Spiroplasma citri, the causal agent of citrus stubborn disease, is widely distributed in citrus groves and causes heavy losses to the citrus industry in southern Iran. In the present study the genetic diversity of S. citri strains isolated from various hosts and locations in the Fars Province in southern Iran was investigated. The bacterium was cultured from stubborn affected citrus trees, sesame and safflower plants, and leafhopper vector Circulifer haematoceps. Based on PCR-RFLP of the spiralin gene (spi), four groups could be clearly identified among Iranian S. citri isolates. Group 1 was prominent with 71.8% of isolates found in both citrus and non-citrus hosts. Members of groups 2 (18%), and 5 (5.1%) were identified only in citrus, and members of group 6 only in non-citrus hosts. Phylogenetic analyses based on spi gene sequence could not clearly discriminate isolates of groups 1 and 2. In most cases, RAPD-PCR allowed the differentiation of isolates in different clades based on location or host. However there was no correlation between classification based on RFLP of spi gene and RAPD-PCR of whole genome. Finally, the study was completed by the demonstration that Iranian isolates found only in non-citrus hosts (group 6) including insect vectors are capable of infecting key lime when experimentally transmitted to the plant via a dodder bridge.

柑橘螺旋体是柑橘顽固病的病原体，广泛分布于柑橘园，给伊朗南部的柑橘产业造成重大损失。在本研究中，研究了从伊朗南部法尔斯省的不同宿主和地点分离的S. citri菌株的遗传多样性。该细菌是从顽固感染的柑橘树、芝麻和红花植物以及叶蝉载体Cir​​culifer haematoceps中培养出来的。基于spiralin基因（spi）的PCR-RFLP，可以清楚地鉴定出伊朗S. citri中的四组隔离。第 1 组突出，在柑橘和非柑橘宿主中发现了 71.8% 的分离株。第 2 组 (18%) 和 5 (5.1%) 的成员仅在柑橘中发现，第 6 组的成员仅在非柑橘宿主中发现。基于spi基因序列的系统发育分析不能清楚地区分第 1 组和第 2 组的分离株。在大多数情况下，RAPD-PCR 允许根据位置或宿主区分不同进化枝中的分离株。而spi基因的RFLP分类与全基因组的RAPD-PCR没有相关性。最后，该研究通过证明仅在非柑橘宿主（第 6 组）中发现的伊朗分离株（包括昆虫载体）在通过菟丝子桥实验传播到植物时能够感染关键石灰而完成。