First identification of ‘Candidatus Phytoplasma aurantifolia’ infecting Fallopia japonica in the United Kingdom

Abstract

In July 2008, plants of Japanese knotweed (F. japonica) growing along a boundary fence in Egham, England, exhibited symptoms of severe stunting and witches' brooms. Symptoms were most pronounced in the emerging shoots, which displayed proliferation, shortened internodes and small leaves. Infected plants also exhibited a pronounced silver flecking on the leaves, which superficially resembled thrip-damage. The knotweed stand occupied an area of approximately 50 of the 88 plants (56.8%) showed obvious symptoms. Leaves from 4 plants with symptoms and one healthy-looking plant were collected, and DNA was extracted and indexed in a nested PCR assay with universal primers. The 16S rDNA sequence was compared with those held in the GenBank using BLAST. The closest matches (99%) were to phytoplasma members of group 16SrII, 'Candidatus Phytoplasma aurantifolia' (Phytoplasma aurantifolia), including those associated with crotalaria witches' broom (EU650181 and EF656454) and sweet potato little leaf (EU170353). The new phytoplasma sequence was deposited in GenBank (FJ008924). This is thought to be the first record of a phytoplasma infecting F. japonica, and the first identification of a phytoplasma from group 16SrII in the UK