First Report of 16SrIII-B Phytoplasma Subgroup Associated with Virescence of Arnica montana in Serbia.

Arnica montana L. is a high altitude perennial plant, indigenous to Europe, but it is not native in the flora of Serbia. Plantain introduction of A. montana began a few years ago in the Tara mountain region, Western Serbia (43°53'44.17″N 19°33'11.62″E, 1,008 m ASL). The mountainous climate in this region is characterized by 850 mm of precipitation per year and an average decade temperature range from 11 to 25°C in the vegetation period of May through September. The main soil type is dystric cambisol, exhibiting a slightly acidic reaction (pH 6.4). Seeds of A. montana cv. ARBO were obtained from the Agricultural Research Centre of Finland. Seedlings were produced in a greenhouse during the period March through April and planted in May 2008. Virescence symptoms were observed starting from May 2010. A. montana exhibited symptoms mainly on flowers, like green leaflike structures instead of flowers and proliferation of acillary buds. Later in the season, flowers were malformed and consequently failed to produce seeds. Plant material for analyses was collected during 2010 and 2011 from an experimental field located at Tara mountain. Total DNA was extracted from the leaf midveins of 14 symptomatic and six symptomless plants (3). Nested PCR was carried out with primers P1/P7 followed by P1/16S-Sr and R16F2n/R16R2 primers, resulting with the DNA fragments amplification of expected size: 1.8, 1.5, and 1.2 kb, respectively, in all symptomatic samples tested. No phytoplasmas were detected in symptomless samples. PCR products of 1.2 kb, obtained by R16F2n/R16R2 primers from symptomatic samples, were digested independently with four restriction enzymes (Alu I, Tru I, Hpa II and Hha I) and the RFLP patterns were compared with those of Stolbur (Stol), Aster Yellows (AY), Flavescence Doree-C (FD-C), Poinsettia Branch-Inducing (PoiBI) and Clover Yellow Edge (CYE) phytoplasmas (2). RFLP patterns from all symptomatic A. montana samples were identical to CYE pattern. Comparison of the 16S rDNA sequence of representative symptomatic sample Am4, deposited under accession number JX297491 in NCBI GenBank, with other phytoplasmas from the database revealed 99% identity with members of 16SrIII-B phytoplasma group: Clover yellow edge phytoplasma strain CYE (JQ944798.1), 'Euscelidius variegatus' phytoplasma strain AP-I (HQ589197.1), Clover phyllody phytoplasma strain CP (HQ589196.1), etc. In Serbia, phytoplasma belonging 16SrIII-B subgroup has been identified in Cirsium arvense (4) and pear plants (1). To our knowledge, this is the first report of a natural infection of A. montana by phytoplasma. Cultivation of A. montana provides the necessary raw material for medicament production. The flower heads are widely used for the topical treatment of bruises and sprains in phytopharmaceutical preparations.Taking into consideration that monoculture plantation growing of perennials favorites rapid spreading of infections, the present study tended to examine the potential threat of virescence, which could be the limiting factor of ex-situ conservation of this endangered plant by its cultivation. References: (1) B. Duduk et al. Acta Hortic. 781:351, 2008. (2) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (3) J. P. Prince. Phytopathology 83:1130, 1993. (4) D. Rancic et al. Plant Pathology 54:561, 2005.