First report of Diplodia corticola in Greece on kermes oak (Quercus coccifera)

In 2007, symptoms of extensive branch and shoot dieback were observed on kermes oak (Quercus coccifera) shrubs and trees in some localities in the Messinia prefecture of south western Peloponnese, Greece. The symptoms were more intense during summer, with abundant dead branches and twigs with wilted leaves (Fig. 1). Upon close examination, cankers were detected on the branches and twigs showing symptoms. Cankers were also evident on larger branches with no apparent foliar symptoms. In many of the branch samples taken, dark brown to black pycnidia were observed to emerge through the bark on the canker surfaces (Fig. 2).

Fungal isolates from bark and wood tissues on symptom-bearing branches, as well as from spore masses in the pycnidia, were morphologically very similar and typical of the Botryosphaeriaceae. Colonies on malt extract agar (MEA) showed dense aerial mycelium that was initially white, gradually becoming dark grey olivaceous, with a radial growth rate of 1.3 cm/day at 25^°C. Conidiomata were formed on sterile poplar twigs placed on cultures grown on water agar and incubated under lights for three to four weeks. Conidia formed in culture and those from pycnidia on cankerswere similar in shape and size: cylindrical with rounded ends, hyaline and unicellular (Fig. 3), becoming light brown and two-celled (Fig. 4) with age, (20-)24-32(-38) x (10-)12-16(-17) μm. Morphological characteristics and nucleotide sequences of the ITS region of ribosomal DNA (GenBank Accession Nos. GQ396149-GQ396153) confirmed the identification of the fungus as Diplodia corticola (teleomorph: Botryosphaeria corticola) described by Alves et al. (2004).

Pathogenicity tests were carried out in the summer of 2008 on Q. coccifera shrubs and trees growing in the same area as the naturally infected plants. Βranches (0.7-5.0 cm in diameter) were wound inoculated with mycelium on agar plugs. Necrosis of bark and wood tissues was evident on the branches six weeks after inoculation, with the formation of characteristic cankers and wood discolouration beneath the cankered area. Pycnidia formed on the majority of inoculated branches. The fungus was consistently re-isolated from necrotic bark and wood tissue, as well as from pycnidial spore masses on the inoculated branches. No symptoms developed on control branches inoculated with sterile MEA. D.corticola has been reported to occur on oak species in Spain, Portugal, Italy and Morocco (Alves et al. 2004). This is the first record of D. corticola in Greece and Q. coccifera is a new host of the fungus in Europe.