Occurrence of Phytophthora species in riparian stands of black alder (Alnus glutinosa) in Slovakia

During the monitoring period of alder decline phenomenon in Slovakia, indicative symptoms of Phytophthora diseases were observed in riverside stands in Slovakia. The study aimed to test the presence and diversity of Phytophthora species in declining alder stands. The samples were collected from six stands situated by rivers/streams in the central and eastern parts of Slovakia. Phytophthora plurivora and P. cactorum were detected in soil, root and water samples. The most isolated species was P. plurivora. Both Phytophthora species have been recognized in the literature as the perpetrators of black alder dieback together with other species, such as P. alni or P. polonica. To our knowledge, this is the first report of P. plurivora and P. cactorum in riverside stands with the main share of black alder in Slovakia.     

Pathogenicity of Phytophthora alni complex and P. plurivora in Alnus glutinosa seedlings

The ecological importance of riparian forests is well known. However, these forest habitats have been disturbed by human activities over the past century as a result of the introduction of flow regulations. Mortality of the riparian alder population caused by Phytophthora has become an important issue in Europe in the past two decades. The main objective of this study was to examine the pathogenicity of the Phytophthora alni complex (P. xalni, P. uniformis and P. xmultiformis) and P. plurivora in Alnus glutinosa seedlings. Phytophthora alni complex has traditionally been identified as the main causal agent of alder decline; however, in this study, P. plurivora was found to cause as much damage in inoculated seedlings as P. alni complex. In fact, Spanish isolates of P. xalni caused mortality rates of ca. 30%, whereas P. plurivora killed ca. 50% of seedlings. Likewise, there were no differences between P. xalni ‐ and P. plurivora‐inoculated seedlings in either the length of lesion or biomass allocation. The pathogenicity of the species within P. alni complex did not differ significantly. The findings confirm that P. plurivora, which is one of the most common species of Phytophthora found in European nurseries, is highly pathogenic to alder seedlings. Urgent implementation of measures to prevent the risk of spread of the pathogen from nurseries to natural ecosystems is required. Further studies are required to clarify the role that P. plurivora is playing in alder decline both individually and in combination with P. alni complex.     

Occurrence and diversity of Phytophthora species in declining broadleaf forests in western Ukraine

In western Ukraine, forest decline and dieback of several broadleaved tree species have become increasingly evident during recent years, and surveys in some areas have shown symptoms indicative of Phytophthora infections. In this study, we aimed to determine the occurrence and diversity of Phytophthora species associated with several broadleaved tree species (Alnus glutinosa, Betula pendula, Castanea sativa, Fagus sylvatica and Quercus robur) from forest stands where dieback has been observed. Rhizosphere soil samples were collected from 14 forest stands during 2017 and 2018 and tested for the presence of Phytophthora species using morphological and molecular methods. Seven Phytophthora species (P. bilorbang, P. cactorum, P. gallica, P. gonapodyides, P. lacustris, P. plurivora and P. polonica), and two other clade six taxa were detected from the various forest types, several of which are probable agents responsible for decline. Four of the Phytophthora species (P. bilorbang, P. gallica, P. plurivora and P. polonica) have previously never been reported from broadleaf forests in Ukraine.     

Pathogenicity to alder of Phytophthora species from riparian ecosystems in western Oregon

