Additional Index Words: genetics, germplasm, Ribes, currants, gooseberries, pines
Abstract: The center of diversity for white pine blister rust (WPBR) is most likely in central Siberia east of the Ural Mountains. The co-hosts for WPBR, Asian five-needled pines and Ribes, native to that region have developed WPBR resistance. Because the dispersal of C. ribicola to Europe and North America occurred within the last 200 years, the North American Pinus subsections, Strobus and Parya, five-needled white pines, had no evolutionary pressure to develop such resistance. North American establishment of WPBR required plants to be transported both ways across the Atlantic Ocean. In 1705, Lord Weymouth had white pine seedlings brought to England. These trees were subsequently planted throughout eastern Europe. In the mid-1800's, WPBR outbreaks were first reported in Ribes and then in white pines in Eastern Europe, the fungus having been brought in on an infected pine from Russia. In the late 1800's American nurserymen, unaware of the European rust incidence, imported many infected white pine seedlings from France and Germany for re-forestation efforts. By 1914 rust-infected white pine nursery stock was imported into Connecticut, Indiana, Massachusetts, Minnesota, New Hampshire, Ohio, Pennsylvania, Vermont, Wisconsin and in the Canadian Provinces of Ontario, Quebec, and British Columbia. The range of WPBR is established in eastern North America and has recently expanded to several western states. New infection sites in Nevada, South Dakota, New Mexico and Colorado have been observed during the past several years.
1 USDA ARS National Clonal Germplasm Repository, 33447 Peoria Road, Corvallis, OR 97333-2521
Detlev R. Vogler1
Abstract: Traditional views of fungal evolution have proposed that rust fungi of Pinaceae are among the most ancient of the Uredinales, primarily because of the phylogenetic age of their hosts. Recent results from cladistic analyses of morphological and molecular characters have challenged this assumption. Ongoing molecular studies on the phylogeny of the pine stem rust fungi (Cronartium and Peridermium spp.) and of their Pinus hosts provide an opportunity to test co-evolutionary hypotheses among these genera. In general, individual pine stem rust species form clades by telial host family, but without regard to the phylogenetic relatedness of their aecial hosts.
Additionally, there is evidence for an evolutionary trend toward greater specialization among telial hosts. Results suggest that these fungi have had a longer co-evolutionary relationship with their
Angiosperm than with their Gymnosperm hosts. Most research on this group has been pursued from the forestry perspective, focusing on genetic interactions of these fungi with aecial hosts (Pinus spp.), while ignoring associations with telial hosts (Angiosperms), which have generally been of minor economic importance. Two recent trends in North America - an ecosystem management approach to forestry, and burgeoning interest in cultivating new fruit crops for a restless and growing population - have obliged us to look more closely at the biology of both plant hosts and of the fungi that infect them. These trends are especially relevant to the C. ribicola/white pine/Ribes host/pathogen association. The once-exotic fungus unites these disparate plant species in a biological relationship that has near-term economic and long-term ecosystem consequences that cannot be ignored.
1 2044 Eunice Street, Berkeley, California 94709-1960 USA.
John A. Muir1 and R.S. Hunt2
Abstract: Introductions of blister rust to eastern and western North America in 1910-1920 caused extensive damage, and western white pine was essentially abandoned as a manageable forest tree species for over 60 years. Western white pine is a desirable component in many forested areas in southern regions of BC because of its faster growth and much higher value compared to many other associated tree species, and lower susceptibility to infection by Armillaria ostoyae. Whitebark pine(Pinus albicaulis), also susceptible, is valued as a major component for wildlife habitat in mountainous ecosystems. Recent positive results from blister rust (Cronartium ribicola) 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 in British Columbia(BC). Regulations in the Forest Practices Code of BC Act require anyone who harvests timber and uses white pine for reforestation to either plant genetically resistant white pine stock or prune susceptible young trees for protection. Given experience with the disease, and our recent success at re-establishing western white pine as a valuable forest tree species, we are concerned about proposals to increase cultivation of currants(Ribes spp.). Although risks of increased blister rust associated with increased cultivation of currants have yet to be determined, major threats appear to include: 1)increase in local amounts of spores for nearby infection of pines; and 2) with increased cultivation and inter-provincial or international shipments of currants, possible introductions or development of new, virulent races of the blister rust fungus from eastern North America localities to Pacific Northwest regions. Fortunately, in contrast to general prevalent indifference about protecting forest and agricultural resources in 1910-1920, most agencies and governments in western North America now are vitally concerned about assessing risks and ensuring adequate protection from damaging agents such as blister rust. We are hopeful that existing scientific working groups and interagency committees, including the present conference, will make a reasonable assessment of the risks of increased cultivation of currants, and recommend appropriate amendments, if necessary, to current legislation to protect white pines.
