Host Diversity and Phylogenetic Evolution of Phytoplasmas on Hainan Island in China, Bringing Challenges to Monitoring and Prevention of Related Plant Diseases

Phytoplasmas are a group of wall-less, unculturable prokaryotic pathogenic bacteria that colonize the phloem of plants and are transmitted by piercing–sucking insects. As a typical tropical island province in China, Hainan Island has abundant biodiversity due to its unique geographical location and climatic conditions, which provide a favorable ecological environment for the survival and propagation of phytoplasmas, which infect different hosts, cause different symptoms, or belong to different subgroups. Based on host species, disease symptoms and 16Sr subgroups, 69 representative phytoplasma records from four 16Sr groups have been identified on Hainan Island, showing rich diversity in host range and pathogen species. The diversity of plant hosts and the evolutionary relationship of phytoplasmas not only affect the occurrence and prevalence of phytoplasma-related diseases but also bring great challenges to the epidemic monitoring, detection, diagnosis and prevention management of these diseases. This review summarizes current research progress on host diversity, phylogenetic evolution, mixed infection, diversity of transmission vectors, and geographical isolation differentiation, as well as adaptive evolution of phytoplasmas on Hainan Island. Furthermore, the challenges brought by plant host diversity and phylogenetic evolution to disease monitoring, diagnosis and prevention management are discussed. This review aims to provide a comprehensive theoretical basis for the in-depth study of phytoplasma-related diseases on Hainan Island, and to offer practical guidance for scientific monitoring, early warning and comprehensive prevention and control of these diseases.