Phytophthora alni causing decline of black and grey alders in the Czech Republic

Abstract

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...

Phytophthora alder decline: disease symptoms, causal agent and its distribution in the Czech Republic

“…In 2006, the pathogen was known to be present in about 60 sites and to be spreading rapidly, particularly in the western part of the Czech Republic (Cerny et al 2008). The loss of trees in affected areas has increased enormously: tens of thousands of alder trees have disappeared to date in the area of the Upper Vltava River Authority alone.…”

“…In morphological studies ten selected isolates were examined. In a previous study, DNA sequences of the ITS region of two of these isolates (GenBank accession numbers EF194776 and EF194777) were compared with sequences available from the GenBank (Cerny et al 2008). One isolate has been deposited in the Culture Collection of Fungi, Prague, under No.…”

“…In the Czech Republic, the pathogen was first isolated from damaged common alder trees in western Bohemia in 2001 (Černý et al 2003). Six years later, the pathogen was identified in about 60 alder stands, mostly in the western part of the country (Cerny et al 2008). To date, the pathogen has caused considerable losses of alder trees along hundreds of kilometres of riverbanks and has spread beyond control.…”

The effects of flooding and Phytophthora alni infection on black alder

“…Therefore, it was likely that this decline was connected to the flooding that occurred in 2002 (Vyhlídková et al 2005) because the increased water level and flooding could damage the alders and induce morphological changes as seen by McVean (1956). The dangerous pathogen of alders Phytophthora alni has been spreading rapidly in alder stands, particularly in the western part of the Czech Republic in recent years, and has leading to significant losses in highly affected stands (Cerny et al 2008). We felt it important to distinguish which of these factors was the real cause of the decline.…”

Factors affecting the development of Phytophthora alni ssp. alni infections in Alnus glutinosa L.

“…Gibbs et al 1999;Szabó et al 2000;Streito et al 2002;Oszako, Orlikowski 2005) and has caused a devastating epidemic in alders. In the Czech Republic, the pathogen was first isolated from damaged black alder trees in Western Bohemia in 2001 (Černý et al 2003) but was properly identified only later (Cerny et al 2008). To date, the pathogen has been found in approximately 150 sites, although the disease symptoms have been detected in approximately 300 sites throughout the Czech Republic.…”