Swiss Needle Cast Research Articles

Effects of Swiss Needle Cast on the Profitability and Optimal Management of Douglas-fir Plantations in Western Oregon

Abstract This study conducts an economic analysis to evaluate the impact of Swiss needle cast (SNC) caused by Nothophaeocryptopus gaeumannii on Douglas-fir (Pseudotsuga menziesii) plantations at the stand level in western Oregon. We examine timber and nontimber benefits across varying degrees of SNC severity considering timber benefits and carbon sequestration benefits. By comparing these values with unaffected Douglas-fir stands, our aim is to quantify the economic losses associated with SNC in terms of the land expectation values. The total land expectation value for a stand affected by SNC ranges from $556 to $2,179/ac, representing an average decrease of 50% ($1,066/ac) in economic revenues compared with a Douglas-fir stand without SNC infestation. Engaging in cost-effective annual management activities, with maximum costs of $43–$56/ac, could offset the profitability decline. On average, the total losses in profits for the current plantations affected by SNC are estimated to be around $206.5–430 million. Study Implications: In this study, we examine the economic impacts of Swiss needle cast (SNC) on the profitability of western Douglas-fir in Oregon. Our results reveal that profits for landowners can be, on average, reduced by $1,066/ac when their stand is infested by SNC, representing a 50% loss in profitability. Landowners could potentially mitigate these losses by engaging in annual management activities aimed at preventing Douglas-fir infestation, incurring a cost ranging between $43–56/ac, which could offset the reduction in profitability.

Genetic architecture of disease resistance and tolerance in Douglas-fir trees.

Understanding the genetic basis of how plants defend against pathogens is important to monitor and maintain resilient tree populations. Swiss needle cast (SNC) and Rhabdocline needle cast (RNC) epidemics are responsible for major damage of forest ecosystems in North America. Here we investigate the genetic architecture of tolerance and resistance to needle cast diseases in Douglas-fir (Pseudotsuga menziesii) caused by two fungal pathogens: SNC caused by Nothophaeocryptopus gaeumannii, and RNC caused by Rhabdocline pseudotsugae. We performed case-control genome-wide association analyses and found disease resistance and tolerance in Douglas-fir to be polygenic and under strong selection. We show that stomatal regulation as well as ethylene and jasmonic acid pathways are important for resisting SNC infection, and secondary metabolite pathways play a role in tolerating SNC once the plant is infected. We identify a major transcriptional regulator of plant defense, ERF1, as the top candidate for RNC resistance. Our findings shed light on the highly polygenic architectures underlying fungal disease resistance and tolerance and have important implications for forestry and conservation as the climate changes.

Genome sequences of three genetic lineages of the fungus Nothophaeocryptopus gaeumannii, the causal agent of Swiss needle cast on Douglas-fir trees.

Here, we present the nearly complete genome sequences of the three main genetic lineages of Nothophaeocryptopus gaeumannii, an endophytic ascomycete fungus responsible for Swiss needle cast, a foliar disease that is emerging as a significant threat to the Douglas-fir tree in its natural distribution range.

Site-level estimates of Douglas-fir foliage retention from climate, soil, and topographic variables

Cohort-based live foliage retention of Douglas-fir (Pseudotsuga menziesii), repeatedly shown to be directly related to tree growth, was estimated for areas in western Oregon and Washington by correlating nearly 1000 plot-level estimates of foliage retention with variables of climate, soils, and topography. Sampling of Douglas-fir foliage retention, motivated by the Swiss needle cast-induced loss of foliage (causal agent Nothophaeocryptopus gaeumanii) in western Oregon and Washington, covered the period from 1998 to 2021, with estimates collected from the Oregon Coast Range near the California border to the Olympic Peninsula and the foothills of the northern Oregon Cascades and the foothills near the border of Washington and Canada. Douglas-fir foliage retention was found to be correlated with average June/July relative humidity, December maximum temperature, and May precipitation averaged for the periods of budbreak for the 2–4 yr old needle cohorts, a transformation of slope and aspect, the number of meters above 400 m elevation, topographic position index, and soil cation exchange capacity. Using the constructed equation, foliage retention was estimated across a systematic grid of points in western Oregon and Washington and combined with a regional growth model to estimate potential volume growth loss across the region. The greatest implied average growth losses (∼23%) were in the zones closest to the Pacific Ocean between 46° and 48°N. Premature loss of Douglas-fir foliage in the Pacific Northwest has been primarily associated with Swiss needle cast, and this work may help explain conditions that favor Swiss needle cast or describe additional foliage retention drivers.

