New Disease Reports (2007) 15, 16.

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

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

*wzh-36@163.com

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Accepted: 28 Feb 2007

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).

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 Parmessuret al.(2002) and used as a template in nested PCR with primers R16mF2/R16mR1 and R16F2/R2 (Leeet 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 (Leeet 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.

Figure1a+Figure1b+Figure1c+
Figure 1: Small pink-coloured leaves and proliferated flower heads (left) and shoots (centre) with shortened internodescompared to healthy Praxelis plants (right)
Figure 1: Small pink-coloured leaves and proliferated flower heads (left) and shoots (centre) with shortened internodescompared to healthy Praxelis plants (right)
Figure2+
Figure 2: Phylogenetic tree comparing the partial 16SrDNA sequences of the PrWB with those of other phytoplasmas from GenBank.Acholeplasma palmaewas used as the outgroup. GenBank accession numbers for sequences are given in parenthesis.
Figure 2: Phylogenetic tree comparing the partial 16SrDNA sequences of the PrWB with those of other phytoplasmas from GenBank.Acholeplasma palmaewas 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

  1. King RM and Robinson H, 1970. Studies in theEupatorieae(Compositae) XXVIII. The genusPraxelis.Phytologia20,193-195.
  2. 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 Bacteriology48, 1153-1169.
  3. Parmessur Y, Aljanabi S, Saumtally S, Dookun-Saumtally A, 2002. Sugarcane yellow leaf virus and sugarcane yellows phytoplasma: elimination by tissue culture.Plant Pathology51,561-566.
  4. Waterhouse BM, 2003. Know your enemy: recent records of potentially serious weeds in northern Australia, Papua New Guinea and Papua (Indonesia).Telopea10,477-485.

This report was formally published in Plant Pathology

©2007 The Authors