First report of Eutypella canker of Acer pseudoplatanus in Europe

D. Jurc¹*, N. Ogris¹, B. Slippers² and J. Stenlid²

¹ Slovenian Forestry Institute, Večna pot 2, 1000 Ljubljana, Slovenia
² Swedish University of Agricultural Sciences, Department of Forest Mycology and Pathology, Box 7026, S-750 07 Uppsala, Sweden

Accepted for publication 08/12/05

At the end of May 2005 distinctive oval bark lesions were found on the trunks of Acer pseudoplatanus (sycamore) on Rožnik Hill in the centre of Ljubljana; the capital of Slovenia. A characteristic feature of the cankers was that the bark remained in place except at the centre (the oldest part). The cankers were located mostly on the lower portions of the trunks. Intensive surveys around Rožnik Hill revealed a further 19 affected trees by the end of June. The disease was well established and the main trunks of three trees had snapped and fallen over. The furthest distance between affected trees was 10.6 km, suggesting an initial slow spread. It is not known when the disease first appeared.

Figure 1: Eutypella canker on sycamore maple. Dead bark is persistent and falling off only in the oldest part of the canker; black perithecial necks are visible	Figure 2: Asci with ascospores (A), conidia from culture (B) (bar = 20 µm)

White-to-light cream coloured mycelial fans were present in the bark and were significantly more developed along the advancing edge of the lesions. Perithecia were always present on the older parts of the cankers and were extensive (Fig. 1), with necks up to 5 mm long and poorly developed stroma. Ascospores measured 8.5 (5.5-12) × 3 (2-4) µm, asci 85.5 (61-117) × 7.5 (5-10) µm (Fig. 2A), and conidia 25 (12.5-35) × 2 (1-2.5) µm (Fig. 2B). This fungus was identified as Eutypella parasitica. Although the range of sizes was slightly different to those given by Davidson & Lorenz (1938), all other morphological characteristics (Fig. 3) agreed with the original description. The rDNA ITS region of two isolates were sequenced (GenBank accession numbers DQ118964-65) and compared with the ex-type isolate of E. parasitica (CBS No 210.39, GenBank accession number DQ118966). All three sequences were identical.

Figure 3: Perithecia and stroma (bar = 0.5 mm)

In June 2005, trunks of sycamore were inoculated with two isolates of E. parasitica. After 40 days, control wounds without the fungus had begun to heal, while inoculated wounds showed some advancing necrosis. However it was impossible to reisolate the fungus. Despite this, there is little doubt that the symptoms observed are due to E. parasitica, as disease development is slow, with up to two years required to obtain positive results (French, 1969). As a result, these trials will continue to be monitored.

Eutypella canker of Acer spp. (maples) is a destructive disease, that was until recently only found in North America. Sycamore and other Acer spp. are widespread in Europe and this first report from Slovenia is therefore of immediate concern.

References

Davidson RW, Lorenz RC, 1938. Species of Eutypella and Schizoxylon associated with cankers of maple. Phytopathology 28, 733-745.

French WJ, 1969. Eutypella canker on Acer in New York. Syracuse, New York, USA: State University of New York: New York State College of Forestry Technical Publication 94.

The British Society for Plant Pathology