Western White Pine Research Articles

Survey of oomycetes and pathogenicity of Phytophthora cinnamomi associated with root rot disease of western white pine (Pinus monticola)

Western white pine (Pinus monticola) with genetic tolerance to white pine blister rust disease caused by Cronartium ribicola constitutes an invaluable resource for the mitigation of this disease as well as the restoration of the species and its utilization in managed forests. In the last several years, typical root-rot symptoms and sudden tree death have been observed in some western white pine plantations located in British Columbia (BC) in Canada, and a few Phytophthora species were found to be associated with symptomatic trees. Our objectives were to survey one of the plantations located in south-west BC on Vancouver Island to confirm the presence of these Phytophthora species and other oomycetes and test their pathogenicity on western white pine by completing Koch’s postulates. We used direct plating of root samples on PARP(H)-CMA media and by baiting for oomycetes in soil and root samples. Ten oomycetes, including four Phytophthora species (Phytophthora cinnamomi, P. cactorum-like, P. cryptogea and P. pseudocryptogea) were isolated from roots and soil samples of diseased Pi. monticola trees. The Phytophthora species were identified using ITS, β-tubulin and TEF1 gene regions. Koch’s postulates were validated with controlled inoculations of 1-year old seedlings; mortality occurred as early as 15 days after inoculation with P. cinnamomi when the seedlings were maintained in warm temperature conditions (25°C). Molecular typing of two P. cinnamomi cultures using Oxford Nanopore MinIONTM sequencing indicated that they belong to one of the two main clonal clusters of mating type A2 that have been recognized as the main drivers of the global P. cinnamomi epidemic.

Non-Contact Laser Doppler Vibrometer for Characterization of Guided Waves in Timber Structures with Varying Moisture Content and Grain Orientations

Timber structures have been widely used in critical engineering applications throughout history. The need for Non-Destructive Testing of timbers has arisen, and ultrasonic-guided waves (GWs) have proved their efficacy in studying structural integrity. The effect of the grain direction in orthotropic timber structures on the propagation characteristics of GWs is not well understood, especially in the presence of moisture. This study aims to comprehend the effects of timber-grain orientations and the moisture content (MC) on dominant GW modes, specifically, on the anti-symmetric A0 mode. The study is based on samples extracted from a Western White Pine utility pole, in three different orientations including longitudinal, tangential, and radial. The MC is introduced using a desiccator with a saturated salt solution. The studied MC conditions included dry, ambient MC, and high MCs varying from 10% to 27%. The GWs were excited using piezoelectric actuators and sensed with a Scanning Laser Doppler Vibrometer with Free-Free boundary condition. Phase velocities were obtained using the frequency-wavenumber plots of the measured line scans and were compared to the analytical curves for mode analysis. The results showed that the experimental A0-mode phase velocities match well with those generated analytically. The difference was negligible for longitudinally oriented specimens with a percentage difference ranging from 0.28% to 5.34%, as the MC varied. The phase velocity decreased by about 7% as the MC increased from 0% to 27%. A noticeable difference in the phase velocity was measured with different orientations; at dry conditions, the A0 propagated at 958 m/s in the longitudinal specimens, while it decreased in the tangential specimens to about 760 m/s, and had the lowest phase velocity in the radial direction reaching 433 m/s. The results show a high sensitivity of the propagating GWs to the direction of the fibers and the MC present in the timber.

Prefire Drought Intensity Drives Postfire Recovery and Mortality in Pinus monticola and Pseudotsuga menziesii Saplings

