First report of Ascochyta sonchi in Turkey

Perennial sowthistle (Sonchus arvensis) is a native of Eurasia, including Turkey. The plant is found in wide range of habitats. In July 2004, a leaf spot disease of S. arvensis was observed on pastures in the province of Erzurum, Turkey. The symptoms began as small, circular, brown spots on leaves. The circular spots increased in size, developing into irregular lesions, in which pycnidia developed (Fig. 1).

Leaves showing symptoms were surface disinfected and plated onto potato dextrose agar (PDA) and incubated at room temperature. Pycnidia producing hyaline, ellipsoidal conidia (6-10 x 2-3.5 µm) were observed after 4 to 5 days. The fungus was consistently isolated on PDA from diseased leaves and identified as Ascochyta sonchi (Sacc.) Grove based on morphological characteristics (Mel’nik, 2000).

To satisfy Koch’s postulates, a conidial suspension (1 x 10⁶ conidia per ml) of the fungus was sprayed onto leaves of S. arvensis plants (45 days old). Conidia were harvested from 10-day-old cultures grown on PDA. Both inoculated plants and control plants (inoculated with sterile water) were covered with plastic bags for 72 h in a glasshouse at 23 ± 2°C. After 8-10 days, the symptoms were similar to those previously observed. No symptoms developed on control plants. The pathogen was consistently reisolated from inoculated plants. A. sonchi has been recorded previously on S. arvensis in Russia (Evidente et al., 2006) and USA (Farr et al., No Date). To our knowledge, this is the first report of A. sonchi from Turkey on any host.