In June of 2008, rapidly developing necrotic symptoms were observed on 2-month-old seedlings of German statice (Goniolimon tataricum, synonym Limonium tataricum) that were started from field-collected seeds and grown in plastic pots under greenhouse conditions in the region of Plovdiv, Bulgaria. Initial symptoms were slight yellowing and wilting of single, lower leaves. Subsequently, necrosis affected several petioles and stem bases, which led to complete plant collapse. Isolations from symptomatic petioles, stem bases, and main roots were performed on potato dextrose agar (PDA) and corn meal agar (CMA). When incubated at 24 to 25°C, white, round, arachnoid colonies with fluffy aerial mycelium developed on the PDA isolation plates, whereas the mycelium was less dense on CMA. Sporangia were formed sporadically when cultures were maintained on V8 medium and formed abundantly in nonsterile soil extract after 1 to 2 days of incubation at 20°C. Sporangia were noncaducous, ovoid to spherical, semipapillate (sometimes with two papilla), measured 47.5 to 65 μm (average 53.6 μm) × 35 to 53.5 μm (average 42.9 μm) with an average length/width ratio of 1.25:1. Terminal and intercalary chlamydospores (25 to 48 μm in diameter; average 37 μm) and hyphal swellings were also present. Maximum temperature for growth was 36°C. Pathogenicity of the presumable Phytophthora nicotianae (1) isolate was proved by placing 5-mm-diameter mycelial plugs of 7-day-old cultures grown on V8 medium onto the petiole bases of three 3-month-old G. tataricum plantlets. Each inoculation site was first wiped with 70% ethanol and then scalpel wounded. Sterile V8 plugs were used as controls and all inoculated sites were wrapped with Parafilm. The plantlets were incubated at room temperature (22 to 26°C) and the first necrotic lesions around the mycelial plugs appeared 5 to 7 days after inoculation. Plantlets collapsed approximately 2 weeks later. Additionally, three plantlets were inoculated under the same conditions by watering their stem bases with a 15-ml suspension of mycelium and spores obtained by washing 2-week-old V8 cultures with sterile distilled water. Within a 4-week period, the plantlets died due to a stem base and petiole necrosis. Simultaneously, the pathogen was reisolated from all inoculated samples but not from any control plants that were symptomless. The internal transcribed spacer (ITS) region of mycelial DNA was amplified (ITS6 and ITS4 primers) and the PCR product was sequenced (GenBank Accession No. FJ410333). BLAST analysis showed 100% homology with P. nicotianae. To our knowledge, this is the first report of P. nicotianae on G. tataricum in Bulgaria and one of the few reports from Europe of Phytophthora invasion of related Limonium species (2,3).
References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) E. Ilieva et al. Plant Dis. 85:445, 2001. (3) A. Pane et al. J. Plant Pathol. 87:301, 2005.