Genetic diversity of strains of Spiroplasma citri isolated in southern Iran

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

Spiralin Diversity Within Iranian Strains of Spiroplasma citri

The first-cultured and most-studied spiroplasma is Spiroplasma citri, the causal agent of citrus stubborn disease, one of the three plant-pathogenic, sieve-tube-restricted, and leafhopper vector-transmitted mollicutes. In Iranian Fars province, S. citri cultures were obtained from stubborn affected citrus trees, sesame and safflower plants, and from the leafhopper vector Circulifer haematoceps. Spiralin gene sequences from different S. citri isolates were amplified by PCR, cloned, and sequenced. Phylogenetic trees based on spiralin gene sequence showed diversity and indicated the presence of three clusters among the S. citri strains. Comparison of the amino acid sequences of eleven spiralins from Iranian strains and those from the reference S. citri strain GII-3 (241 aa), Palmyre strain (242 aa), Spiroplasma kunkelii (240 aa), and Spiroplasma phoeniceum (237 aa) confirmed the conservation of general features of the protein. However, the spiralin of an S. citri isolate named Shiraz I comprised 346 amino acids and showed a large duplication of the region comprised between two short repeats previously identified in S. citri spiralins. We report in this paper the spiralin diversity in Spiroplasma strains from southern Iran and for the first time a partial internal duplication of the spiralin gene