Phytoplasmas associated with grapevine yellows in Virginia belong to group 16SrI, subgroup A (tomato big bud phytoplasma subgroup), and group 16SrIII, new subgroup I.
RFLP analysis of PCR-amplified 16S rDNA indicated that a Virginia grapevine yellows phytoplasma, designated VGYIII, was distinct from all other phytoplasmas studied, but was most closely related to spirea stunt, walnut witches' broom, and poinsettia branch-inducing phytoplasmas in subgroups E, G, and H, respectively, of 16S rRNA group 16SrIII. RFLP analysis also indicated the existence of sequence heterogeneity between the two rRNA operons in the genomes of SP1 and WWB. Based on the results from RFLP and sequence comparisons with other group 16SrIII phytoplasmas, the VGYIII phytoplasma was classified in a new subgroup, designated 16SrIII-I. A second phytoplasma (VGYI) was detected in cultivated grapevines (Vitis vinifera) and in wild grapevines (V. riparia), and identified as a member of subgroup 16SrI-A. There was no evidence of flavescence dorée, bois noir, or Australian grapevine yellows phytoplasmas in Virginia.