Detection of sugarcane grassy shoot phytoplasma infecting sugarcane in India and its phylogenetic relationships to closely related phytoplasmas.
In several sugarcane-growing areas in India, sugarcane plants showing typical symptoms of sugarcane grassy shoot (SCGS) disease, non-symptomatic sugarcane plants, and sugarcane with non-specific yellowing and stunting symptoms were examined for phytoplasmal infections by means of polymerase chain reaction (PCR) using primers directed to phytoplasma ribosomal DNA (rDNA) sequences. From all field-collected symptomatic sugarcane plants, plants without non-specific symptoms, and most of the non-symptomatic plants, detectable PCR products were obtained through highly sensitive nested-PCR assays. The phylogenetic relationship among the SCGS phytoplasma strains, including those whose rDNA sequences were determined in this study, and between the SCGS phytoplasma strains and other closely related phytoplasmas was investigated at the 16S rRNA gene and 16S/23S rDNA spacer region sequence levels. The SCGS phytoplasma is a member of the Rice yellow dwarf (RYD) phytoplasma group or 16SrXI group, which was very closely related to the sugarcane with leaf (SCWL) agent. More distantly related to the SCGS agent were sorghum grassy shoot, Bermuda grass white leaf ('Candidatus Phytoplasma cynodontis') and RYD ('Candidatus Phytoplasma oryzae') phytoplasmas. The survey of phytoplasmal infections in sugarcane plants in India and the analysis of the phylogenetic relationship among the SCGS phytoplasma strains, and between the SCGS phytoplasma strains and other closely related phytoplasmas, at the 16S rRNA gene and 16S/23S rDNA spacer region sequence levels had not been previously reported.