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Title: FIRST REPORT OF WITCHES'-BROOM DISEASE OF BROUSSONETIA PAPYRIFERA AND ITS ASSOCIATION WITH A PHYTOPLASMA OF ELM YELLOWS GROUPS (16SRV)

Author
item LIU, QINGZHONG - CHINA
item WU, TIANQI - CHINA
item Davis, Robert
item Zhao, Yan

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2004
Publication Date: 7/11/2004
Citation: Liu, Q., Wu, T., Davis, R.E., Zhao, Y. 2004. First report of witches'-broom disease of broussonetia papyrifera and its association with a phytoplasma of elm yellows groups (16srv). Plant Disease. 88(7):770.

Interpretive Summary: Phytoplasmas are small cell wall-less bacteria that often cause serious diseases in vegetables, fruit trees, and ornamental trees. Paper mulberry (Broussonetia papyrifera), a fast-growing ornamental tree native to northeastern Asia, is an important component of the biological diversity in natural ecosystems as well as a popular shade tree in the region. In the fall of 2003, a disease characterized by uncontrolled branching (witches'-broom disease) was observed in paper mulberry trees growing near a jujube (Chinese date) orchard in Taian, China. DNA finger printing analysis revealed that this disease is associated with infection by a phytoplasma that is closely related to the one that causes devastating jujube witches'-broom disease and belongs to elm yellows phytoplasma group. This is the first report of the occurrence of a witches'-broom disease in paper mulberry and the first report of its association with a phytoplasma. Since this new disease occurred in an area where jujube witches'-broom disease is prevalent and since both diseases are associated with phytoplasmas of the same group, it is important to assess impacts of this type of phytoplasma on the 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 for implementation of new quarantine regulations.

Technical Abstract: Broussonetia papyrifera, commonly known as paper mulberry, is an ornamental tree native to northeastern Asia. Because of its fast-growing nature and tolerance of dust, smoke and high temperatures, paper mulberry is an important component of the biological diversity in natural ecosystems as well as a favorable shade-tree in the region. In September 2003, a disease characterized by pronounced witches'-broom symptoms was observed in paper mulberry trees growing near a jujube (Ziziphus jujuba) orchard located in Taian, Shandong, China. The diseased trees developed dense clusters of highly proliferating branches with shortened internodes; leaves on the affected branches were chlorotic and greatly reduced in size. Phytoplasma infection was first suspected in this paper mulberry witches' broom (PMWB) disease, because the disease occurred in an area where other phytoplasmal diseases, including jujube witches'-broom (JWB) disease and paulownia witches'-broom (PaWB) disease, are commom. Results from nested polymerase chain reactions (PCR), performed by using phytoplasma-universal 16S rDNA primers, revealed that all diseased trees tested contained phytoplasma, whereas PCR assay of leaf samples from nearby symptomless paper mulberry trees were negative. Subsequent restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified 16S rDNA indicated that all diseased trees contained the same phytoplasma and that the PMWB phytoplasma belongs to the subgroup B of the elm yellows (EY) phytoplasma group (16SrV-B). Nucleotide sequence analysis of the cloned PMWB phytoplasma partial rRNA operon suggested that PMWB phytoplasma is most closely related to JWB phytoplasma. To our knowledge, this is the first report of a paper mulberry witches'-broom disease and the first report of its association with a phytoplasma. Further work is underway to determine whether the PMWB phytoplasma is distinct from previously characterized phytoplasmas in group 16SrV and to assess impacts of the phytoplasma on the ecosystems in the region.