1 RPF, PhD, Provincial Forest Pathologist, Forest Practices Branch, British Columbia Ministry of Forests.
2 PhD, Research Scientist, Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, British Columbia, Canada
Richard S. Hunt1 and G.D. Jensen2
Additional Index Words: currants, resistance
Abstract: One character used to select blister rust resistance seedlings is to select seedlings with reduced infection lesions (spots) based on a fall inoculation of currant needles. However, in the literature there is confusion as to the time of year Cronartium ribicola infects white pine and what age of needles are most susceptible. To determine when western white pines are infected, groups of potted seedling were placed under infected currants for one week periods from early summer to late fall. Seedlings developed needle lesions and became cankered from exposure to diseased currants in the early summer through to leaf drop in November. Many infection episodes occurred. To determine what age of foliage was most susceptible, 87 five-year-old seedlings were placed in a disease garden, and 14 older trees wee inoculated in the field. All age classes of foliage were susceptible to infection. For the 87 seedlings each age class was about equally susceptible. On some older trees, the current year's foliage appeared more resistant than older foliage. This, and the lack of a correlation between family cankering data in field plots and infection spots from inoculations, suggests that spotting data should not be too heavily weighted as a selection trait for blister rust resistance in western white pine. Perhaps natural inoculations, which occur over several months, as opposed to a single fall inoculation during screening may explain the lack of a correlation between field cankering and inoculation spotting data.
1 Research Scientist and 2 Biologist respectively, Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, 506 W. Burnside Rd, Victoria, BC V8Z 1M5.
Brian W. Geils1
Additional index words. Cronartium ribicola, introduction
Abstract. Cronartium ribicola is a recently established pathogen of southwestern white pine (Pinus strobiformis) in New Mexico. Based on the apparent age of the oldest blister rust cankers found, the outbreak began about 1970 on the western escarpment of the Sacramento Mountains (Otero County). Since then, white pine blister rust has spread throughout the Sacramento and adjacent White Mountains, into the Capitan Mountains, and to Gallinas Peak (100 miles north of the point of origin). The incidence of rust-cankered white pine trees varies across the infested area from less than 1% to over 95%. Blister rust is a special threat in the Southwest because white pine are generally isolated into small populations subject to local extinction. These scattered populations could provide a bridge to white pines in Mexico and the southern Rocky Mountains. Potential impacts of the outbreak include adverse ecological effects on disturbance regimes and associated species. Expansion of outbreak may be hastened with greater planting of Ribes and white pines in forest-urban areas such as Flagstaff, Arizona. Research is being conducted on rust epidemiology, Ribes ecology, and meteorology to rank sites for blister rust hazard. Results can be used to develop and evaluate recommendations for disease control (e.g., sanitation) and strategies for protection of biological resources (e.g., genetic conservation).
1 Research Plant Pathologist. USDA Forest Service, Rocky Mountain Research Station, Southwest Forest Science Complex, 2500 South Pine Knoll Drive. Flagstaff, AZ 86001.
Geral I. McDonald1
Abstract: White pine blister rust has become a governing force in western forest ecosystems supporting five-needle pines since its introduction at Grey's Point, British Columbia in 1910. Resistant populations of western white pine were selected for the Pacific Northwest and remain effective. Rust hazard varies significantly across the landscape and on low hazard sites even susceptible pines can be grown. One local race of the rust is more aggressive on one resistant population. Integrated blister rust management programs are one way to manage these complexities. Epidemiological simulators developed to assist with interpretation of complex site and weather interactions are parameterized to simulate development of local rust epidemics. Different Ribes species and weather conditions can interact to create large variations in rust behavior. Because various epidemiological fitness traits of rust development show genetic variation, Ribes x rust x site interactions must be understood to facilitate integrated management.
