Characterization of 16SrII group phytoplasma associated with sesame phyllody disease in different cropping seasons

A survey was conducted in the sesame fields of Karnataka, India during April–June 2010 (summer) and in Telangana State, Maharashtra and Karnataka during July–September 2010 (Kharif). In summer, disease incidence of 18.57–31.6% was recorded, whereas, in Kharif, incidence of 44.66–68%, 13–47.14% and 32.14% was recorded in Telangana State, Karnataka and Maharashtra respectively. Three symptomatic and two non-symptomatic samples from summer crop and sixteen symptomatic and two non symptomatic samples from Kharif season fields were collected. The disease etiology was confirmed using nested polymerase chain reaction (PCR) with phytoplasma universal primers P1/P7 followed by R16F2n/R16R2 which amplified ~ 1.8 and ~ 1.25 kb in the 16SrDNA gene. The BLAST and phylogenetic analysis of 16S rDNA gene further revealed that phytoplasma associated with phyllody disease in both the season were belonged to peanut witches’ broom group (16SrII). Further, iPhyClassifier analysis of 1.25 kb product of 16S rDNA sequence classified the isolates into 16SrII-A and 16SrII-D subgroups. All summer crop isolates were classified under 16SrII-D subgroup whereas; Kharif season isolates were grouped under 16SrII-A and 16SrII-D group. Phylogenetic analysis revealed the distinct subgroup-wise as well as season-wise clustering pattern where subgroup 16SrII-A and 16SrII-D clustered separately and summer and Kharif season isolates clustered separately. Our study reports that the sesame phyllody disease in Kharif season is caused by the taxonomically distinct strains (16SrII-A and 16SrII-D) whereas, in the summer crop, it is associated with 16SrII-D subgroup alone.