First report of phytoplasma belongs to 16SrXXXII group associated with witches'-broom symptoms in Trema tomentosa in China.

Trema tomentosa (Roxb.) Hara belonging to Ulmaceae displayed abnormal symptoms including witches'-broom, internode shortening, leaf chlorosis and leaflet that affected seriously their growth causing financial loss and ecological damage in China. During August through September 2020, these plants with the symptoms were first found and collected in Dingan and Qinghai counties of Hainan province, China. PCR were performed using the primers R16mF2/R16mR1 and secAfor1/secArev3 specific for phytoplasma 16S rRNA and secA gene fragments. The two gene fragments of the DNA extracted from the four disease samples were identical, with length of 1303 bp 16S rRNA and 587 bp secA gene fragments. The phytoplasma strain was named as Trema tomentosa witches'-broom (TtWB) phytoplasma, TtWB-hn strain. Phylogenetic and computer-simulated RFLP analyses based on the nearly full-length 16S rRNA gene sequence indicated that the TtWB phytoplasma strain is more closely related to the 16SrXXXII-A subgroup than to the other subgroups within 16SrXXXII group. It may represent a new subgroup, designed as 16SrXXXII-D subgroup, which is distinct from the other phytoplasma subgroups within the 16SrXXXII group. To our knowledge, this is the first report showing the occurrence of the phytoplasma strain belongs to 16SrXXXII-D subgroup associated with witches'-broom disease in Trema tomentosa in China. Genetic analysis indicated that the TtWB strain was closely related to the phytoplasma strains infecting periwinkle, oil palm, coconut palm in Malyasian, Camptotheca acuminate in Yunnan province of China and Elaeocarpus zollingeri in Japan.