Update on the 35‐year expansion of the invasive root pathogen,Phytophthora lateralis,across a landscape of Port Orford cedar (Chamaecyparis lawsoniana)

Port Orford cedar (Chamaecyparis lawsoniana) is endemic to northern California and southwestern Oregon and is considered a foundation species that plays critical roles in riparian areas and on nutrient‐poor soils. Since 1952, a non‐native, pathogenic oomycete (Phytophthora lateralis) has been spreading throughout the range of the cedar. Most spread occurs by vehicles carrying infested soil along gravel roads primarily used for timber harvest. In a previous study conducted in 1998 and 1999, Port Orford cedar and P. lateralis were censused in a 37‐km² study area and dendrochronology was used to reconstruct the history of pathogen invasion. That work, which represents the only detailed analysis of spread rates for P. lateralis, showed that the first successful invasion into the study area took place in 1977 and that 43% of the susceptible host sites (stream crossings) were infested by 1999. In the work presented here, all sites that were uninfested in 1999 were re‐censused in 2012, extending the historical reconstruction of P. lateralis spread to 35 years. Two new infestations were initiated between 1999 and 2012, suggesting that the rate of spread of P. lateralis has slowed greatly. Between 1980 and 1989, the average number of new site infestations was 1.8 infestations per year, while between 1990 and 1999 the average was 0.4 infestations per year and between 2000 and 2009 the average was 0.2 infestations per year. Several potential explanations for the reduced number of new infestations are discussed.     

Root and aerial infections of Chamaecyparis lawsoniana by Phytophthora lateralis: a new threat for European countries

Phytophthora lateralis has been isolated from root and collar lesions in Port‐Orford Cedar (POC) trees (Chamaecyparis lawsoniana) in north‐western France (Brittany). These trees, planted in hedgerows, displayed symptoms similar to the typical symptoms of POC root disease. Until now, the disease has been found outside of the nurseries only in western North America. Aerial symptoms, not associated with root or collar infections, were also observed, and P. lateralis was isolated from branch lesions. Similar symptoms were previously observed only in one POC root disease site, located in the Pacific coast of Oregon where climatic conditions are similar to those occurring in Brittany. The reported aetiology as well as the morphological characteristics (deciduous sporangia) of P. lateralis suggests that this species could be air‐dispersed, as described for P. ramorum, a closely related species. This outbreak of P. lateralis in Brittany in farming landscapes associated with the aerial spread of this pathogen represents a new threat for European countries.     

Insights into the potential host range of Phytophthora foliorum

During a survey for Phytophthora ramorum undertaken in north‐west Scotland in early 2016, Phytophthora foliorum was found infecting foliage of the invasive shrub Rhododendron ponticum. Prior to this, P. foliorum had only been reported from foliage of hybrid azaleas in nurseries in California and Tennessee and from azalea plants in an ornamental nursery in Spain. No other hosts were known, and much of the behaviour of P. foliorum remained enigmatic. The species is classified in Phytophthora Clade 8c, with closest relatives, P. ramorum and Phytophthora lateralis, both of which are highly damaging tree pathogens. To explore the threat that P. foliorum might pose to trees, its growth–temperature responses on agar media and ability to cause lesions in the living bark of various hosts were contrasted with the behaviours of P. ramorum and P. lateralis. Phytophthora foliorum proved faster growing and more tolerant of temperature extremes than the other Phytophthora species. Comparisons of bark colonization initially focussed on R. ponticum and larch species Larix decidua and Larix kaempferi as all three are significant hosts of P. ramorum in the UK. Further experiments included another P. ramorum host, Fagus sylvatica (European beech), and the main host of P. lateralis, Chamaecyparis lawsoniana (Lawson cypress). Findings suggested that as well as being a significant pathogen of R. ponticum, damage caused by P. foliorum to both species of larch and beech was very similar to that of the EU1 lineage of P. ramorum, although growth in host tissue was also influenced by season.     

