A New Strain of 16SrI Group Phytoplasma Associated With Witches' Broom and Decline of Pacific Willow (Salix lucida)

Phytoplasmas are transmitted by phloem‐sucking insect vectors and by vegetative propagation of infected plants. Pacific willow is an ecologically valuable and excellent wetland restoration plant in western North America. Pacific willow trees showing witches' broom (WB) and decline were observed growing on southern Vancouver Island, British Columbia, Canada. Phytoplasma infection was confirmed using a real‐time PCR assay targeting 16S rRNA genes. In silico restriction analysis of the F2nR2 region sequence, with iPhyClassifier, revealed that the restriction pattern of the detected phytoplasma was different from all previously established 16Sr subgroups, and the detected phytoplasma may represent a new strain in the 16SrI group. CpnClassiPhyR analysis of cpn60 universal target (UT) indicated that the detected phytoplasma is a probable new subgroup in Cpn60 UT I. Complete 16S rRNA, rpsP and rplS gene sequences were assembled from short‐read phytoplasma genome sequence data obtained from symptomatic willow trees. Phylogenetic analysis of 16S rRNA, rpsP and rplS genes also confirmed that the phytoplasma detected in WB symptomatic Pacific willow trees represents a new strain belonging to the 16SrI group.