First report of leaf blight caused by phytophthora colocasiae infecting taro in Turkey

Taro or golevez (Colocasia esculenta (L.) Schott.) is a very important root vegetable in Anamur and Bozyazi Districts of Mersin Province on the Mediterranean coast of Turkey. It is grown commercially or by home gardeners in both districts. Taro plants (unknown cultivar) with leaf blight were observed in a home garden in Anamur (36°4'39¨ N, 32°49'58¨ E) in October 2004. The disease severity (percentage leaf area diseased) was nearly 30% and the disease incidence was 50%. The leaves were exhibiting white sporulation on the brown, water-soaked lesions. Sporangia with apical papilla were produced on unbranched or sparingly branched sporangiophores (Brooks 2005). Three diseased leaves, cut into 3-cm2 pieces from margins of lesions were surface sterilized with 1% NaClO for 1 min and cultured on modified PARPH Phytophthora selective medium (Jeffers and Martin 1986) in the dark at room temperature for 5 days. Three isolates transferred to carrot agar at 24°C in the dark for 2 to 3 days. Five plugs from each of the three isolates from actively growing mycelium were placed in petri plates and flooded with sterilized water. The plates were placed under continuous fluorescent lights at room temperature for 24 h and examined for sporangia formation. Sporangia were ovoid or elipsoid, caducous, hyaline, semipapillate, and measured 25 to 50 × 15 to 30 µm (Bandyopadhyay et al. 2011) with a length-to-width ratio of 1.7 and pedicels 3.0 to 10 µm long (Brooks 2005). To confirm pathogen identity, total DNA was extracted using the PowerSoil DNA Isolation Kit (MO BIO Laboratories, Inc., Carlsbad, CA) directly from 3-day-old cultures grown in carrot agar. The ribosomal DNA internal transcribed spacer (ITS) region was amplified by PCR using the primer pair ITS1 and ITS4 (White 1990) and sequenced. The sequences were 99% identical to that ofPhytophthora colocasiae isolates from Taiwan (GU111605) and Hawaii (JN661139). This confirmed the identity as Phytophthora colocasiae Raciborski. Five detached leaves of taro were inoculated with 105/ml zoospore suspension of three individual isolates and incubated on a wet paper towel in a sealed, clear plastic bag in 12-h dark/light conditions at room temperature. Sterilized water was applied on five detached leaves as controls and noninoculated leaves were maintained in the same environment. One to two days after inoculation, water-soaked lesions developed on all inoculated detached leaves and P. colocasiae was reisolated from detached leaves. All control leaves remained disease-free and no pathogen was reisolated. Pathogenicity test was done once. P. colocasiae has been reported to infect taro in the Pacific, Asia, and West Africa (Singh et al. 2012). To our knowledge, this is the first report of leaf blight caused by P. colocasiae infecting taro in Turkey. This indicates that taro plants could be at risk for infection. Vegetatively propagated material and soil movement can play a role for disease distribution (Singh et al. 2012). Therefore, cultural practices such as using disease-free propagating materials and good sanitation practices in plantations and chemical control are very important. © 2015 The American Phytopathological Society