Abstract Increasing frequency of droughts and wildfire are sparking concerns that these compounded disturbance events are pushing forested ecosystems beyond recovery. An improved understanding of how compounded events affect tree physiology and mortality is needed given the reliance of fire management planning on accurate estimates of postfire tree mortality. In this study, we use a toxicological dose-response approach to quantify the impact of variable-intensity drought and fire on the physiology and mortality of Pinus monticola and Pseudotsuga menziesii saplings. We show that the dose-response relationship between fire intensity and mortality shifts toward increased vulnerability under drought, indicating higher mortality with increasing drought at any fire intensity. The trajectory we observed in postfire chlorophyll fluorescence, an indicator of photosynthetic efficiency and stress, was an effective early warning sign of impending tree death. Postfire mortality modeling shows that accurate mortality classification can be achieved using prefire physiology and morphology metrics combined with fire intensity. Variable importance measures indicate that physiological condition and fire intensity have greater influence on the classification accuracy than morphological metrics. The wide range in drought and fire responses observed between this study and others highlights the need for more research on compound disturbance effects. Study Implications: An improved understanding of how drought and fire affect tree physiology and mortality is needed by natural resource managers looking to predict postfire tree mortality. This study advances our compound disturbance understanding by subjecting conifer saplings to variable drought and fire intensities and quantifying and modeling moderate-term recovery and mortality. The results show reduced physiological recovery and amplified mortality in saplings exposed to greater drought and fire intensity. Overall, this study highlights the importance of physiological condition when modeling tree mortality and could potentially be used to inform current postfire tree mortality models.

Evaluating Predictive Models of Tree Foliar Moisture Content for Application to Multispectral UAS Data: A Laboratory Study

Water supply is a critical component of tree physiological health, influencing a tree’s photosynthetic activity and resilience to disturbances. The climatic regions of the western United States are particularly at risk from increasing drought, fire, and pest interactions. Existing methods for quantifying drought stress and a tree’s relative resilience against disturbances mostly use moderate-scale (20–30 m) multispectral satellite sensor data. However, tree water status (i.e., water stress) quantification using sensors like Landsat and Sentinel are error-prone given that the spectral reflectance of pixels are a mixture of the dominant tree canopy, surface vegetation, and soil. Uncrewed aerial systems (UAS) equipped with multispectral sensors could potentially provide individual tree water status. In this study, we assess whether the simulated band equivalent reflectance (BER) of a common UAS optical multispectral sensor can accurately quantify the foliar moisture content and water stress status of individual trees. To achieve this, water was withheld from groups of Douglas-fir and western white pine saplings. Then, measurements of each sapling’s foliar moisture content (FMC) and spectral reflectance were converted to BER of a consumer-grade multispectral camera commonly used on UAS. These bands were used in two classification models and three regression models to develop a best-performing FMC model for predicting either the water status (i.e., drought-stressed or healthy) or the foliar moisture content of each sapling, respectively. Our top-performing models were a logistic regression classification and a multiple linear regression which achieved a classification accuracy of 96.55% and an r2 of 82.62, respectively. These FMC models could provide an important tool for investigating tree crown level water stress, as well as drought interactions with other disturbances, and provide land managers with a vital indicator of tree resilience.

Disease resistance in whitebark pine and potential for restoration of a threatened species

Societal impact statementForests world‐wide are being negatively affected by non‐native, invasive pathogens and pests, and some tree species face uncertain futures. To retain these species as components of future forests, the rare genetic resistance that exists needs to be identified and harnessed. The applied tree improvement program for whitebark pine (Pinus albicaulis), a threatened (in the United States) and endangered (in Canada) keystone species in many forests in western North America, provides an example of what can be accomplished in a relatively short timeframe. The level and frequency of resistance vary by location, and this information will be used to implement the national restoration plan.Summary Forest trees face serious threats from non‐native diseases and pests, often causing high mortality of both the existing trees and regeneration. Developing populations with genetic resistance can help restore forests and retain affected species. Resistance programs have historically focused on species of high economic importance; however, the threats to species of little direct economic value that provide other important ecosystem services are also great. We examined the frequency, level, and geographic variation in genetic resistance to white pine blister rust in the threatened Pinus albicaulis (whitebark pine), a keystone species in high‐elevation ecosystems in western North America. In the two trials reported here, 2‐year‐old seedling progeny of 225 whitebark pine parent trees were inoculated with two geographic sources of the fungal pathogen Cronartium ribicola and evaluated over 5 years for an array of resistance traits. The trials focused primarily on parent trees from the Oregon and Washington populations. We found unexpectedly high levels of quantitative resistance in some seedling families and populations, in stark contrast to levels observed in similar resistance programs with other North American white pine species such as Pinus monticola and Pinus lambertiana. The level of resistance found in some whitebark pine populations provides optimism about potential recovery efforts for this species. Restoration efforts are underway by government agencies, tribes, and non‐government organizations in both the United States and Canada. These efforts may help boost support for applied genetic resistance programs in other forest tree species severely affected by non‐native pathogens or pests.

