Pierce's Disease of Grapevines in Taiwan: Isolation, Cultivation and Pathogenicity of Xylella fastidiosa
Characteristic symptoms of Pierce's disease (PD) in grapevines (Vitis 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 (Xylella fastidiosa). Koch's postulates were fulfilled by artificially inoculating two purified PD bacteria to grape cultivars Kyoho, Honey Red and Golden Muscat. 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 Taiwan 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 16S rRNA gene and 16S-23S rRNA internal transcribed spacer region (16S-23S ITS) of 12 PD strains from Taiwan with the sequences of 13 X.fastidiosa strains from different hosts and different geographical areas. Results showed that the PD strains of Taiwan were closely related to the American X.fastidiosa grape strains but not to the pear strains of Taiwan, suggesting that the X.fastidiosa grape and pear strains of Taiwan may have evolved independently from each other.