Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/1/2005
Publication Date: 1/1/2005
Citation: Liu, Q., Sun, Q., Wu, T., Davis, R.E., Zhao, Y. 2005. First report of witches'-broom disease of Pterocarya stenoptera in China and its association with a phytoplasma of aster yellows group (16SrI). Plant Disease. 89:529. Interpretive Summary: Phytoplasmas are small bacteria without a cell wall. These bacteria often cause serious diseases in vegetables, fruit trees, and ornamental trees. Chinese wingnut (Pterocarya stenoptera) is a fast-growing deciduous tree native to China. Because of its high resistance to pests and diseases, it is a popular shade-tree and a favorable rootstock for walnuts propagation. In spring 2004, a disease characterized by uncontrolled branching (witches'-broom disease) was observed in Chinese wingnut trees growing in suburban Taian, Shandong, China. DNA finger printing analysis revealed that this disease is associated with infection by a phytoplasma that is related to the one that causes devastating paulownia witches'-broom disease. This is the first report of the occurrence of a witches'-broom disease in Chinese wingnut trees and the first report of its association with a phytoplasma. Since this new disease occurred in an area where paulownia witches'-broom disease is common 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 and on walnut rootstock selection. 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: Pterocarya stenoptera, commonly known as Chinese wingnut, is a fast-growing deciduous tree with tough bark and attractive foliage. Because of its tolerance of poor soil, drought, heat, and compaction, Chinese wingnut is an important component of the biological diversity in natural ecosystems as well as a favorable shade-tree in its native habitat, China. In the fruit industry, Chinese wingnut has been used as a rootstock for walnuts for its high resistance to the soil-borne Phytophthora fungi. In spring 2004, a disease characterized by typical witches'-broom symptoms was observed in Chinese wingnut trees growing in suburban Taian, Shandong, China. The diseased trees developed dense clusters of highly proliferating branches with shortened internodes; leaves on the affected branches were greatly reduced in size; and some branches and twigs suffered dieback. Phytoplasma infection was first suspected in this Chinese wingnut witches' broom (CWWB) disease, because the disease occurred in an area where other phytoplasmal diseases, such as paulownia witches'-broom (PaWB) disease and jujube witches'-broom (JWB) disease, are common. Results from nested polymerase chain reactions (PCR), performed by using phytoplasma-universal 16S rDNA primers, revealed that all six diseased trees tested were infected with phytoplasma, whereas PCR assays of leaf samples from two nearby symptomless Chinese wingnut 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 CWWB phytoplasma belongs to the subgroup B of the Aster yellows (AY) phytoplasma group (16SrI-B). Nucleotide sequence analysis of the cloned CWWB phytoplasma near full-length16S rRNA gene suggested that CWWB phytoplasma is related to but distinct from PaWB phytoplasma, another member of the subgroup16SrI-B. To our knowledge, this is the first report of a Chinese wingnut witches'-broom disease and the first report of its association with a phytoplasma. Further work is being undertaken to examine the ecological and evolutionary relationship between CWWB and PaWB phytoplasmas and to assess the impact of CWWB phytoplasma on walnut rootstock selection.