16S rDNA sequence analysis of Xylella fastidiosa strains

The 16S rDNA encoding the small subunit ribosomal RNA were amplified by PCR , cloned, and sequenced from 16 strains of Xylella fastidiosa originating f rom nine different hosts. In pair-wise comparisons, X. fastidiosa strains s howed a maximum variation of 1.0% or 14 nucleotide positions. When all 16 s equences were considered as a set, 54 variable positions were found. Analys is of the sequence data indicated that the X. fastdiosa strains formed thre e rDNA groups. Group one includes Pierce's disease and mulberry leaf scorch strains; Group two, periwinkle wilt, plum leaf scald, phony peach, oak lea f scorch, and elm leaf scorch strains; and Group three, citrus variegated c hlorosis and coffee leaf scorch strains. All X. fastidiosa strains exhibite d significantly higher levels of sequence heterogeneity (63 to 83 nucleotid e positions) when compared to species from Xanthomonas and Stenotrophomonas . Our data demonstrate that 16S rDNA sequence data could provide valuable i nformation for future classification of X. fastidiosa at the sub-species le vel.