Soil disturbance, amelioration and rehabilitation affect forest growth, health, soil carbon and chemistry on five long-term soil productivity (LTSP) sites in southeastern British Columbia

Soil disturbance amelioration affected tree survival, growth, health, mineral soil chemistry, and their covariation on five Long-Term Soil Productivity (LTSP) sites in southeastern British Columbia. The two most different LTSP treatments (baseline disturbance of no compaction / all organic matter left, versus most severe of heavy compaction / forest floor removed) were compared to five amelioration treatments: rehabilitation of most severe LTSP treatment (soil tillage with or without incorporation of removed forest floor [Rehab + FF]), root disease (Armillaria ostoyae (Romagn.) Herink) amelioration treatments (stump removal or biological with Hypholoma fasiculare), and enhancement of soil organic matter (tilling extra forest floor into mineral soil). Treatment significantly (p < 0.05) affected 10-year mineral soil carbon, nitrogen, sulfur, mineralizable nitrogen, and potassium, which were lower on forest floor removal treatments and higher on forest floor addition treatments (27 to 97% of baseline versus 78 to 183% of baseline, respectively). Western white pine (Pinus monticola Dougl. ex D.Don) 15-year productivity (m3/ha) was significantly affected by treatment (Rehab + FF yielding a 10 fold increase in productivity versus the poorly growing baseline treatment), with treatment also significant when total disease was a covariate and for average and total volume when mineral soil Ca:Al ratio was a marginally significant (p < 0.1) covariate, and for survival when the incidence of total disease or white pine blister rust (Cronartium ribicola) were significant covariates; or with mineral soil C:N ratio as a significant covariate. The incidence of blister rust and total disease were significantly influenced by treatment when C:N was a significant covariate. For 20-year lodgepole pine (Pinus contorta Dougl. Ex Loud) there were no direct relationships apparent, but western gall rust (Endocronartium harknessii) had treatment significant when total sulfur was a significant covariate. Fifteen- and twenty-year Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) had no significant relationships. Results demonstrate that restoring or adding extra organic matter (forest floor) into mineral soil increased soil carbon and related nutrients and can increase above ground carbon (forest productivity). Conversely, removing forest floor lowered mineral soil carbon and generally lowered tree volume. Varied effects due to growth limiting factors like frost and competing vegetation affected results on a few plots. Recommendations include leaving or enhancing organic matter onsite for soil carbon, nutrients, forest health and site productivity. Further analysis with the larger LTSP dataset and ongoing monitoring is encouraged to determine if the results persist in the long-term and to better understand the significant covariate relationships.

Fire intensity impacts on physiological performance and mortality in Pinus monticola and Pseudotsuga menziesii saplings: a dose-response analysis.

Fire is a major cause of tree injury and mortality worldwide, yet our current understanding of fire effects is largely based on ocular estimates of stem charring and foliage discoloration, which are error prone and provide little information on underlying tree function. Accurate quantification of physiological performance is a research and forest management need, given that declining performance could help identify mechanisms of-and serve as an early warning sign for-mortality. Many previous efforts have been hampered by the inability to quantify the heat flux that a tree experiences during a fire, given its highly variable nature in space and time. In this study, we used a dose-response approach to elucidate fire impacts by subjecting Pinus monticola var. minima Lemmon and Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco saplings to surface fires of varying intensity doses and measuring short-term post-fire physiological performance in photosynthetic rate and chlorophyll fluorescence. We also evaluated the ability of spectral reflectance indices to quantify change in physiological performance at the individual tree crown and stand scales. Although physiological performance in both P. monticola and P. menziesii declined with increasing fire intensity, P. monticola maintained a greater photosynthetic rate and higher chlorophyll fluorescence at higher doses, for longer after the fire. Pinus monticola also had complete survival at lower fire intensity doses, whereas P. menziesii had some mortality at all doses, implying higher fire resistance for P. monticola at this life stage. Generally, individual-scale spectral indices were more accurate at quantifying physiological performance than those acquired at the stand-scale. The Photochemical Reflectance Index outperformed other indices at quantifying photosynthesis and chlorophyll fluorescence, highlighting its potential use to quantify crown scale physiological performance. Spectral indices that incorporated near-infrared and shortwave infrared reflectance, such as the Normalized Burn Ratio, were accurate at characterizing stand-scale mortality. The results from this study were included in a conifer cross-comparison using physiology and mortality data from other dose-response studies. The comparison highlights the close evolutionary relationship between fire and species within the Pinus genus, assessed to date, given the high survivorship of Pinus species at lower fire intensities versus other conifers.

