Submitted to: Journal of Microbiological Methods
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2008
Publication Date: 3/1/2008
Citation: Chen, J., Livingston, S., Groves, R.L., Civerolo, E.L. 2008. High throughput PCR detection of Xylella fastidiosa directly from almond tissues. Journal of Microbiological Methods. 73:57-61. Interpretive Summary: Almond Leaf Scorch Disease (ASLD) caused by Xylella fastidiosa is currently re-emerging as a serious problem in California. The primary diagnosis of ALSD relies on pathogen detection. We have developed a simple and accurate method, pulverized freeze-tissue PCR (PFT-PCR) for high throughput detection of X. fastidiosa from almond tissue. PFT-PCR was compared to pathogen isolation method, generally considered as the "gold standard" for pathogen detection but more time consuming and labor intensive. PFT-PCR had a 90.8% detection confidence for the "gold standard" on fully symptomatic samples. PFT-PCR was also used to detect X. fastidosa from both symptomatic and asymptomatic samples during the 2005 growing season. PFT-PCR matched with the "gold standard" at 92.8% in the result. The simplicity and reliability of PFT-PCR is advantageous for future ALSD epidemiological studies and screening germplasm for resistance to X. fastidiosa infection.
Technical Abstract: Xylella fastidiosa, the causal agent of almond leaf scorch disease (ASLD), is currently re-emerging as a serious disease in California. Pathogen detection is a critical step for ALSD diagnosis because the disease symptoms are often confused with salt toxicity and other environmental stresses. We have developed a simple PCR method to detect X. fastidiosa directly from pulverized freeze-dried tissue (PFT-PCR). The PFT-PCR was simultaneously compared to the "gold standard" in vitro cultivation method using 102 symptomatic leaf samples from an almond orchard and showed a predictive value of 90.8%. The PFT-PCR was further used to monitor the pathogen population dynamics in four almond trees from two orchards in 2005 and showed a 92.8% correlation with the "gold standard". Considering the simplicity, we concluded that PFT-PCR is a valuable option for high throughput rapid detection of X. fastidiosa in the ALSD epidemiological studies.