First report of 16SrII–A phytoplasma associated with witches’ broom in Heliotropium arboreum (Blanco) Mabb. from Xisha Islands, with Halticus minutus as a putative vector

<i>Heliotropium arboreum</i> (Blanco) Mabb. (syn. <i>Tournefortia argentea</i>), a key pioneer plant in tropical coastal ecosystems, plays a vital role in stabilizing coral islands. In China's Xisha Islands, <i>H. arboreum</i> exhibited witches' broom symptoms (leaf deformities, reduced leaf size, floral phyllody). PCR assays were employed-using universal and phytoplasma-specific primers to amplify the 16S rRNA, s<i>ecY</i>, and <i>secA</i> genes-yielding amplicons of 1,248 bp (PV640668), 779 bp (PV854866), and 440 bp (PV854867), confirming a phytoplasma infection (designated <i>H. arboreum</i> witches' broom phytoplasma, HaWB). BLASTn analysis showed 100% sequence identity with 16SrII-group phytoplasmas, while phylogenetic and virtual RFLP analyses classified HaWB as a 16SrII-A subgroup strain. Additionally, morphological and molecular analyses of insects collected from symptomatic plants identified <i>Halticus minutus</i> as a putative vector. This is the first report of phytoplasma infecting <i>H. arboreum</i> in China, providing critical insights for disease surveillance in fragile coastal ecosystems.