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The cover image is based on the Original Article Epicuticular wax content of western white pine is involved in Cronartium ribicola resistance by David Noshad et al., https://doi.org/10.1111/efp.12793

Epicuticular wax content of western white pine is involved in Cronartium ribicola resistance

AbstractThe introduction of Cronartium ribicola, the causative agent of white pine blister rust, has been devastating for white pines in North America, including western white pine. Among the observed partial resistance responses to white pine blister rust is a mechanism referred to as difficult‐to‐infect (DI), which is characterized by lower frequency of infection spots on needles and a lower incidence of branch and stem cankers than susceptible host plants. Parents with the DI trait were selected and bred to produce nine full‐sib families. Progeny were propagated and cloned using in vitro techniques in controlled environmental conditions. Explants were inoculated with a single strain of C. ribicola and characterized by using a disease assessment index (DAI), which was used to compare DI full‐sib families to several other full‐sib families (from Idaho) selected for other partial resistance traits. Most DI families had significantly lower DAI scores and higher epicuticular wax content. When the wax was removed from the surface of needles, the DAI of all full‐sib families increased. Scanning electron microscopy revealed that stomata in DI full‐sib families are mostly occluded by epicuticular wax. The results of this study suggest that the DI resistance mechanism of western white pine is related to needle surface epicuticular wax, which likely hinders the penetration of stomata by fungal hyphae. The occurrence and magnitude of this trait in the breeding population remains unknown, and special assessment technique for large‐scale screening will have to be developed.

White pine blister rust, logging, and species replacement increased streamflow in a montane watershed in the northern Rockies, USA

Vegetation changes can strongly influence the hydrological cycle, including streamflow, but the effects of plant diseases have seldom been described. In the mid-20th century, the invasion of an exotic disease, white pine blister rust, precipitated widespread mortality of western white pine (WWP; Pinus monticola Dougl.) in the northern Rocky Mountains, USA. These events converted a forest dominated by white pine into one dominated by more shade-tolerant tree species. The long-term hydrological implications of this historical shift in forest composition have not been adequately explored, in part because collocated long-term vegetation, meteorology, and hydrology data are rare. We assembled long-term streamflow, climate, and vegetation records for a small (4.0 km2) forested watershed in the U.S. northern Rocky Mountains. We used a minimally-calibrated, physically-based model to simulate historical changes in the water budget based on observed vegetation changes along with the historical climate. The observed hydrological anomalies were attributed to a combination of white pine blister rust induced tree mortality, harvest, and eventual species replacement. Small increases in streamflow began in the basin in the 1940s, when the basal area of WWP began to decrease. More dramatic increases in streamflow started after harvesting began in 1966. Based on both observations and modeling, streamflow increased by ∼131–179 mm between the 1940s and the 2000s (30–40% of the 2000s’ streamflow) in contrast to documented regional streamflow declines. Approximately 1/3 of the flow changes were attributed to blister rust and 2/3 to harvest, as shade-tolerant species instead of WWP regenerated in response to both. This study highlights the importance of long-term ecohydrological data, which made it possible to detect the influence of the invasion of an exotic pathogen against a backdrop of periodic timber harvest. It also showed that the species replacement after these disturbances caused long-term changes in the flow regime, providing a clear and relevant example of how land cover changes can affect interannual hydrological dynamics.

Plant Seeds Commonly Host Bacillus spp., Potential Antagonists of Phytopathogens.

