Summary Sooty bark disease (SBD) caused by the pathogen Cryptostroma corticale is currently one of the risks to the population of Acer pseudoplatanus in Europe. After a number of records of symptomatic and dead trees in Prague, assessment of the latent non‐symptomatic stage of SBD was questioned as a means to forecast the health risk of the A. pseudoplatanus population. We used two methods of early detection of C. corticale in non‐symptomatic trees: cultivation from wood tissue on agar plates and a culture‐free approach based on nested PCR with newly designed species‐specific primers. The pathogen was detected in 25% of 112 examined trees from seven localities in Prague, but the disease incidence might be higher if more A. pseudoplatanus trees in Prague were included and if the crown infections were considered. The presence of C. corticale was positively correlated with discoloured wood, but its presence did not depend on the occurrence of external symptoms. Infected trees were more frequently found in groups on steep sites at higher elevations. In addition, heavier NOx pollution combined with more paths and roads increased the incidence of C. corticale.

Summary The anamorphic fungus Cryptostroma corticale (Xylariaceae) causing sooty bark disease (SBD) of Acer pseudoplatanus has been reported within the past decade in several European countries. In the last decade, severe drought conditions during summer also resulted in an outbreak of SBD in park areas in Prague (Czech Republic). Trees with the typical syndromes were recorded in four localities in Prague. Some trees were also located in the alluvial plain of the Vltava River with groundwater available all year long. We suppose that the trees were stressed by full water saturation for several months after flood in 2012 and that SBD was triggered by anoxia and subsequent phytopththora root rot. Sterile fungi isolated from one tree and one lesion were identified as C. corticale based on the similarity of their ITS rDNA sequences with strains of C. corticale in a public collection. Furthermore, C. corticale was placed in the family Xylariaceae within the genus Biscogniauxia based on phylogenetic analysis of four genes (ITS nrDNA, actin, RPB2 and β‐tubulin). The closest relatives are B. bartholomei and Graphostroma platystoma.

AbstractČerný K., Strnadová V. (2010): Phytophthora alder decline: disease symptoms, causal agent and its distribution in the Czech Republic. Plant Protect. Sci., 46: 12-18.Phytophthora decline of riparian alder populations has recently become an important problem in many European countries, including the Czech Republic. The causal agent, Phytophthora alni, has spread quickly in the Czech Republic. Hundreds of kilometres of riparian alder stands, especially in the western part of the country, have been severely affected to date. Diseased trees show symptoms characteristic of Phytophthora root and collar rot; these include small, sparse and yellowing foliage, crown dieback, presence of exudates on the bark and necroses of collar and root tissues. Infected trees usually die within a few years, or they become irreversibly damaged, and their function in bank reinforcement declines. The ecological and mechanical functioning of severely affected alder stands may be seriously disrupted.

Summary The impact of ash dieback caused by Hymenoscyphus fraxineus on 17 provenances of Fraxinus excelsior and one provenance of Fraxinus angustifolia was studied in an extensive field trial established in the Czech Republic prior to the H. fraxineus invasion in 1999. A difference in the level of resistance to ash dieback between the species was found: F. angustifolia was significantly less affected by the disease than F. excelsior. Moreover, particular provenances of F. excelsior showed important differences in the level of resistance to H. fraxineus. A relationship between the impact of ash dieback and altitude was also discovered – the provenances from altitudes above 600 m a.s.l. were less affected by the pathogen than were the provenances from lower areas. No difference in the impact of the disease among provenances of F. excelsior from different ecotopes (ravine, calcareous ravine and alluvial) was found. Substantial among‐tree variability in resistance to H. fraxineus was observed throughout the trial – promising genotypes (with crown defoliation up to 5%) were identified in all 18 tested provenances. In regard to this finding, it appears that the main source of resistance to the pathogen is probably at the individual genotype level in the trial. A secondary but massive attack by Hylesinus fraxini was identified in the trees that had been greatly damaged by ash dieback, and the beetle caused their health to deteriorate significantly. A significant negative effect of the presence of collar necroses caused by H. fraxineus and browse damage was also identified.

Bleeding canker and decline of riparian alder populations has been an important problem in many European countries, including the Czech Republic. Initially, an 'alder Phytophthora ' was isolated from damaged black alder trees in western Bohemia near the town of Karlovy Vary in 2001 ( d ern y et al ., 2003). The exact species identification was unknown at this time. Since its original discovery, we have isolated similar Phytophthora species from damaged innerbark and conductive tissues of declining trees of Alnus glutinosa and A. incana from approximately 60 alder stands in the Czech Republic. The pathogen has been spreading rapidly in the affected alder stands, particularly in the western part of the Czech Republic. The pathogen has been frequently found in catchments of the Vltava river and Ohre river (western, northern, middle, southern Bohemia, western part of Vysocina region). Extensive decline of alder trees has not been detected in the eastern part of country (Moravia) yet, but the pathogen has been found in watercourses in the upper part of catchment of the Dyje river (Vysocina region) and is likely spreading to the east. In 2004, the causal agent of alder decline in Britain was determined to be a new hybrid, designated as Phytophthora alni subsp. alni (Brasier et al ., 2004).Symptoms on diseased trees were characteristic of bleeding canker and alder decline in other regions (Jung & Blaschke, 2004): small, yellowing, and sparse foliage, dieback in the canopy and bleeding cankers on tree trunks. Many isolated cultures were similar morphologically and had characteristics that were consistent with P. alni subsp. alni (Brasier et al ., 2004). Colonies growing on carrot agar (CA) were uniform, appressed with sparse aerial mycelium. Radial growth was 7-9 mm per day at 20 ° C on CA. Optimal growth temperature was 23-25 ° C , with several isolates failing to grow at 6 and 33 ° C. Isolates were homothallic with two-celled (22-31 × 12-20 μ m) amphigynous antheridia, producing abundant terminal, spherical oogonia (28-55 μ m in diam.) with moderately ornamented walls. Many oogonia aborted at a rate of 20 to 60%. Sporangiophores were simple with terminal sporangia, proliferating internally, often nested, ellipsoid in shape, measuring 38-65 × 25-41 μ m (length × width ratio 1·4-1·6), and had minute papilla or were non-papillate.Comparison of DNA sequences of ITS region of two isolates (GenBank Acc. Nos EF194776, EF194777) with acquired sequences with those deposited in GenBank, confirmed their identity as P. alni . Pathogenicity was tested by artificial infection of 4-year-old black alder plants. Twenty plants were inoculated by placing segments of agar with mycelium, taken from the colony margin growing on CA, on the underbark at the collar of plants. The characteristic necroses of collars and wilting of plants were observed after several weeks and the pathogen was reisolated from damaged tissues. The control group of alder plants inoculated with sterile agar remained healthy. This is the first positive identificatio...