Regions representing about 80% of the 16S rDNA sequences of nine phytoplasma isolates were amplified by polymerase chain reaction (PCR). These partial 16S rDNA sequences amplified from the various phytoplasmas were used in DNA heteroduplex mobility assays (HMA). Based on DNA distances derived from HMA analysis, the nine phytoplasma isolates may be classified into four distinct groups: group I, paulownia witches'-broom (China), potato purple top (France); group II, tomato stolbur (France); group III, eastern aster yellows (U. S.A.), faba bean phyllody (Sudan), vinca phyllody (Sudan), tomato big bud (Australia); group IV, crotalaria witches'-broom (Thailand), clover proliferation (Canada).
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