First report of Pierce’s disease of grapevine (Xylella fastidiosa) in Taiwan
In 2002, characteristic symptoms of Pierce's disease (caused by Xylella fastidiosa – EPPO A1 List) were observed in commercial vineyards in the major grapevine (Vitis vinifera) production areas of central Taiwan. Leaf scorch symptoms appeared at the onset of berry ripening (veraison) in late May to early June. Necrotic tissue with yellow or burgundy red margins developed at the edge of the leaves and then coalesced. Severely affected leaves became fully necrotic and fell prematurely, leaving matchstick-like petioles attached to the cane. Affected twigs and branches declined and plant dieback was observed within 1 to 5 years. Samples (petioles) were collected from diseased plants and tested (ELISA, PCR) for the presence of X. fastidiosa. Koch's postulates were fulfilled by artificially inoculating the isolated bacterium to V. vinifera cvs. ‘Kyoho’, ‘Honey Red’ and ‘Golden Muscat’. The inoculated plants developed typical leaf scorch symptoms and the bacterium could be reisolated from them, thus confirming that the grapevine leaf scorch disease in Taiwan is caused by X. fastidiosa. This is the first time that Pierce’s disease is reported from Taiwan and from Asia.
In Taiwan, it can be recalled that X. fastidiosa was first reported in 1993 causing a leaf scorch disease in Asian pear (Pyrus pyrifolia) (EPPO RS 94/049, 96/204, 2007/187). Phylogenetic analyses were performed by comparing the 16S rRNA gene and 16S-23S rRNA internal transcribed spacer region (16S-23S ITS) of 12 Pierce’s disease strains from Taiwan with the sequences of 13 X. fastidiosa strains from different hosts and different geographical areas. Results showed that the Pierce’s disease 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. Concerning insect vectors, extensive field surveys conducted in Taiwan have showed that in affected commercial vineyards, one xylem-feeding leafhopper Kolla paulula (Hemiptera: Cidadellidae) might be a potential vector (the most efficient vector in America, Homalodisca coagulata, does not occur in Taiwan). The bacterium was detected in K. paulula but further studies are needed to verify that it can transmit the disease. Since the first observation of Pierce’s disease symptoms in 2002, a total of 12;023 affected grapevines have been destroyed in commercial vineyards. However, the disease has not been successfully controlled 10 years after its initial discovery, possibly due to the inefficient suppression of the bacterium in other host plants acting as reservoirs in the vicinity of vineyards. Further studies are needed to identify these potential host plants and develop management strategies to control the disease.
Sources
Su CC, Chang CJ, Chang CM, Shih HT, Tzeng KC, Jan FJ, Kao CW, Deng WL (2013) Pierce's disease of grapevines in Taiwan: isolation, cultivation and pathogenicity of Xylella fastidiosa. Journal of Phytopathology 161(6), 389-396.