Genetic Lineage Distribution Modeling to Predict Epidemics of a Conifer Disease

A growing body of evidence suggests that climate change is altering the epidemiology of many forest diseases. Nothophaeocryptopus gaeumannii (Rhode) Petrak, an ascomycete native to the Pacific Northwest and the causal agent of the Swiss needle cast (SNC) disease of Douglas-fir [Pseudotsuga menziesii (Mirbel) Franco], is no exception. In the past few decades, changing climatic conditions have coincided with periodic epidemics of SNC in coastal forests and plantations from Southwestern British Columbia (B.C.) to Southwestern Oregon, wherein an increase in the colonization of needles by N. gaeumanii causes carbon starvation, premature needle shedding and a decline in growth. Two major sympatric genetic lineages of N. gaeumannii have been identified in the coastal Pacific Northwest. Past research on these lineages suggests they have different environmental tolerance ranges and may be responsible for some variability in disease severity. In this study, we examined the complex dynamics between biologically pertinent short- and long-term climatic and environmental factors, phylogenetic lineages of N. gaeumannii and the severity patterns of the SNC disease. Firstly, using an ensemble species distribution modeling approach using genetic lineage presences as model inputs, we predicted the probability of occurrence of each lineage throughout the native range of Douglas-fir in the present as well as in 2050 under the “business as usual” (RCP8.5) emissions scenario. Subsequently, we combined these model outputs with short-term climatic and topographic variables and colonization index measurements from monitoring networks across the SNC epidemic area to infer the impacts of climate change on the SNC epidemic. Our results suggest that the current environmental tolerance range of lineage 1 exceeds that of lineage 2, and we expect lineage 1 to expand inland in Washington and Oregon, while we expect lineage 2 will remain relatively constrained to its current range with some slight increases in suitability, particularly in coastal Washington and Oregon. We also found that disease colonization index is associated with the climatic suitability of lineage 1, and that the suitability of the different lineages could impact the vertical patterns of colonization within the crown. We conclude that unabated climate change could cause the SNC epidemic to intensify.

Distribution of a Foliage Disease Fungus Within Canopies of Mature Douglas-Fir in Western Oregon.

Nothophaeocryptopus gaeumannii is a common native, endophytic fungus of Douglas-fir foliage, which causes Swiss needle cast, an important foliage disease that is considered a threat to Douglas-fir plantations in Oregon. Disease expression is influenced by fungal fruiting bodies (pseudothecia), which plug the stomata and inhibit gas exchange. Trees are impacted when pseudothecia plug stomates on 1-year-old and older needles resulting in early needle abscission. Mature (100 years+) trees appear to be less impacted from disease, and we hypothesize this is due to the greater emergence of pseudothecia on older than younger needles, which allows for more needle retention. We measured the density of pseudothecia occluding stomates across 2- to 5-year-old needles from upper, middle, and lower canopy positions of mature trees at three sites in the Oregon Coast Range and two sites in the western Oregon Cascade Mountains. Binomial generalized linear mixed model (GLMM) was used to test for the effects of canopy position (upper, middle, and lower), sites, needle age (2-5 years old), and years (2016 and 2017), and their interactions on the pseudothecia density. Pseudothecia density varied annually depending on sites, needle age and canopy positions. Pseudothecia density peaked on 3-, and 4-year-old needles, however, needles emerging from the same year, like 2-year-old needles in 2016 and 3-year-old needles in 2017 both emerged in 2014, had consistently similar patterns of pseudothecia density for both years, across site and canopy positions. Canopy position was important for 3-, and 4-year-old needles, showing less pseudothecia in the lower canopy. This research confirms that N. gaeumannii pseudothecia density is greatest in 3- and 4-year old needles in mature trees in contrast to plantations where pseudothecia density usually peaks on 2-year-old needles, and that pseudothecia density (disease severity) is generally lower in mature trees. Something about mature forest canopies and foliage appears to increase the time it takes for pseudothecia to emerge from the needles, in contrast to younger plantations, thus allowing the mature trees to have greater needle retention.

Tree-ring history of Swiss needle cast impact on Douglas-fir growth in Western Oregon: correlations with climatic variables.

