First reported outbreak of charcoal disease caused by Biscogniauxia mediterranea on Turkey oak in Slovenia

D. Jurc* and N. Ogris

Slovenian Forestry Institute, Večna pot 2, 1000 Ljubljana, Slovenia

*dusan.jurc@gozdis.si

Accepted for publication 25/05/05

In August 2003, the leaves of about 50% of coppice-grown Turkey oak (Quercus cerris), covering about 180 ha, turned brown. In spring 2004, whole trees were dead and the bark of the others died off in strips; there were shoots only from parts of the tree crowns. The same phenomenon also occurred patchily over approximately 16,000 ha of mixed forests in the Karst region of Slovenia. The bark began to crack and fall off in June 2004 (Fig. 1) and in August the first perithecial stromata of Biscogniauxia mediterranea were observed in bark cracks on tree trunks and branches (Fig. 2). At the beginning of March 2005 there were a large number of stromata on the bark of dead trees; more than hundred of them could be found on a single tree with a diameter of 27 cm at chest height. Stromata measured (3-) 19.6 (-36) × (1.5-) 3.4 (-7.5) cm, perithecia were tubular (0.43-) 0.62 (-0.81) × (0.08-) 0.14 (-0.22) mm, ascospores measured (13-) 16 (-19.5) × (6-) 7.5 (-9) µm, asci (114-) 145 (-175) × (8.5-) 10.5 (-14) µm, the outer dehiscing layer was (0.07-) 0.16 (-0.24) mm thick (Fig. 3). Measurements indicate that the fungus could be classified as B. mediterranea var. microspora (Ju et al., 1998). The perithecial stromata and pure cultures were deposited in the Herbarium of the Slovenian Forestry institute with accession nos. 1505, 1506 and 1507.

Figure 1: Symptoms of charcoal disease: tree crown is partially dead and bark is peeling off

The disease symptoms appeared after severe drought and unusually hot weather. Total rainfall before the onset of symptoms in June, July, and August 2003 was 27, 12 and 66% respectively of the 30-year average, while average monthly temperatures for the same months were 5.8, 3.6 and 5.6°C higher than the 30-year average. The development of charcoal disease on oaks after drought is well documented (Vannini & Valentini, 1994). The endophytic presence of this fungus in living bark enables it to quickly overgrow the stressed tissues of the host and destroy them (Vannini, 1998).

Figure 2: Perithecial stroma of H. mediterraneum on trunk; the bark was removed; outer dehiscing layer is beginning to fall off; the margin of the stroma is raised	Figure 3: Section through stroma; outer dehiscing layer and perithecia are visible (bar 1 mm)

Charcoal disease is a serious problem in cork oak (Quercus suber) and Turkey oak in the Mediterranean area but it had never been detected further north than southern Tuscany (Vettraino et al., 2002). The appearance of this new disease in Slovenia, approximately 350 km north-east of Tuscany, indicates that the predicted climate change could lead to outbreaks of this disease further north.

We thank Mr. B. Košiček (Slovenian Forest Service) for the information about Turkey oak dieback.

Ju Y-M, Rogers JD, San Martin F, Granmo A, 1998. The genus Biscogniauxia. Mycotaxon 66, 1-98.

Vannini A, 1998. Endophytes and oak decline in Southern Europe – the role of Hypoxylon mediterraneum. Abstract, 7th International Congress of Plant Pathology Edinburgh, Scotland, (http://www.bspp.org.uk/icpp98/2.9/5S.html).

Vannini A, Valentini R, 1994. Influence of water relations on Quercus cerris–Hypoxylon mediterraneum interaction: a model of drought-induced susceptibility to a weakness parasite. Tree Physiology 14, 129-139.

Vettraino AM, Barzanti GP, Bianco MC, Ragazzi A, Capretti P, Paoletti E, Luisi N, Anselmi N, Vannini A, 2002. Occurrence of Phytophthora species in oak stands in Italy and their association with declining oak trees. Forest Pathology 32, 19-28.

The British Society for Plant Pathology