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Title: Molecular identification of a new phytoplasma strain associated with the first observation of jujube witches'-broom disease in northeastern China

Author
item WEI, WEI - LIAONING, CHINA
item HUA, JIANG - LIAONING, CHINA
item YANG, YANG - LIAONING, CHINA
item YOUFU, WANG - LIAONING, CHINA
item Davis, Robert
item Zhao, Yan

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2007
Publication Date: 10/1/2007
Citation: Wei, W., Hua, J., Yang, Y., Youfu, W., Davis, R.E., Zhao, Y. 2007. Molecular identification of a new phytoplasma strain associated with the first observation of jujube witches'-broom disease in northeastern China. Plant Disease. 91:1364.

Interpretive Summary: Jujube, commonly known as Chinese date, is an economically important fruit crop in Asia. It produces tasty fruits and strong wood, and has valuable medicinal uses. Jujube trees are vulnerable to infection by phytoplasmas -- a group of small bacteria that lack a cell wall. Phytoplasma infection on jujube disturbs normal growth and induces a disease with symptoms characterized by uncontrolled branching (witches'-broom disease). In summer of 2006, jujube trees exhibiting typical witches’-broom symptoms were observed in suburban Dalian, northeastern China. DNA finger printing analysis of several genetic markers revealed that the diseased jujube trees were infected by a distinct and previously unreported phytoplasma strain. Since this is the first observation of jujube witches'-broom disease in northeastern China, and since this disease incidence is associated with a new phytoplasma strain, it is important to assess impacts of this new phytoplasma on the natural- and agro-ecosystems in the region. This information will be of interest to scientists and extension personnel who are concerned with phytoplasma diseases and to regulatory agencies that are concerned with implementing new quarantine regulations.

Technical Abstract: Jujube (Zizyphus jujuba Mill.) is a deciduous tree native to northern Africa and Syria. Because of its tolerance to a broad range of climatic conditions, jujube has attained a wide natural distribution from southeastern Europe to eastern Asia. Jujube has a long history of cultivation, especially in Asia, for its valuable medicinal properties, its strong wood, and its nutritious fruits. Jujube trees are susceptible to phytoplasma infections and develop jujube witches'-broom (JWB) disease. To date, JWB diseases have been reported in Korea, Japan, and central China. In this report, we describe a new phytoplasma strain associated with the first observation of JWB disease in northeastern China. In summer of 2006, six jujube trees exhibiting pronounced witches'-broom symptoms were observed in suburban Dalian, Liaoning Province. The trees developed dense clusters of highly proliferating branches with shortened internodes. Leaves on the affected branches were chlorotic and significantly reduced in size. A DNA segment characteristic of phytoplasma rRNA partial operons was amplified, from DNA samples extracted from leaves of all diseased trees, in polymerase chain reactions (PCR) using phytoplasma-universal primer pair P1/P7. No PCR product was obtained from DNA samples extracted from two symptomless jujube trees in the same region. The PCR-amplified DNA segment, spanning a near full-length 16S rRNA gene, a 16S-23S rRNA intergenic spacer, a tRNA-Ile gene, and a partial 23S rRNA gene, was cloned and sequenced to achieve 4X coverage. Results from analysis of the sequence data suggested that the six jujube trees were infected by a phytoplasma of elm yellows group (16SrV), to which other reported JWB phytoplasma strains belong. However, the JWB phytoplasma strain identified in the present study, hereby designated as JWB-DL, displayed sequence variations within the partial rRNA operon comparing to that of other JWB strains, indicating that JWB-DL is a distinct strain. To further characterize the JWB-DL phytoplasma, a genomic segment covering full-length ribosomal protein genes rplV and rpsC was PCR-amplified using primer pair rp(V)F2A/rpR1, cloned and sequenced. The nucleotide sequence of the JWB-DL phytoplasma rplV-rpsC locus is also distinct from that of JWB phytoplasma strains described previously. To our knowledge, this is the first report of a JWB disease in northeastern China, and JWB-DL represents a new, distinct member of group 16SrV.