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Diagnosis of Pierce's Disease Using Biomarkers Specific to Xylella fastidiosa rRNA and Vitis vinifera Gene Expression

First and sixth authors: Department of Genetic Engineering, Dong-A University, Busan 604-714, Republic of Korea; first, fifth, and seventh authors: Department of Plant Pathology, University of California, Davis 95616; second author: Bio-Rad Inc., Hercules, CA 94547; third author: Department of Medical Laser, Dankook University, Cheonan 330-714, Republic of Korea; and fourth author: Monsanto Inc., Davis, CA 95616.

Pierce's disease (PD), caused by Xylella fastidiosa, represents one of the most damaging diseases of cultivated grape. Management of PD in the vineyard often relies on the removal of infected individuals, which otherwise serve as a source of inoculum for nearby healthy vines. Effective implementation of such control measures requires early diagnosis, which is complicated by the fact that infected vines often harbor high titers of the pathogen in advance of visual symptom development. Here, we report a biomarker system that simultaneously monitors Xylella-induced plant transcripts as well as Xylella ribosomal (r)RNA. Plant biomarker genes were derived from a combination of in silico analysis of grape expressed sequence tags and validation by means of reverse-transcriptase polymerase chain reaction (RT-PCR). Four genes upregulated upon PD infection were individually multiplexed with an X. fastidiosa marker rRNA and scored using either real-time RT-PCR or gel-based conventional RT-PCR techniques. The system was sufficiently sensitive to detect both host gene transcript and pathogen rRNA in asymptomatic infected plants. Moreover, these plant biomarker genes were not induced by water deficit, which is a component of PD development. Such biomarker genes could have utility for disease control by aiding early detection and as a screening tool in breeding programs.