In agriculture, horticulture and plantation forestry, Bacillus species are the most commonly applied antagonists and biopesticides, targeting plant pathogens and insect pests, respectively. Bacillus isolates are also used as bacterial plant biostimulants, or BPBs. Such useful isolates of Bacillus are typically sourced from soil. Here, we show that Bacillus - and other antagonistic microbes - can be sourced from a broad range of plant seeds. We found that culturable Bacillus isolates are common in the seeds of 98 plant species representing 39 families (i.e., 87% of the commonly cultured bacteria belonged to Bacillales). We also found that 83% of the commonly cultured fungi from the seeds of the 98 plant species belonged to just three orders of fungi-Pleosporales, Hypocreales and Eurotiales-that are also associated with antagonism. Furthermore, we confirmed antagonism potential in agaro with seed isolates of Bacillus from Pinus monticola as a representative case. Eight isolates each of seed Bacillus, seed fungi, and foliar fungi, all from P. monticola, were paired in a total of 384 possible pair-wise interactions (with seed and foliar fungi as the targets). Seed Bacillus spp. were the strongest antagonists of the seed and foliar fungi, with a mean interaction strength 2.8 times greater than seed fungi (all either Eurotiales or Hypocreales) and 3.2 times greater than needle fungi. Overall, our study demonstrates that seeds host a taxonomically narrow group of culturable, antagonistic bacteria and fungi.

Genomic Comparisons of Two Armillaria Species with Different Ecological Behaviors and Their Associated Soil Microbial Communities.

Armillaria species show considerable variation in ecological roles and virulence, from mycorrhizae and saprophytes to important root pathogens of trees and horticultural crops. We studied two Armillaria species that can be found in coniferous forests of northwestern USA and southwestern Canada. Armillaria altimontana not only is considered as a weak, opportunistic pathogen of coniferous trees, but it also appears to exhibit in situ biological control against A. solidipes, formerly North American A. ostoyae, which is considered a virulent pathogen of coniferous trees. Here, we describe their genome assemblies and present a functional annotation of the predicted genes and proteins for the two Armillaria species that exhibit contrasting ecological roles. In addition, the soil microbial communities were examined in association with the two Armillaria species within a 45-year-old plantation of western white pine (Pinus monticola) in northern Idaho, USA, where A. altimontana was associated with improved tree growth and survival, while A. solidipes was associated with reduced growth and survival. The results from this study reveal a high similarity between the genomes of the beneficial/non-pathogenic A. altimontana and pathogenic A. solidipes; however, many relatively small differences in gene content were identified that could contribute to differences in ecological lifestyles and interactions with woody hosts and soil microbial communities.

Efficacy of delayed entry low branch sanitation pruning in preventing mortality of western white pine infected with white pine blister rust

White pine blister rust, caused by the fungus Cronartium ribicola J. C. Fisch., is a virulent mortality agent of five-needle pines like western white pine (Pinus monticola D. Don.). For decades, low branch pruning has been recommended as a control by removing cankers that can migrate from infected branches to the tree stem and kill the host. These recommendations are mainly based on studies done on eastern white pine (Pinus strobus L.), or on western white pine growing primarily in the Interior Pacific Northwest of the United States. It is not clear whether these recommendations are transferable to geographically and climatically dissimilar Pacific coastal areas, where pruning often shows little benefit in commercial forest plantations. We summarize over 30 years of post-treatment data from coastal and interior sites in British Columbia. Sanitation pruning was done on 12–22-year-old stands using one or two pruning lifts and infection and mortality were tracked over the subsequent decades. Our results show that while pruning had little negative effect on treated tree height or diameter growth, mortality was not significantly different between treated and untreated groups across all sites. Cumulative mortality after three decades was >80% for coastal sites, and nearly 60% for the interior site, indicating a lack of treatment efficacy. Our results differ from earlier shorter duration studies and those from other jurisdictions. It is clear that delaying pruning until trees are older and carrying many existing branch and stem infections results in ineffective control of rust in coastal white pine stands.

Biophysical Settings that Influenced Plantation Survival During the 2015 Wildfires in Northern Rocky Mountain Moist Mixed-Conifer Forests

Abstract Fire suppression and the loss of western white pine (WWP) have made northern Rocky Mountain moist mixed-conifer forests less disturbance resilient. Although managers are installing hundreds of plantations, most of these plantations have not experienced wildfire since establishment. In 2015, wildfires burned through 100 WWP plantations in this region, providing an opportunity to evaluate the effects of wildfires on sapling survival. A Weibull distribution approach was used to characterize the variation of fire severity pixels, as indicated by the differenced normalized burn ratio. The distribution parameters provided a method to identify the biophysical setting and plantation characteristics influencing fire severity and sapling survival. Plantations located on lower slope positions were more resistant to wildfires than plantations located midslope or close to the ridges. Snow water equivalent was positively correlated with wildfire resistance and resilience. Results will help focus reforestation efforts and identify locations where future plantations can potentially survive wildfires.