Described as one of the most destructive pathogens of agricultural crops and forest trees, Phytophthora is a genus of microorganisms containing over 100 known species. Phytophthora alni has caused collar and root disease in alders throughout Europe, and a subspecies has recently been isolated in North America. Reports of canopy dieback in red alder, Alnus rubra, prompted a survey of their overall health and to determine whether P. alni was present in western Oregon riparian ecosystems. Over 1100 Phytophthora isolates were recovered, representing 20 species and 2 taxa. Phytophthora‐type cankers were observed in many trees, and their incidence was positively correlated with canopy dieback. High levels of mortality for red alder were not observed, which suggests these Phytophthora species are not aggressive pathogens. To test this hypothesis, three stem wound inoculations and one root dip were conducted on red alder seedlings using 13 Phytophthora species recovered from the riparian survey. Ten of the 13 Phytophthora species produced significant lesions in at least one pathogenicity test. Phytophthora siskiyouensis produced the largest lesions on red alder from the two stem wound inoculation tests conducted under summer conditions, while P. taxon Pgchlamydo caused the largest lesions during the winter stem wound inoculation test. Phytophthora gonapodyides, P. taxon Pgchlamydo and P. siskiyouensis have previously been found associated with necrotic alder roots and bole cankers in the field, and with the pathogenicity results reported here, we have established these species as causes of Phytophthora root disease and Phytophthora bole canker of alder in Oregon. While none of the Phytophthora species were especially aggressive towards red alder in the pathogenicity tests, they did cause localized disease symptoms. By weakening the root systems or boles of alders, the Phytophthoras could be leaving alders more susceptible to other insects and pathogens.     

Phytophthora species isolated from ash stands in Białowieża Forest nature reserve

Five Phytophthora species were isolated from the rhizosphere of ash‐dominated areas of the Bia?owieza European lowland forest nature reserve area. Morphological and DNA analyses identified Phytophthora fragariaefolia, P. plurivora, P. cactorum, P. lacustris and P. pseudosyringae. This is the first record of P. fragariaefolia in ash forests and demonstrates that several species in the potentially highly damaging Phytophthora genus are present within a near‐pristine ecosystem.     

Susceptibility of common tree species in Sweden to Phytophthora cactorum,P. cambivora and P. plurivora

In Sweden, invasive Phytophthora pathogens have been recognized as a growing threat to urban and production forests, calling for an urgent update of regeneration strategies for infested areas. Stem inoculation tests were performed to test the relative susceptibility of common conifer and broadleaved tree species Pinus sylvestris, Picea abies, Larix x eurolepis, Betula pendula, Quercus robur, Fagus sylvatica, Populus trichocarpa and Tilia cordata to the root pathogens Phytophthora cactorum, P. cambivora and P. plurivora commonly isolated from Swedish soils. Results indicate that all the species tested were susceptible and formed lesions following stem inoculation with all three Phytophthora species, but to varying degrees. Of particular interest are the high levels of susceptibility in P. trichocarpa to all three Phytophthora species compared to other tested tree species.     

Rapid diagnosis of pathogenic Phytophthora species in soil by real‐time PCR

Real‐time PCR assays based on the TaqMan system and using ITS sequences were developed for the identification of Phytophthora species, including P. cactorum, P. megasperma, P. plurivora, P. pseudosyringae and P. quercina, all of which are currently causing significant damage to roots of forest trees in both managed stands and natural ecosystems. Total genomic DNA was extracted from mycelia of aforementioned Phytophthora isolates. Species‐specific primers for P. cactorum, P. megasperma, P. plurivora, P. pseudosyringae and P. quercina were designed based on ITS sequences of rDNA. The amplification efficiency of target DNA varied from 93.1% (P. pseudosyringae) to 106.8% (P. quercina). The limit of the detection was calculated as 100 – 1,000 fg DNA, depending on the Phytophthora species. In mixed soil samples, all Phytophthora species were detected for Ct values shifted by 0.7 – 2.1 cycles. Based on these real‐time PCR assays we were able to identify the five Phytophthora species. These techniques will be of value in the identification of these pathogens, which may cause up to 80 – 90% fine root loss in oak stands.     

