First report of leaf spot of Phoenix theophrasti caused by Paraconiothyrium variabile in Greece

In the spring of 2011, a severe leaf spot disease of Phoenix theophrasti was observed in the vicinity of Heraklion (Crete), Greece. Initial symptoms were small, round-ovoid spots of varying shades of brown on the leaves, later being transformed into oblong streaks (average dimensions 7.3 ± 1.0 × 3.3 ± 0.5 mm), surrounded by dark brown rings. As the disease progressed, the expanding streaks often coalesced to form enlarged necrotic lesions. Similar symptoms were also detected on petioles and leaf bases. Extended spotting and blighting occasionally resulted in leaf death. A filamentous fungus was consistently isolated onto potato dextrose agar plates from the periphery of the characteristic lesions, with cultures invariably producing brick to cinnamon colonies with sparse aerial mycelium, subglobose and dark brown superficial pycnidial conidiomata on pine needles, 1- to 3-celled hyaline conidiophores, and hyaline, subcylindrical to ellipsoidal, 1-celled, smooth- and thin-walled conidia, with average dimensions of 3.5 ± 0.6 × 1.7 ± 0.4 μm (n = 100). Total DNA of two isolates 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 (4). Both sequences (GenBank Accession Nos. JX456476 and JX456477) were 100% identical to deposited Paraconiothyrium variabile ITS sequences (EU295640 to 48, JN983440 and 41, and JF934920), and were clustered together as a single group with these sequences with good support by phylogenetic analysis that included representatives of the relative P. brasiliense and P. africanum species. Based on the morphological, molecular, and phylogenetic analyses, the pathogen was identified as P. variabile Riccioni, Damm, Verkley & Crous (2). To prove pathogenicity, 10 P. theophrasti 2-year-old seedlings were sprayed with a conidial suspension of the fungus (107 conidia ml-1, 10 ml per plant), while five additional control plants were treated with sterile distilled water. All plants were maintained in the greenhouse at 15 ± 5°C, with 90% humidity. Characteristic leaf spots were evident 4 weeks post inoculation on the older leaves, and P. variabile was consistently reisolated from all inoculated plants. No symptoms were observed on control plants. Paraconiothyrium variabile has been isolated from various woody host plants such as Prunus persica, P. salicina, and Malus sp. in South Africa (1,2), Actinidia chinensis and A. deliciosa in Italy (2), Laurus nobilis in Turkey (2), and Salix matsudana in China (3). To our knowledge, this is the first report of P. variabile naturally infecting and causing a leaf spot disease on a palm species. Palms are extensively used as ornamentals throughout Greece and the occurrence of P. variabile can potentially result in economic loss to the local ornamental industry. © The American Phytopathological Society

Phytopathogenic, morphological, genetic and molecular characterization of a Verticillium dahliae population from Crete, Greece

A population of 84 V. dahliae isolates mainly originating from Crete, Greece, was characterized in terms of pathogenicity and virulence on different hosts, in parallel with morphological/physiological characterization, vegetative compatibility grouping and mating type determination. Tomato race 2 was found to have supplanted race 1 and was more virulent on a tomato-susceptible cultivar than race 1. Using a differential host classification system which tests pathogenicity to tomato, eggplant, sweet pepper and turnip, 59 isolates were assigned to tomato, 19 to eggplant, one to sweet pepper and five to tomato-sweet pepper pathogenicity groups. All isolates from Crete fell into VCG subgroups 2A, 2B and 4B, while a remarkably high incidence of bridging isolates (compatible with two or more VCGs) was recorded. The tomato-sweet pepper pathogenicity group was morphologically quite distinct from the others, while conidial length and pigment intensity were discriminatory parameters among VCGs 2A, 2B and 4B. PCR-based molecular marker Tr1/Tr2 was reliable in race prediction among tomato-pathogenic isolates, except for members of VCG 4B, while the application of markers Tm5/Tm7 and 35-1/35-2 was highly successful for tomato-pathogenic isolates. E10 marker was related to VCG 2B, rather than to pathogenicity groups. A single nucleotide polymorphism in the ITS2 region, and two novel molecular markers, M1 and M2, proved useful for the fast and accurate determination of major VCGs 2A, 2B and 4B, and can be used for high-throughput population analyses in future studies. The mating type was unrelated to VCG classification and probably does not control heterokaryon incompatibility in V. dahliae. © 2013 KNPV