First Report of Spiroplasma citri in Carrot in Europe

Abstract

In 2008 and 2009, symptoms of curling, yellow and purple discoloration of leaves, stunting of shoots and tap roots, and formation of bunchy, fibrous secondary roots were observed in commercial carrot (Daucus carota L.) fields located in several production areas of Spain (Alicante, Albacete, Segovia, and Valladolid). Incidence of this disease was almost 100% in individual affected fields. Similar symptoms were reported from 1997 to 1998 in various carrot production areas of Spain (the Canary Islands, Segovia, and Madrid) and were associated with infection of stolbur and aster yellows phytoplasmas (2). Moreover, the observed symptoms resembled those caused by Spiroplasma citri in carrots affected by the carrot purple leaf disease recently reported in the United States (4). Studies were conducted to investigate whether S. citri and phytoplasmas were associated with the observed carrot symptoms. Total DNA was extracted from 0.5 g of phloem tissue of 13 symptomatic and 3 asymptomatic plants with DNeasy Plant Mini Kit (Qiagen, Valencia, CA). DNA samples were analyzed by nested-PCR assays using primers pair P1/P7 (1) and R16F2n/R16R2n (3) for phytoplasmas and ScR16F1/ScR16R1 followed by ScR16F1A/ScR16R2 (4) for S. citri detection. DNA of a known strain of S. citri (Sediag, Longvic, France) was used as a positive control of the assay. Analyses revealed that 8 of the 13 symptomatic plants tested positive for S. citri; the plants were collected from three different provinces of Spain, namely, Alicante, Valladolid, and Segovia. Two symptomatic plants were double infected by S. citri and a phytoplasma strain belonging to the Aster yellows group (16SrI), subgroup 16SrI-A. However, none of the symptomatic plants presented single infection with phytoplasmas. S. citri identity was determined by sequencing two nested PCR products (1.1 kb) that yielded identical sequences deposited in the GenBank database (Accession Nos. HM124555 and HM124556). BLAST analysis showed 100% nt identity with a sequence of S. citri from carrot (Accession No. DQ112019) associated with the new carrot disease referred to as ‘carrot purple leaf reported in Washington State (4). To our knowledge, this is the first report of S. citri associated with carrot in Europe. References: (1) S. Deng and C. Hiruki. J. Microbiol. Methods 14:53, 1991. (2) M. I. Font et al. Bol. San. Veg. Plagas 25:415, 1999. (3) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (4) I. M. Lee et al. Plant Dis. 90:989, 2006.