Genetic diversity of Pierce's disease strains and other pathotypes of Xylella fastidiosa

Strains of Xylella fastidiosa isolated from grape, almond, maple, and olean der were characterized by enterobacterial repetitive intergenic consensus s equence-, repetitive extragenic palindromic element (REP)-, and random ampl ified polymorphic DNA (RAPD)-PCR; contour-clamped homogeneous electric fiel d (CHEF) gel electrophoresis; plasmid content; and sequencing of the 16S-23 S rRNA spacer region. Combining methods gave greater resolution of strain g roupings than any single method. Strains isolated from grape with Pierce's disease (PD) from California, Florida, and Georgia showed greater than prev iously reported genetic variability, including plasmid contents, but formed a cluster based on analysis of RAPD-PCR products, NotI and SpeI genomic DN A fingerprints, and 16S-23S rRNA spacer region sequence. Two groupings of a lmond leaf scorch (ALS) strains were distinguished by RAPD-PCR and CHEF gel electrophoresis, but some ALS isolates were clustered within the PD group. RAPD-PCR, CHEF gel electrophoresis, and 16S-23S rRNA sequence analysis pro duced the same groupings of strains, with RAPD-PCR resolving the greatest g enetic differences. Oleander strains, phony peach disease (PP), and oak lea f scorch (OLS) strains were distinct from other strains. DNA profiles const ructed by REP-PCR analysis were the same or very similar among all grape st rains and most almond strains but different among some almond strains and a ll other strains tested. Eight of 12 ALS strains and 4 of 14 PD strains of X. fastidiosa isolated in California contained plasmids.;ill oleander strai ns carried the same-sized plasmid; all OLS strains carried the same-sized p lasmid. A plum leaf scald strain contained three plasmids, two of which wer e the same sizes as those found in PP strains. These findings support a div ision of X. fastidiosa at the subspecies or pathovar level.