Candidatus phytoplasma asteris, belongs to 16SrI Aster yellows group, causes yellowing, whitches’ broom, leaf stunting and phyllody symptoms in different plant hosts such as vegetable, field crops, fruit tree and ornamentals. Losses induced by C.Phytoplasma asteries are mainly economic and lead to significant reduction in crop yield and quality. Aster yellows group phytoplasmas are now considered to divide in several subgroups on the basis of the nucleotide sequence of conserved genes.In recent years, Ca . Phytoplasma asteris has been reported as the causal agent of phytoplasma diseases of several plants in Iran. Although the phytoplasma has been detected from different locations in central part of Iran, the prevalence of subgroups related to aster yellows in the region phytoplasmas is unknown. The purpose of this study reported here was to analysis the genetic differences of Candidatus Phytoplasma asteris strains detected in central part of Iran to determine their relevant subgroups.During 2008- 2009, various vegetables, field crops, ornamentals and weeds showing phytoplasma symptoms including yellowing and hyacinth leaves, phyllody, witches'-broom, excessive branching of axillary shoots and general stunting were collected from Esfahan, Chaharmahal-va-Bakhtiari, Yazd and Markazi provinces of Iran. DNA was extracted from the midribs and petiols of the samples through Muray and Thompson method. Direct PCR method, using P1/P7 primer pairs, was employed to detect phytoplasma 16 S rRNA sequences as the amplification target region. The PCR amplification with purified DNA as template yielded the expected 1800bp product from some of the samples, but not from all the samples tested. Use of nested PCR increased the sensitivity of detection over single round PCR. Using primer pairs R16F2n/R16R2 in nested-PCR, after the first round PCR with primer pairs P1/P7, directed to detect a 1240 ~bp fragment in the majority of the samples showing phytoplasma associated symptoms. Specificity of the test was validated as no amplification was found in case of negative control plants. Nested PCR successfully identified 67 phytoplasma associated diseases among 120 samples. In order to distinguish Ca. Phytoplasma asteris based on amplified fragment from 16S-23S intergenic spacer region (using primer pairs R16F2n/R16R2), Hha I( Cfo I) restriction endonuclease analysis was performed. The results on the basis of the pattern of restriction fragments suggest that there is a sufficient diversity within the phytoplasmas identified in this Key words: Phytoplasma, PCR-RFLP, Strain, Aster yellows
