White Pine Blister Rust Research Articles

First Report of the White Pine Blister Rust Pathogen, Cronartium ribicola, in Arizona.

White pine blister rust, caused by Cronartium ribicola J.C. Fisch., was found on southwestern white pine (Pinus flexilis James var. reflexa Engelm., synonym P. strobiformis Engelm.) near Hawley Lake, Arizona (Apache County, White Mountains, 34.024°N, 109.776°W, elevation 2,357 m) in April 2009. Although white pines in the Southwest (Arizona and New Mexico) have been repeatedly surveyed for blister rust since its discovery in the Sacramento Mountains of southern New Mexico in 1990 (1,2), this was the first confirmation of C. ribicola in Arizona. Numerous blister rust cankers were sporulating on 15- to 30-year-old white pines growing in a mixed conifer stand adjacent to a meadow with orange gooseberry bushes (Ribes pinetorum Greene), a common telial host in New Mexico. Most of the observed cankers were producing their first aecia on 5-year-old branch interwhorl segments (i.e., formed in 2004). The two oldest cankers apparently originated on stemwood formed about 14 and 21 years before (1995 and 1988). Neither uredinia nor telia were seen on expanding gooseberry leaves in late April, but these rust structures were found later in the season. Voucher specimens deposited in the Forest Pathology Herbarium-Fort Collins (FPF) were determined by host taxa and macro- and microscopic morphology as C. ribicola-white pine with typical cankers, aecia, and aeciospores (1). Six collections of aeciospores from single, unopened aecia provided rDNA sequences (ITS1-5.8S-ITS2, primers ITS1F and ITS4) with two different repeat types (GenBank Accession Nos. HM156043 and HM156044 [J. W. Hanna conducted analysis with methods described in 3]). A BLASTn search with these sequences showed 100 and 99% similarities, respectively, with sequences of C. ribicola, including accessions L76496, L76498, and L76499 from California (4). Additional reconnaissance of white pines on the Fort Apache Indian Reservation and neighboring Apache-Sitgreaves National Forests was conducted from May through September 2009. Although the blister rust infestation was distributed over more than 100 km2 of forest type, infected trees were restricted to mesic and wet canyon bottoms (climatically high-hazard sites) and were not found on dry sites-even where aecial and telial hosts occurred together. Recent dispersal within the White Mountains was suggested by a presence of infected gooseberry plants on several sites where infected white pines were not yet evident. Geils et al. (1) concluded that the initial infestation in New Mexico had originated by long-distance, aerial transport from California to the Sacramento Mountains in 1969. Since then, numerous additional infestations in the Southwest have been discovered; but we do not know which of these (including Arizona) resulted by dispersal from California or New Mexico. Although rust may eventually infest many host populations in the Southwest and disease may kill most trees in some locations, differences in site hazard and spread provide managers with numerous opportunities to maintain white pines and Ribes spp.

Earliest documented report of Scleroderris canker in North America: damage believed until now to be caused by summer frost

In 1934, over 200,000 red pine (Pinus resinosa) seedlings were planted at Valcartier, near Quebec City. By 1939, more than 28% of these pines were dead. Fifteen years after plantation, red pine mortality reached 93% and the plantation was considered a total loss. Summer frost was thought to be the cause of red pine mortality, while white pine (Pinus strobus) trees planted at the same time were killed by white pine blister rust (Cronartium ribicola), without any trace of frost damage. However, while summer frost was not listed in insect and disease survey reports published from 1953 to 1993, it was reported in the Valcartier area. Analysis of archival documents and publications shows that Scleroderris canker caused by Gremmeniella abietina was responsible for this mortality. This disease was not known in Canada before 1960. Our diagnosis is based on the description of signs and symptoms, on photographs of damage and on samples collected on site. Gremmeniella abietina, North American race, was isolated and identified. The age of the trees confirms the identity of the plantation; the age of the cankers on residual pines shows that the disease reached the trunks around 1945. High snow depth - not frost - in topographic depressions created conditions conducive to the development of the disease at the epidemic level. This is the earliest documented report of Scleroderris canker in North America.

