First report of Eutypella parasitica causing cankers on field maple (Acer campestre) in Croatia

In September 2007, a survey for Eutypella parasitica was performed in Croatia along the border with Slovenia, since a risk assessment showed more than half of Croatia to be at high risk for E. parasitica establishment (Ogris et al., 2006). In Prišlin, less than 1 km from the border with Slovenia, 13 field maples (Acer campestre) showing characteristic symptoms of Eutypella canker of maple were found. Two trees showed young infection (Fig. 1A), nine had old cankers where bark remained in place except at the centre of the canker (Fig. 1B), and two trees had already snapped due to the progress of the disease (Fig. 1C).

Extensive perithecia were always present on older parts of the cankers (Fig. 2A), with necks up to 2 mm long and poorly developed stroma. White-to-light cream coloured mycelial fans were present in the bark (Fig. 2B). Ascospores measured 8.4 (6.0-11.8) x 2.8 (1.9-3.9) µm and asci 78 (65-96) x 7.2 (5.9-9.3) µm. The perithecial body measured 0.64 (0.44-0.77) x 0.51 (0.33-0.71) mm. Morphological identification of E. parasitica was confirmed by PCR using E. parasitica specific primers EpR and EpF (PiÅ¡kur et al., 2007). A fragment of the expected size was successfully amplified from an isolate of E. parasitica obtained at PriÅ¡lin, Croatia. Surprisingly, Eutypella canker was found only on A. campestre but not on A. pseudoplatanus, which was growing abundantly near the infected area. Acer campestre was only recently recognized as a new host to Eutypella canker (Ogris et al., 2005).

The disease is distributed in a continuous area in Slovenia and Croatia. In the previous report of the establishment of E. parasitica in Slovenia (Jurc et al., 2006), Koch's postulates were not completed at the time of publication due to the length of time required for disease symptoms to develop. Here we report completion of Koch's postulates performed with the E. parasitica isolate (SFI, Accession No. 34), obtained in Slovenia in 2005. Mycelial plugs (8 mm diameter) were taken from a 12-day old culture growing on malt extract agar (MEA) and placed on the wounded maple twigs. After 11 months, control wounds, inoculated with sterile MEA plugs, healed, but E. parasitica-inoculated wounds showed lesions in the bark and wood discoloration. The fungus was successfully re-isolated from the infected parts in bark and wood. This is the first report of the establishment of E. parasitica in Croatia.