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   Cronartium ribicola (fungus)
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      Symptoms of Cronartium ribicola (Photo: Joseph O   Cronartium ribicola causes orange or yellow discoloration of thin bark of young trees (Photo: USDA Forest Service, www.forestryimages.org) - Click for full size   Cronartium ribicola sporulating on the bole of an infected tree (Photo: John W. Schwandt, USDA Forest Service, www.forestryimages.org) - Click for full size   Cronartium ribicola - stem cankers eventually girdle and kill trees (Photo:Susan K. Hagle, USDA Forest Service, www.forestryimages.org) - Click for full size   Spores of Cronartium ribicola are produced within the blisters (Photo: USDA Forest Service, www.forestryimages.org) - Click for full size   Uredia stage of Cronartium ribicola (Photo: Robert L. Anderson, USDA Forest Service, www.forestryimages.org) - Click for full size   Damage from Cronartium ribicola (Photo: Rocky Mountain Region Archives, USDA Forest Service, www.forestryimages.org) - Click for full size
    Taxonomic name: Cronartium ribicola A. Dietr
    Synonyms:
    Common names: white pine blister rust (English)
    Organism type: fungus
    White pine blister rust, a widely known tree disease in North America, is caused by the introduced fungus Cronartium ribicola. C. ribicola is a heteroecious (requires two hosts to complete its lifecycle) and macrocyclic rust fungus . The two host groups of this fungus are five-needle Pinus spp. and plants of the currant / gooseberry genus (Ribes spp.). Spores on infected pines are carried by wind to infect Ribes spp. during spring and spores on infected Ribes spp. are also disseminated by wind to infect five needle pines during autumn. Large-scale weather events that bring moist conditions to a region increase opportunities for infection and spore travel distance. Infection is also influenced by topographic features combined with microclimate, such as in saddles or on mountaintops frequented by late summer fog.
    Description
    According to Foster and Wallis (1974), infected trees can be identified by the presence of dead branches in the crown. Infections on young stem and branch tissues are characterised by swollen or sunken areas with discoloured margins. On older stems, resinosus is often present in cankered regions. In the spring, blister-like aecia are produced on cankered stems and release large quantities of powdery whitish-orange spores.
    Similar Species
    Endocronartium harknessii

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    Occurs in:
    natural forests, planted forests, scrub/shrublands
    Habitat description
    USDA (Undated) indicates that Cronartium ribicola favours cool, moist conditions during summer and autumn. According to Scharpf (1993), C. ribicola's North American hosts are eastern white pine (Pinus strobus), western white pine (P. monticola), sugar pine (P. lambertiana), limber pine (P. flexilis), whitebark pine (P. albicaulis), bristlecone pine (P. aristata and P. longaeva), foxtail pine (P. balfouriana), and Mexican white pine (P. strobiformis). In addition, it infects all currants and gooseberries (Ribes spp.), its alternate hosts.

    McDonald et al. (2006), demonstrate that some species in the family Orobanchaceae (Pedicularis racemosa and Castilleja miniata) are alternate hosts to C. ribicola in a natural ecosystem of North America. McDonald et al. (2006) summary states "White pine blister rust disease, caused by the introduced pathogen Cronartium ribicola, has severely disrupted five-needled pine ecosystems in North America. A 100-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. The current study presents the first conclusive demonstration that some species in the family Orobanchaceae (Pedicularis racemosa and Castilleja miniata) are functioning as alternate hosts in a natural ecosystem of North America. This finding has implications for improving our understanding of epidemiology, pathogen adaptation and host–pathogen interactions within white pine blister rust".

    General impacts
    According to Foster and Wallis (1974), the fungus grows in the phloem and bark with no visible symptoms for at least three years, when white blister-like fungal fruiting bodies (aecia) break through the bark. C. ribicola is particularly serious in young trees; very few survive infection and are killed within a few years. Cankers on young trees generally occur within 2.5m of the ground, where environmental conditions are favourable. Open-grown trees with persistent branches are more likely to be infected than trees with self-pruned branches growing in dense stands. In older trees, the rust is often confined to isolated branches or the upper crown so that only part of the tree is killed. According to Scharpf (1993), some stands have been completely destroyed in the western United States and Canada. C. ribicola has caused more damage and costs more to control than any other conifer disease in North America.
    Geographical range
    Native range: Cronartium ribicola is native to Asia (Foster and Wallis, 1974).
    Known introduced range: Scharpf (1993) indicates that the disease was introduced to North America in the early 1900's on seedlings of Pinus strobus grown in Europe. It is believed to have been introduced to Europe from Asia. C. ribicola is now widely found in the western and northeastern United States as well as the Lake States. C. ribicola was introduced into British Columbia in 1910 and has spread from there throughout most white pine regions of Washington, Idaho, Montana, Wyoming, Oregon, and California.
    Introduction pathways to new locations
    Other: Large-scale weather events that bring moist conditions to a region increase levels of infection and long distance travel of fragile spores (Southwest Oregon Forest Insect and Disease Service Center, Undated).


    Local dispersal methods
    On animals (local): According to NRC (Undated), the blisters contain millions of spores (aeciospores) that when released are carried by wind to infect Ribes spp. These spores are long-lived and have been known to infect Ribes spp. at distances of more than 160 km.
    Other (local): Infection is influenced by topographic features combined with microclimate, such as in saddles or on mountaintops frequented by late summer fog (NRC, Undated), which apparently acts as a vector for spores.
    Management information
    Physical: According to NRC (Undated), cultivated black currants (Ribes nigrum), which are more susceptible to the rust, should be removed if growing within a 1.5 km distance from susceptible pine hosts. Pruning of lower branches and high stem density are also recommended for plantation forestry. In addition to the removal of currant and gooseberry plants near infected ornamental trees, it is also advisable to remove diseased branches. This should be done in the spring when the orange-yellow blisters make rust detection easy. Infected branches should be pruned 20 to 25cm below the diseased area. Although excision of existing cankers from stems may be unsuccessful since detection of infected tissue can be difficult, certain reccomendations can be made to improve success. For example, trunk cankers should be treated by removing all diseased bark and stripping off healthy bark 10 to 13cm wide around the canker. Trees that have been treated should be inspected yearly to detect additional infections that may have escaped treatment.

    Please follow this link to Maloy, O. C. 2003. White pine blister rust that outlines symptoms, disease cycle and epidemiology and management including establishment of 'rust hazard zones' and eradication.

    Reproduction
    Cronartium ribicola begins on Ribes spp. leaves when teliospores produce basidiospores, which are carried to five-needle Pinus spp. (Maloy, 2001).
    Reviewed by: Joel A. Jurgens. Research Scientist, Department of Plant Pathology University of Minnesota. USA
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Monday, 24 January 2005


ISSG Landcare Research NBII IUCN University of Auckland