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Todd A. Burnes, Robert A. Blanchette, Jason A. Smith, and James J. Luby

; Zambino, 2000 ). After field evaluations, a red currant ( Ribes rubrum L.) cultivar, ‘Viking’ was thought to have immunity to C. ribicola ; however, uredinial sori developed after artificial inoculations ( Zambino, 2000 ). It was suggested that an error

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Margie Luffman

The search for appropriate white pine blister rust (WPBR) (Cronartium ribicola J.C. Fischer) resistant germplasm to use in black currant (Ribes nigrum L.) breeding programs began in 1935 in Ottawa. Crosses were made in 1938 and 1939 with three different Ribes L. species and two standard black currant cultivars. The resulting seedlings from these crosses were evaluated for rust resistance. Three promising selections resulted from this program and were named `Coronet', `Crusader' and `Consort'.

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Steven McKay

Recent interest in expanding commercial currant and gooseberry (Ribes L.) plantings in the United States has put pressure on the states with Ribes restrictions to review their regulations. A meeting on 9 January 1998 initiated discussion between the state agriculture regulatory agencies, forest pathologists, and horticulturists. Since then a white pine blister rust (WPBR), Cronartium ribicola J.C. Fischer) World Wide Web (Web) site (McKay, 1998) and list serve have been activated to facilitate communication. Vermont is a state that has no regulations on the books at this time. Connecticut and New York also have mentioned that infection rates are low. Maine retains a Ribes reduction program, and Massachusetts is strictly enforcing their regulations. The following summarizes the general consensus among the majority of regulating states: 1) It is desirable to find a way for both white pines (Pinus L.) and commercial Ribes plantings to coexist. 2) More research is needed to survey existing Ribes and pines, the potential impact of commercial plantings versus the impact of existing Ribes, and the potential impact of escape /volunteer seedlings from immune Ribes cultivars. 3) There is interest in permitting immune Ribes cultivars to be planted. 4) There is interest in having consistency in regulations from state to state.

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Kim E. Hummer

The center of diversity for white pine blister rust (WPBR) (Cronartium ribicola J.C. Fischer) most likely stretches from central Siberia east of the Ural Mountains to Asia, possibly bounded by the Himalayas to the south. The alternate hosts for WPBR, Asian five-needled pines (Pinus L.) and Ribes L. native to that region have developed WPBR resistance. Because the dispersal of C. ribicola to Europe and North America occurred within the last several hundred years, the North American five-needled white pines, Pinus subsections, Strobus and Parya, had no previous selection pressure to develop resistance. Establishment of WPBR in North American resulted when plants were transported both ways across the Atlantic Ocean. In 1705, Lord Weymouth had white pine (P. strobis L.), also called weymouth pine in Europe, seed and seedlings brought to England. These trees were planted throughout eastern Europe. In the mid-1800s, WPBR outbreaks were reported in Ribes and then in white pines in eastern Europe. The pathogen may have been brought to Europe on an infected pine from Russia. In the late 1800s American nurserymen, unaware of the European rust incidence, imported many infected white pine seedlings from France and Germany for reforestation efforts. By 1914, rust-infected white pine nursery stock was imported into Connecticut, Indiana, Massachusetts, Minnesota, New Hampshire, Ohio, Pennsylvania, Vermont, and Wisconsin, and in the Canadian provinces of Ontario, Quebec, and British Columbia. The range of WPBR is established in eastern North America and the Pacific Northwest. New infection sites in Nevada, South Dakota, New Mexico and Colorado have been observed during the 1990s.

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John A. Muir and Richard S. Hunt

Introductions of white pine blister rust (WPBR, causal fungus: Cronartium ribicola J.C. Fischer) to eastern and western North America before 1915 caused such extensive damage that western white pine (Pinus monticola D. Don) was essentially abandoned as a manageable forest tree species for over 60 years. Recent results from WPBR resistance selection and breeding programs, and from field trials of tree spacing, pruning and bark excision treatments have supported efforts to increase establishment and to intensively manage western white pine. Western white pine is a desirable component in many forested areas because of its faster growth and much higher value compared to many other associated tree species. It also has a low susceptibility to armillaria root disease caused by Armillaria ostoyae (Romagnesi) Herink and laminated root rot, caused by Phellinus weirii (Murr.) Gilb. Some regulations, e.g., Forest Practices Code of British Columbia (BC) Act, require anyone who harvests timber on provincial forestland and uses western white pine for reforestation to either plant genetically resistant western white pine stock or prune susceptible young trees for protection. Risks of increased WPBR associated with increased commercial cultivation of gooseberries and currants (Ribes L.) have yet to be determined. However, major threats appear to include 1) increase in local amounts of spores for nearby infection of pines; and 2) possible introductions or development of new, virulent races of C. ribicola, particularly from eastern to Pacific northwestern North America. In view of these possible threats, we recommend that existing regulations and legislation should be amended, or possibly new measures enacted, to permit propagation and commercial cultivation only of varieties of Ribes that are immune or highly resistant to WPBR.

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D.R. Bergdahl and H.B. Teillon

White pine blister rust (WPBR) (Cronartium ribicola J. C. Fischer) has been present in Vermont and other northeastern states since the early 1900s. The fungus is commonly observed on currants and gooseberries (Ribes L.) every year, but incidence varies on eastern white pine (Pinus strobus L.). Our general impression has been that Vermont has had a relatively low level of infection on eastern white pines; however, we recently found rust incidence in Christmas tree plantings in northern Vermont to range from 10 to 42% (average 20%) based on 721 trees surveyed. Also, in pole-sized stands in southern Vermont, incidence ranged from 12 to 46% (average 32%) and 76% of these trees had main stem infections. In the southern survey, 98% of wild ribes plants had varied amounts of both urediniospores and teliospores. These preliminary survey data suggest that incidence of WPBR may be more significant than previously thought and therefore, additional survey work is needed. We screened cultivars of Ribes for susceptibility to WPBR. Eighteen cultivars were inoculated in the field with a mass collection of aeciospores of C. ribicola. The percentages of leaf area infected ranged from 0 to 49 for the urediniospore stage and from 0 to 55 for teliospores. The gooseberry (Ribes uva-crispa L.) `Welcome' had the highest percentage of leaf area with urediniospores, while black currants (R. nigrum L.) `Coronet,' `Consort,' and `Crusader' had no visible infection. Presently, Vermont has no WPBR regulations. However, previous federal laws did restrict black currant cultivation. Little is known about the genetic diversity of WPBR or its potential for change. Caution must be used when considering any cultivation of Ribes for the purpose of producing fruit because our valued white pine resources could be negatively impacted.