Temperature Effects on Germination of Uredospores of Melampsoridium betulinum and on Rust Development. H. L. Dooley, Research Plant Pathologist, USDA-ARS, Horticultural Crops Research Laboratory, Corvallis, OR 97330. Plant Dis. 68:686-688. Accepted for publication 5 February 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/PD-68-686.

Uredospores of Melampsoridium betulinum germinated in vitro at temperatures of 1–20 C, with an optimum at 10 C. Uredospores were killed when exposed to 30 C for 6 hr or 35 C for 30 min. Uredospores did not germinate during incubation for 24 hr at 25 C or 3 hr at 30 C but did germinate during a subsequent incubation for 24 hr at 10 C. Uredospores germinated within about 3 hr at optimum conditions. Uredia developed on detached leaf disks at 10–20 C and 100% relative humidity. Uredia developed on attached and detached leaves within 13–14 days at 12 C. The presence of uredospores beneath dormant bud scales and stem infection by M. betulinum are reported. Sixteen of 40 dormant European birch trees from a rust-infected nursery became infected with M. betulinum when vegetative growth was forced in February of the following year.