First Report of Palm Rot of Phoenix spp. Caused by Neodeightonia phoenicum in Greece.

Abstract

In July 2007, a severe rot was observed on Phoenix dactylifera and P. canariensis palms in the vicinity of Heraklion (Crete), Greece. Initial symptoms were pale, elongated spots that gradually turned to dark brown streaks extending along the leaf base and rachis. In early stages, the upper parts of the leaves usually remained unaffected. Eventually decay and premature death of leaves occurred, followed by terminal bud necrosis. Shoot blights and stalk rots were also observed. A filamentous fungus was consistently isolated onto potato dextrose agar (PDA) from leaf base necrotic lesions. Immersed pycnidial conidiomata on pine needles in culture were multiloculate and dark brown to black. Pycnidial paraphyses were absent. Conidiogenous cells were hyaline, cylindrical, and swollen at base. Conidia were thick-walled, ovoid to ellipsoid, with rounded apex and base; initially hyaline and aseptate, 15.2 ± 0.4 × 11.7 ± 0.3 μm, later becoming dark brown and 1-septate, 21.3 ± 0.4 × 11.8 ± 0.3 μm, with a striate appearance. Total DNA was extracted and used for PCR amplification and sequencing of the ITS1-5.8S-ITS2 region, together with parts of the flanking 18S and 28S rRNA genes (1). The sequence (GenBank Accession No. JX456475) was found 99% identical to Neodeightonia phoenicum ITS sequences (GenBank Accession Nos. EU673338 to EU673340), and was clustered together as a single group with the above sequences with good support by phylogenetic analysis that included representatives of other Neodeightonia species and several other Botryosphaeriaceae members. Based on the morphological, molecular, and phylogenetic analyses, the pathogen was identified as N. phoenicum A. J. L. Phillips & Crous (2) (syn. Diplodia phoenicum (Saccardo) H. S. Fawcett & Klotz), formerly also known as Macrophoma phoenicum Saccardo and Strionemadiplodia phoenicum (Saccardo) Zambettakis. To prove pathogenicity, the petioles of the older leaves of seven 2-year-old seedlings of each of three palms, P. canariensis, P. theophrasti, and Washingtonia filifera were wounded with a sterile scalpel (shallow cuts 0.5 to 1.0 cm wide, made parallel to the surface) and inoculated with agar discs from a 1-week-old PDA culture of the fungus. For controls, PDA discs without fungal mycelium were placed on the wounds of four seedlings of each host. Petiole rot, blight, and leaf necrosis were evident on all inoculated plants 6 weeks post inoculation and the pathogen was consistently reisolated from all three inoculated palm species, whereas no symptoms were observed on control plants. N. phoenicum has repeatedly and globally been reported on P. dactylifera (3). To the best of our knowledge, this is the first report of the occurrence of N. phoenicum infecting Phoenix species in Greece. Palms are extensively used as ornamental trees throughout Greece. A potential spread of palm rot caused by N. phoenicum might have a substantial economic impact and should be urgently addressed through appropriate disease management programs.