Fifteen-year tree growth on standard long-term soil productivity trials and various adjacent amelioration treatments at Interior Cedar-Hemlock sites in southeastern British Columbia and northern Idaho

Understanding the relationship between soil disturbance and tree growth is key to sustainable forest management. We report fifteen-year tree growth results of Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) and western white pine (Pinus monticola Dougl. ex D.Don) growth following clearcut harvesting and installation of three replicates of the international Long-Term Soil Productivity (LTSP) trial protocols. Additional amelioration plots were also established on each replicate site to study rehabilitation of the most severe disturbance, treatment of Armillaria root disease, and enhancement of soil organic matter. Stark differences were found among the various treatments and species. Vegetation control resulted in significantly better growth for both tree species across the core LTSP treatments and amelioration treatments. On the core LTSP treatments, organic matter removal had a significant negative effect on Douglas-fir growth. Amelioration treatments resulted in similar survival and similar or better volume growth than the core LTSP treatments, with the exception of poor volume growth after compaction rehabilitation with no organic matter returned into the soil. Compaction significantly influenced Douglas-fir survival and was often higher on moderate compaction plots. On some sites there was decreased survival and growth associated with heavy compaction that will likely influence longer-term outcomes with a more variable and changing climate. Overall, results to date on the core LTSP treatments, amelioration treatments, and adjacent miniplots reported elsewhere suggest that forest floor removal causes negative growth and, combined with severe compaction, caused both negative growth and poor survival. In the Interior Northwest it is still prudent to minimize soil disturbance and leave organic matter onsite unless there is site specific evidence to the contrary. Additional work is required to reap the full, long-term benefit of the installations. Recommendations are provided highlighting the critical work that should be completed in the near future before biological evidence is lost to decay, including suggestions for further data analysis and extension, the need to continue LTSP core, amelioration and miniplot measurements to demonstrate and calibrate sustainable forest resource management. Our data suggest considering changes to current soil disturbance policy and forest operations based on the current results regarding forest floor displacement.

Susceptibility of sugar pine, Shasta red fir and Sierra lodgepole pine to mountain hemlock dwarf mistletoe (Arceuthobiumtsugense subsp. mertensianae, Viscaceae) in south central Oregon

AbstractIn southern Oregon and northern California, mountain hemlock dwarf mistletoe (MHDM; Arceuthobium tsugense subsp. mertensianae) commonly parasitizes mountain hemlock (Tsuga mertensiana) in multiple mountain ranges such as the Cascades, Sierra Nevada and Klamath Mountains. However, limited information is available on the susceptibility of sugar pine (Pinus lambertiana), Shasta red fir (Abies magnifica var. shastensis) and lodgepole pine (Pinus contorta) to MHDM. From 2015–2019, I found MHDM on sugar pine at multiple sites in northwestern Klamath County, Oregon. To evaluate the susceptibilities of sugar pine, Shasta red fir and Sierra lodgepole pine to MHDM infection, 41 temporary, fixed‐radius plots (area 182.4 m2) were established at five sites in 2018 and 2019 around an overstory tree (western white, sugar and whitebark pines along with one mountain hemlock) severely infected with MHDM in each plot centre. Live trees ≥2.6 cm in diameter at breast height (1.37 m; dbh) were assigned a dwarf mistletoe severity rating (6‐class system) and incidence (% infection) of MHDM on live trees at the tree level were used to estimate host susceptibilities. To confirm the identity of the dwarf mistletoe infecting live trees in each plot, dwarf mistletoe specimens were collected from the severely infected tree at the centre of each plot and from all tree species bearing dwarf mistletoe in each plot. Morphological characters were used to identify the dwarf mistletoe plants on each tree species and included plant heights, length of the third internode and plant colour. Dwarf mistletoe plants were collected from each affected tree species, and morphological characteristics of aerial shoots of dwarf mistletoes were examined in the laboratory. Morphological measurements confirmed the dwarf mistletoe infesting each plot was MHDM. Mountain hemlock dwarf mistletoe was found on sugar pine in all 41 plots. At the tree level after pooling larger sugar pine trees from all plots (total of 164 live trees ≥2.6 cm dbh), incidence was 76%. Morphological characteristics of MHDM aerial shoots, such as colour, shoot height and third internode length, were consistent with previous descriptions of MHDM plants. These data indicate that sugar pine should be classified as a secondary host of MHDM in the Oregon East Cascades, and not as a rare host as previously reported. No dwarf mistletoe plants were found on 98 living Shasta red fir trees ≥2.6 cm dbh in 26 plots. Shasta red fir should be classified as immune to MHDM. No MHDM was found on 573 living lodgepole pines of this size in 41 plots, and the tree species should be classified as immune to MHDM. Western white (Pinus monticola) and whitebark (Pinus albicaulis) pines were severely parasitized by MHDM with 92% and 100% incidence, respectively. However, because the sample sizes for these white pines were relatively small, additional work is needed to evaluate the susceptibility of these pines to MHDM.