The fungal pathogen, Nothophaeocryptopus gaeumannii, occurs wherever Douglas-fir is found but disease damage is believed to be limited to the Coast Range and is of no concern outside the coastal fog zone (Shaw, et al., 2011). However, knowledge remains limited on the history and spatial distribution of Swiss Needle Cast (SNC) impacts in the Pacific Northwest (PNW). We reconstructed the history of SNC impacts on mature Douglas-fir trees based on tree ringwidth chronologies from the west slope of the Coast Range to the high Cascades of Oregon. Our findings show that SNC impacts on growth occur wherever Douglas-fir is found in western Oregon and is not limited to the coastal fog zone. The spatiotemporal patterns of growth impact from SNC disease were synchronous across the region, displayed periodicities of 25-30 years, strongly correlated with winter and summer temperatures and summer precipitation, and matched the patterns of enriched cellulosic stable carbon isotope indicative of physiological stress. While winter and summer temperature and summer precipitation influenced pathogen dynamics at all sites, the primary climatic factor of these three limiting factors varied spatially by location, topography, and elevation. In the 20th century, SNC impacts at low- to mid-elevations were least severe during the warm phase of the Pacific Decadal Oscillation (PDO, 1924-1945) and most severe in 1984-1986, following the cool phase of the PDO (1945-1977). At high elevations on the west slope of the Cascade Mountains, SNC impacts were the greatest in the 1990s and 2000s, a period of warmer winter temperatures associated with climate change. Warmer winters will likely continue to increase SNC severity at higher elevations, north along the coast from northern Oregon to British Columbia, and inland where low winter temperatures currently limit growth of the pathogen. Surprisingly, tree-ring records of ancient Douglas-fir logs dated ~53K radioactive years B.P. from Eddyville, OR displayed 7.5- and 20-year periodicities of low growth, similar to those found in modern day coastal Douglas-fir tree-ring records which we interpret as being due to cyclic fluctuations in SNC severity. Our findings indicate that SNC has persisted for as long as its host, and as a result of changing climate, may become a significant forest health problem in areas of the PNW beyond the coastal fog zone.

Persistence of the Swiss Needle Cast Outbreak in Oregon Coastal Douglas-Fir and New Insights from Research and Monitoring.

Swiss needle cast (SNC), caused by Nothophaeocryptopus gaeumannii, is a foliage disease of Douglas-fir (Pseudotsuga menziesii), that reduces growth in native stands and exotic plantations worldwide. An outbreak of SNC began in coastal Oregon in the mid-1990s and has persisted since that time. Here we review the current state of knowledge after 24 years of research and monitoring, with a focus on Oregon, although the disease is significant in coastal Washington and has recently emerged in southwestern British Columbia. We present new insights into SNC distribution, landscape patterns, disease epidemiology and ecology, host-pathogen interactions, trophic and hydrologic influences, and the challenges of Douglas-fir plantation management in the presence of the disease. In Oregon, the SNC outbreak has remained geographically contained but has intensified. Finally, we consider the implications of climate change and other recently emerged foliage diseases on the future of Douglas-fir plantation management.

ESTADO NUTRIMENTAL E INFESTACIÓN EN Pseudotsuga menziesii POR EL TIZÓN SUIZO (Phaeocryptopus gaeumannii) EN AQUIXTLA, PUEBLA

Las plantaciones de árboles de navidad con la especie Pseudotsuga menziesii (Mirb.) Franco ocupan 10% de la superficie total de este tipo de plantaciones en México. El tizón suizo es una enfermedad propia de del género Pseudotsuga, originada por el hongo Phaeocryptopus gaeumannii (T. Rohde) Petrak (1938). Los principales síntomas incluyen follaje clorótico y abscisión prematura de acículas infectadas, lo que resulta en copas ralas. El objetivo de este estudio fue determinar la relación entre la fertilización química y el estado nutrimental de los árboles con los niveles de severidad e incidencia de la enfermedad. La hipótesis fue que hay una correlación entre el estado nutrimental y la variación del grado de infestación del tizón suizo en P. menziesii. El estudio se estableció en el predio multifuncional “El Manantial” en Aquixtla, Puebla. Los tratamientos fueron fertilización con urea y sulfato de potasio y control fitosanitario químico con propiconazol y prochloraz. El diseño experimental fue bloques al azar generalizado, evaluando dos factores controlados con tres niveles (factorial 32) y como factor de confusión o bloqueo el nivel visual de transparencia de copa asociado al tizón suizo. La incidencia y la severidad se evaluaron. Los resultados del ANDEVA no indicaron diferencias significativas. De las variables nutrimentales las de mayor asociación a la severidad e incidencia fueron el contenido de Ca y Mn, y en menor medida, Cu, Mg y N. Entre los tratamientos se observaron antagonismos y sinergismos con efecto en el estado nutrimental. Los fungicidas influyen en la absorción, transporte y asimilación de los nutrimentos.

