First report of a phytoplasma associated with Praxelis witches’ broom in China

Z. H. Wang^*, Q. B. Chen, A. Q. Ye and H. Zhang

Rubber Research Institute, Key Lab for Tropical Crop Physiology, CATAS, Danzhou 571737, Hainan, China;

^*wzh-36@163.com

Accepted for publication 28/02/07

Praxelis (Praxelis clematidea) is native to South America (King & Robinson, 1970), but in the last 20 years has become highly invasive in Australia, Southeast Asia and more recently in south China (Waterhouse, 2003). As one of the most highly invasive plants in these regions, it poses a serious threat to their ecosystems. Biological control may offer the most promising sustainable control strategies for exotic weeds and since 2005, disease surveys have been conducted in the hope of identifying potential biocontrol pathogens for Praxelis. Witches’ broom symptoms, suggestive of phytoplasma infection, were observed in Hainan, China. Plants showed small pink-coloured leaves and much proliferation of shoots with shortened internodes. These plants failed to produce seed (Fig. 1).

Figure 1: Small pink-coloured leaves and proliferated flower heads (left) and shoots (centre) with shortened internodescompared to healthy Praxelis plants (right)

Healthy and infected Praxelis were collected from Danzhou, Hainan and tested by PCR for phytoplasmas. Nucleic acids were extracted from fresh leaves as described by Parmessur et al. (2002) and used as a template in nested PCR with primers R16mF2/R16mR1 and R16F2/R2 (Lee et al., 1998). DNA from phytoplasma infected periwinkle was used as a positive control. A DNA fragment (1189bp) was amplified from diseased plants but not from known healthy or symptomless plants. PCR products were purified and sequenced, and the sequence deposited in GenBank (accession no. EF061924). Using a multiple alignment program (DNASTAR Version 6.13) the sequence showed a high similarity with members of the 16SrII group of phytoplasmas, and had the highest similarity (98.5%) with phytoplasmas from the 16SrII (Peanut witches'-broom) group (L33765), sub group-A (Lee et al., 1998), including sweet potato witches’ broom (DQ452417) and Chinese pigeon pea witches’ broom (AF028813) (Fig. 2). To our knowledge, this is the first report of a phytoplasma from the peanut witches’ broom group infecting Praxelis.

Figure 2: Phylogenetic tree comparing the partial 16SrDNA sequences of the PrWB with those of other phytoplasmas from GenBank. Acholeplasma palmae was used as the outgroup. GenBank accession numbers for sequences are given in parenthesis.

Acknowledgements

The authors would like to thank Mr Yang Jianghua, Dr. Yang Lifu and Ms Li Yu for their technical assistance and helpful suggestions.

References

King RM and Robinson H, 1970. Studies in the Eupatorieae (Compositae) XXVIII. The genus Praxelis. Phytologia 20, 193-195.

Lee I-M, Gundersen-Rindal DE, Davis RE, Bartoszyk IM, 1998. Revised classification scheme of phytoplasma based on RFLP analyses of 16S rRNA and ribosomal protein gene sequences. International Journal of Systematic Bacteriology 48, 1153-1169.

Parmessur Y, Aljanabi S, Saumtally S, Dookun-Saumtally A, 2002. Sugarcane yellow leaf virus and sugarcane yellows phytoplasma: elimination by tissue culture. Plant Pathology 51, 561-566.

Waterhouse BM, 2003. Know your enemy: recent records of potentially serious weeds in northern Australia, Papua New Guinea and Papua (Indonesia). Telopea 10, 477-485.

The British Society for Plant Pathology