesions did not develop on old foliage. Infection occurred with 7 hr incubation at 100% relative humidity, 24 C. Infection occurred over the range 12 to 32 C; intensity was greater at 24 and 28 C. Symptoms, consisting of small, light-colored lesions, developed 3 to 5 days after inoculation. Disease development was enhanced by high postincubation temperatures (32 C). Pycnidia with viable spores developed 3 weeks after inoculation. Germination of spores, germ-tube development, and growth in culture were optimum near 24 C. Spores from tendrils exposed to high (43 C) and low temperatures (-22 C) still germinated. Spores that had been hydrated, then desiccated, subsequently caused infection when conditions became suitable. Light had no effect on spore germination, germ-tube development, growth of the fungus in culture, or infection.