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First Report of Diplodia seriata Causing Shoot Blight and Cankers of Cotoneaster salicifolius in Bulgaria

Shoot and branch blight was observed on shrubs of Cotoneaster salicifolius in the region of Plovdiv, Bulgaria in autumn and winter surveys during 2005 and 2006. Scattered pycnida were found on the withered branches, which bore sunken cankers with marginal bark cracks. Fungal colonies obtained from affected host tissue developed on potato dextrose agar (PDA) at 24 to 25°C in the dark. Colonies grew rapidly, were floccose, initially white, becoming grayish brown, and finally went from gray to black. Dark brown, unilocular pycnida formed after 2 to 3 weeks in culture. Conidia that formed at the tips of cylindrical, percurrently, proliferating, conidiogenous cells were ovoid, straight, pale brown to dark brown, internally verruculose, aseptate or occasionally with a single median septum. The mean conidial dimensions were 20 × 12 μm, the extreme range was 15 to 25 × 11 to 15 μm. These characters correspond to Diplodia seriata De Not., which is the anamorph of “Botryosphaeria” obtusa (2). Identity was confirmed from the nucleotide sequences of the internal transcribed spacer (ITS) from the rRNA repeat as described elsewhere (1). BLAST searches in GenBank showed 100% identity of isolates with reference sequences of D. seriata including that from the ex-epitype culture. The ITS sequence of a representative isolate (CAP337) has been deposited in GenBank (Accession No. EU483658). Pathogenicity was tested by inserting 3-mm-diameter mycelia plugs from 7-day-old PDA cultures into scalpel-wounded mature apple fruits (cv. Granny Smith) and wounded shoots of C. salicifolius. Sterile PDA plugs were placed into similarly made wounds of control specimens. There were three replicates for each treatment and the inoculated wounds were subsequently covered with Parafilm. Small necrotic lesions occurred on the apple fruits 3 to 5 days after inoculation and after 10 to 12 days on the shoots. Within 4 to 5 weeks, all apple fruits were entirely rotten, shrunken, and covered with pycnida, whereas the shoots withered and typical blight symptoms developed above the inoculation sites. The pathogen was reisolated from all inoculated samples but not from any control treatment. To our knowledge, this is the first report of D. seriata on C. salicifolius in Bulgaria. It is likely that this pathogen will be found increasingly more frequently because of the intensive introduction of decorative Rosaceae species into urban districts.

References: (1) A. Alves et al. Mycologia 96:598, 2004. (2) A. J. L. Phillips et al. Fungal Divers. 25:141, 2007.