Chaste tree(Vitex negundo var.heterophylla)witches’-broom was a new disease found in Mountain Taishan and the neighboring region.Phytoplasmal cells could be easily observed in the phloem sieve elements of diseased plants under electron microscope.The 16S rRNA gene of phytoplasma associated with this disease(CTWB)was amplified with nested-PCR with the universal primer pairs R16mF2/R16mR1 and R16F2n/R16R2.An amplified fragment of ca.1.2 kb was sequenced and subjected to identity and phylogenetic analyses.Phytoplasma CTWB shared identities of more than 99.0% with members of Aster yellows group(16SrI)in 16S rRNA genes.It had the highest identity of 99.8% with phytoplasmas associated with Maize bushy stunt(subgroup 16SrI-B),and clustered into a common branch with phytoplasmas of the subgroup in the phylogenetic tree constructed with 16S rRNA genes.These results indicated that CTWB belonged to subgroup B of Candidatus Phytoplasma asteris(16SrI-B).
