Occurrence of Cercospora cantuariensis on hop in Austria and Slovenia

During a long period of rainfall in August 2005, necrotic lesions on cones and leaves were observed on hop (Humulus lupulus) plants in the Kärnten (Leutschach) region of Austria. Similar weather conditions in late August 2007, favoured further development and spread of disease to the nearby (30 km air distance) hop growing area in KoroÅ¡ka (Radlje ob Dravi), Slovenia. Leaf symptoms were irregular to circular, purplish brown spots, 1-10 mm in diameter (Fig.1b). Affected cones showed irregular brown necrotic areas on the bracts and bracteoles, which in some cases had progressed throughout the entire cone (Fig.1a). Microscopic examination of the affected tissue revealed the presence of pale olive brown conidiophores and conidia (Fig.1c). Conidiophores were unbranched, 1-7 septate, straight, 10 (8-20) × 40 (25-200) µm, with a sinuous tip. Conidia were cylindrical, straight to mildly curved, 13 (10-21) × 250 (135-510) µm, 5-19 septate, with rounded to conical ends. On the basis of the morphological characters, the fungus was identified as Cercospora cantuariensis Salmon & Wormald; (synonym Mycocentrospora cantuariensis Deighton) (Chupp, 1953; Index Fungorum, 2008).

Identification was confirmed by sequencing the ITS region spanning ITS 1, 5.8S rDNA and ITS 2 of two isolates (1CCA and 2CCS) and one C. cantuariensis isolate obtained from CBS (CBS 112.24). All isolates yielded the same 566 bp sequence, which showed the highest identity (95%, 491/515) to M. acerina isolate MA12 ITS sequence (AY266155) in GenBank. These sequencing data, together with previous reports (Goodwin et al., 2001), suggest that the species M. cantuariensis is more appropriate for this fungus, and the current accepted name is C. cantuariensis (Index Fungorum, 2008). The nucleotide sequences have been assigned GenBank Accession Nos. EU346862 (1CCS), EU346863 (2CCS) and EU346864 (CBS 112.24).

Pathogenicity tests were performed by spraying leaves and mature cones of detached lateral shoots (cv. Celeia) with a spore suspension (10⁵ conidia/ml). The first lesions developed on leaves and cones three days after inoculation. Controls sprayed with distilled water showed no symptoms. The fungus was previously recorded on H. lupulus and H. japonicus in England, Germany, China, Korea and Russia (CBS, 2008; Wormald, 1928). This is the first report of C. cantuariensis causing severe damage to the leaves and cones of hop in Austria and Slovenia.