First Report of Fusarium dimerum on Solanum tuberosum in Turkey

Potato (Solanum tuberosum) is the most important crop in Eastern Anatolia region of Turkey. In 2005, a routine disease survey was conducted in potato fields in seven districts in Kars, Turkey. Leaf lesions were frequently observed in different fields in the Akyaka district at one location (Demirkent village). The observed symptoms consisted of irregularly-shaped, small dark brown-to-black leaf spots that expanded and coalesced (Fig.1).

Leaves displaying symptoms were surface disinfected for 2 min in 2% NaOCl, plated on potato dextrose agar (PDA) and incubated at 25°C. A Fusarium species was consistently isolated from the leaves (66.7% of the samples) and transferred into pure culture. Single spore cultures from these colonies were grown on PDA and water agar (WA) to assist species identification. The fungus was identified as F. dimerum Penzig based on its micro-morphology and cultural features (Nelson et al., 1983) (Fig.2, 3).

To satisfy Koch’s postulates, conidia were harvested from 15-day-old cultures grown on PDA. A conidial suspension (5 x 10⁶ conidia per ml) was sprayed onto leaves of S. tuberosum ‘Agria’ plants (4-weeks-old). 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. Symptoms, similar to those originally observed in the field, began to appear on the leaves 9 days after inoculation. No symptoms developed on control plants. The fungus was successfully reisolated from artificially developed symptoms. F. dimerum has been recorded previously on S. tuberosum in Australia and USA (Farr et al., 2007). This is the first report of F. dimerum on S. tuberosum in Turkey.