Overview of phytoplasma diseases in Asian countries

Phytoplasmas have emerged as one of the most severe constraints in the production of several crops all around the Asian countries during the past two decades. All-important crops that are cultivated mainly in South and East Asian countries are reported to be infected with phytoplasmas with severe losses in yield and quality every year. Significant progress on the identification and characterization of phytoplasmas, epidemiology, complete genome sequencing, and management of phytoplasma strains has been achieved in the past twodecades in Asia. A significant genetic diversity of phytoplasma strains associated with different crops was also reported. So far, 17 ribosomal groups and 36 subgroups of phytoplasmas have been identified on about 250 plant species in Asia. The most widespread phytoplasma species are ‘Candidatus Phytoplasma asteris,’ ‘Candidatus Phytoplasma australasia,’ ‘Candidatus Phytoplasma aurantifolia,’ ‘Candidatus Phytoplasma ziziphi,’ ‘Candidatus Phytoplasma trifolii,’ ‘Candidatus Phytoplasma sacchari,’ and ‘Candidatus Phytoplasma cynodontis’ belonging to the RFLP groups 16SrI, 16SrII, 16SrV, 16SrVI, 16SrXI, and 16SrXIV. Sugarcane, bamboo species, sesame, vegetables, legumes, brassicas, palms, stone fruits, seasonal ornamentals, and tree species are the major crops infected by phytoplasmas in Asia. Members of 14 ‘Candidatus Phytoplasma’ species were also identified, and the great majority of them were only detected in the Asian continent. Several leafhoppers, plant hoppers and psyllid and over 50 weed species were identified as vectors or potential vectors and reservoirs, respectively, of phytoplasma strains in Asia. This chapter provides a comprehensive overview concerning the diversity of phytoplasma strains associated with the major crops in Asian countries. This updated knowledge and literature review about the geographical distribution of phytoplasma diseases in different countries of Asia would help focusing on the most important diseases for developing management strategies in the respective countries and also alarm about emerging phytoplasma diseases of quarantine concern.