Immunodepletion of α‐plurivorin effector leads to loss of virulence of Phytophthora plurivora towards Fagus sylvatica

Phytophthora species secrete several proteins during their interaction with plants. Some of these proteins manipulate host metabolism favouring infection, while others can be recognized by plants thus triggering defence. Elicitins are known to elicit plant defences, leading to resistance. Here, we characterized the elicitin α‐plurivorin and proved that it was essential for the virulence of Phytophthora plurivora towards Fagus sylvatica. The immunodepletion of this peptide impaired its penetration into host tissue and in parallel P. plurivora lost its ability to colonize beech roots. Furthermore, the lack of α‐plurivorin inside the host led to an up‐regulation of several defence‐related genes of both salicylic acid and jasmonate/ethylene pathways, suggesting that α‐plurivorin might act as an effector‐triggered susceptibility during infection. Consequently, plants survived infection with P. plurivora after α‐plurivorin immunodepletion, whereas the majority of the infected control plants had died at the end of the experiment. Because canonical elicitins are ubiquitously secreted by many Phytophthora species, it is possible that these molecules may play a similar role in other susceptible interactions, being a potential target for controlling Phytophthora diseases.     

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.     

Phytophthora disease of alder (Alnus glutinosa) in France: investigations between 1995 and 1999

A severe decline of alder associated with an undescribed Phytophthora species was identified for the first time in England in 1993. No generalized decline of alder was reported in France before 1990. The first diebacks and mortalities of common alder were observed at the beginning of the 1990s, but the so‐called alder Phytophthora was not isolated in France until 1996. First, a synthesis about alder declines that were known in France before 1995 is presented. Then, a survey was established in north‐eastern France; 108 sites were visited and the alder Phytophthora was isolated from 57 of them. All the main rivers were found to be affected and damage levels are significant along some of them. The frequency of the alder Phytophthora and other fungi isolated from declining alders is discussed. Finally, information on other alder declines in France is presented region by region, and a map summarizes the known distribution of the disease. The alder Phytophthora is quite common and widespread in France, with western and north‐eastern France being especially affected; however, the number of diseased or dead trees varies greatly from one site to another. All records are from Alnus glutinosa; other Alnus species were seldom seen in the surveys.     

Aboveground biomass and nutrient accumulation dynamics in young black alder, silver birch and Scots pine plantations on reclaimed oil shale mining areas in Estonia

The growth, aboveground biomass production and nutrient accumulation in black alder (Alnus glutinosa (L.) Gaertn.), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) plantations during 7 years after planting were investigated on reclaimed oil shale mining areas in Northeast Estonia with the aim to assess the suitability of the studied species for the reclamation of post-mining areas. The present study revealed changes in soil properties with increasing stand age. Soil pH and P concentration decreased and soil N concentration increased with stand age. The largest height and diameter of trees, aboveground biomass and current annual production occurred in the black alder stands. In the 7-year-old stands the aboveground biomass of black alder (2100 trees ha⁻¹) was 2563 kg ha⁻¹, in silver birch (1017 trees ha⁻¹) and Scots pine (3042 trees ha⁻¹) stands respective figures were 161 and 1899 kg ha⁻¹. The largest amounts of N, P, K accumulated in the aboveground part were in black alder stands. In the 7th year, the amount of N accumulated in the aboveground biomass of black alder stand was 36.1 kg ha⁻¹, the amounts of P and K were 3.0 and 8.8 kg ha⁻¹, respectively. The larger amounts of nutrients in black alder plantations are related to the larger biomass of stands. The studied species used N and P with different efficiency for the production of a unit of biomass. Black alder and silver birch needed more N and P for biomass production, and Scots pine used nutrients most efficiently. The present study showed that during 7 years after planting, the survival and productivity of black alder were high. Therefore black alder is a promising tree species for the reclamation of oil shale post-mining areas.     

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.     