In the fall of 1981, cuttings were obtained from 60 individuals (clones) belonging to Ribes lacustre, R. sanguinium, and R. bacteosum growing at 2 locations (Champion Mine and Still Creek) in the Cascade Mountains of Oregon. Forty cuttings of R. viscosissimum were collected at 2 sites (Priest River Experimental Forest and the west fork of Merry Creek) in the northern Rocky Mountains of north Idaho. Merry Creek supplied 10 cuttings of R. hudsonianum and Priest River supplied 10 of R. lacustre. Cuttings were propagated at Moscow, Idaho. Five cones were chosen to represent each species and site combination (30 combinations from Oregon and 20 from Idaho). Six leaf disks (1.54 cm2 in area) from each Ribes clone and a microscope slide cover slip (spore trap) were placed in a Petri dish for inoculation. The 50 dishes were placed at random on the floor of an inoculation chamber. In the spring of 1982, bulked aeciospores were collected from 5 trees at each of the 4 sites. Each group of 50 combinations (clone x Ribes species x location) were inoculated (calibrated mixtures of dry talc and dry spores) with each aeciospore source within 3 days of collection to give 200 clone x site x aeciospore source combinations. Each inoculation was replicated 4 times to yield a total experiment of 4800 inoculated leaf disks. After inoculation, dishes were stored at room temperature under ambient light. The 16 inoculations (4 sites x 4 replications) were performed 2 to 3 days apart and each 50-dish set was inspected daily for 30 days. Number of spores/dish was recorded to calculate infection efficiency (infections/spore). Number of infections, days from inoculation to lesion appearance (incubation period), and the number of days from lesion to urediospore appearance (latent period) were recorded for each disk.Ninety-eight percent of the 4800 disks supplied data. One clone of R. hudsonianum out of 50 clones representing five species was immune to all aeciospore sources. All remaining clones were susceptible to all sources. However, infection efficiency, incubation period, and latent period all show highly significant site x species x aeciospore source interaction. Infection efficiency ranged from 0.041 to 0.216 infections/spore, incubation period from 7.3 days to 12.5 days, and latent period from 1.5 days to 5.2 days. Such magnitudes of variation need to be incorporated into model parameterization and they indicate acclimation/adaptation of C. ribicola to local conditions. Source x clone interaction was tested for infection efficiency and incubation period and was significant. Values ranged from 0.001 to 0.328 and 6 to 21 days.
1 USDA Forest Service, Rocky Mountain Research Station, 1221 South Main Street, Moscow, Idaho 83843.
Abstract: Four species of Cronartium (C. kamtschaticum Joerst., C. ribicola J.C. Fischer, C. flaccidum (Alb. Et Schw.) Winter, C. quercuum (Berk.) Mly. Ex Shiral), and one species Peridermium (P. kurilense Dietel) were encountered in the Russian Far East (Azbukina, 1974, 1984, 1995). However, taxnomic distinctness and biological relationships between C. kamtschaticum and C. ribicola, as well as taxonomical status of P. kurilense have not been studied sufficiently. During 1992-1994 and 1996-1997 the additional blister rust materials on Pinus spp. were collected in several areas of Russian Far East (Kakishima et al., 1995). These data allow to treat C. kamtschaticum as a synonym or C. ribicola. P. Kurilense is morphologically and biochemically similar to Endocronartium sanounum mazu et Kakishima var. hokkaidoense Imazi et Kakishima. However, the taxonomical status of this fungus will be established only as a result of the investigation of its nucleous cycle.
1 Institute of Biology and Soil Science, Vladivostok, Russia
Abstract: A search for appropriate germplasm to use in black currant breeding programs for rust resistance began in 1935 in Ottawa. One bush in the Ribes block, later identified as Ribes ussuriense Jancz., was found to be remarkably free of rust. Two other species, R. aureum Pursh. and R. odoratum Wendl. which were present in the same block were the least susceptible of the remaining plants. Crosses were made in 1938 and 1939 with various combinations of these 3 species and the standard black currant cultivars Boskoop Giant and Kerry. The resulting seedlings from these crosses were evaluated for rust resistance. Out of this program 3 very promising selections were made.
1 Agriculture & Agri-Food Canada. Canadian Clonal Genebank Program. Greenhouse and Processing Crops Research Ctr., 2585 County Road 20, Harrow, Ontario, N0R 1G0. Canada.
Additional index words: currants, gooseberries, white pine blister rust.
Abstract: For many years the commonly held solution to white pine blister rust in North America was to eradicate all Ribes. That approach was tried to no avail. The world production of currants and gooseberries in 1998 was a little more than 750,000 metric tons. Germany, Poland and the Russian Federation produce a little more than 600,000 (MT) or approximately 80 percent of this. North America did not even show up on the list. Can currants and gooseberries be successfully grown in North America? You bet they can! Vast areas of the United States and Canada are ideal for Ribes production. Black currant production should not be compared to strawberry or raspberry production; those are much, much more labor intensive. Black currants are a process fruit and production may compare more closely to that of grain. Ribes can be machine harvested; they don't have to planted each year; they come into production in a relatively short time; they require a minimal amount of input after the initial planting. American plantings will have a higher per/acre production than those in Europe. Many of the areas that presently grow berries could easily grow Ribes. Black currant juice has an intense pleasant flavor and color, is high in ascorbic acid and several other nutrients. Consumers are buying more healthful and unusual fruits and black currant is the most healthful of fruits.
