White pines, especially young trees, and plants belonging to the genus Ribes currants and gooseberries are susceptible to the disease. The fungus is native to Europe and Asia, and white pines native to Europe and Asia are generally resistant to the disease, while those native to North America are more susceptible. Although WPBR is occasionally a severe foliar disease on Ribes plants, on white pines it is lethal if allowed to spread from an infected branch into the trunk. Distribution The fungus occurs throughout Europe and Asia at low levels wherever white pines occur, causing little damage to the species which have evolved alongside it. It was introduced accidentally to eastern North America early in the 20th Century, and soon spread across the range of Eastern White Pine, causing extensive mortality.
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White pines, especially young trees, and plants belonging to the genus Ribes currants and gooseberries are susceptible to the disease. The fungus is native to Europe and Asia, and white pines native to Europe and Asia are generally resistant to the disease, while those native to North America are more susceptible. Although WPBR is occasionally a severe foliar disease on Ribes plants, on white pines it is lethal if allowed to spread from an infected branch into the trunk. Distribution The fungus occurs throughout Europe and Asia at low levels wherever white pines occur, causing little damage to the species which have evolved alongside it.
It was introduced accidentally to eastern North America early in the 20th Century, and soon spread across the range of Eastern White Pine, causing extensive mortality.
By the s it had appeared in the Pacific Northwest, introduced accidentally on Eastern White Pine nursery stock. Resulting mortality in Western White Pine, Sugar Pine and Whitebark Pine has been even higher than in Eastern White Pine, though the spread of the fungus into southern California has been slowed by the hot dry summer climate there.
Symptoms On white pine, the initial symptoms appear in late summer or autumn as small, yellow spots on needles. The infection spreads down the needle and into the twig, where slight swelling and yellowing develops during the next growing season. Numerous pale yellow blisters called aecia may be as large as 3 mm across and break through the infected bark in mid-April to mid-May a year or more after the bark first becomes infected.
These blisters rupture and release large numbers of dry, yellow-orange spores figure 1. Blisters disappear after spore discharge and form again the next year. As the bark dries out it appears roughened.
The sporulation pattern continues over years until the stem is girdled. Figure 1. Close-up view of typical blisters aecia on white pine stem. Rodents frequently feed on rust-infected bark because of its high sugar content.
Bark injured by the rodents yields copious amounts of resin, often obscuring the typical symptoms of rust infection. On Ribes, the symptoms develop throughout the growing season and are comparatively mild. The lower leaf surface, when infected, becomes pale. This is followed within a few days by the development of tiny orange pimple-like fruiting bodies uredinia in which yellow-orange rust spores are produced.
These spores cause repeated new infections on Ribes leaves from May through late summer, when another spore-bearing structure of the rust fungus appears. This structure, called a telium, is a short, yellow-brown, hair-like filament figure 2. Large numbers of these filaments give the lower leaf surface a fuzzy brown appearance. Figure 2. Disease Cycle During moist weather in August and early September, after seasonally cool weather has prevailed for about 2 weeks, telia on leaves of Ribes plants produce spores that cause new infections on pine needles.
The rust fungus grows slowly within the pine needle and twig; aecia blisters first rupture the bark in April-May of the second or third growing season after a pine needle becomes infected. The spores from these blisters aeciospores cause new infections on the growing leaves of Ribes plants but are not capable of causing infections on pine. This alternation of host plants is essential for the perpetuation of the fungus; it cannot complete its life cycle on the pine or Ribes alone.
The pimple-like uredinia that develop on infected Ribes leaves produce orange spores urediniospores that cause new infections on Ribes leaves throughout the growing season. These spores, however, are not capable of causing infections on pines. The telia that develop on infected Ribes leaves in late summer produce spores called basidiospores that cause new infections on pines.
The infected pines provide a place where the rust fungus may safely overwinter; it cannot survive in the Ribes leaves or outside a living host plant.
However, f. Successful inoculations of Castilleja miniata using aeciospores from infected pines were obtained by Hiratsuka and Maruyama and Patton and Spear The latter also infected Pedicularis resupinata and P. However, Hunt did not obtain infection visible to the eye of Castilleja hispida or C. Hunt and Patton and Spear , inoculated Ribes species successfully. Hiratsuka and Maruyama reported telia on Castilleja stems, whereas Patton and Spear found extensive mycelia in leaves, but no spore production from any Castilleja, Pedicularis or Phaseolus plants. Yi and Kim successfully inoculated native Pedicularis and Ribes montigenum from Pinus koraensis, but not R.
EPPO Global Database
In the specific case of Cronartium ribicola, the aecial host of this pathogen is the white pine Pinus subgenus Strobus , family Pinaceae and the telial hosts are those of the genus Ribes , specifically currants and gooseberries. Species of both telial and aecial hosts have varying levels of resistance or immunity to infection. On the aecial host the first signs of C. Looking at the infected plant as a whole, the Pinus will appear chlorotic , and stunted with dead branches or tops that turn a bright red color.
According to Scharpf , C. In addition, it infects all currants and gooseberries Ribes spp. McDonald et al. A year effort to manage this disease was predicated in part on the premise that the pathogen utilizes only species of Ribes Grossulariaceae as alternate hosts on this continent.