The destructive invasive pathogen Phytophthora lateralis found on Chamaecyparis lawsoniana across the UK

In 2010–2011, Phytophthora lateralis was isolated from diseased Chamaecyparis lawsoniana exhibiting dieback and mortality at eight geographically separate forest, parkland and shelterbelt locations in England, Scotland and Northern Ireland. In 2011, P. lateralis was also isolated from young symptomatic nursery plants of C. lawsoniana and Thuja occidentalis recently imported into Scotland from mainland Europe. These are the first findings of P. lateralis in the UK. At six of the field sites, only collar and root lesions were observed. However, at two sites, large stem and branch lesions unconnected to the collar region were also observed. Phytophthora lateralis was readily isolated from both aerial and basal lesions. In artificial inoculation experiments, two Scottish isolates of the pathogen caused lesions on C. lawsoniana shoots and were readily reisolated from the lesions, their pathogenicity being comparable to that of P. lateralis isolates originating from outside the UK. Isolates from six field sites and the two nursery interceptions exhibited ITS and cox II sequences identical to published sequences of French and North American isolates. However, the isolates from two field sites shared an ITS sequence with Taiwanese isolates and differed from North American, French and Taiwanese isolates by a single‐base substitution in cox II, suggesting a separate evolutionary history. It is clear that P. lateralis now presents a significant threat to C. lawsoniana in Britain. The main source of the outbreaks is likely to be imported infested nursery stock.     

New insights into the survival strategy of the invasive soilborne pathogen Phytophthora cinnamomi in different natural ecosystems in Western Australia

Despite its importance as one of the most notorious, globally distributed, multihost plant pathogens, knowledge on the survival strategy of Phytophthora cinnamomi in seasonally dry climates is limited. Soil and fine roots were collected from the rhizosphere of severely declining or recently dead specimens of 13 woody species at 11 dieback sites and two dieback spots and from healthy specimens of five woody species at four dieback‐free sites in native forests, woodlands and heathlands of the south‐west of Western Australia (WA). Phytophthora cinnamomi was recovered from 80.4, 78.1 and 100% of tested soil, fine root and soil–debris slurry samples at the 11 dieback sites, in some cases even after 18‐month storage under air‐dry conditions, but not from the small dieback spots and the healthy sites. Direct isolations from soil–debris slurry showed that P. cinnamomi colonies exclusively originated from fine roots and root fragments not from free propagules in the soil. Microscopic investigation of P. cinnamomi‐infected fine and small woody roots and root fragments demonstrated in 68.8, 81.3 and 93.8% of samples from nine woody species the presence of thick‐walled oospores, stromata‐like hyphal aggregations and intracellular hyphae encased by lignitubers, respectively, while thin‐walled putative chlamydospores were found in only 21.2% of samples from five woody species. These findings were confirmed by microscopic examination of fine roots from artificially inoculated young trees of 10 woody species. It is suggested that (i) the main function of chlamydospores is the survival in moderately dry conditions between consecutive rain events and (ii) selfed oospores, hyphal aggregations, and encased hyphae and vesicles in infected root tissue of both host and non‐host species are the major long‐term survival propagules of P. cinnamomi during the extremely dry summer conditions in WA.     

An improved method for qPCR detection of three Phytophthora spp. in forest and woodland soils in northern Britain

Using TaqMan qPCR assays, DNA of P. ramorum, P. kernoviae and P. austrocedri was detected in 500 g soil samples collected from twelve infected forest and woodland sites in northern Britain. Phytophthora DNA was also amplified in soil adhering to boots after walking transects along footpaths or animal trails. At two sites, Phytophthora DNA was detected in soil over a 4‐year period following removal of infected hosts. This new method enabling assessment of larger quantities of soil demonstrates the contamination risk of these pathogens in soil at infected sites and improves our understanding of the mechanisms of persistence and spread.     

The susceptibility of selected conifer foliage to infection with Phytophthora lateralis

The foliage of seven different genera of conifers including 10 species and 17 different cultivars was tested for its susceptibility against two isolates of Phytophthora lateralis from two different lineages. Detached green shoot tips were floated in zoospore suspension and the lesion size was assessed after 7 days. xCupressocyparis leylandii, Juniperus media and Cedrus deodara were the most resistant hosts, whereas Chamaecyparis obtusa was most susceptible. Thuja plicata and Thuja occidentalis, Chamaecyparis pisifera and Chamaecyparis lawsoniana, Taxus baccata and Cupressus macrocarpa were of medium susceptibility. For comparison, a small subset of four hosts was also tested for stem susceptibility. The stems of whole potted plants were inoculated with the same two isolates as used for the leaf susceptibility tests. Chamaecyparis lawsoniana was highly susceptible, whereas the stems of xC. leylandii, T. baccata and T. plicata were not susceptible. Most conifers were similarly affected by both tested lineages of P. lateralis although the isolate of the Pacific Northwest lineage caused slightly longer lesions on C. lawsoniana in the stem inoculation tests.     

