Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2009
Publication Date: 1/10/2010
Publication URL: http://www.ndrs.org.uk/article.php?id=020035
Citation: Davis, R.E., Dally, E.L., Zhao, Y., Lee, I., Jomantiene, R., Detweiler, A.J., Putnam, M.L. 2010. First report of a new subgroup 16SrIX-E, 'Candidatus Phytoplasma phoenicium'-related, phytoplasma associated with juniper witches' broom disease in Oregon. Plant Pathology. 20:35. Interpretive Summary: Phytoplasmas are very small bacteria that cause damaging diseases in agriculturally important crops and in plants growing in natural areas. There is need to determine whether phytoplasmas are involved in newly recognized diseases of plants, including the juniper witches’-broom disease, and to identify phytoplasmas associated with emerging diseases, so that appropriate disease control measures may be devised based on knowledge of the disease-causing agents. The present work focused on a disease of juniper trees (Juniperus occidentalis) in western USA; the cause o the disease was unknown. Using molecular methods for detection and identification, we found that a phytoplasma is the apparent cause of the disease, which we have named juniper witches’-broom (JunWB). The JunWB phytoplasma is related to a phytoplasma associated with a disease of almond trees reported in Lebanon and Iran, but the juniper witches’-broom phytoplasma represents a previously undescribed lineage. Finding this phytoplasma in J. occidentalis expands the known biodiversity of phytoplasmas discovered to infect conifers. Only one other phytoplasma has been reported to infect conifers (pine trees in Europe). Our results raise the question of whether J. occidentalis, previously undescribed as a phytoplasma host, could play a role in the spread of phytoplasmal disease potentially damaging to forest and landscape conifers in western USA. This report will be of interest to diagnostics laboratories, research scientists, foresters monitoring disease spread in forest and landscape trees, and scientists researching factors affecting carbon sequestration by forests. By revealing a new tree disease and its apparent cause, the work immediately impacts natural resources research and efforts to attain sustainable forestry systems.
Technical Abstract: Western juniper (Juniperus occidentalis) is a native tree indigenous to parts of Oregon, Washington, Idaho, Nevada and California. The tree has increased in density since settlement of these areas, raising concern over loss of understory plants, decreased wildlife habitat, and increased soil erosion. A newly recognized disease, juniper witches’ broom (JunWB), affecting at least 1% of trees in central Oregon, is characterized by abnormal proliferation of shoots, reduced size of leaves, shortened internodes, and growths having a ball-like appearance. DNA was extracted from leaf samples from ball-like growths and used as template in polymerase chain reactions primed by primer pair P1/P7. 1.8 kb DNA fragments amplified from two samples were sequenced and the sequences deposited in the GenBank database (accessions: GQ925918 and GQ925919). RFLP patterns of 16S rDNA, observed as virtual patterns using iPhyClassifier, indicated that JunWB phytoplasma represents a new subgroup lineage, designated 16SrIX-E. 16S rDNA sequence similarity confirmed that JunWB is a ‘Candidatus Phytoplasma phoenicium’-related phytoplasma. JunWB is one of two phytoplasmas found thus far to infect gymnosperms and is the only phytoplasma known to infect Juniperus sp. Occurrence of two distinct phytoplasmas, JunWB phytoplasma and ‘Ca. Phytoplasma pini’, in gymnosperms of two different families (Pinaceae and Cupressaceae, Division Coniferae) in Europe and North America, suggests that phytoplasmal infection of conifers may be more common than previously envisioned.