Potential Use of the Pigments from Scytalidium cuboideum and Chlorociboria aeruginosa to Prevent ‘Greying’ Decking and Other Outdoor Wood Products

UV-light degradation of wood is one of the top reasons for consumer replacement of outdoor wooden structures. This type of degradation is seldom mechanical, and is instead often motivated by loss of aesthetics (graying). There are numerous commercial products available on the market that deal with this loss of color, many of which contain added pigments to ‘rejuvenate’ or ‘revitalize’ greyed wood. These pigments are almost uniformly synthetic. In contrast, pigments from wood decay fungi (spalting), which have been used in woodworking since the 1400s (intarsia), have remarkable optical (UV-light resistance) properties due to their naphthoquinonic configuration. In recent years the pigments made from these fungi have been extracted and tested across numerous substrates, from solar cells to textile dyes. In this work, researchers extracted pigments from Scytalidium cuboideum (red pigmentation) and Chlorociboria aeruginosa (blue-green pigmentation), solubilized the pigments in raw linseed oil, and tested the resulting solution on samples of Douglas-fir (Pseudotsuga menziesii) and western white pine (Pinus monticola). These mixtures were compared against a ‘stain and coat’ treatment (utilizing an aniline stain and coated with raw linseed oil), raw linseed oil, and untreated wood. The wood samples were then placed in an accelerated weathering machine (Q-UV) following the ASTM G154 standard, for 500 and 1000 h. The results showed that while no visible color change occurred to the wood when the pigmented oil was applied, the red pigment oil significantly lowered the coating degradation for both wood types at an exposure of 500 h. The results show the potential applications for fungal pigments in the wood coating industry, as it offers an increased coating service life. As there is a shift to renewable products, the pigments from wood decay fungi show potential as additives for wood coatings.

Comparative Transcriptomics and RNA-Seq-Based Bulked Segregant Analysis Reveals Genomic Basis Underlying Cronartium ribicola vcr2 Virulence.

Breeding programs of five-needle pines have documented both major gene resistance (MGR) and quantitative disease resistance (QDR) to Cronartium ribicola (Cri), a non-native, invasive fungal pathogen causing white pine blister rust (WPBR). WPBR is one of the most deadly forest diseases in North America. However, Cri virulent pathotypes have evolved and can successfully infect and kill trees carrying resistance (R) genes, including vcr2 that overcomes MGR conferred by the western white pine (WWP, Pinus monticola) R gene (Cr2). In the absence of a reference genome, the present study generated a vcr2 reference transcriptome, consisting of about 20,000 transcripts with 1,014 being predicted to encode secreted proteins (SPs). Comparative profiling of transcriptomes and secretomes revealed vcr2 was significantly enriched for several gene ontology (GO) terms relating to oxidation-reduction processes and detoxification, suggesting that multiple molecular mechanisms contribute to pathogenicity of the vcr2 pathotype for its overcoming Cr2. RNA-seq-based bulked segregant analysis (BSR-Seq) revealed genome-wide DNA variations, including about 65,617 single nucleotide polymorphism (SNP) loci in 7,749 polymorphic genes shared by vcr2 and avirulent (Avcr2) pathotypes. An examination of the distribution of minor allele frequency (MAF) uncovered a high level of genomic divergence between vcr2 and Avcr2 pathotypes. By integration of extreme-phenotypic genome-wide association (XP-GWAS) analysis and allele frequency directional difference (AFDD) mapping, we identified a set of vcr2-associated SNPs within functional genes, involved in fungal virulence and other molecular functions. These included six SPs that were top candidate effectors with putative activities of reticuline oxidase, proteins with common in several fungal extracellular membrane (CFEM) domain or ferritin-like domain, polysaccharide lyase, rds1p-like stress responsive protein, and two Cri-specific proteins without annotation. Candidate effectors and vcr2-associated genes provide valuable resources for further deciphering molecular mechanisms of virulence and pathogenicity by functional analysis and the subsequent development of diagnostic tools for monitoring the virulence landscape in the WPBR pathosystems.