Molecular diagnosis of Phytophthora lateralis in trees,water, and foliage baits using multiplex polymerase chain reaction

A polymerase chain reaction (PCR)‐based protocol for detection of Phytophthora lateralis in plant tissues and water is described. Base‐pair (bp) deletions in both of the ribosomal DNA internal transcribed spacer (ITS) regions in P. lateralis were used to design complementary PCR primer sequences that amplify a 738 bp fragment only if P. lateralis DNA is present in the sample. Universal control primers based on conserved sequences of the nuclear ribosomal small subunit are included in a multiplexed reaction, providing an internal check on the procedure. The universal primers amplify an approximately 550 bp fragment that is common to plants, protists, and true fungi. The procedure reliably detects P. lateralis in cedar stem tissues and in roots. Positive reactions were obtained with as few as 200 P. lateralis zoospores in water.     

Land‐use changes influence the sporulation and survival of Phytophthora agathidicida,a lethal pathogen of New Zealand kauri (Agathis australis)

Phytophthora agathidicida is the accepted causal agent of dieback in remnant stands of long‐lived indigenous New Zealand kauri (Agathis australis) and poses a significant threat to the long‐term survival of this species. Little is known about the effect of key soil physicochemical characteristics on the growth of P. agathidicida. In this study, we investigated the growth of P. agathidicida in soils collected from adjacent areas under original kauri forest, short rotation pine (Pinus radiata) plantation forest and grazed pastures. A growth response assay was used to quantify asexual (sporangia) and sexual (oospore) spore counts over 8 days in soils sampled from each land‐use. Significantly higher numbers of sporangia (p < 0.001) and oospores (p < 0.01) were found in pasture and pine forest soil within 2 days of the growth assay trials, suggesting these soils may favour asexual/sexual reproduction in the early stages of P. agathidicida establishment compared to kauri forest soils. Additionally, oospore production significantly increased over 8 days in pine forest soil, suggesting that with an increase in inoculum loads, these soils potentially act as pathogen reservoirs. The soil physicochemical properties (e.g., pH, C and N, phosphorus content and electrical conductivity) investigated in this study did not significantly correspond to spore count data between land‐uses, suggesting that differences in growth response are driven by other edaphic factors not explored in the present study.     

Identification of Phytophthora species baited and isolated from forest soil and streams in northwestern Yunnan province,China

Phytophthora species were surveyed by collecting soil samples and placing bait leaves in selected streams during June–October in the years 2005, 2006 and 2010 at three sites in oak forests in Diqing Tibetan Autonomous Prefecture of NW Yunnan province, China. Seventy‐three isolates of Phytophthora spp. were recovered from 135 baited leaf samples and 81 soil samples. Eight Phytophthora species were identified by observation of morphological features and ITS1‐5.8S‐ITS2 rDNA sequence analysis. The eight taxa included two well‐known species P. gonapodyides and P. cryptogea, two recently described species P. gregata and P. plurivora, two named but as yet undescribed taxa, P. taxon PgChlamydo and P. taxon Salixsoil, and two previously unrecognized species, Phytophthora sp.1 and P. sp.2. The most numerous species, P. taxon PgChlamydo, and the second most abundant species, P. taxon Salixsoil, were recovered at all three sites. Phytophthora cryptogea was detected only once at site Nixi. Phytophthora gregata and P. sp.2 were isolated from a stream only at site Bitahai, while the other three species were each found at two sites. Phylogenetic analysis revealed that the isolates belonged to three ITS clades, one species including six isolates in clade 2, six species including 66 isolates in clade 6 and one species in clade 8. There was a relatively rich species and genetic diversity of Phytophthora detected in the investigated regions where the forest biotic and abiotic factors affecting the growth and evolution of Phytophthora populations were diverse.     

