Identification of a novel subgroup 16SrII-U phytoplasma associated with papaya little leaf disease

Papaya is an important fruit crop cultivated in tropical and subtropical regions. Papaya little leaf (PLL) disease was observed in China. The phytoplasma 16S rRNA gene was detected from symptomatic papaya trees via PCR using phytoplasma universal primers P1/P7 followed by R16F2n/R16R2. No amplification products were obtained from templates of asymptomatic papaya trees. These results indicated a direct association between phytoplasma infection and PLL disease. Comparative and phylogenetic analyses of 16S rRNA gene sequences indicated that the papaya-infecting phytoplasmas under study belonged to the peanut witches' broom phytoplasma group (16SrII). Genotyping through use of computer-simulated RFLP analysis of 16S rRNA genes and coefficients of RFLP pattern similarities (0.97) reveal that the PLL phytoplasma was placed in a new subgroup. In this article, we describe the molecular characterization of a new phytoplasma associated with PLL disease and propose that the PLL phytoplasma be considered as a novel subgroup, 16SrII-U.