Characterization of Phytoplasma Associated with Witches' Broom Disease of Sesame Using 16S rRNA Gene Sequencing

Abstract

Witches’ broom disease is an emerging threat to sesame production, characterized by excessive shoot proliferation, phyllody, stunting, and reduced seed yield. Phytoplasmas, cell wall–less prokaryotes inhabiting phloem tissues, are commonly associated with such symptoms in a wide range of host plants. The present study aimed to characterize the phytoplasma associated with witches’ broom disease of sesame using 16S rRNA gene sequencing. Field surveys were conducted in sesame-growing regions, and symptomatic plants exhibiting abnormal branching, reduced internode length, and floral malformations were collected. Total genomic DNA was extracted from infected and healthy plant tissues, and phytoplasma detection was performed using PCR assays with universal primers targeting the 16S rRNA gene. Amplification products were obtained only from symptomatic samples, confirming phytoplasma infection. Sequencing of the PCR products followed by phylogenetic analysis revealed close association of the detected phytoplasma with known phytoplasma groups infecting dicotyledonous crops. Comparative sequence analysis indicated genetic similarity with related strains reported from other geographic regions, suggesting possible regional spread and host adaptation. The results confirmed that witches’ broom disease of sesame is associated with a distinct phytoplasma lineage. Molecular characterization provided reliable identification of the pathogen and clarified its phylogenetic position within established phytoplasma clades. The study highlights the importance of molecular diagnostics for accurate detection and classification of phytoplasmas in oilseed crops. These findings contribute to a better understanding of disease etiology and support the development of effective management strategies, including vector control and the use of disease-free planting material, for sustainable sesame production.