The development of new tools for field and laboratory diagnosis of Pierces Disease
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Pierce’s Disease (PD), caused by Xylella fastidiosa, is a devastating bacterial disease of grapevines. One of the few control options is roguing. Roguing depends on precise diagnosis of PD in vines. These experiments were conducted to improve available diagnostic protocols and enhance levels of disease control. Plots were selected from four different Texas vineyards with a total of four different varieties (Blanc duBois, Cabernet Sauvignon, Chardonnay, and Merlot). An infrared thermometer was used to take temperature measurements of the vines. Samples were taken of each of these vines at the same time and were tested for X. fastidiosa by culturing, Enzyme-Linked ImmunoSorbent Assay (ELISA), and Quantitative Real-Time Polymerase Chain Reaction (QRT-PCR). ELISA found an increase in plant temperature in samples that tested positive for X. fastidiosa, but QRT-PCR did not. An infrared thermometer could be used to detect asymptomatic vines, but there are several variables to consider such as grape variety and vineyard location. Grape varieties differed significantly in mean temperatures, as did vineyard locations. PD does not seem to have a pattern in which it spreads, although this could be because of the high level of disease incidence in the chosen vineyards. Both the ELISA and QRT-PCR tests have their own pros and cons for X. fastidiosa detection. ELISA takes approximately 6 hours and can be inaccurate in detecting X. fastidiosa. QRT-PCR takes 2-3 hours and is a much more sensitive test. A combination of techniques (PrepMan Ultra® and nucleic acid precipitation) can be used to clean QRTPCR samples when they have degraded and are being affected by inhibitors.
Bryan, Kelly Asbill (2008). The development of new tools for field and laboratory diagnosis of Pierces Disease. Master's thesis, Texas A&M University. Available electronically from