Occurrence of a ‘Candidatus Phytoplasma asteris’ strain associated with onion yellows disease in Iran

In a 2022 survey for phytoplasma diseases, onion yellows symptoms were observed in seed production fields of Zarghan, Beedzard and Kavar areas (Fars province, Iran). The main symptoms were virescence, phyllody, yellowing, witches’ broom and sterility. The disease incidence was recorded up to 4%. Nested polymerase chain reaction using P1/P7 followed by R16F2n/R16R2 primer pairs was carried out with DNAs extracted from twelve symptomatic and four symptomless onion plants for phytoplasma detection. DNA fragments of about 1.8 and 1.25 kbp respectively were obtained from symptomatic onion plants but not from the symptomless ones. The R16F2n/R16R2 sequences of twelve samples showed 100% identity with each other and a representative of these sequences from Zarghan (strain ZOY) was deposited in GenBank under accession number OQ332407. BLASTn analysis of this 16S rRNA sequence showed 100% identity with ‘Candidatus Phytoplasma asteris’. Phylogenetic analysis using neighbor-joining method showed that ZOY phytoplasma strain clustered within members of subgroup 16SrI-B. Computer-simulated analysis using iPhy Classifier also showed that the RFLP pattern of the ZOY phytoplasma 16S rRNA gene was identical to the reference strain of 16SrI-B subgroup. This is the first detection of a 16SrI-B phytoplasma strain in onion yellows in Iran.