The main barriers for production in North America are state restriction and the availability of up-to-date information and data for growers, processors, legislators and the consuming public. I suggest that this conference and the people herein form that Task Group and initiate the cooperative dialogue and set forth a process to approach the WPBR problem in a holistic manner.
1 Past President, The International Ribes Association.
Dale R. Bergdahl1 and H. B Teillon
Additional index words: Cronartium ribicola, cultivars, infection, Pinus, Ribes.
Abstract. White pine blister rust (WPBR) caused by Cronartium ribicola has been present in Vermont and the other northeastern states since its introduction in the early 1900's. The fungus is commonly observed on Ribes spp. every year but infection levels seem to vary on eastern white pine (Pinus strobus) depending on many environmental parameters. In the past, our general impression has been that Vermont has a relatively low level of infection on white pines; however, in a survey conducted in August (1999), we found infection levels in 6 Christmas tree plantings in northern Vermont to range from 10 to 42%(avg. 20%) based on 721 trees surveyed. Also, in pole-sized stands of white pine in southern Vermont, infection levels ranged from 12 to 46% (avg. 32%) and 76% of these trees had main stem infections. In the southern survey, it was also noted that 98% of wild Ribes plants had varied amounts of both urediospores and teliospores. These preliminary survey data suggest that WPBR may be more significant than previously thought and therefore additional survey work needs to be considered.
Currently, the state of Vermont does not have any WPBR control regulations; however, in the past, laws did restrict the growing of black currents (R. nigra) but other species were allowed if the grower could certify there were no valuable white pines within 900 feet of the planting site. Also, Vermont did require a shipping permit for in-state and out-of-state nursery sales of all Ribes spp.
In 1989, we screened 18 cultivars of Ribes for susceptibility to C. ribicola. Results of this study were published in Phytopathology (80:118-119). In summary: eighteen cultivars of gooseberries and currants (Ribes spp.) were inoculated in the field with a mass collection of aeciospores of Cronartium ribicola. The percentages of leaf area infected for each cultivar were: Welcome, 50%; Red Jacket, 40%; Green Hansa, 28%; Poorman, 26%; Wilder, 20%; Champion, 20%; Pixwell, 15%; Canada-0273, 14%; Spinefree, 14%; Whitesmith, 10%; Friedl, 9%;Red Lake, 6%; Jumbo, 4%; Cherry, 4%; White current 3%. The cultivars Consort, Coronet and Crusader had no infection which conforms to previous reports.
The white pine forests of Vermont and the other northeastern states have changed substantially during the last century; however, white pines remain a highly significant part of our landscape and rural economy. White pine blister rust is an exotic pest of white pines and a serious pathogen. We know little about genetic diversity of WPBR or its potential for change. The various cultivars of Ribes are also exotics when introduced to the landscape. Many of these cultivars may appear resistant to the current races of WPBR but it is unknown how resistance is likely to change over time. Also, these exotic cultivars have potential to interbreed with native species of Ribes and progeny from these out-crosses will be disseminated across the landscape and may bear little resemblance to their parentage in terms of growth habit or resistance to WPBR. Therefore, caution must be used when introducing exotic cultivars of Ribes; especially, knowing there could be a significant negative impact on white pines.
1 Deptartment of Forest Pathology, University of Vermont, Burlington, VT 06405
Abstract: Recent interest in expanding commercial Ribes plantings in the U.S. has put pressure on the states with Ribes restrictions to review their regulations. A meeting on January 9, 1998 initiated discussion between the state agriculture regulatory agencies, forest pathologists, and horticulturalists. Since then a white pine blister rust web site (www.cce.cornell.edu/Columbia/smckay/wpbr.html) and list serve have been activated to facilitate communication. Vermont is a state that has no regulations on the books at this time, and reports a very low blister rust infection rate. 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 Extension Educator, Cornell Cooperative Extension, 479 Route 66, Hudson, NY 12534.
Richard A. Sniezko1, Jude Danielson1, and Andrew Bower1
Abstract: In the Pacific Northwest Region (Oregon and Washington), the USDA Forest Service has been screening sugar pine (Pinus lambertiana) and western white pine (Pinus monticola) trees for resistance to white pine blister rust (Cronartium ribicola) since the late 1950's. The operational rust resistance program has been patterned after research done at the USDA Forest Service's Rocky Mountain Research Station, but has also recently incorporated findings from the Pacific Southwest Research Station.
Progeny of over 10,000 phenotypic selections from natural stands from a range of land ownerships have been evaluated for resistance to blister rust. Generally, following inoculation, over 95 percent of seedlings develop needle lesions and most develop stem cankers, and subsequently die within the five year evaluation period. Seedlings are examined for five years following inoculation for an array of resistance mechanisms. Seed orchards composed of resistant selections have been established and seed from some of these orchards is currently available. For some breeding zones, orchard seed for western white pine should yield at least 25 -50% more canker-free trees than general forest collections.
