Detection and molecular characterization of cactus witches'-broom disease associated with a group 16SrII phytoplasma in northern areas of China

in july 2010, cacti with typical phytoplasma symptoms were observed in yangling district, shaanxi province, china. based on amplification of 16s rrna gene, phytoplasmas were detected by polymerase chain reaction (pcr) driven with universal primer pairs p1/ p7, followed by a nested pcr with universal primer pairs r16f2n/r16r2. fragments of expected sizes (1.8 kb and 1.2 kb) were obtained from symptomatic samples, but not from the asymptomatic samples. sequencing results and blastn analysis of the 1806 bp products (p1/p7) showed that the phytoplasma belonged to group 16srii. phylogenetic analysis to the r16f2n/r16r2 region and virtual restriction fragment length polymorphism (rflp) indicated that this phytoplasma was a member of subgroup 16srii-c. this is the first reported occurrence of a peanut witches'-broom phytoplasma infecting plants in northern areas of china.