Blister Rust Incidence in Treeline Whitebark Pine, Glacier National Park, U.S.A.: Environmental and Topographic Influences

Whitebark pine (Pinus albicaulis) is a foundation and keystone species of upper subalpine and treeline ecosystems throughout the western United States and Canada. During the past several decades, Cronartium ribicola, an introduced fungal pathogen that causes white pine blister rust in five-needled pines, has caused significant declines in whitebark pine throughout its range. Our research objectives were to examine geographic variation in blister rust infection (total canker density) in whitebark pine found at six alpine treelines east of the Continental Divide in Glacier National Park, Montana, and to determine which environmental factors have the greatest influence on blister rust infection at treeline. Within a total of 30 sampling quadrats (five at each treeline study site), we measured the number of cankers on each whitebark pine in order to assess how blister rust infection varied throughout our study area. We created high-resolution digital elevation models to characterize surface microtopography, and used a geographic information system (GIS) to derive environmental variables of interest. A mixed effects, Poisson regression model determined environmental correlates of blister rust from the resulting set of field and GIS-derived variables. We found that rates of infection varied considerably among treelines, and that treeline sites exhibiting high flow accumulation rates, greater distances to wetlands, slopes facing southwest, higher curvature, greater wind speeds, and close proximity to Ribes and perennial streams had the highest rates of blister rust infection.

Genomic organization, induced expression and promoter activity of a resistance gene analog (PmTNL1) in western white pine (Pinus monticola)

Cronartium ribicola causes white pine blister rust (WPBR) in subgenus Strobus. Various genetic and molecular approaches were used to detect white pine genes contributing to host resistance. The molecular role of the NBS-LRR family is highly related to plant immuno-activity against various pathogens and pests. In the present study, genomic organization of a resistance gene analog (RGA), designated as PmTNL1, and its allelic variants were characterized in Pinus monticola. PmTNL1 showed high identity with TIR-NBS-LRR proteins from other plants. qRT-PCR revealed that the PmTNL1 transcript was expressed at low basal levels in different tissues and exhibited similar patterns during compatible and incompatible interactions of P. monticola with C. ribicola at early stages post inoculation. In comparison, PmTNL1 was up-regulated significantly in diseased P. monticola tissues with WPBR symptoms. Expression of the PmTNL1 promoter::GUS fusion gene in transgenic Arabidopsis demonstrated that GUS signal appeared only inside phloem tissues of young seedlings and at hydathodes and branching and organ-connecting points in mature Arabidopsis plants. Similar to the endogenous expression pattern for this gene in pine, GUS activity was up-regulated significantly around vascular tissues locally at pathogen infection sites, but little or no induction was observed in response to abiotic stresses. A DNA marker was developed based on variation of the LRR-coding region, and PmTNL1 was mapped to one genetic linkage group using a pedigree with major dominant gene (Cr2) conferring HR resistance to C. ribicola. These results suggest that PmTNL1 may play an important role in white pine partial resistance against C. ribicola.

Castilleja and Pedicularis confirmed as telial hosts for Cronartium ribicola in whitebark pine ecosystems of Oregon and Washington

The primary objective of this research was to determine whether native species of Castilleja and Pedicularis are naturally infected by Cronartium ribicola in whitebark pine ecosystems of the Oregon and Washington Cascade Range, USA. Secondary objectives were to monitor the phenology of aecial and telial hosts to determine whether there is sufficient time for C. ribicola to complete its life cycle within high-elevation stands and to evaluate the variety of susceptible native host species within these genera through field and growth chamber inoculation. These objectives were approached through fieldwork in 2008 and 2009 in whitebark pine ecosystems at Mt. Rainier, Mt. Adams, Mt. Hood, Mt. Bachelor, Tumalo Mtn. and Crater Lake. Forty-nine observational study plots were established and monitored. Natural C. ribicola infection was detected on 84 Pedicularis racemosa plants and five Castilleja plants (C. applegatei, C. miniata and C. parviflora). Field observation provided evidence that there is sufficient time for C. ribicola to complete its life cycle on hosts within high-elevation whitebark pine stands. In 2009, 18 field inoculation plots were established at Mt. Rainier and Crater Lake. Field inoculation confirmed the susceptibility of two additional species within these genera, C. arachnoidea and P. bracteosa. All four Castilleja species inoculated in the growth chamber developed infection, with an overall infection incidence of 62% (167 out of 270 plants). The identity of the rust species on field specimens as C. ribicola was verified through PCR and sequencing of the ITS1-5.8S-ITS2 region of DNA. Improved understanding of the role of these newly recognized hosts in white pine blister rust epidemiology should be used to prioritize sites for the restoration of ecologically valuable whitebark pine.

