New Disease Reports (2009) 19, 49.

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

R. Reeder 1*, P. Kelly 1 and Y. Arocha 2

*r.reeder@cabi.org

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Accepted: 22 Jun 2009

Japanese knotweed (Fallopia japonica), family Polygonaceae, is a tall, invasive, perennial weed, first introduced into the UK in the 1850’s. It has since spread to occupy more than half of the 10 km squares used to map plant distribution in the British Isles. The plant causes problems in both rural and urban habitats due to its vigorous growth and ability to form dense thickets. In urban environments its growth can damage buildings and push up tarmac.

In July 2008, plants of F. japonica growing along a boundary fence in Egham were seen with severe stunting and witches’ brooms. Symptoms were most pronounced in the emerging shoots, which displayed proliferation, shortened internodes and small leaves (Figs 1 & 2). Infected plants also exhibited a pronounced silver flecking on the leaves, which superficially resembled thrip-damage (Fig 3). The knotweed stand occupied an area of approximately 35 m2 and 50 of the 88 plants (56.8%) displayed obvious symptoms.

Leaves from four plants with symptoms and one healthy-looking plant were collected and the DNA extracted and indexed in a nested PCR assay with universal primers P1m (Hren et al., 2007) /P7 (Gundersen & Lee, 1996) and fU5/rU3 (Lorenz et al., 1995). PCR products of expected size (~880 bp) were obtained from all plants displaying symptoms, but not from the healthy-looking plant. Nested PCR products of a representative plant were purified, cloned (pGEM-T Easy Vector, Promega), and sequenced in both directions using M13 sequencing primers (www.dnaseq.co.uk). The 16S rDNA sequence was compared with those held in GenBank using BLAST. The closest matches (99%) were to phytoplasma members of group 16SrII, ‘Candidatus Phytoplasma aurantifolia’, including those associated with crotalaria witches’ broom (EU650181, EF656454) and sweet potato little leaf (EU170353). The new phytoplasma sequence was deposited in GenBank (FJ008924).

The severe stunting of Japanese knotweed (Fig. 4) has important implications for its competitive ability and it was noted that stinging nettles (Urtica dioica) were overgrowing many of the stunted plants. We believe this is the first record of a phytoplasma infecting F. japonica,and the first identification of a phytoplasma from group 16SrII in the UK.

Figure1+
Figure 1: Symptoms of witches’ broom in young shoots of Fallopia japonica.
Figure 1: Symptoms of witches’ broom in young shoots of Fallopia japonica.
Figure2+
Figure 2: Range of symptoms observed in infected Fallopia japonica plants. Plant on far left is healthy.
Figure 2: Range of symptoms observed in infected Fallopia japonica plants. Plant on far left is healthy.
Figure3+
Figure 3: Symptoms of leaf ‘silvering’, superficially resembling damage caused by thrips
Figure 3: Symptoms of leaf ‘silvering’, superficially resembling damage caused by thrips
Figure4+
Figure 4: Stunted and healthy plant of Fallopia japonica
Figure 4: Stunted and healthy plant of Fallopia japonica

References

  1. GundersenDE, Lee IM, 1996. Ultrasensitive detection of phytoplasmas by nested-PCR assays using two universal primer pairs. Phytopathologia Mediterranea 35, 144-151.
  2. Hren M, Boben J, Rotter A, Kralj P, Gruden K, Ravnikar M, 2007. Real time PCR detection system for flavescence dorée and bois noir phytoplasma in grapevine: comparison with conventional PCR detection and amplification in diagnostics. Plant Pathology 56, 785-796
  3. Lorenz K-H, Schneider B, Ahrens U, Seemüller E, 1995. Detection of the apple proliferation and pear decline phytoplasmaby PCR amplification of ribosomal and non-ribosomal DNA. Phytopathology 85, 771-776.

This report was formally published in Plant Pathology

©2009 The Authors