In 2014, carrot plants in Zacatecas, Mexico, were found with yellow, brown, or purple-colored leaves, which were occasionally smaller and rolled. Roots of these affected plants were hairy, deformed, and small. Molecular diagnostics failed to detect phytoplasmas in these samples, but identified Spiroplasma citri in 58 and 94% of the samples using PCR targeting the spiralin and adhesion-related protein 1 (arp1) genes, respectively. Sequence analysis confirmed the presence of S. citri, and identified a novel, putative arp gene in one carrot sample. S. citri is a phytopathogenic mollicute transmitted by leafhopper species. Beet leafhoppers (Circulifer tenellus Baker) collected in the same state of Zacatecas, Mexico, were subsequently tested for S. citri infection, and 36.5% were positive using PCR targeting the arp1 gene. Sequencing analysis confirmed the presence of S. citri in the leafhoppers. This is the first report of S. citri in carrot and C. tenellus in Mexico. Previously in the Americas, S. citri in carrot was only reported in Washington and California in the United States. The presence of S. citri in carrots and the beet leafhopper in Mexico, suggests that this pathogen could become a threat to vegetable industries in this region of Mexico, including the carrot industry.

Motility in a Mollicute

Phytoplasmas for which 16S rDNA sequences are available have been classified into 20 major phylogenetic groups or subclades. Further phytoplasmas have been assigned to these groups, according to other molecular data such as RFLP analysis of PCR-amplified ribosomal DNA, nucleic acid hybridization, and serological comparison. A total of 75 phytoplasmas were distinguishable among the molecularly characterized phytopathogenic mollicutes.