'Candidatus Phytoplasma asteris' identified in Senecio jacobaea in the United Kingdom

R. Reeder^1*and Y. Arocha²

¹ Global Plant Clinic, CABI-Biosciences, Bakeham Lane, Egham, TW20 9TY, UK
² National Centre for Animal and Plant Health, CENSA. Apdo 10, San José de Las Lajas, Havana, Cuba

*r.reeder@cabi.org

Accepted for publication 09/10/07

Common ragwort (Senecio jacobaea) is a widespread biennial species native to the British Isles. It contains toxins which are potentially lethal if ingested by grazing animals, and is a specified weed under the Weeds Act 1959.  Where no threat is posed to livestock, ragwort forms part of the natural British flora and is a beneficial plant that supports a wide range of insects.

During June 2007, plants of S. jacobaea growing in a field behind the CABI-Bioscience site, in Egham, showed symptoms of little leaf (Fig. 1.), chlorosis, and proliferation of axillary shoots (Fig. 2). Infected plants frequently had fewer stems and reduced numbers of flower heads. The distribution of disease was patchy, with approximately 60% of plants displaying obvious symptoms. 

Figure 1: Bunching of axillary shoots, due to shortening of the internodes and little leaf symptoms.	Figure 2: Comparison of leaf symptoms.  The pinnae of a diseased leaf (right) are smaller and much more dissected than those of healthy leaf (left).

Symptomatic and apparently healthy plants were collected, and the DNA extracted and assayed in a nested PCR with phytoplasma universal 16S rDNA primers R16F2m/R1 and R16F2n/R16R2 (Gundersen & Lee, 1996). All symptomatic samples yielded PCR products of expected size (1250 bp), and identical HaeIII, RsaI and AluI RFLP profiles. No PCR products were produced with DNA from asymptomatic plants. Nested PCR products were purified and direct sequenced (www.dnaseq.co.uk). The sequence was compared with those of other phytoplasmas in GenBank using BLAST, and deposited in GenBank (Accession No. EU096553). It had the highest similarity (96%) with the phytoplasma associated with yellows of Festuca arundinacea from Lithuania (GenBank Accession No. DQ640504) of the 16SrI group, ‘Candidatus Phytoplasma asteris’.

A phytoplasma belonging to 16SrI group was previously identified in common groundsel (Senecio vulgaris) in Canada (Chang et al., 2000), and first reported in the UK affecting Hebe (Veronica scutellata) (Jones et al., 2006). As far as we know, this is the first record of a phytoplasma infecting S. jacobaea in the UK.   

References

Chang KF, Hwang SF, Kawchuk LM, Howard RJ, 2000. Detection and molecular characterization of an aster yellows phytoplasma in common groundsel (Senecio vulgaris L.). Journal of Plant Disease and Protection 107, 295-303.

Gundersen DE, Lee IM, 1996. Ultrasensitive detection of phytoplasmas by nested-PCR assays using two universal primer pairs. Phytopathologica Mediterranea 35, 144-51.

Jones P, Arocha Y, 2006. A natural infection of Hebe is associated with an isolate of ‘Candidatus Phytoplasma asteris’ causing a yellowing and little-leaf disease in the UK. Plant Pathology 55, 821.