First Report of Phytophthora cryptogea on Potato Tubers in Turkey
Authors: Çakır E. , Demirci F. 
Published: April 2012

Potato (Solanum tuberosum L.) is an important agricultural crop in Turkey, with 150,000 ha and a production of about 4 million tons per year. There are numerous pathogens that limit potato production. In 2011, a new disease was observed on the potato cultivar Ramos in Erzincan Province in Turkey. Disease symptoms were similar to pink rot. Infected tubers had a rubbery texture and when cut, infected areas were cream colored. When the infected area was exposed to air for 10 min, the color turned to salmon pink and after 15 to 20 min it turned black. A funguslike organism was isolated from diseased tubers on carrot agar. The colonies were uniform and there were no petaloid patterns. Soil extract solution was prepared using 1,000 ml of distilled water and 15 g of field soil according to Jeffers and Aldwinckle (2) and used for sporangia production. Agar discs from 5-day-old colonies were placed in soil extract solution and incubated under continuous fluorescent light at room temperature. Sporangia began forming after 24 h and were abundant after 48 h. Oogonia were not observed on corn meal agar plates supplemented by beta-cytosterol. Sporangia were nonpapillate and noncaducous, mostly ovoid, but some were obpyriform. The mean size of the sporangia was 43 ± 4 × 30 ± 2 μm. The Oomycete was identified as Phytophthora cryptogea Pethybr. & Laff., according to its morphological characters (1). Isolate identity was confirmed by sequence analysis of the ribosomal DNA internal transcribed spacer using primers ITS1 and ITS4. The ITS sequence was a 99% match to P. cryptogea strains (GenBank Accession Nos. AF087475.1, AF228101.1, GU111626.1, AY995400.1, GU111624.1, AY995400.1, and GU111624.1). The isolate from Turkey was deposited in GenBank as Accession No. JQ071495. Pathogenicity tests were conducted on potato tubers (cv. Ramos). Tubers were surface disinfected with 0.5% NaOCl for 5 min., then washed twice with sterile water. When dried, 20 tubers were wounded with a shallow cut made parallel to the surface by a sterile knife. An agar disc from a 1-week-old colony was placed on the artificial wound on each of 10 potatoes. For controls, agar discs without fungal mycelia were placed on the wounds of the other 10 potatoes. Each inoculated and uninoculated potato was incubated for 5 days at 24°C in the dark and in separate plastic cups containing moistened filter paper at the bottom. Tubers were then cut open and examined for disease. Cream colored lesions were first observed; after 10 min lesions turned salmon pink and after 20 min they turned black. Cream colored lesions were not observed inside uninoculated potatoes. To the best of our knowledge, this is the first report of P. cryptogea causing pink rot of potato in Turkey. Pink rot disease of potato is commonly caused by P. erytroseptica, but P. cryptogea can cause similar symptoms (3) and severe tuber rot. This pathogen could cause important losses of potato in Turkey, especially during storage of tubers.

References: (1) M. E. Gallegly and C. Hong, Phytophthora: Identifying Species by Morphology and DNA Fingerprints. APS Press, St. Paul, MN, 2008. (2) S. N. Jeffers and H. S. Aldwinckle, Phytopathology 77:1475, 1987. (3) E. C. Rowe and A. F. Schimitthenner, Plant Dis. Rep. 61:807, 1977.