Investigations on the diagnosis, colonization, and epidemiology of grapevines with Pierce's disease

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Title: Investigations on the diagnosis, colonization, and epidemiology of grapevines with Pierce's disease
Author: Vest, Mandi Ann
Abstract: Pierce ?s disease (PD ) of grapevines , caused by Xylella fastidiosa , is devastating Texas vineyards . Two rapid diagnostic techniques , real -time polymerase chain reaction (PCR ) and enzyme -linked immunosorbent assay (ELISA ) , were compared on the basis of cost , reliability , and their ability to quantify X . fastidiosa in diseased tissues . A high correlation was found between the two techniques for measuring bacterial titer in vitro . A similar relationship was not detected when applying the methods to diseased tissue . There was a 75 % similarity between the techniques when used to diagnose PD in artificially infected grapevines . Where the two methods differed , real -time PCR was more successful in identifying plants known to be infected with the bacterium . In uninoculated grapevines , the two techniques were similar , where the positive rates were 7 % and 4 % for ELISA and real -time PCR respectively . In a second study , 3 grape cultivars , ?Cynthiana ? , ?Cabernet Sauvignon ? , and ?Chardonnay ? , were inoculated with 2 isolates of X . fastidiosa to measure disease development and colonization by the pathogen . The bacteria colonized similar distances from the inoculation point over a 25 week period in all three cultivars . Real -time PCR and ELISA absorbance values suggest that the concentrations of bacteria ranged between 104 and 106 cells /ml in a 1 .27 cm section of grapevine cane . Concentrations of bacteria didn ?t vary based on distance from the inoculation point . Marginal leaf -scorch symptoms were seen on ?Cabernet Sauvignon ? and ?Chardonnay ? grapevines 9 weeks post -inoculation . Leaf -scorch symptoms were not observed on ?Cynthiana ? . The vigor of all inoculated grapevines was reduced compared to negative control grapevines the season after initial infection . In a third study , a Texas vineyard planted in Viognier grapevines was surveyed for PD symptoms on 3 separate dates . In October 2003 , 45 /50 rows had significant aggregation of symptomatic grapevines according to Ordinary Runs Analysis . Aggregation of symptomatic grapevines was found down the row more often than across the row . The rapid rate of disease progress and mortality rate of vines in this vineyard suggest that vine -to -vine spread is occurring and that Viognier vines are highly susceptibly to PD .
URI: http : / /hdl .handle .net /1969 .1 /1407
Date: 2005-02-17

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Investigations on the diagnosis, colonization, and epidemiology of grapevines with Pierce's disease. Available electronically from http : / /hdl .handle .net /1969 .1 /1407 .

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