ALIEN INVASIVE PATHOGENS: THE MAJOR THREAT TO OUR FOREST ECOSYSTEMS IN A TIME OF RAPID CLIMATE CHANGE

Forest ecosystems face unprecedented challenges from the rising rate of influx of alien invasive pests and pathogens resulting from increased global trade. Moreover, climate change predictions suggest that many additional alien pests and pathogens may become problems in forests as temperatures increase and rainfall patterns change. Recent indications of the potential for pathogens to transfer between hosts and the inter-specific hybridisation possible between related pathogens increase concerns over the possibility of escalations in damage in the future. Why are these organisms such a threat? Using examples drawn from wide-scale environmental damage caused to tree populations and forest ecosystems in Europe and elsewhere in the world, in this talk, we will illustrate the potential of alien pathogens to reduce biodiversity, alter ecosystems beyond recognition and impact on human requirements of forests. Classic examples of devastation by alien invasive pathogens affecting trees include Dutch elm disease, caused by Ophiostoma novo-ulmi, Jarrah dieback caused by Phytophthora cinnamomi, canker stain disease of Platanus caused by Ceratocystis platani, and white pine blister rust arising from accidental trans-Atlantic transfer of Cronartium ribicola. Many other examples exist in Europe and elsewhere in the world. Each of these pathogens still causes severe ecosystem damage in areas of introduction. Recent findings obtained from the application of state-of-the-art tools in molecular biology are reshaping our knowledge of alien invasive pathogens. The advent of these molecular biological techniques has greatly enhanced our ability to analyse aspects related to the biology, taxonomy, hidden biodiversity and temporal and spatial structuring of genetic diversity in organisms. Molecular diagnostic assays have resulted in improved detection methods for pests and pathogens based on molecular profiles, that are essential for accurate and rapid detection and enhanced understanding of the pathways of dispersal locally and internationally. This information greatly increases the reliability of pest risk assessment procedures and the development of phytosanitary measures aimed at eradicating, containing or managing these pests. The possibility of regulating the ‘plants for planting’ pathway, one of the major routes through which alien invasive problems are now entering and being dispersed in Europe, will be discussed.

The Effects of Raking on Sugar Pine Mortality following Prescribed Fire in Sequoia and Kings Canyon National Parks, California, USA

Prescribed fire is an important tool for fuel reduction, the control of competing vegetation, and forest restoration. The accumulated fuels associated with historical fire exclusion can cause undesirably high tree mortality rates following prescribed fires and wildfires. This is especially true for sugar pine (Pinus lambertiana Douglas), which is already negatively affected by the introduced pathogen white pine blister rust (Cronartium ribicola J.C. Fisch. ex Rabenh). We tested the efficacy of raking away fuels around the base of sugar pine to reduce mortality following prescribed fire in Sequoia and Kings Canyon national parks, California, USA. This study was conducted in three prescribed fires and included 457 trees, half of which had the fuels around their bases raked away to mineral soil to 0.5 m away from the stem. Fire effects were assessed and tree mortality was recorded for three years after prescribed fires. Overall, raking had no detectable effect on mortality: raked trees averaged 30% mortality compared to 36% for unraked trees. There was a significant effect, however, between the interaction of raking and average pre-treatment forest floor fuel depth: the predicted probability of survival of a 50 cm dbh tree was 0.94 vs. 0.96 when average pre-treatment fuel depth was 0 cm for a raked and unraked tree, respectively. When average pre-treatment forest floor fuel depth was 30 cm, the predicted probability of survival for a raked 50 cm dbh tree was 0.60 compared to only 0.07 for an unraked tree. Raking did not affect mortality when fire intensity, measured as percent crown volume scorched, was very low (0% scorch) or very high (>80% scorch), but the raking treatment significantly increased the proportion of trees that survived by 9.6% for trees that burned under moderate fire intensity (1% to 80% scorch). Raking significantly reduced the likelihood of bole charring and bark beetle activity three years post fire. Fuel depth and anticipated fire intensity need to be accounted for to maximize the effectiveness of the treatments. Raking is an important management option to reduce tree mortality from prescribed fire, but is most effective under specific fuel and burning conditions.

