German statice (Goniolimon tataricum) is a protected, herbaceous, perennial plant species that occurs sporadically throughout Bulgaria. Some varieties, however, are cultivated outdoors because of their dry flowers, which are widely utilized by florists. For the past 3 years, a severe leaf disease has been observed on the lower and middle leaves of German statice plants growing in fields in the region of Plovdiv, Bulgaria. Symptoms consisted of brown, round to elliptical leaf spots (as much as 15 mm in diameter) that led to leaf yellowing and death. Similar sunken lesions were also observed on leaf petioles and flower bases. A cercosporoid fungus was consistently associated with disease symptoms. Conidiophores were fasciculate, unbranched, brown, and smooth. Conidiogenous cells were predominantly terminal, but also lateral, and had darkened, thickened, refractive scars. Conidia were solitary, hyaline, smooth, acicular, slightly curved, multiseptate, with subtruncate bases and acutely rounded apices, 30 to 105 × 2.5 to 4 (average 64.5 × 3.5) μm, in vivo (n = 30), with thickened, darkened, refractive hila. Colonies derived from single conidial isolates were established on potato dextrose agar (PDA). To confirm Koch's postulates, colonized mycelial plugs (5 mm in diameter) from 10-day-old PDA cultures were used to inoculate 3-month-old German statice pot plants (three replicates per treatment, three leaves per plant). Control plants were inoculated with uncolonized agar plugs. Healthy leaves were surface disinfested with 70% ethanol, wounded with a sterile needle, and covered with an agar plug. Inoculated plants were incubated at 20°C in a humidified chamber with a 12-h day/night light cycle. Eight to ten days after inoculation, small necrotic lesions developed around the points of inoculation, leading to necrosis and lesions (8 to 10 mm in diameter). The pathogen was successfully reisolated from all inoculated leaves, while control plants remained healthy. Five isolates (CPC 14616--14620) were subjected to multilocus sequence typing as described by Groenewald et al. (1) and the ITS, translation elongation factor 1-alpha, actin, calmodulin, and histone H3 gene sequences (GenBank Accession Nos. FJ473422--FJ473446) were found to be identical to that of the ex-type strain of Cercospora beticola Sacc. (GenBank Accession Nos. AY840527, AY840494, AY840458, AY840425 and AY840392, respectively). Two strains from Goniolimon were deposited in the CBS Fungal Biodiversity Centre in the Netherlands (CBS 123907 and 123908). To our knowledge, this is the first report of C. beticola occurring on and being destructive to Goniolimon tataricum under field conditions.
Reference: (1) M. Groenewald et al. Phytopathology 95:951, 2005.
