Primers designed from sequences of the gene encoding the elongation factor Tu ( gene) of several culturabie mollicutes amplified most of the gene from phytoplasmas of the aster yellows, stolbur and X-disease groups. About 85% of the gene from two aster yellows strains and a tomato stolbur phytoplasma was sequenced. The nucleotide sequence similarity between these related phytoplasmas was between 87.8 and 97.0%, whereas the homology with other mollicutes was 66.3-72.7%. The similarity of the deduced amino acid sequence was significantly higher, ranging from 96.0 to 99.4% among the phytoplasmas and 78.5% to 83.3% between phytoplasmas and the culturabie mollicutes examined. From the nucleotide sequences of the phytoplasma strains, two pairs of primers were designed; one amplified the phytoplasmas of most phylogenetic groups that were established, the other was specific for the aster yellows and stolbur groups. The phytoplasmas of the various groups that were amplified could be distinguished by RFLP analysis using 3AI, I and ll. The aster yellows group could be divided into five 3AI RFLP groups. These results showed that the gene has the potential to be used to differentiate and classify phytoplasmas. Southern blot analysis revealed that the gene is present as a single copy.


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