‘Candidatus Phytoplasma asteris’ identified in blackberry (Rubus fruticosus agg.) in the United Kingdom

Abstract

Blackberries (Rubus fruticosus agg.) also known as brambles are a widespread and well-known aggregate species of several hundred micro-species native throughout the temperate Northern hemisphere. Tolerating poor soils, they are early colonizers of wasteland and building sites and grow vigorously in woods, scrubland, hedgerows and roadside verges. Plants produce many soft fruits notable for their high nutritional content, making them a popular ingredient in desserts, jams and wines. Numerous cultivars have been selected for commercial cultivation. In July 2008, a small patch of R. fruticosus growing by the roadside in Egham, UK, was observed showing unusual witches’ broom symptoms. Proliferations of shoots were seen at the branch nodes, midway along the stem. Symptoms on new growth presented as shortened, narrowed almost leafless branches with reduced, flower production or none at all. No other plants in the near vicinity appeared affected. Total DNA was extracted from plants with symptoms and from healthy looking blackberry plants and used as a template in a nested PCR assay with universal primers P1m (Hren et al., 2007) /P7 (Gundersen & Lee, 1996) and fU5/rU3 (Lorenz et al., 1995). Amplicons of expected size (∼880 bp) were obtained from plants with symptoms. Nested amplicons of a representative plant were purified, cloned (pGEM-T Easy Vector, Promega) and sequenced in both directions using M13 sequencing primers (http://www.dnaseq.co.uk). The phytoplasma 16Sr rDNA sequence (GenBank Accession No. FJ008925) was compared with those held in GenBank using blast. The greatest similarity (99%) was with phytoplasmas of group 16SrI, ‘Candidatus Phytoplasma asteris’, including those associated with gaillardia yellows (EF583066), poa stunt (DQ640502), and festuca yellows (DQ640504). The occurrence of two phytoplasmas belonging to groups 16SrV (‘Ca. P. ulmi’) and 16SrIII (X-disease) have previously been reported in Rubus species in the UK (Davies, 2000). This is the first record of a phytoplasma from 16SrI group recorded from Rubus in the UK. It is not known which insect vectors are associated with transmission.