Target seed moisture content,chilling and priming pretreatments influence germination temperature response in Alnus glutinosa and Betula pubescens

Abstract

The response of common alder [Alnus glutinosa (L.) Gaertn.] and downy birch (Betula pubescens Ehrh.) seeds to germination temperature was examined following chilling and priming. Seeds of two seed lots of each species were subjected to combinations of chilling (4±1°C) and priming (20°C) treatments in fully imbibed (FI) state or a lower target seed moisture content (TMC) level (30% and 35% in alder and birch, respectively). After treatment, the seeds were allowed to germinate for 56 days at constant temperatures of 7.5, 10, 15, 20, 25 or 30°C. The response to temperature and pretreatment differed between species, but the effect was consistent in each seed lot within each species. In alder, the TMC seeds germinated well across the full range of temperatures, whereas there was an optimum temperature (22–23°C) for seeds given the FI pretreatment. Priming had no significant effect on the germination response of the TMC seeds in alder, but priming greatly improved germination in the FI seeds, especially at the lower germination temperatures (optimum 18–19°C). In contrast, in birch, the TMC seeds germinated better across the full temperature range, but the optimal germination temperature (15°C) was the same for all seed pretreatments. Priming improved germination in both the FI and TMC seeds in birch.     

Phytophthora root and collar rot of mature Fraxinus excelsior in forest stands in Poland and Denmark

In recent years, Common ash (Fraxinus excelsior) throughout Europe has been severely impacted by a leaf and twig dieback caused by the hyphomycete Chalara fraxinea. The reasons for its current devastating outbreak, however, still remain unclear. Here, we report the presence of four Phytophthora taxa in declining ash stands in Poland and Denmark. Phytophthora cactorum, Phytophthora plurivora, Phytophthora taxon salixsoil and Phytophthora gonapodyides were isolated from rhizosphere soil samples and necrotic bark lesions on stems and roots of mature declining ash trees in four stands. The first three species proved to be aggressive to abscised roots, twigs and leaves of F. excelsior in inoculation experiments. Soil infestation tests also confirmed their pathogenicity towards fine and feeder roots of ash seedlings. Our results provide first evidence for an involvement of Phytophthora species as a contributing factor in current decline phenomena of F. excelsior across Europe. Specifically, they may act as a predisposing factor for trees subsequently infected by C. fraxinea. Phytophthora species from ash stands also proved to be aggressive towards a wide range of tree and shrub species commonly associated with F. excelsior in mixed stands. Although damage varied considerably depending on the Phytophthora species/isolate–host plant combination, these results show that many woody species may be a potential source for survival and inoculum build‐up of soilborne Phytophthora spp. in ash stands and forest ecosystems in general.     

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.     

Effect of thermomechanical densification on surface roughness of wood veneers

The effect of short-term thermomechanical densification of veneer on the surface roughness and surface anatomical changes in four wood species – alder (Alnus glutinosa Gaertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) – was studied. Veneer sheets were densified at a temperature of 100, 150, or 200°C and at a pressure of 4, 8, or 12 MPa for 4 minutes. Seven roughness parameters such as R_a, R_z, R_q, R_p, R_v, R_sk, and R_ku were determined. Profile surface was recorded using a modified Carl Zeiss ME-10 profile gauging profilometer. Surface anatomical changes of veneer were examined using scanning electron microscopy. The results showed that densification temperature and pressure affect surface roughness of veneer. The surface became smoother, and roughness values decreased significantly (except for R_ku which increased slightly) with increasing temperature and pressure of densification. The effect of temperature on surface roughness changes is more pronounced compared with that of densification pressure. The lowest values of surface roughness were recorded for pine veneer samples followed by alder, birch, and beech samples. These results can be used to provide initial data for adhesive application processes in woodworking industry.     

Beech decline in Central Europe driven by the interaction between Phytophthora infections and climatic extremes

