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spruce broom rust
Spruce broom rust or yellow witches' broom rust is a fungal plant disease caused by the basidiomycete fungus known as ''Chrysomyxa arctosphyli''. It occurs exclusively in North America, with the most concentrated outbreaks occurring in northern Arizona and southern Colorado on blue and Engelmann spruce, as well as in Alaska on black and white spruce.〔Peterson, Roger S. Effects of Broom Rusts on Spruce and Fir. Vol. 7. Ogden, Utah, Intermountain Forest & Range Experiment Station: Forest Service, U.S. Dept. of Agriculture, 1963.〕 This disease alternates its life cycle between two hosts, with the spruce serving as the primary host and bearberry (also known as kinnickinnick) serving as the secondary or alternate host. The name for the disease comes from the distinctive “witches broom”, commonly yellow in color,〔Klingström, A., and G. Lundeberg. "Control of Lophodermium and Phacidium needle cast and Scleroderris canker in Pinus silvestris." European Journal of Forest Pathology 8.1 (1978): 20-25.〕 which forms on the spruce after young needles have been infected. Management must be carried out through physical or mechanical methods, such as the pruning of brooms or the removal of the secondary host from the area, because no chemical control measures (e.g. fungicides) have yet been determined to be economically effective. Generally, spruce broom rust is seen as a mostly cosmetic issue, and it is very rarely the direct cause of tree death; however, research has shown a reduction in overall productivity and health of infected trees, making it an important issue for logging and timber companies.
== Hosts ==
Since this pathogen is a heteroecious rust, ''C. arctostaphyli'' has a primary and an alternate host upon which it produces different fruiting structures and different spores unique to each structure. As implied in the disease name, spruce broom rust mainly affects four spruce species: white (''Picea glauca''), black (''Picea mariana'') Engelmann (''Picea engelmannii'') and Colorado blue (''Picea pungens'').〔Broom Rusts of Spruce and Fir. US Forest Service Dept. of Agriculture: Rocky Mountain Region.〕 The alternate host is bearberry, which can be any of three species in the genus ''Arctostaphylos''.〔 This host is also sometimes referred to as kinnikinnick, which is the Native American name for common bearberry (''Arctostaphylos uva-ursi''), which is in the family ''Ericaceae''. The plant is named for the red edible berries it produces, which are a favorite food of bears when they can get them. They follow a similar life cycle to spruce, as they are both evergreens.〔Cameron, Ward (2005). Mountain Nature Field Guide.〕 There is also another far less common, yet still viable alternate host, manzanita (''Arctostaphylos spp''.).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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