Sesame plants with yellows symptoms and shortened internodes were observed in the surveyed sesame fields of a non-citrus-growing region in southeastern Iran. Leaf samples were collected from both symptomatic and asymptomatic plants. Concurrently, insects (Circulifer haematoceps) were also captured from the plants using a sweep net. Then, DNA was extracted from the symptomatic and non-symptomatic samples, likewise from the collected C. haematoceps insects. In the PCR assays, a DNA fragment with the expected size of 336 bp was amplified from the symptomatic plant’s DNA using Spiroplasma citri–specific primers. Besides, in the PCR assays, approximately 72.4% of the tested leafhopper samples were positive for S. citri, and in the experimental transmission assays, 26.6% of the periwinkle plants that were fed on by the field-collected leafhoppers showed symptoms. S. citri was also cultured from the symptomatic plants as well as the insects. Finally, the spiralin gene of an S. citri strain (KSC) isolated from one of the periwinkle plants was cloned and partially sequenced. BLAST and phylogenetic analysis of the obtained sequence revealed 100% and 87% homology of the KSC strain with the Iranian S. citri Marvdasht strain and the R8A2 reference strain, respectively. The present findings contribute to the knowledge on the sesame yellows disease caused by S. citri, as well as the high-frequency infectivity of the leafhopper C. haematoceps to S. citri, in the surveyed region. Furthermore, the finding of unique spiralins within Iranian populations of S. citri, including the KSC strain, may indicate that these strains are endemic in Iran. Due to the principal role of the leafhopper vector C. haematoceps in spreading the pathogen, controlling the vector insects is the key strategy for the management of the disease.
