Identification of phytoplasma associated with witches' broom and virescence diseases of sesame in Oman

Sesame (Sesamum indicum L.) is an important field crop grown in the northern and interior regions of Oman for oil and animal feed. Phyllody, virescence and witches' broom symptoms, resembling those caused by phytoplasma infection were observed during 2004 - 2006. A nested PCR assay using primer pair Pl/16S-Sr followed by R16F2n/R16R2n was used to amplify a 1.53 kb and 1.2 kb fragment of the phytoplasma 16S rRNA gene, respectively. Restriction fragment length polymorphism (RFLP) analysis of 16S rDNA of sesame witches' broom phytoplasma strains singly digested with AluI, MseI, TaqI, and Tsp509I yielded patterns similar to those of alfalfa witches' broom phytoplasma belonging to subgroup 16SrII-D. The RFLP profiles of sesame witches' broom phytoplasma strains SIL and SIF were indistinguishable. Phylogenetic analysis showed that the sesame witches' broom phytoplasma strains (SIL, SIF) clustered with Omani alfalfa witches' broom forming a distinct lineage separate from peanut witches' broom and sesame phyllody (Thailand) phytoplasma strains.