Fine root dynamics of oak saplings in response to Phytophthora cinnamomi infection under different temperatures and durations

The belowground effects of Phytophthora cinnamomi on 1‐year‐old saplings of two common oak species in mid‐Atlantic US forests, white (Quercus alba) and red oak (Q. rubra), were examined after incubation in pathogen‐infested soilless potting mix. Fine root lengths (0–1.5 mm in diameter) of both oak species were quantified after incubation at successive 30‐day intervals up to 300 days, for a total of 10 incubation periods. In addition, colony‐forming units (CFU) of P. cinnamomi were quantified after white oak saplings were incubated in infested soilless potting mix at different temperature/duration combinations that reflect soil conditions present in the mid‐Atlantic United States. Impact of P. cinnamomi on fine root lengths of red and white oak saplings varied considerably over time. Significant periods of fine root loss occurred primarily during spring, when bud break and leaf flush began for both oak species. Red oaks had 17% fine root loss on average, while white oaks appeared more resistant to P. cinnamomi infection with a 2% decrease in fine roots over the course of the experiment. Phytophthora cinnamomi CFU declined significantly with exposure to all incubation temperatures except 8°C. This was in contrast to in vitro experiments, where the optimum temperature for mycelial growth was determined to be 21°C and above. Significant fine root loss caused by P. cinnamomi depended on plant phenology and the oak species tested. Extreme soil temperatures have a significant adverse impact on temporal changes of P. cinnamomi population.     

The role of yellow lupin (Lupinus luteus) in the decline affecting oak agroforestry ecosystems

Phytophthora cinnamomi is a soilborne pathogen causing root rot in Mediterranean Quercus species growing in ‘dehesa’ rangeland ecosystems. Recently, it has been reported causing wilting and death of Lupinus luteus (yellow lupin), a spontaneous plant in southern Spain rangelands, but also frequently sowed for livestock grazing. In soils artificially infested with P. cinnamomi chlamydospores and planted with different cultivars of yellow lupin, a significant increase in the density of propagules was detected in comparison with the initial levels of inoculum and with the infested but not planted soil (control). In oak‐rangelands in which yellow lupine was planted, isolation and counting of colonies of P. cinnamomi from soil samples have shown the ability of this plant to maintain or even increase the inoculum density and thus facilitate the infection of trees. Results suggested that cultivation of yellow lupin in oak‐rangeland ecosystems should be avoided whether oak trees are affected by root disease caused by P. cinnamomi or not. This leguminous plant can act as an inoculum reservoir or even enhance inoculum soil levels available for oak root infections, exacerbating the oak decline severity in the region.     

Root recovery rates for Phytophthora cinnamomi and rate of symptom development from root rot on Abies fraseri trees over 7 years

Phytophthora root rot on Abies fraseri trees was monitored from 2001 to 2007 within the disease front of a 12‐year‐old Virginia plantation where trees had been dying of the disease since 1994. After a slow increase in early foliage symptom development from July 2001 to September 2002, the frequency of A. fraseri trees with early symptoms accelerated for about 15 months. While the slow increase occurred during a 18.7% lower than normal rainfall period and the acceleration occurred during a 31.2% higher than normal rainfall period, the percentage of trees with early symptoms continued to increase during the mid‐winter months (December–February) when the estimated mean minimum daily soil temperature (25 cm depth) was unfavourable (<10°C) to Phytophthora cinnamomi pathogenic activity. The time required for trees to progress from early foliage symptoms to completely dead foliage, from November 2000 to October 2007, was highly variable, ranging from 4 to 35 months. Root recovery rates for P. cinnamomi, assayed on a selective medium, were 6.4 times greater for symptomatic foliage trees than for asymptomatic foliage trees in this deep, silt‐loam soil. Following an atypical cold period in February 2007, when the mean minimum daily soil temperature was 0.8°C, symptomatic roots yielded only a low level of germinable propagules of P. cinnamomi. Further, during an atypical midsummer in 2007 (June–August), when the soil water potential was at or below ?9 bars for 68 of 92 days, symptomatic roots yielded no germinable propagules of P. cinnamomi. Addition of thiophanate‐methyl to the selective medium aided P. cinnamomi isolation by inhibiting many undesired pythiaceous colonies growing from symptomatic roots.     

