New Disease Reports
New Disease Reports (2018) 37, 6. [http://dx.doi.org/10.5197/j.2044-0588.2018.037.006]
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First report of a 'Candidatus Phytoplasma asteris'-related strain (16SrI-B) associated with Sonchus oleraceus (common sowthistle) phyllody disease in Iran

M. Salehi 1*, S.A. Esmailzadeh Hosseini 2 and E. Salehi 1

*salehi_abarkoohi@yahoo.com

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Received: 05 Jan 2018; Published: 02 Feb 2018

Keywords: aster yellows 

Common sowthistle (Sonchus oleraceus) is a major weed problem in Iran and is also used for medicinal purposes. During 2012-2015 surveys of Fars and Yazd provinces (Iran) for phytoplasma diseases, a phyllody disease was observed in S. oleraceus plants growing as weeds within and/or in the surroundings of fields and orchards. The main symptoms of the disease were yellowing and reddening of leaves, shortened internodes, flower virescence, phyllody, proliferation and witches' broom (Fig. 1).

Total DNA was extracted from 0.2 g of leaf midribs of eight symptomatic (four plants per province) and four symptomless (collected in Fars province) S. oleraceus plants using the CTAB method of Zhang et al. (1998). DNA samples were tested for phytoplasma presence by a nested PCR assay primed by primer pairs P1/P7 followed by R16F2n/R16R2 (Lee et al., 1998). Amplicons of ~1.25 kb were obtained in the nested round from all eight diseased plants but not from the four symptomless plants. Eight nested amplicons were separately cloned and sequenced. The obtained sequences were identical and a consensus sequence corresponding to the Abarkooh (Yazd Province, Iran) S. oleraceus phyllody phytoplasma was deposited in GenBank (Accession No. MG652627). The S. oleraceus phyllody phytoplasma strain had 99.78% sequence identity with the 'Ca. P. asteris' reference strain (M30790). A BLAST search showed that this sequence had maximum identity (99-100%) with members of the 16SrI subgroup B. Phylogenetic analysis using the neighbour-joining method (MEGA7) (Fig. 2) showed that the Abarkooh S. oleraceus phyllody phytoplasma was clustered within the 16SrI group closest to onion yellows phytoplasma (NC_005303), representative of subgroup 16SrI-B. 

A 16SrI-A phytoplasma has been previously reported in S. oleraceus in Canada (Khadhair et al., 2008), however to our knowledge this is the first report of a 16SrI-B phytoplasma associated with S. oleraceus phyllody disease. The occurrence of 16SrI-B phytoplasma strains were previously reported in Iran on Brassica napus (Salehi et al., 2011), Eruca sativa (Esmailzadeh Hosseini et al., 2017) and Eucalyptus camaldulensis (Salehi et al., 2016); S. oleraceus may act as a reservoir host. 

Figure1+
Figure 1: Symptoms of phyllody disease in a Sonchus oleraceus plant including yellowing and reddening of leaves, flower virescence, phyllody and witches' broom (right), compared to a healthy plant (left). 
Figure 1: Symptoms of phyllody disease in a Sonchus oleraceus plant including yellowing and reddening of leaves, flower virescence, phyllody and witches' broom (right), compared to a healthy plant (left). 
Figure2+
Figure 2: Phylogenetic tree based on partial 16S rDNA sequences from the Sonchus oleraceus phyllody phytoplasma in this study (bold) and selected phytoplasma sequences (GenBank accession numbers in parentheses). The tree was constructed by the neighbour-joining method, numbers on branches are bootstrap values of 1,000 replicates. Acholeplasma laidlawii was used as an outgroup. Bar indicates the number of substitutions per nucleotide position.
Figure 2: Phylogenetic tree based on partial 16S rDNA sequences from the Sonchus oleraceus phyllody phytoplasma in this study (bold) and selected phytoplasma sequences (GenBank accession numbers in parentheses). The tree was constructed by the neighbour-joining method, numbers on branches are bootstrap values of 1,000 replicates. Acholeplasma laidlawii was used as an outgroup. Bar indicates the number of substitutions per nucleotide position.

References

  1. Esmailzadeh Hosseini SA, Salehi M, Salehi E, Bertaccini A, 2017. Incidence and molecular characterization of a 16SrI-B phytoplasma strain associated with Eruca sativa phyllody in Iran. Phytopathogenic Mollicutes 7, 45-51.  [http://dx.doi.org/10.5958/2249-4677.2017.00003.2]
  2. Khadhair A-H, Hiruki C, Deyholos M, 2008. Molecular characterization of aster yellows phytoplasma associated with valerian and sowthistle plants by PCR-RFLP analyses. Journal of Phytopathology 156, 326-331.  [http://dx.doi.org/ 10.1111/j.1439-0434.2007.01348.x]
  3. Lee I-M, Gundersen-Rindal DE, Davis RE, Bartoszyk IM, 1998. Revised classification scheme of phytoplasmas based on RFLP analyses of 16S rRNA and ribosomal protein gene sequences. International Journal of Systematic Bacteriology 48, 1153-1169.  [http://dx.doi.org/10.1099/00207713-48-4-1153]
  4. Salehi M, Esmailzadeh Hosseini SA, Salehi E, 2016. First report of a 'Candidatus phytoplasma asteris' related phytoplasma associated with eucalyptus little leaf disease in Iran. Journal of Plant Pathology 98, 175.  [http://dx.doi.org/10.4454/JPP.V98I1.054]
  5. Salehi M, Izadpanah K, Siampour M, 2011. Occurrence, molecular characterization and vector transmission of a phytoplasma associated with rapeseed phyllody in Iran. Journal of Phytopathology 159, 100-105.  [http://dx.doi.org/10.1111/j.1439-0434.2010.01731.x]
  6. Zhang Y-P, Uyemoto JK, Kirkpatrick BC, 1998. A small-scale procedure for extracting nucleic acids from woody plants infected with various phytopathogens for PCR assay. Journal of Virological Methods 71, 45-50.  [http://dx.doi.org/10.1016/S0166-0934(97)00190-0]
To cite this report: Salehi M, Esmailzadeh Hosseini SA, Salehi E, 2018. First report of a 'Candidatus Phytoplasma asteris'-related strain (16SrI-B) associated with Sonchus oleraceus (common sowthistle) phyllody disease in Iran. New Disease Reports 37, 6. [http://dx.doi.org/10.5197/j.2044-0588.2018.037.006]

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