Analysis of Swiss needle cast disease on Pseudotsuga menziesii var. glauca within a Christmas tree plantation in Mexico

AbstractNothophaeocryptopus gaeumannii causes Swiss needle cast disease in Douglas‐fir forest trees and ornamental plantations. This study analysed disease and pathogen behaviour from summer 2011 to spring 2012. An untreated plot within a Pseudotsuga menziesii var. glauca plantation in Valle de Bravo, Mexico was divided into 12 sub‐plots. At each sampling date, needles were collected from four trees per sub‐plot. The analysis included seven needle age cohorts from branches from two canopy sections, as well as fallen needles from five random trees inside the entire plot. Airborne ascospores were collected weekly in slide traps. Sequencing identified the pathogen from DNA extracted from 18 mycelial colonies (isolates) and ascospores DNA from four selective slide traps. Disease and pathogen characteristics were mostly similar to other reports, except for ascospores inside pseudothecia on the youngest age class of foliage. Defoliation affected lower canopies frequently, while in the middle canopy it ranged from 6% to 98% depending on the needle age. In fallen needles, mature pseudothecia contained ascospores and isolated colonies developed in an agar‐based medium. Ascospore fluctuation peaked in two periods, but the most relevant occurred from 11 February to 17 March 2012, coinciding with bud break. These results contribute further understanding of SNC disease useful in improving the health of Christmas trees and the less‐studied P. menziesii var. glauca.

Effects of radial growth rate on outerwood properties of coastal Douglas-fir in healthy stands versus stands impacted by Swiss needle cast

A common belief in forestry is that rapid growth in coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) results in decreased outerwood quality. In Oregon, the opposite pattern has been reported for stands affected by Swiss needle cast, whereby a native fungus causes premature needle drop and an increase in latewood proportion (LW%), wood density, stiffness (MOE), and strength (MOR). Using a combination of new and existing data, we compared the properties of ∼25-year-old outerwood from 18 healthy and 14 diseased stands using direct tests (6–8 beams from 7–12 trees per stand, 2614 beams total) and indirect SilviScanII tests (1 sample for each of the 366 trees). As seen before, diseased stands showed a decrease in wood quality with growth rate: ring count was strongly and positively correlated with density, MOE, and MOR (r2 = 0.74, 0.65, and 0.63), and LW% was positively correlated with ring count, density, MOE, and MOR (r2 = 0.50, 0.62, 0.30, and 0.44). In contrast, healthy stands showed no significant effect of ring count on density, MOE, or MOR. LW% was weakly and significantly correlated with MOE (r2 = 0.25) but not with ring count, density, or MOR. Among healthy stands, growth acceleration had no adverse effects on outerwood properties.

Douglas-fir foliage retention dynamics across a gradient of Swiss needle cast in coastal Oregon and Washington

Swiss needle cast (SNC) is an important foliage disease of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) caused by the native pathogen Nothophaeocryptopus gaeumannii (T. Rohde) Videira, C. Nakash., U. Braun & Crous, which has been present in epidemic proportions in coastal Douglas-fir forests since the 1990s. Under conducive environmental and stand conditions, the fungal fruiting bodies emerge on young needles, inhibiting gas exchange and causing premature needle casting and subsequent growth losses. Using a new regional plot network, which extends and approximately doubles the area of SNC-susceptible coastal forest sampled, we investigated the distribution of SNC disease indices across the region and throughout individual tree crowns. Foliage retention varied from 1.15 to 3.9 years, and disease severity index (incidence × % occluded stomata) ranged from 0.05% to 52.11%. Foliage retention was positively correlated with distance from the coast and elevation, while foliage retention and disease severity were negatively associated across the study area. Within crowns, disease severity was negatively associated with crown depth, and foliage retention was positively associated with crown depth, regardless of distance from coast. Across the entire study area, foliage retention was found to decrease and disease severity increase with latitude, all else being equal. Tree growth metrics are positively associated with increasing foliage retention, and normal growth occurs greater than ∼3.2 years.

