First report of a new subgroup 16SrIX-E (‘Candidatus Phytoplasma phoenicium’-related) phytoplasma associated with juniper witches’ broom disease in Oregon, USA

Authors


E-mail: robert.davis@ars.usda.gov.

Western juniper (Juniperus occidentalis) is a native tree indigenous to parts of Oregon, Washington, Idaho, Nevada and California (USA). 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 (Deng & Hiruki, 1991; Schneider et al., 1995). DNA fragments of 1·8 kb amplified from two samples were sequenced and the sequences deposited in GenBank (Accession Nos. GQ925918 and GQ925919). RFLP patterns of 16S rDNA, observed as virtual patterns using iPhyClassifier (Zhao et al., 2009), indicated that JunWB phytoplasma represents a new subgroup lineage, designated 16SrIX-E. 16S rDNA sequence similarity confirmed that JunWB is a ‘Ca. Phytoplasma phoenicium’-related phytoplasma.

JunWB is one of three phytoplasmas found thus far to infect gymnosperms and is the only phytoplasma known to infect Juniperus sp. Occurrence of three distinct phytoplasmas, JunWB phytoplasma (this study), a group 16SrIII strain, and ‘Ca. Phytoplasma pini’ (Schneider et al., 2005), 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.

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