Influences of the biophysical environment on blister rust and mountain pine beetle, and their interactions, in whitebark pine forests

Aim To understand how the biophysical environment influences patterns of infection by non-native blister rust (caused by Cronartium ribicola) and mortality caused by native mountain pine beetles (Dendroctonus ponderosae) in whitebark pine (Pinus albicaulis) communities, to determine how these disturbances interact, and to gain insight into how climate change may influence these patterns in the future. Location High-elevation forests in south-west Montana, central Idaho, eastern and western Oregon, USA. Methods Stand inventory and dendroecological methods were used to assess stand structure and composition and to reconstruct forest history at sixty 0.1-ha plots. Patterns of blister rust infection and mountain pine beetle-caused mortality in whitebark pine trees were examined using nonparametric Kruskal–Wallis ANOVA, Mann–Whitney U-tests, and Kolmogorov–Smirnov two-sample tests. Stepwise regression was used to build models of blister rust infection and mountain pine beetle-related mortality rates based on a suite of biophysical site variables. Results Occurrence of blister rust infections was significantly different among the mountain ranges, with a general gradient of decreasing blister rust occurrence from east to west. Evidence of mountain pine beetle-caused mortality was identified on 83% of all dead whitebark pine trees and was relatively homogenous across the study area. Blister rust infected trees of all ages and sizes uniformly, while mountain pine beetles infested older, larger trees at all sites. Stepwise regressions explained 64% and 58% of the variance in blister rust infection and beetle-caused mortality, respectively, indicating that these processes are strongly influenced by the biophysical environment. More open stand structures produced by beetle outbreaks may increase the exposure of surviving whitebark pine trees to blister rust infection. Main conclusions Variability in the patterns of blister rust infection and mountain pine beetle-caused mortality elucidated the fundamental dynamics of these disturbance agents and suggests that the effects of climate change will be complex in whitebark pine communities and vary across the species’ range. Interactions between blister rust and beetle outbreaks may accelerate declines or facilitate the rise of rust resistance in whitebark pine depending on forest conditions at the time of the outbreak.

The Reemergence and Management of Currant Cane Dieback in the Northeastern United States.

Currant cane dieback, caused by the fungus Botryosphaeria ribis (syn. Neofusicoccum ribis), devastated currant production in the northeastern United States approximately a century ago. Later epidemics of this disease were halted by bans on the planting of Ribes spp. to control white pine blister rust, but since regulations restricting the planting of currants were removed in the 1980s and 1990s, currant cane dieback has reemerged in the northeastern United States. In this study, we obtained fungal isolates from diseased canes at four production operations in New York and Connecticut. We confirmed the isolates as N. ribis on the basis of morphology and ribosomal DNA sequence analysis, and verified pathogenicity through inoculation of healthy currant bushes. Furthermore, field trials to study the effects of cultivar, pruning of symptomatic canes, and fungicide applications were conducted over 2 years. Differences in Ribes cultivar susceptibility to N. ribis were demonstrated, with a pink fruiting cultivar (Pink Champagne) having lower levels of dieback compared to two red cultivars (Rovada and Jonkheer van Tets) and one white cultivar (Blanka) evaluated. While there were no consistent reductions in cane dieback incidence over both years and for all cultivars when pruning or fungicide treatments (copper hydroxide and sulfur applications) were used alone, fungicide treatment combined with pruning resulted in significant (P < 0.05) reductions (>80%) in the incidence of dieback compared to bushes not treated with fungicide or pruned.

Comparative mapping in Pinus: sugar pine (Pinus lambertiana Dougl.) and loblolly pine (Pinus taeda L.)

