255 Host Range and Genetic Characterization of a Phytoplasma Causing Tomato Stolbur Disease in Turkey N. Özdemir 1 , H. Saygili 2 , F. Sahin 3 , Y. Karsavuran 2 , O.F. Bayrak 4 and B. Oral 4 1 Ege University, Odemis Training School 2 Ege University, Faculty of Agriculture, Department of Plant Pathology, Bornova, Izmir, Turkey 3 Yeditepe University, Faculty of Engineering and Architecture, Department of Genetic and Bioengineering, Kayisdagi, Istanbul, Turkey 4 Ataturk University, Biotechnology Research and Application Centre, Erzurum, Turkey Keywords: stolbur, tomato, phytoplasma, Polymerase Chain Reaction (PCR), vector and alternative host Abstract An outbreak of new stolbur like tomato disease occurred in Marmara region of Turkey causing a serious defect on yield and quality of tomato production during last 10 years. Therefore, the aim of this present study was to identify and characterize the causal agent of stolbur like disease on tomato in Turkey. Between 2004 and 2007, plant and pest samples collected from diseased tomato fields or neighboring areas were examined by nested polymerase chain reaction (PCR) assay using phytoplasma- universal 16S rDNA based primer sets (P1/P7 and P1/P6) to detect the presence of phytoplasmas. The data showed that tomato stolbur disease was distributed in tomato produc- tion areas in the provinces of Western Anatolia, Turkey. Dodder (Cuscuta campestris), broomrape (Orobanche ramosa), jimsonweed (Datura stramonium), ladysthumb (Polygonum persicaria), foxtails (Setaria spp.), lambsquarters (Chenopodium album), pigweed (Amaranthus albus) were determined as alternative host of tomato phyto- plasmas among the plant species tested. Only one, Tyhlocyba quercus among 22 insect species collected from tomato fields were found to be potential vector of tomato stolbur disease. The results showed that all aboveground part of diseased tomato plants, weeds and vector pests give a unique PCR amplicon (1500 and 1800 bp) with P1/P6 and P1/P7 primer sets, respectively. INTRODUCTION Phytoplasmas, also known as mycoplasma-like organisms, are wall-less prokaryotes that are pathogens of many plant species throughout the world. In European and Mediterranean countries, stolbur phytoplasma causes dangerous diseases of economically important crops, especially solanaceous plants such as tomato, potato and pepper (McCoy et al., 1989; Berizikova and Linhartova, 2007). In the host plant, phytoplasmas are restricted to the phloem sieve tubes, in which they move down to the roots and up to the top of plants but never settle in the meristems (Pracros et al., 2006). Phytoplasmas occur in the phloem of host plants and are transferred in persistent by insects. Another possible transfer is via parasitic dodder (Cuscuta spp.) (Afat, 2004; Berizikova and Linhartova, 2007). Phytoplasmas can cause variety of symptoms, including yellowing, stunting, proliferations, malformations, some of which are specific to certain phytoplasma isolates (Pracros et al., 2006). The aims of this study were to identify and classify the phytoplasma associated with infected tomatoes in Western Anatolia region of Turkey. We observed stunting, proliferation of lateral shoots, hypertrophic calyxes and greening of flower petals on affected tomato plants. In the field studies in Western Anatolia, Turkey in 2004-2007, it was shown that a number of crops and weeds could act as source as of phytoplasma infecting tomato (Özdemir, 2008). Proc. II nd Intl. Symposium on Tomato Diseases Eds.: H. Saygili et al. Acta Hort. 808, ISHS 2009