During the past decade, and in particular after the wet year 2002 and the dry year 2003, an increasing number of trees and stands of European beech (Fagus sylvatica L.) in Bavaria were showing symptoms typical for Phytophthora diseases: increased transparency and crown dieback, small‐sized and often yellowish foliage, root and collar rot and aerial bleeding cankers up to stem heights of >20 m. Between 2003 and 2007 134 mature beech stands on a broad range of geological substrates were surveyed, and collar rot and aerial bleeding cankers were found in 116 (86.6%) stands. In most stands the majority of beech trees were declining and scattered or clustered mortality occurred. Bark and soil samples were taken from 314 trees in 112 stands, and 11 Phytophthora species were recovered from 253 trees (80.6%) in 104 stands (92.9%). The most frequent species were P. citricola, P. cambivora and P. cactorum. Primary Phytophthora lesions were soon infected by a series of secondary bark pathogens, including Nectria coccinea, and wood decay fungi. In addition, infected trees were often attacked by several bark and wood boring insects leading to rapid mortality. Bark necroses were examined for their probable age in order to determine whether the onset of the current Phytophthora epidemic was correlated to rainfall rates recorded at 22 Bavarian forest ecosystem monitoring stations. A small‐scale survey in nine Bavarian nurseries demonstrated regular infestations of all beech fields with the same range of Phytophthora species. The results indicate that (1) Phytophthora species are regularly associated with beech decline and may also be involved in the complex of ‘Beech Bark Disease’, (2) excessive rainfalls and droughts are triggering the disease, and (3) widespread Phytophthora infestations of nursery stock might endanger current and future silvicultural projects aiming on the replacement of non‐natural conifer stands by beech dominated mixed stands.     

Phytophthora ×alni and Phytophthora lacustris associated with common alder decline in Central Portugal

Since the early 1990s, an emerging disease induced by the highly aggressive oomycete Phytophthora ×alni has caused widespread alder decline across Europe. In parallel, P. lacustris, a recently described species associated with riparian habitats, has been subject of increasing interest. A field survey conducted in 2014 showed high mortality rates in alder stands located in the riparian gallery along two rivers in Central Portugal. The pathogens isolated from necrotic alder stem base during this study were identified as P. ×alni and P. lacustris. This paper is the first to report the occurrence of P. lacustris in Portugal and presents the first finding of P. ×alni affecting mature trees in natural ecosystems located in Central Portugal.     

Field survey,isolation, identification and pathogenicity of Phytophthora species associated with a Mediterranean‐type tree species

Corymbia calophylla (marri), a keystone tree species in the global biodiversity hot spot of southwestern Australia, is suffering decline and mortality associated with a canker disease caused by the endemic fungus Quambalaria coyrecup. Phytophthora species are frequently isolated from the rhizosphere of C. calophylla, and a hypothesis is that Phytophthora root infection is predisposing C. calophylla to this endemic canker pathogen. Field surveys were conducted in both anthropogenically disturbed and undisturbed C. calophylla stands, from where a total of 100 rhizosphere soil samples, from both healthy and cankered trees, were collected. Phytophthora species were isolated from 26% of the samples collected, with Phytophthora incidence significantly higher on disturbed stands than in natural forests (73% and 27%, respectively). Five Phytophthora species were recovered, including P. cinnamomi, P. elongata, P. multivora, P. pseudocryptogea and P. versiformis. Under‐bark inoculations with the Phytophthora isolates caused significant lesion lengths in excised C. calophylla stems. Corymbia calophylla response to pot infestation trials in the glasshouse varied between Phytophthora species and isolates, with isolates of P. cinnamomi and P. multivora causing a significant reduction in seedling root volume and often leading to seedling death. This study demonstrates that root disease caused by Phytophthora species, especially P. cinnamomi and P. multivora, has the ability to adversely affect C. calophylla health. This study leads the way to do a dual inoculation trial with the canker pathogen Q. coyrecup, and different Phytophthora species to investigate if Phytophthora root infection predisposes C. calophylla to this canker disease.     

Does Pythium anandrum contribute to the dieback of sessile oak (Quercus petraea) in Turkey?

During investigations into the causes of oak decline in six Regional Forestry Directories of the Black Sea Region of Turkey, Phytophthora spp. were obtained from one region and Pythium spp. were collected from three regions. The most frequently isolated Pythium species, Pythium anandrum, when inoculated on stem bases, caused longer cankers than two isolates of both Phytophthora plurivora and 2 of the P. quercina. This is the first report of Pythium anandrum causing disease on sessile oak. P. anandrum may contribute oak decline in Turkey.