The majority of genomic research in conifers has been conducted in the Pinus subgenus Pinus mostly due to the high economic importance of the species within this taxon. Genetic maps have been constructed for several of these pines and comparative mapping analyses have consistently revealed notable synteny. In contrast, little genomic research has been conducted on the Pinus subgenus Strobus, even though these pines have strong ecological relevance. We report a consensus genetic linkage map for sugar pine (Pinus lambertiana Dougl.) constructed with 399 single nucleotide polymorphisms markers derived from annotated genes. The map is 1,231 cM in length and organized into 19 linkage groups. Two of the mapping populations were derived from trees that were segregating for the major gene of resistance (Cr1) to Cronartium ribicola, the fungal pathogen responsible for white pine blister rust. The third mapping population was derived from a full-sib cross segregating for partial resistance to white pine blister rust. In addition, we report the first comparative mapping study between subgenera Strobus and Pinus. Sixty mapped markers were found in common between sugar pine and the loblolly pine reference map with 56 of them (93%) showing collinearity. All 19 linkage groups of the sugar pine consensus map coaligned to the 12 linkage groups of the loblolly pine reference map. The syntenic relationship observed between these two clades of pines provides a foundation for advancing genomic research and genetic resources in subgenus Strobus.

A New Look at Spread Rates of Exotic Diseases in North American Forests

Abstract Exotic pathogens threaten ecosystems in novel ways, particularly where they are facilitated by stresses such as climate change and forest fragmentation. Although chestnut blight (CB), Dutch elm disease (DED), beech bark disease (BBD), and white pine blister rust (WPBR) are well-studied pathogens, this investigation is the first to provide estimated rates of spread based on an expansive geospatial database and a consistent, rigorous analytical framework. We use quantile regression to analyze 850 records of infection over the last (20th) century. The results show that in the past, forest disease complexes have spread at rates between 7.4 and 31 km year−1, and two-thirds of the estimates were less than 17 km year−1. We estimated the spread of CB at 31 km year−1, DED in eastern North America at 25 km year−1, DED in western North America at 14 km year−1, BBD at 16 km year−1, WPBR in eastern North America at 7.4 km year−1, and WPBR in western North America at 10 km year−1. These results do not predict the rate of spread of future exotic pathogens in North American forests; rather they provide context for predictive models and a heuristic guide until more scientific data are available.

Factors Contributing to Seasonal Fluctuations in Rust Severity on Ribes missouriense Caused by Cronartium ribicola

Cronartium ribicola, causal agent of white pine blister rust, is a macrocyclic heteroecious rust that cycles between white pines and members of the genus Ribes, which are typically wild plants in North America. To improve predictability of inoculum available for infection of ecologically and commercially important white pines, this research was conducted to identify the factors that influence the development and persistence of uredinia and telia on Ribes in their natural habitats. Numbers of infectious C. ribicola rust lesions (with potentially sporulating rust sori) on tagged Ribes missouriense plants in the woods fluctuated during the season. Changes in numbers of infectious rust lesions were related to rain that occurred 13 days earlier. In field experiments, supplemental leaf wetness provided for 2 days on Ribes shoots resulted in the development of rust lesions more frequently than on control shoots. Viable inoculum and susceptible hosts were present, and the environment was the limiting factor for disease development. Lesion necrosis and leaf abscission contributed to decreases in numbers of infectious rust lesions. Higher lesion density was significantly related to earlier leaf abscission. Telial fruiting bodies occurred in low numbers from early June throughout the remainder of the season.

Susceptibility of Pedicularis spp. to Cronartium ribicola and C. flaccidum in Finland

Summary Aeciospores of Cronartium ribicola and C. flaccidum were collected from several locations in Finland and used to inoculate Pedicularis spp. and some known and suspected alternate hosts in 2008–2009. In all trials, C. ribicola formed uredinia and telia on leaves of Ribes nigrum. No uredinia or telia of C. ribicola formed on older leaves of Pedicularis spp. but both uredinia and telia were found on young leaves of P. palustris ssp. palustris. Cronartium flaccidum produced uredinia and/or telia on leaves of P. palustris ssp. palustris, P. lapponica, Vincetoxicum hirundinaria and Melampyrum sylvaticum. Neither rust infected P. sceptrum-carolinum, Vaccinium myrtillus, Calluna vulgaris or Ledum palustre. Similar to rusts in Asia and North America, the results showed that European C. ribicola exhibit more variable host reactions and wider alternate host ranges than earlier described. Pedicularis palustris may play a role in the spread of Cronartium in natural forests.

