FIRST REPORT OF CYTOSPORA PUNICAE ASSOCIATED WITH WOOD CANKER AND BRANCH DIEBACK DISEASE OF POMEGRANATE IN TUNISIA

Abstract

Pomegranate (Punica granatum L.) is an economically important crop in Tunisia with an annual production of 23.000 tons. During May and June of 2014, severe branch dieback was observed in pomegranate plants cv. Gabsi located in Gabes region with about 8% of disease incidence. Symptoms of the disease included leaf yellowing, wood lesion and canker formation. Isolation of the pathogen was performed from 10 samples of active cankers plated onto PDA medium amended with 100 mg l-1 of tetracycline hydrochloride. Fungal colonies were then sub-cultured onto PDA medium at 22°C. All isolates were identified as Cytospora sp. based on colony morphology, conidial characteristics and pycnidia formation (Palavouzis et al., 2015). The isolates developed white mycelium, which turned green to dark brown with hyaline, allantoid, aseptate conidia (average 4-5 μm x 1.75 μm) and production of dark coloured pycnidia 300 to 450 μm in diameter after 15 days (Peduto Hand et al., 2014). Identity of these isolates was confirmed by sequencing the internal transcribed spacer region. The ITS sequences were deposited in GenBank (Accession No. KT272402). These sequences revealed 99% genetic identity with those of Cytospora punicae species available in GenBank (KJ621689; KJ621688). Pathogenicity of Cytospora punicae was evaluated by inoculation of two isolates in 1-year-old shoots of pomegranate cv. Gabsi (Palavouzis et al., 2015). The inoculated shoots developed necrotic spots with vascular discoloration spreading downward and upward from the inoculation site. Cytospora punicae was recovered from 100% of the inoculated shoots. This is the first report of Cytospora punicae causing wood canker and branch dieback of pomegranate in Tunisia.