Pathogenicity of Malaysian Phytophthora palmivora on cocoa,durian, rubber and oil palm determines the threat of bud rot disease

The epidemic of bud rot disease affecting oil palm in Colombia is primarily caused by Phytophthora palmivora. The pathogen has a cosmopolitan presence that includes Southeast Asia, but to date, bud rot has not been reported in this region. This study provides an overview of the potential risk of Malaysian P. palmivora isolates cross‐infecting other host species, including cocoa, durian, rubber and Malaysian oil palm planting materials (Dura × Pisifera, D × P). On cocoa pods, the durian isolate PP7 caused dark brown necrotic lesions. Detached leaf bioassays showed that P. palmivora isolates PP3 and PP7 infected different hosts, except rubber foliage without wounding. Inoculation tests on cocoa, durian and rubber seedlings caused brown necrotic lesions when stems were wounded, with 10% mortality in cocoa and durian at 17 days post‐inoculation (dpi). However, no further infection was observed, and lesions closed within 14–28 dpi on the non‐wounded seedlings. Pathogenicity tests of oil palm seedlings inoculated with isolates PP3 and PP7 indicated that Malaysian P. palmivora isolates were not pathogenic to oil palms based on localized infection observed only through wounding. Overall, the work demonstrated that Malaysian P. palmivora isolates were able to cross‐infect multiple hosts but did not show severe infections on oil palms.     

Behaviour and survival of Phytophthora cambivora inoculum in soil‐like substrate under different water regimes

Phytophthora cambivora is a soil‐borne pathogen responsible for root and collar rot of woody species including Castanea spp., on which it causes Ink disease. P. cambivora does not produce chlamydospores, and the prevalence of a single mating type in nature limits the production of oogonia and oospores. Thus, survival of P. cambivora, in the absence of suitable hosts, relies mainly on sporangia, zoospores and mycelium. However, inoculum survival in soils or substrates represents a major factor in disease epidemics and is probably dependant on environmental factors. The aim of this article was to study the behaviour of P. cambivora in a peat‐based substrate (PbS) in the absence of a host, under controlled conditions, and by varying the substrate water regimes. Total inoculum in the substrate was quantified by qPCR, using customized rDNA primer sets, whilst zoospores were quantified after elution, and their vitality was determined by a specific staining procedure. Inoculum infectivity was assessed using chestnut root baits. Results indicated that during the initial 48 h after infestation (matric potential, pF 1.2; 70% water content), the inoculum level increased producing microsporangia and mycelium before decreasing, regardless of the water regime applied. The number of free zoospores increased over a period of (maximum) 7 days after substrate inoculation. Vitality of zoospores declined to 45% at day 18, with no statistical differences amongst water regime treatments. Both rDNA and zoospore number increased in flooded samples at day 23, illustrating the vitality of the inoculum. Inoculum was able to infect chestnut root baits up to 45 days at pF 1.2 and 3.5, before and after flooding, but at pF 6.3, only in the absence of flooding. Although based on experiments carried out in microcosms, these results highlight an unexpected resistance of P. cambivora zoospores to environmental constraints. Furthermore, the infectivity ability of the inoculum to survive in PbS over time even in the absence of the host adds relevance to the risk of movement of soil and substrates associated with plant trading worldwide.     

Isolation,identification and pathogenicity of Phytophthora species from declining oak stands

Within the scope of a research project on the condition of roots of declining oaks (Quercus robur, Quercus petraea), samples of fine roots and surrounding soil, specimens of stripe cankers on the stem base, and samples of stream water were examined for the presence of Phytophthora species using both baiting methods and selective agar media. At 27 sites in Germany (Bavaria, Rheinland-Pfalz, Schleswig-Holstein), Switzerland, Hungary, Italy and Slovenia the following species were isolated (mainly from soil): Phytophthora citricola, Phytophthora cactorum, Phytophthora cambivora, Phytophthora gon-apodyides, Phytophthora undulata, a species with affinity to Phytophthora drechsleri, and two additional species with close affinity to the Phytophthora cactorum group. Moreover, Pythium group P, Pythium anandrum, Pythium chamaehyphon, and many other Pythium species that have not yet been identified could be recovered. In a soil infestation test most isolates induced dieback of long root tips and necrotic lesions in the root cortex and at the root collar of Quercus robur seedlings. All Phytophthora species tested and Pythium group P caused cortical necrosis after stem inoculation of young Quercus robur trees. It could be shown in vitro that Phytophthora gonapodyides and Pythium group P were able to produce a wilting toxin. Nitrogen input and climatic changes are discussed as predisposing factors for root damage observed in the field.     