Little is known about how individuals selected for the different resistance mechanisms in short-term screening perform in the field in the Pacific Northwest, especially mechanisms such as bark reaction and tolerance which are exhibited after the fungus has entered the stem. At least one type of major gene resistance (a hypersensitive reaction on the needles that prevents stem infection) appears to be present in both sugar pine and western white pine, but it appears to occur at low frequency in natural stands. There are localized strains of blister rust that render these mechanisms ineffective (different rust strain for sugar pine and western white pine). There is some evidence that not all families having a high incidence of canker-free seedlings have the identified major gene resistance. The operational screening methods used thus far do not allow for clear separation of several possible mechanisms that may yield canker-free seedlings
In the Pacific Northwest, little field data is available on the relative resistance of western white pine and sugar pine to blister rust. Until very recently, few well replicated field plantings have been established to examine gains from rust resistance screening, and examine performance of resistance families. Results presented here examine species differences in rust resistance using a 1996 planting of 12 sugar pine and 13 western white pine families at one outplanting site (Happy Camp, California.). This site has been noteworthy for the presence of the "Happy Camp" strain of blister rust which renders the major gene resistance in sugar pine ineffective.
Results from the first assessment (in summer 1999) of this site show that sugar pine has a higher incidence of stem infection (active and inactive cankers) than western white pine. A higher percentage of sugar pine trees have stem infections, and sugar pine has more stem infections per infected tree than does western white pine. An unexpected result from the 1999 assessment is the very high percentage of infections that are bark reactions (completely inactived infections). Only some of the families of both species were selected at Dorena for the bark reaction mechanism, yet the incidence of bark reactions in both species was high. Assessments in subsequent years will be used to track the performance of the two species and of the individual families.
1 USDA Forest Serv, Dorena Genetic Resource Ctr, 34963 Shoreview Rd., Cottage Grove, OR 97424.
Richard A. Sniezko1, Andrew D. Bower1, Robert S. Danchok1, Bohun B. Kinloch2, and Joseph M. Linn1.
Abstract: Canker-free seedlings from western white pine full-sib families exposed to white pine blister rust by artificial inoculation were outplanted from 1968 to 1973 on two sites of high rust hazard (Blodgett Creek, (BC); and Grass Creek, (GC)). These sites are within 8 and 3 miles, respectively, of the Champion Mine on the Umpqua National Forest in the Cascade Mountains of western Oregon. Champion Mine was the site of origin of many of the phenotypically resistant parent tree selections, as well as the notorious 'Champion Mine strain' of rust, which appeared after 1970 and killed all white pines on the site by 1994. The plantations were abandoned early after establishment, and the fate of many trees lost, but in 1996 and 1997, both sites were remonumented, mapped, and assessed for survival and infection. Rust infection was quantified by counting (or in cases of severe infection, estimating) cankers on each tree. The database included 404 trees at BC and 1579 at GC, with the number of trees planted per family varying from less than 5 to 180. Most trees on both sites were infected (99%, BC; 94% GC), and although the mean number of cankers/tree varied dramatically by planting year at GC, overall, BC had almost a third more cankers/tree on average (63) than GC (47). Since many of the families planted on these sites had been identified as segregants for a dominant major gene for resistance (MGR) against "wild type" rust inoculum, presumably the rust infecting these trees is the CM strain, with specific virulence to this gene (assay of inoculum collected at GC in two sequential years and inoculated onto known pine genotypes confirmed the presence of CM at high frequencies). In spite of heavy incidence of infection, there was striking variation in its intensity: individual trees ranged from 0 to >200 cankers, and family means from 5.0 to 107.1 at BC, and 0 to 125.0 at GC. Many of the trees at both sites continue to grow well, despite heavy infection. The data suggest that with high enough inoculum potential specific virulence may arise and increase exponentially. Wide variation in infection frequency on these sites demonstrates that resistance mechanisms other than MGR may be at work. Combining all types of resistances should provide a mutual buffering against racial change in the rust, resulting in durable resistance. This will increase the potential to restore white pine in the northwest forest ecosystem.