Swiss needle cast tolerance in British Columbia’s coastal Douglas-fir breeding population

Abstract Substantial growth losses in Douglas-fir can be the result of Swiss needle cast, a foliar disease caused by the fungus Nothophaeocryptopus gaeumannii. Although the disease is native to western North America, it is expected to become increasingly problematic in regions where climates become warmer in winter and wetter in spring, such as in coastal British Columbia (BC), Canada. Previous research suggests that tolerance to this disease is under partial genetic control. We therefore aim to screen for tolerance and resistance to the disease in the tree breeding population of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) in BC. We evaluated if early screening for resistance or tolerance to this disease is possible. We worked with 32 families grown for 18-years on two full-sibling genetic field trial sites representing different climates. We assessed >900 trees for disease signs and symptoms from 2017 to 2019. Needle retention was assessed in the field. In the laboratory, the proportion of stomata occluded with pseudothecia was measured, deoxyribonucleic acid (DNA) was extracted, and the proportion of fungal DNA in the needles was assessed using quantitative polymerase chain reaction. Strong differences were observed among families for needle retention, stomatal occlusion and fungal load. The milder and wetter site closer to the coast was generally more severely affected. Families showed rank changes between the two sites for all response variables. Higher needle retention was correlated with increased tree volume. No correlation was found between the proportion of stomata occluded with pseudothecia, fungal DNA load and needle retention. These results indicate that a more complex pathology is involved in causing needle loss. We conclude that screening for Swiss needle cast tolerance in the coastal BC Douglas-fir breeding population is possible if needle retention can be assessed and that area-specific deployment strategies may be needed given family rank changes in different environments.

Contrasting the Pathogen Loads in Co-Existing Populations of Phytophthora pluvialis and Nothophaeocryptopus gaeumannii in Douglas Fir Plantations in New Zealand and the Pacific Northwest United States.

The emergence of Phytophthora pluvialis as a foliar pathogen of Douglas fir in New Zealand and the Pacific Northwest United States has raised questions about its interaction with the widespread Swiss needle cast (SNC) disease. During Spring 2017, we repeatedly sampled 30 trees along an environmental gradient in each region and 292 additional trees in a longitudinal transect to assess the P. pluvialis epidemic and the association between P. pluvialis and Nothophaeocryptopus gaeumannii, which are causal agents of SNC. Both pathogens were consistently more abundant in the host's exotic environment in New Zealand. In both areas, the two pathogens co-exist in different spatial scales for regions and needles. The relative abundance of both pathogens was negatively correlated in the Pacific Northwest, where both presumably have co-existed for longer. Our findings confirmed the interaction of P. pluvialis and N. gaeumannii as foliar pathogens of Douglas fir and suggest a within-site spatial variation in the Pacific Northwest.

Environmental variables associated with Nothophaeocryptopus gaeumannii population structure and Swiss needle cast severity in Western Oregon and Washington.

The environment has a strong influence on the abundance and distribution of plant pathogenic organisms and plays a major role in plant disease. Climatological factors may also alter the dynamics of the interactions between plant pathogens and their hosts. Nothophaeocryptopus (=Phaeocryptopus) gaeumannii, the causal agent of Swiss needle cast (SNC) of Douglas‐fir, is endemic to western North America where it exists as two sympatric, reproductively isolated lineages. The abundance of this fungus and the severity of SNC are strongly influenced by climate. We used statistical and population genetic analyses to examine relationships between environment, pathogen population structure, and SNC severity. Although N. gaeumannii Lineage 2 in western Oregon and Washington was most abundant where SNC symptoms were most severe, we did not detect a significant relationship between Lineage 2 and disease severity. Warmer winter temperatures were inversely correlated with foliage retention (AFR) and positively correlated with the relative abundance of Lineage 2 (PL2). However when distance inland, which was strongly correlated with both AFR and PL2, was included in the model, there was no significant relationship between Lineage 2 and AFR. Spring/early summer dew point temperatures also were positively associated with total N. gaeumannii abundance (colonization index (CI)) and inversely correlated with AFR. Warmer summer mean temperatures were associated with lower CI and higher AFR. Our results suggest that the two lineages have overlapping environmental optima, but slightly different tolerance ranges. Lineage 2 was absent from more inland sites where winters are colder and summers are warm and dry, while Lineage 1 occurred at most sites across an environmental gradient suggesting broader environmental tolerance. These relationships suggest that climate influences the abundance and distribution of this ecologically important plant pathogen and may have played a role in the evolutionary divergence of these two cryptic fungal lineages.