Silvicultural approaches for management of eastern white pine to minimize impacts of damaging agents

SummarySince the arrival to North America of Cronartium ribicola, management of eastern white pine has been driven by the need to avoid the actual or, in many areas, the perceived damage caused by white pine blister rust. Although white pine has lost much of its former dominance, it remains a valuable species for biotic diversity, aesthetics, wildlife habitat and forest products. Understanding its silvics and damaging agents provides a sound basis for the silvicultural activities of site selection, regeneration and stand tending. The species can be successfully grown in many locations despite herbivory, competition, white pine weevil and blister rust. Forest managers can minimize damage by applying knowledge of local conditions (climate, soils, physiography and vegetation) to hazard assessment, site selection and preparation, vegetation management, and pruning. With appropriate management and a long‐term commitment, many eastern forests can be beneficially reforested to eastern white pine with little impact from blister rust and other damaging agents.

White pine blister rust in Korea, Japan and other Asian regions: comparisons and implications for North America

SummaryThis article briefly reviews the history of white pine blister rust, attributed to Cronartium ribicola, and addresses current research and management issues in South Korea, Japan and other regions of eastern Asia (China, Russia and Himalaya). For each region, the distribution, damage, aecial hosts, telial hosts and management of C. ribicola and other blister rust fungi on native and introduced white pines are summarized. In addition, blister rust behaviours in eastern Asia and North America are compared; and the potential evolutionary and management implications are discussed.

Biology and pathology of Ribes and their implications for management of white pine blister rust

Summary Ribes (currants and gooseberries) are telial hosts for the introduced and invasive white pine blister rust fungus, Cronartium ribicola. Knowledge of wild and introduced Ribes helps us understand the epidemiology of blister rust on its aecial hosts, white pines, and develop disease control and management strategies. Ribes differ by species in their contribution to initial establishment and subsequent intensification of blister rust. Their significance to pine infection depends on their inherent capacities to become infected and support spore production, their abundance and environmental interactions. Ribes and white pines are adapted to disturbance and frequently co‐occur in forest and woodland ecosystems. Differences in light and moisture requirements affect how long various species of Ribes occupy a site. Natural or artificial selection increases rust resistance in white pines, Ribes, and other host genera; but selection also affects virulence and aggressiveness of C. ribicola. Blister rust pathosystems evolve. Local pathosystems wherein the rust and its hosts coexist with reduced damage could arise by several processes.

Current and future molecular approaches to investigate the white pine blister rust pathosystem

SummaryMolecular genetics is proving to be especially useful for addressing a wide variety of research and management questions on the white pine blister rust pathosystem. White pine blister rust, caused by Cronartium ribicola, is an ideal model for studying biogeography, genetics, and evolution because: (1) it involves an introduced pathogen; (2) it includes multiple primary and alternate hosts occurring in large, relatively undisturbed ecosystems; (3) some hosts exhibit endemic resistance; and (4) the disease interaction is long enduring. Molecular techniques are used to investigate population genetics, phylogenetics, hybrids, and proteomics in white pine (Pinus, subgenus Strobus) and blister rust (Cronartium) and the genetics of resistance and virulence in the blister rust pathosystem. These techniques include genetic markers, mapping, microarrays, sequencing, association genetics, genomics, and genecology. Molecular genetics contributes to gene conservation, breeding for resistance, and ecosystem management.

