Molecular detection and identification of phytoplasmas in a novel 16SrI subgroup in sunflowers and cocklebur weeds

Sunflowers (Helianthus annuus L.) exhibiting symptoms of stem fasciation and cluster of multiple inflorescences were observed in Baicheng, Jilin province, China. Coincidently, cockleburs (Xanthium strumarium L.), a weed in the sunflower fields, showing similar symptoms were observed as well. Based on successful amplification of 16S rRNA and secY genes of phytoplasmas, the sunflower fasciation disease (SFD) and cocklebur fasciation disease (CFD) were determined to be associated with phytoplasmas. Based on virtual and actual RFLP analysis of the F2nR2 region of the 16S rRNA genes, the SFD and CFD associated phytoplasmas were classified into a novel 16SrI subgroup, designated 16SrI-AI. This was the first report of SFD associated phytoplasma in China, and the first evidence of phytoplasma infecting cocklebur worldwide.