Increased streamflow in catchments affected by a forest disease epidemic.

Natural disturbances help maintain healthy forested and aquatic ecosystems. However, biotic and abiotic disturbance regimes are changing rapidly. For example, the Swiss needle cast (SNC) epidemic in the Coast Range of Oregon in the U.S. Pacific Northwest has increased in area from 53,050 to 238,705ha over the 1996-2015 period. We investigated whether the hydrologic regime (i.e., annual streamflow, runoff ratio, and magnitude and timing of peak flows and low flows) was affected by SNC in 12 catchments in western Oregon. The catchments ranged in size from 183 to 1834km2 and area affected by SNC from 0 to 90.5%. To maximize the number of catchments included in the study, we analyzed 20years of SNC aerial survey data and 15-26years of stream discharge (Q) and PRISM precipitation (P) and air temperature (Tair) data to test for trends in hydrologic variables for each catchment. As expected, we found that runoff ratios (Q/P) increased in five catchments, all with an area impacted by SNC >10%. This was likely due to the effects of SNC on the hydraulic architecture (i.e., needle retention, sapwood area, sapwood permeability) of affected trees, leading to decreased canopy interception and transpiration losses. Interestingly, two catchments with the greatest area affected by SNC showed no changes in hydrologic regime. The lack of hydrologic response could either be due to compensatory transpiration by vegetation unaffected by the disease or sub-canopy abiotic evaporation, which counteracted reductions in transpiration. This study is the first to illustrate that chronic canopy disturbance from a foliage pathogen can influence catchment scale hydrology.

Associations between Swiss Needle Cast Severity and Foliar Nutrients in Young-Growth Douglas-Fir in Coastal Western Oregon and Southwest Washington, USA

Abstract Swiss needle cast (SNC) is a foliage disease of Douglas-fir (Pseudotsuga menziesii) caused by Nothophaeocryptopus gaeumannii, an ascomycete fungus (Mycosphaerellaceae) that causes tree growth reductions in the Pacific Northwest. The epidemiology of the fungus is generally well known, but the relations between disease expression and foliar nutrition are unclear. In this study, we used data from the Swiss Needle Cast Cooperative research and monitoring plot network in western Oregon and SW Washington to assess associations between SNC severity, carbon, and nine foliage nutrients (nitrogen, Na, K, P, Ca, Mg, Mn, Al, S). Foliage samples were collected from midcrown of selected Douglas-firs from each plot. SNC severity was determined on 2-year-old needles by multiplying disease incidence and fungal reproductive (pseudothecia) density. Disease severity and nutrient relations were determined using linear mixed models. SNC severity showed statistically significant positive trends with concentrations of carbon, nitrogen, Na, K, and S, no relation with concentrations of Ca, Mg, or Al, and slightly negative trends that were not significant for P and Mn. This is the first such analysis of associations between a conifer foliage disease and foliage nutrients across a landscape; subsequently, there is little published literature on how or why these nutrients may interact with disease.

Severity of Swiss needle cast in young and mature Douglas-fir forests in western Oregon, USA