1 USDA Forest Service, Dorena Genetic Resource Center, Cottage Grove, OR 97424
2 USDA Forest Service, Pacific Southwest Research Station, Box 245, Berkeley, CA 94701
Brian W. Geils1, Richard S. Hunt2, and Kim E. Hummer3
Abstract: Additional index words. white pine blister rust, Ribes, performance trial Abstract. Ribes species and cultivars vary in their response to infection by Cronartium ribicola. Especially important are differences in their capacity for supporting production of rust spores infecting white pines. Populations of Cronartium ribicola distributed geographically also demonstrate variability in a number of epidemiological traits. Not only has white pine blister rust spread to new regions and species of Ribes, but increased cultivation and distribution) of Ribes has the potential to bring together new host-pathogen combinations in new environments. We propose a series of Ribes performance trails be conducted with well-controlled, experimental gardens of clonal material planted in different regions where blister rust is already established. The trials would be conducted as a cooperative p rogram with participants across North America. The cooperators would develop standardized procedures for testing Ribes susceptibility and use those procedures for assessing its geographic stability.
1 Research Plant Pathologist, USDA Forest Service, Rocky Mountain Research Station, Southwest Forest Science Complex, 2500 South Pine Knoll Drive, Flagstaff, AZ 86001.
2 Research Plant Pathologist, Canadian Forestry Service, Pacific Forest Research Centre, 506 West Burnside Road, Victoria, BC V8Z 1M5.
3 Research Leader, USDA ARS, National Clonal GermplasmRepository, 33447 Peoria Road, Corvallis, OR 97333-2521.
Ellen M. Goheen1, R. Danchok2, D. J. Goheen1, K. Marshall1, and J. Petrick2
Abstract: There is widespread concern about the status of whitebark pine throughout the west. Whitebark pine is an important species in the southern Oregon Cascade Mountains. However, its condition has not been evaluated in a rigorous fashion. During the summer of 1998 we began to assess the condition of whitebark pine in southwest Oregon by surveying the area along the Pacific Crest National Scenic Trail (PCNST) on the Umpqua National Forest. Twenty-one transects were installed along the PCNST. Sixteen of the 21 transects installed during this survey had whitebark pine on them. Total whitebark pine stocking measured on these transects ranged from 6 to 217 trees per acre with an overall average of 75 whitebark pines per acre. Eighty-seven percent of all whitebark pine measured were less than 15 feet tall. Whitebark pine stocking ranged from 0.1 to 24 percent of total tree stocking on individual transects. White pine blister rust was found on all transects that had whitebark pine. It occurred on 62 of the 79 (78 percent) whitebark pine plots. Across the survey area 52 percent of the live whitebark pine per acre were infected. Seventy percent of the whitebark pine greater than 4.5 feet tall and less than three inches in diameter were infected. The vast majority (92 percent) of the infected trees had bole cankers or cankers within six inches of the bole. Thirty four percent of all white pine blister rust-infected whitebark pine suffered topkill. Ten percent of the whitebark pine stocking in the survey area was dead. White pine blister rust was the most frequently encountered mortality agent. It was found on 84 percent of all dead trees. Evidence of mountain pine beetle (Dendroctonus ponderosae) was found with white pine blister rust on 18 percent of dead whitebark pine. Only one Ribes plant was encountered across the entire survey area. Anecdotal accounts are no longer the only source of whitebark pine information along the PCNST on the Umpqua National Forest. A 1998 reference condition for whitebark pine has been described for the area surveyed and can be used for assessing changes in the status of the species.
1 Plant Pathologists, USDA Forest Service, Southwest Oregon Forest Insect and Disease Service Center, Central Point, Oregon 97502.
2Biological Technician and Silviculturist, respectively, USDA Forest Service, Dorena Genetics Resource Center, Cottage Grove, Oregon 97424.
Bohun.B. Kinloch, Jr.1
Abstract: After a century since introduction to North America from Europe, white pine blister rust has come to be recognized as one of the catastrophic plant disease epidemics in history. It has yet to stabilize, continuing to spread and intensify. The nine native white pine hosts comprise major timber producers, important watershed protectors, keystone ecological species, and the oldest trees on earth. All are highly susceptible and some have been damaged severely in parts of their native range, as well as where they have been planted as exotics. Resistance, the most promising approach to control, requires understanding of genetic interactions between hosts and pathogen, a quest that has been ongoing for half a century.