Assessment of the eradication measures applied to Phytophthora ramorum in Irish Larix kaempferi forests

Phytophthora ramorum is the causal agent of the sudden larch death epidemic in Ireland and the UK. Within the EU, it is a quarantine pathogen and eradication measures are required if it is detected in horticultural or forest environments. Eradication measures in forests include the clearance of susceptible tree hosts from the infected stand along with all host known to support pathogen sporulation within a 250‐m buffer zone of the infected stand. Between 2010 and 2016, these measures have affected over 18,000 ha of Larix kaempferi forests in Ireland and the UK, but the epidemic continues to spread. An assessment of the efficacy of the eradication measures has not been published to date. Here, we provide details of the detection frequency of P. ramorum from aerial (rainwater) and terrestrial (soil, watercourses, plant material) sources in three forest locations in Ireland that had significant areas of L. kaempferi affected by P. ramorum before their removal. Monitoring of six plots with differing infection and eradication management histories was carried out from September 2013 to 2015. Presence of P. ramorum was confirmed by plating plant material onto selective media, followed by morphological identification. Phytophthora ramorum was detected in 65 of 1283 samples, in all sample types and in 17 of the 20 months sampled. Only three of the 295 soil samples were positive for P. ramorum, with all of these coming from an area under perennial standing water. The most positive samples came from a plot where symptomatic Larix trees had not been removed and the findings occurred consistently over the 2‐year study. Plots where infected Larix had been removed were rarely positive for P. ramorum across all the sample types indicating a level of success from the eradication measures in reducing pathogen levels on the sites.     

Involvement of Phytophthora spp. in chestnut decline in the Black Sea region of Turkey

Chestnut blight caused by Cryphonectria parasitica is a serious disease of Castanea sativa in the Black Sea region of Turkey. During disease surveys, dieback and decline symptoms were observed on trees without apparent blight and ink disease symptoms. Black necroses, similar to those caused by Phytophthora infections, were noted on some of the chestnut coppices and saplings in one nursery in Ordu and led to an investigation into this disease complex. Only symptomatic plants showing dieback symptoms were investigated. Soil samples together with fine roots were collected from two directions, north and north‐east, approximately 150 cm away from the main stems. Phytophthora spp. were baited with young chestnut leaves. Three Phytophthora spp., P. cambivora, P. cinnamomi and P. plurivora, were identified from 12 soil samples collected from 73 locations, while from the nurseries, only P. cinnamomi was obtained. Phytophthora cinnamomi was the most common species, obtained from seven locations in five provinces and from four nurseries having similar symptoms mentioned above in different locations. Phytophthora cambivora and P. plurivora were less frequently obtained, from three to two stands, respectively. Phytophthora cinnamomi and P. cambivora were the most aggressive species when inoculated at the stem base on 3‐year‐old chestnut saplings, killing six saplings of eight inoculated in 2 months. The three Phytophthora species were first recorded on chestnut in Black sea region of Turkey with the limited samples investigated in a large area about 150 000 ha chestnut forest.     

Phytophthora species associated with dieback of sweet chestnut in Western Turkey

Sweet chestnut (Castanea sativa) is an important tree species in the Marmara and Aegean regions of Turkey as these two regions produce the great majority of edible nuts, especially those used for marron glacé production. Chestnut forests and orchards in these regions showing severe dieback symptoms not associated with chestnut blight were investigated to determine the role of Phytophthora spp. in the decline syndrome. Soil samples were collected from around 108 symptomatic chestnut trees at 29 sites and Phytophthora spp. isolated using soil baiting technique and selective medium. Species isolated were identified by cultural characteristics and ITS sequencing. Phytophthora x cambivora was the dominant species detected in 13 sites, followed by P. cinnamomi (5 sites), P. plurivora (3 sites) and P. cryptogea (1 site). Phytophthora x cambivora was present in both regions, while P. cinnamomi was found only in the Marmara region in coastal areas around Istanbul. When inoculated at the stem bases of 3‐year‐old chestnut saplings, P. cinnamomi produced significantly longer necrotic lesions (7.8–12.0 cm) than P. x cambivora (2.6–6.3 cm) by 12 days after inoculation. Phytophthora plurivora was the least aggressive species causing only small lesions. Phytophthora cryptogea, which represents the first record on chestnut in Turkey, produced intermediate sized lesions in between P. x cambivora and P. plurivora. These results indicate that P. x cambivora and in some areas P. cinnamomi play major roles in the observed dieback of sweet chestnut in western Turkey.