White pines, Ribes, and blister rust: integration and action

SummaryThe preceding articles in this series review the history, biology and management of white pine blister rust in North America, Europe and eastern Asia. In this integration, we connect and discuss seven recurring themes important for understanding and managing epidemics of Cronartium ribicola in the white pines (five‐needle pines in subgenus Strobus). Information and action priorities for research and management of the pathogen, telial and aecial hosts, and their interactions are listed in a detailed Appendix. Syntheses focused on genetics, plant disease, invasive species or forest management have provided alternative but knowledgeable lessons on the white pine blister rust pathosystem. Two critical issues for the conservation of white pines are to sustain ecosystems affected by blister rust and to maintain genetic diversity for adaptive traits such as disease resistance. Forest genetics includes tree improvement and molecular techniques for research; their application can increase rust resistance by artificial and natural selection. Silviculture augments genetics with methods to deploy and enhance resistance as well as to regenerate and tend white pine stands. Although cultivated or wild Ribes might serve as inoculum sources, silviculture and horticulture can reduce the risk of serious impacts from blister rust using genetics for breeding and epidemiology for hazard assessment and disease control. Climate change threatens to cause major alterations in temperature and precipitation regimes, resulting in maladapted conifers succumbing to various diseases and insect outbreaks. In contrast, many white pine species have broad ecological ranges and are tolerant of harsh environments—traits that permit successful establishment and growth over wide geographic and altitudinal zones. Given appropriate management, white pines could thrive as valuable commercial and ecologically important keystone species. In an uncertain environment, adaptive management provides a learning and participatory approach for sustaining resilient ecosystems.

White pines, Ribes, and blister rust: a review and synthesis

SummaryFor over a century, white pine blister rust (Cronartium ribicola) has linked white pines (Strobus) with currants and gooseberries (Ribes) in a complex and serious disease epidemic in Asia, Europe, and North America. Because of ongoing changes in climate, societal demands for forests and their amenities, and scientific advances in genetics and proteomics, our current understanding and management of the white pine blister rust pathosystem has become outdated. Here, we present a review and synthesis of international scope on the biology and management of blister rust, white pines, Ribes, and other hosts. In this article, we provide a geographical and historical background, describe the taxonomy and life cycle of the rust, discuss pathology and ecology, and introduce a series of invited papers. These review articles summarize the literature on white pines, Ribes, and blister rust with respect to their status, threats, and management through genetics and silviculture. Although the principal focus is on North America, the different epidemics in Europe and Asia are also described. In the final article, we discuss several of the key observations and conclusions from the preceding review articles and identify prudent actions for research and management of white pine blister rust.

A review of genetic approaches to the management of blister rust in white pines

SummarySince introduced a century ago, Cronartium ribicola has devastated many populations of North American white pines. However, significant genetic resistance to white pine blister rust occurs naturally and can be exploited. In this review, we discuss the progress and different approaches to breeding for resistance in North American white pines. Three broad categories of resistance are: (1) ontogenetic resistance, (2) R‐gene resistance and (3) partial resistance. Ontogenetic resistance is associated with increased host age and indicated by higher susceptibility to infection in primary needles and young seedlings then in grafts and older trees. R‐gene resistance (major gene resistance) is an example of the classic gene‐for‐gene system common in many rust diseases. R‐gene resistance provides immunity but may not be durable. Host resistance and the corresponding rust virulence which defeats it are well described for sugar pine and western white pine. Host plants with partial resistance are able to retard or tolerate disease development without eliminating the pathogen. Partial resistance is also called slow‐rusting resistance or low‐level resistance and is revealed in seedlings by several responses, including slow‐canker‐growth, difficult‐to‐infect, needle‐shed and bark‐reaction. Most of these seedling responses are presumed to be multigenic; but needle‐shed may be controlled by recessive genes. Long‐term, field trials for verification of screening and selection results are sparse. Although 100% higher survival of selected material over unselected occurs in some trials, mortality is high under conditions of high hazard and heavy inoculum load. In several, long‐term trials, some full‐sib crosses expressed a strong phenotypic resistance that indicates specific combining ability between complimentary parents. These and other observations suggest that we might yet find strong and durable resistance. Study of Eurasian white pines infected by blister rust fungi could help us better understand endemic pathosystems. Different strategies are identified for deploying material selected for either R‐gene or partial resistance. Current research suggests that resistance is more complex than previously modelled, but new molecular techniques offer useful methods for investigating the white pine blister rust pathosystem.