Unlike hosts of other spectacular exotic diseases that have not coevolved with their hosts, such as chestnut blight and dutch elm disease, white pines exhibit a number of resistance mechanisms to blister rust, if at only low frequencies. There are three main kinds:
On the pathogen side, estimates of population parameters of Cronartium ribicola in western North America indicate that overall variability is low, with a genetically fragmented, metapopulation structure. Gene flow is also low, in spite of high outcrossing. The epidemiological unity that characterized the spread of blister rust across Europe then to both coasts of North America implies a corresponding genetic unity. No private alleles were found in any of the western or eastern North American populations sampled, and all may share the same gene pool as the European populations from which they derive.Variation in virulence appears limited; none has been found on different Ribes cultivars in extensive trials in Europe and North America, and only two races that neutralize major resistance genes in both sugar pine and western white pine are confirmed. The one on sugar pine is evidently conditioned by a single plasmagene, an unusual phenomenon among virulence genes. Both races appear to have limited distributions. Other races may exist in North American populations, but a greater threat may lie in new introductions from Asia, the ancestral gene center of the pathogen. The specificity that exists in this non-coevolved pathosystem among major genes is intriguing. For example, major gene resistance in sugar pine is not affected by the gene for virulence to a major gene for resistance in western white pine, and vice versa. This simple complementary structure may represent a nascent gene-for-gene system. The problem for breeders, conservationists, and silviculturists is how to concentrate and deploy these various kinds of genes into synthetic or naturally selected populations that are buffered against radical racial shifts to wider virulence in the pathogen, and so provide durable resistance. Two basic strategies are building gene pyramids, developing multilines, or a combination of the two. These are discussed in the context of an ongoing developmental program with sugar pine.
1 USDA Forest Service, Institute of Forest Genetics, Box 245, Berkeley, CA 94701 USA
Abstract: Fruit from Ribes spp. (Black, red and white currants, and gooseberries) were grown commercially in North America at the beginning of the 20th Century. However, when White Pine Blister Rust was introduced into the New World, legislation to eradicate the plants was introduced and the cultivation of Ribes was discontinued. Most of this legislation has now been repealed and interest in Ribes cultivation has increased considerably over the last few years.
Worldwide about 800,000 tons of Ribes fruit are produced; almost entirely in Europe. The fruit is high in vitamin C, and much of it is used to produce juice, although there are many other Ribes products such as jams, pie-fillings, liqueurs, throat lozenges and fragrances.
Presently in North America, very few acres are grown. However, particularly in Canada, a wide range of imported Ribes products are available and there is an increasing Pick-Your-Own market.
Two diseases, powdery mildew and white pine blister rust are the major problems encountered by growers. Fortunately, new cultivars from Europe are available which are resistant to these two diseases and, over the last two years, planting material of these varieties has become available.
Ribes Growers in North America have one advantage over their counterparts in Europe in that North America is free of the Reversion virus and its gall mite vector. This will allow growers to keep their plantings longer than those in Europe, which will help with their profitability.
Commercial acreage of Ribes can be grown in North America in areas where the annual chilling hours are at least 1200. However, there may be locations where, although chilling hours are adequate, summer temperatures are too high.
For a large Ribes industry to develop, there will need to be a concurrent development of a market in North America for juice products . Presently the North American fruit juice industry is worth about $CDN 10 billion and even a 1% market share will require a large acreage of Ribes to be planted. This penetration of the juice market is possible and a potential model for this development would be the cranberry industry.
Although the potential for Ribes in North America is good, its development will only succeed if the crop can be grown profitably. We have developed costs of production figures that indicate that about $CDN 1400 per ton of fruit will be required to break-even on the crop. This is about the present price in Europe, although in recent years, the European price has been has been below this level.
1 University of Guelph, Department of Plant Agriculture, Box 587, 1283 Blueline Road, Simcoe, Ontario N3Y 4N5, Canada
Abstract: The potential for epidemics of white pine blister rust to occur in commercial currant plantations raises the twin specters of periodic yield losses in currant crops and long-term devastation of nearby white pine forests. Planting resistant Ribes cultivars may substantially reduce these risks. Controlled inoculations may be used to assess whether resistance of Ribes cultivars will be effective in field situation, provided they fulfill three criteria. Inoculations must 1) produce consistent infection on susceptible "check" cultivars, 2) identify if "resistant" cultivars have developmental or seasonal periods of susceptibility, and 3) ensure that resistance is effective against diverse strains of the pathogen. Methods of inoculation and Ribes culture in use at our facility for maximizing rust urediniospore and teliospore production were tested to determine if they would be useful for testing Ribes for resistance. In these methods, the under-leaf surfaces of actively growing, single-stem plants of uniform age and stem cuttings of young, fully-expanded single leaves are sprayed with urediniospores of pure-genotype rust strains revived from long-term storage at -80 C and suspended in dilute (0.07%) agar. Plants are kept at 100RH/20C to allow infection, then incubated in cool (20C day / 15C night) growth chambers. Inoculations by these methods caused 100% of leaves of susceptible black currant cultivars to become infected and develop a uniform density of pustules. Urediniospores formed within two weeks and teliospores within three weeks after inoculation. Cultivars carrying the Cr gene did not become infected. Infections on red currant cv. Viking were chlorotic but produced urediniospores and teliospores for up to three weeks before leaf tissues within rust pustules began to develop necrosis. It is assumed that the use of a cool environment and young leaves may have inhibited the more rapid development of the necrotic (sic. "hypersensitive") response usually reported with this "immune" cultivar, as warm temperatures and full sun found in greenhouses have been previously reported to promote some necrosis of leaf tissue within rust pustules for even highly susceptible cultivars.
