Detection and Molecular Identification of Phytoplasmas Associated with Potato in Iran

Potato purple top is a complex phytoplasma disease that poses a serious threat to potato cultivation worldwide. To verify the presence of different phytoplasma strains in potato disease outbreaks in Iran, six major potato-growing provinces in the central and western regions of the country were surveyed, and a total of 270 potato plants, 230 symptomatic and 40 asymptomatic, was sampled. Nested PCR analysis revealed the phytoplasma presence in 45% of symptomatic and 7% of asymptomatic plants. Molecular analysis was performed, analyzing the sequences of the 16S rRNA gene and the ribosomal protein rp, secY, and tufB genes. Four 'Candidatus Phytoplasma' species were identified in the tested potato samples: 'Ca. P. asteris' (16SrI-B), 'Ca. P. tritici' (16SrI-R), 'Ca. P. trifolii' (16SrVI-A), and 'Ca. P. solani' (16SrXII-A). The 'Ca. P. solani' strains were prevalent, occurring in all the surveyed provinces, whereas the 'Ca. P. tritici' strains were restricted to the Chaharmahal and Bakhtiari province. Phylogenetic and multilocus sequence analyses provided a finer resolution, distinguishing among some of the closely related phytoplasma strains. This study represents the first comprehensive molecular survey of potato-infecting phytoplasmas across a wide geographical region of Iran. The findings will aid studies regarding insect vector(s), pathogen biology, host range and disease management strategies.