Swiss needle cast (SNC), caused by Nothophaeocryptopus gaeumannii, is an important foliage disease of Douglas-fir (Pseudotsuga menziesii) forests of the Pacific Northwest. The fungus lives endophytically within the foliage, until forming reproductive structures (pseudothecia) that plug stomates and cause carbon starvation. When pseudothecia appear on one- and two-year-old foliage, significant needle abscission can occur, which reduces productivity of the tree. While there is considerable evidence of SNC disease in coastal Douglas-fir plantations, the severity of SNC in mature and old-growth forests is poorly understood. We compared tree crowns of mature and old-growth conifer forests and nearby young forests at three locations in the Oregon Coast Range and four locations in the western Cascade Range of Oregon. We assessed disease severity for N. gaeumannii on two-year-old foliage, incidence by presence of N. gaeumannii on all foliage, foliage retention for the first four years, and foliar nitrogen of one-year-old foliage. We also compared leaf wetness at three heights in one mature and one young tree at five of the seven sites. Disease severity was greater in young forests than mature forests at all sites except for high elevation Cascade Range areas. Incidence of disease was highest for two-year-old needles in young trees and 3–5 year-old needles in mature trees, except for one coastal site. Retention of 1–4 year-old needle cohorts differed between young and mature trees, and mature trees had much larger complements of > four-year-old needles. Total foliar nitrogen (TN) concentration did not differ in needles of young and mature trees, but at some locations total N differed between canopy positions. Leaf wetness differences were not consistent between young and mature tree crowns. However, at one study site in the core epidemic area, the younger stand had longer periods of wetness in the upper crowns than a nearby old stand. Leaf wetness and foliar N were hypothesized to play a role in SNC disease severity, but they do not explain differences in adjacent young and mature trees. Although the fungus is present in old and young trees, the likelihood of disease expression and lower foliage retention appears to be greater in younger plantation trees than mature and older trees in western Oregon Douglas-fir forests.

Impact of Rhabdocline pseudotsugae and Phaeocryptopus gaeumannii on the Selection of Suitable Provenances of Douglas Fir in Central Europe

Two diseases, Rhabdocline needle cast caused by Rhabdocline pseudotsugae Sydow, and Swiss needle cast caused by Phaeocryptopus gaeumannii (Rohde) Petr., recently became a severe threat to Central European Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) stands. Both pathogens infect assimilative organs causing needle chloritization and drop off. Pervasive infection by these pathogens has been recorded at the Hůrky provenance trial (Písek, South Bohemia, Czech Republic), established in 1971 as part of a series of experiments by International Union of Forest Research Organizations (IUFRO). The intensity and duration of needle cast sporulation were monitored using a Burkard spore trap, and the health status of 24 Douglas fir provenances from the original areal of distribution (British Columbia, Washington, Oregon) was evaluated under this trial. While comparing provenances, the following characteristics were surveyed: trunk volume, defoliation rate, and the difference in tree diameter between measurements in 2011 and 2016. A statistical evaluation was performed using the regression model and a decision tree. The highest sporulation rates on needles for both needle casts were observed from April to July. The Washington provenances 1069 North Bend, 1075 Enumclaw, and 1089 Cathlamet can be recommended for plantation, considering the provenances’ satisfactory productivity and low extent of damage from needle casts, while the provenances such as 1104 Brookings, 1028 Merritt (due to high mortality) and 1010 Barrière, 1021 D’Arcy, and 1067 Skykomish (due to high defoliation) are not suitable for plantation under Central European conditions.

The Genetic Structure of Populations of the Douglas-Fir Swiss Needle Cast Fungus Nothophaeocryptopus gaeumannii in New Zealand.

Swiss needle cast is a foliar disease of Douglas-fir (Pseudotsuga menziesii) that results in premature foliage loss and reduced growth. The causal fungus, Nothophaeocryptopus gaeumannii, was first detected in New Zealand in 1959 and spread throughout the North and South Islands over the following decades. The contemporary genetic structure of the N. gaeumannii population in New Zealand was assessed by analyzing 468 multilocus SSR genotypes (MLGs) from 2,085 N. gaeumannii isolates collected from 32 sites in the North and South Islands. Overall diversity was lower than that reported from native N. gaeumannii populations in the northwestern United States, which was expected given that N. gaeumannii is introduced in New Zealand. Linkage disequilibrium was significantly higher than expected under random mating, suggesting that population structure is clonal. Populations of N. gaeumannii in the North and South Islands were weakly differentiated, and the isolates collected from sites within the islands were moderately differentiated. This suggests that gene flow has occurred between the N. gaeumannii populations in the North and South Islands, and between the local N. gaeumannii populations within each island. Eighteen isolates of N. gaeumannii Lineage 2, which has previously been reported only from western Oregon, were recovered from two sites in the North Island and four sites in the South Island. The most likely explanation for the contemporary distribution of N. gaeumannii in New Zealand is that it was introduced on infected live seedlings through the forestry or ornamental nursery trade, as the fungus is neither seed borne nor saprobic, and the observed population structure is not consistent with a stochastic intercontinental dispersal event.