1 USDA Forest Service, North Central Forest Research Station, Forestry Sciences Laboratory, 5985 Hwy. K, Rhinelander, WI 54501
Mike E. Ostry1
Abstract: After decades of reduced planting because of the concern over the impact of blister rust (Cronartium ribicola), there are now renewed efforts to restore white pine (Pinus strobus) in the Lake States. Although the potential for growing white pine is high on many sites, the disappearance of a seed source caused by logging and fires will require active management to reestablish white pine to these areas. In addition to the damage and tree mortality caused by blister rust, damage caused by deer browsing and attacks by the white pine weevil (Pissodes strobi) reduce the value of white pine. Since 1989, a total of six research/demonstration plantings have been established on the Hiawatha, Chippewa, and Superior National Forests in partnership with Region 9, Northeastern Area State & Private Forestry, and the North Central Research Station. The goal of this study is to determine "best management practices" for restoring white pine on various ecological land types (ELT's) using silvicultural strategies and genetic improvement to minimize damage caused by blister rust, weevil and deer browsing.
We are comparing pest incidence, tree survival and growth of seedling stock from the genetic improvement program of Region 9 and the former Minnesota Quetico-Superior Research Center to non-selected nursery stock in these replicated plantings. Treatments being compared include growing white pine in clearcuts vs. under various types of shelterwoods, lower branch pruning to minimize blister rust and corrective pruning for weevil attack. The effects of different levels of competing vegetation on the ELT's on tree growth and pest incidence also are being examined.
Early results at the Michigan site confirm that white pine survival is greater in the clearcut treatment and the trees are outpacing the trees in the shelterwood, but the incidence of weevil attack is greater. Unexpectedly, however, the incidence of blister rust has been greater in the shelterwood treatment. Rust cankers on the main stems of several pruned trees resulted from infection of needles directly attached to the bole; thus pruning was not effective in these cases. In addition, Armillaria root rot has killed more trees in the northern hardwood clearcut treatment than in the shelterwood. Heavy snow and ice and extremely cold weather also has severely damaged trees at the Michigan site.
Deer browsing has been severe at one of the Minnesota sites, requiring replanting the plots and using a protective bud-capping technique. Competing vegetation, especially on the mesic sites will require much more effort to manage white pine than on the drier, nutrient-poor sites.
Given the biological and economical restraints of restoring white pine using artificial regeneration techniques, we need to use silvicultural strategies and target sites that provide the optimum potential for success. This series of plantings is designed to assist land managers in selecting the best prescription for growing white pine under their set of conditions.
1 USDA Forest Service, North Central Res. Sta., 1992 Folwell Ave. St. Paul, MN 55108.
Danny L. Barney1
Abstract: Large-scale Ribes production in the Inland and Intermountain West, while feasible, has yet to be developed. Small-scale production has increased during the past decade and it is becoming increasingly common to find currants and gooseberries for sale at farmers markets and through market gardeners.
Topography and climate vary tremendously throughout the region, with average minimum winter temperatures ranging from 0 to -40 F and precipitation from less than 10 to more than 60 inches per year. Within this diversity are many locations suitable for commercial Ribes production. With traditional farm commodities providing poor economic returns, prospective and established farmers are becoming more interested in specialty crops.
Factors which limit commercial development include diseases, pests, labor shortages, and marketing challenges. Powdery mildew has the greatest biological impact on currant and gooseberry production. Blister rust is more a political than biological problem for Ribes growers in this region where logging has traditionally been a major contributor to the economy. Inadequate labor to harvest currants and gooseberries seriously hinders expansion of the industry. Importation and development of cultivars suited to mechanical harvesting would help overcome this challenge.
Black currants probably offer the greatest commercial potential, followed by red currants. The following things are needed to facilitate expansion of the Ribes industry in the Inland and Intermountain West. Development and importation of black currant cultivars with improved resistance to powdery mildew and blister rust, and having fruit that can be harvested mechanically and which is suitable for commercial processing. Development and importation of red currants with improved resistance to powdery mildew and long, easy-to-pick strigs for hand harvest or canes and fruit suitable for mechanical harvest.
Those interested in currant and gooseberry production have access to a production guide, cultivar recommendations, and links to other small fruit resources through the University of Idaho Sandpoint R&E Center home page, www.uidaho.edu/~sandpnt/.
1 Ph.D.,University of Idaho, Sandpoint Research & Extension Center, 2105 North Boyer Avenue, Sandpoint, ID 83864.