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Occurrence of Praxelis clematidea Witches’ Broom Disease Associated with 16SrI Group ‘Candidatus Phytoplasma asteris’ in Hainan Island of China

    Affiliations
    Authors and Affiliations
    • Shao-Shuai Yu1
    • Chuan-Sheng Song2
    • Wei-Wei Song1
    1. 1Coconut Research Institute, Chinese Academy of Tropical Agricultural Sciences, Wenchang 571339, China
    2. 2College of Agricultural and Biological Engineering, Heze University, Heze 274015, China

    Praxelis clematidea is an invasive herbaceous plant belonging to the Asteraceae family. From August to November 2020, the plants showing severe witches’ broom symptoms were found in farms and roadsides of Ding’an, Hainan Province, a tropical island of China. The disease symptoms were suggestive of phytoplasma infection. For pathogen detection, P. clematidea samples from six symptomatic and three asymptomatic plants with 40% disease incidence estimated by conducting surveys and statistics were collected from farms and roadsides of Ding’an. Total nucleic acids were extracted from 0.10 g of fresh leaf tissues using the cetyltrimethylammonium bromide DNA extraction method (Doyle and Doyle 1990). Conserved sequences of 16S rRNA and secA genes from phytoplasmas were amplified by direct PCR using the primer pairs R16mF2/R16mR1 (Gundersen and Lee 1996) and secAfor1/secArev3 (Hodgetts et al. 2008), respectively. R16mF2/R16mR1 PCR amplicons were obtained from all symptomatic samples but not from the symptomless plants. The amplicons were purified and sequenced by Biotechnology (Shanghai) Co., Ltd. (Guangzhou, China). Sequences of 16S rRNA (1,323 bp) and secA (732 bp) genes were obtained, and all the gene sequences were identical and designated as PcWB (P. clematidea witches’ broom)-hnda. Representative sequences were deposited in GenBank with accession numbers PP098736 (16S rDNA) and PP072216 (secA). A nucleotide BLAST search based on 16S rRNA gene sequences indicated that PcWB-hnda had 100% sequence identity (1,323/1,323) with ‘Candidatus Phytoplasma asteris’-related strains belonging to the 16SrI group such as Waltheria indica virescence phytoplasma (MW353909) and Capsicum annuum yellow crinkle phytoplasma (MT760793) and had 99.62% sequence identity (1,321/1,326) with the phytoplasma strains of the 16SrI group such as Oenothera phytoplasma (M30790). The restriction fragment length polymorphism pattern derived from 16Sr RNA gene sequences by iPhyClassifier (Zhao et al. 2009) was identical (similarity coefficient = 1.00) to the reference pattern of the 16SrI-B subgroup (GenBank accession no. AP006628). The results obtained demonstrated that the phytoplasma strain PcWB-hnda under study is a member of the 16SrI-B subgroup. A BLAST search based on secA gene sequences indicated that PcWB-hnda shares 100% sequence identity (732/732 bp) with Pericampylus glaucus witches’ broom phytoplasma (MT875200), 99% sequence identify (728/732 bp) with onion yellows phytoplasma OY-M (AP006628), and 99% sequence identify (729/732 bp) with the rapeseed phyllody phytoplasma isolate RP166 (CP055264) among other phytoplasma strains that belong to the 16SrI group. Previous studies demonstrated that P. clematidea can be infected by phytoplasmas affiliated to the 16SrII group (GenBank accession no. KY568717 and EF061924) in Hainan Island of China (Wang et al. 2008; Yang et al. 2017). To our knowledge, this is the first report of a natural infection of P. clematidea by a 16SrI group phytoplasma in Hainan Island of China. The 16SrI group can infect agronomically important species such as areca palm in the island, and P. clematidea can be a reservoir of 16SrI phytoplasmas. Therefore, it is necessary to search for potential vectors of the pathogens, which would contribute to epidemiological monitoring and prevention of the related diseases.

    The author(s) declare no conflict of interest.

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    Funding: This work was supported by the Hainan Provincial Natural Science Foundation of China (no. 323RC524).

    The author(s) declare no conflict of interest.