Molecular detection and identification of Brassica juncea phyllody and witches’ broom-associated phytoplasmas of group 16SrVI-A in Inner Mongolia, China

Abstract

In September 2017, oilseed mustard (Brassica juncea) showing symptoms of phyllody and witches’-broom, indicative of phytoplasma infection, was observed in Ordos, Inner Mongolia, China. Using universal primers P1/P7, the fragment encompassing phytoplasmal 16S rRNA, 16S–23S internal transcribed spacer region and partial 5′ end of 23S rRNA genes was amplified; the ribosomal protein (rp) genes (rplV-rpsC region) and the partial elongation factor TU (tuf) gene of phytoplasmas were amplified using primer pairs rpF1C/rp(I)R1A and fTufu/rTufu, respectively. The 16S rRNA, rp and tuf phylogenies suggested that both the B. juncea phyllody and witches’-broom associated phytoplasmas are closely related to members of 16SrVI (clover proliferation) group. Based on in silico restriction fragment length polymorphism (RFLP) analysis of 16S rRNA genes, the detected phytoplasmas were classified into 16SrVI-A subgroup. The in silico RFLP pattern is consistent with the actual RFLP pattern of the 16S rRNA genes. This was the first record of 16SrVI-A phytoplasma infecting B. juncea in China, probably the first case of phytoplasma on oilseed mustard as well.