Pierce's Disease of Grapevines in T aiwan: Isolation, Cultivation and Pathogenicity of X ylella fastidiosa

Characteristic symptoms of Pierce's disease ( PD ) in grapevines ( V itis vinifera L .) were observed in 2002 in the major grape production fields of central Taiwan. Disease severity in vineyards varied, and all investigated grape cultivars were affected. Diseased tissues were collected from fields for subsequent isolation and characterization of the causal agent of the disease ( X ylella fastidiosa) . Koch's postulates were fulfilled by artificially inoculating two purified PD bacteria to grape cultivars K yoho, H oney R ed and G olden M uscat. The inoculated plants developed typical leaf‐scorching symptoms, and similar disease severity developed in the three cultivars from which the bacterium was readily re‐isolated, proving that the leaf scorch of grapevines in T aiwan is caused by the fastidious X . fastidiosa . This confirmed PD of grapevines is also the first report from the Asian Continent. Phylogenetic analyses were performed by comparing the 16 S rRNA gene and 16S‐23 S rRNA internal transcribed spacer region (16 S ‐23 S ITS ) of 12 PD strains from T aiwan with the sequences of 13 X . fastidiosa strains from different hosts and different geographical areas. Results showed that the PD strains of T aiwan were closely related to the American X . fastidiosa grape strains but not to the pear strains of T aiwan, suggesting that the X . fastidiosa grape and pear strains of T aiwan may have evolved independently from each other.