Multilocus Molecular Characterization of a 16SrII-D Phytoplasma Infecting Black Carrot in Türkiye

During the 2024 growing season, black carrot (Daucus carota subsp. sativus) plants showing symptoms consistent with phytoplasma infection, including leaf chlorosis, reduced leaf size, witches' broom, excessive fibrous root formation, multiple lateral taproots, and floral phyllody, were observed in production fields in Hatay Province, Türkiye. To identify the associated phytoplasma, 23 symptomatic plants and two asymptomatic control plants were analysed using PCR-based molecular detection, sequencing, BLASTn comparison, and phylogenetic analyses of the 16S rRNA, secA, tuf, and imp gene regions. The SAP11 gene was also screened as an additional virulence-associated molecular marker, but no functional characterization was performed. All symptomatic samples yielded amplicons of the expected sizes for the targeted loci, whereas no amplification was obtained from asymptomatic controls. Sequence comparisons revealed >99% nucleotide identity with members of the peanut witches' broom group, and multilocus phylogenetic analyses consistently placed the black carrot phytoplasma isolate within the 16SrII-D subgroup. To our knowledge, this study provides the first documented evidence of a 16SrII-D phytoplasma associated with black carrot in Türkiye. The finding is relevant for plant pathology and plant protection because it indicates the occurrence of a phytoplasma lineage with potential epidemiological importance in an economically important vegetable production area. These results provide a basis for future studies on disease distribution, insect vectors, alternative host plants, epidemiology, and management strategies in black carrot production systems.