In-vitro anti-fungal assay and association analysis reveal a role for the Pinus monticola PR10 gene (PmPR10-3.1) in quantitative disease resistance to white pine blister rust.

Pathogenesis-related (PR) proteins play important roles in plant defense response. However, functional investigation of PR10 genes is still limited and their physiological roles have not been conclusively characterized in biological processes of conifer trees. Here, we identified multiple novel members in the western white pine (Pinus monticola) PmPR10 family by bioinformatic mining available transcriptomic data. Phylogenetic analysis of protein sequences revealed four PR10 and two PR10-like clusters with a high synteny across different species of five-needle pines. Of 10 PmPR10 genes, PmPR10-3.1 was selected and expressed in Escherichia coli. The purified recombinant protein exhibited inhibitory effects on spore hyphal growth of fungal pathogens Cronartium ribicola, Phoma exigua, and Phoma argillacea by in-vitro anti-fungal analysis. Genetic variation analysis detected a total of 21 single nucleotide polymorphisms (SNPs) within PmPR10-3.1 in a collection of P. monticola seed families. A nonsynonymous SNP (t178g) showed significant association with relative levels of quantitative disease resistance (QDR), explaining about 8.7% of phenotypic variation as the peak value across all SNPs. Our results provide valuable insight into the genetic architecture underlying P. monticola QDR and imply that PmPR10-3.1 may function as an important component in conifer basal immunity for non-specific resistance to a wide spectrum of pathogens.

Infectious Disease, Bark Beetles, and Wildland Fire impacts on Southern Sierra White Pines

Photo 1: The triple treat for southern Sierra white pines. Left: White pine blister rust aeciospores on whitebark pine. Top right: Mountain pine beetle pitch tubes in sugar pine. Bottom right: Wildland fire. Photo credit: Joan Dudney. Photo 2: We surveyed four different white pine species, all susceptible to impacts from blister rust, MPB, and fire. From upper left, whitebark pine (Pinus albicaulis), western white pine (Pinus monticola; lower left), foxtail pine (Pinus balfouriana; center), sugar pine (Pinus lambertiana; right). Photo credit: Joan Dudney. Photo 3: Metal monument maker located at the beginning of the plot (upper left). The beginning of a plot transect (lower left). Example of a journal entry left by Duriscoe’s team (center). Crew assessing a diseased tree (upper right). Crew measuring tree growth, or diameter at breast height (dbh; lower right). Photo credit: Joan Dudney. Photo 4: The crews carried heavy packs and gear through some unanticipated extreme conditions, including dense smoke, lightning storms, flash floods, and steep, cross-country terrain. Photo credit: Joan Dudney. Photo 5: Subalpine white pine forests in the southern Sierra Nevada have much lower levels of MPB, fire, and blister rust compared to lower elevation montane forests. Photo credit: Joan Dudney. These photographs illustrate the article, “Compounding effects of white pine blister rust, mountain pine beetle, and fire threaten four white pine species," by Joan Dudney, Jonathan C. B. Nesmith, Matthew C. Cahill, Jennifer E. Cribbs, Dan M. Duriscoe, Adrian J. Das, Nathan L. Stephenson, and John J. Battles, published in Ecosphere. https://doi.org/10.1002/ecs2.3263.