Grants and Contracts Details
Description
A new j;!rapedisease for Kentucky. In September, 2001, Pierce's disease of grapes was
discovered along the Ohio River in a western Kentucky vineyard. Confirmation of the causal
agent, Xylella fastidiosa; was made using rapid cycling real-time polymerase chain reaction
(PCR) technology, by using a serological (ELISA) test, and by electron microscopic observation
of the characteristic undulating cell wall of the causal agent in grape leafpetioles.
Pierce's disease of grapes is endemic to the southeastern United States and has recently
become a major threat to California grapes because of the introduction of a new insect vector.
Pierce's disease had never been found in the Ohio River Valley as far north as Kentucky. Indeed,
analyisis of minimum winter temperature data published by other researchers suggest that most
of Kentucky would be outside the geographic range for this disease. The Kentucky and eastern
U.S. grape and wine industry needs research-based information on the biology and management
of Pierce's disease.
Pathogen detection is complicated. Current assays such aswe have done in our
laboratory and through commercial laboratories only test for X fastidiosa. Bacterial leaf scorch,
another devastating disease caused by X fastidiosa, is widespread in landscape trees in
Kentucky. It is likely that the newly-found grape disease is caused by the Pierce's disease strain
of X fastidiosa, but we really don't know for sure. The grape industry will need answers as to
whether or not the pathogen we see in grapes or in vegetation near vineyards is actually Pierce's
disease or another landscape strain. We have preliminary evidence that X fastidiosa is present in
certain symptomless weeds in the vineyard and in symptomless woody vegetation growing
nearby as well. This is not surprising given that we also find that in landscapes having trees with
bacterial leaf scorch, the pathogen can be found in symptomless grasses, lawn weeds, and
landscape shrubs and vines.
A brief summary of pathogen detection using molecular methods. PCR-based
identification provides a means of accurate detection of extremely low levels of a target
organism, and real-time PCR technologies such as use of TaqMan primers (Heid et al. 1996;
Nasarabadi et al. 1999), allow definitive identification of species or strain-specific DNA
sequences in biological samples. For the research proposed here, it will be necessary to identify
and survey species and individual strains of X fastidiosa in plants and insects. Species
identification can be based on comparisons of gene sequences such as the ribosomal RNA
operons (rDNA), whereas strain identification utilizes the more variable non-coding regions such
as rDNA transcribed spacers. Although extensive databases have many such sequences, DNA
sequences from particular target strains are needed. The most facile way to obtain such
sequences is by a PCR~based approach (Schardl et al. 1997). Based on the sequences obtained,
PCR primer sets both for species detection and strain identification can be synthesized, tested,
and used in surveys of plants and insect vectors. A useful way to accomplish the PCR step for
sequence determination, as well as to optimize the PCR diagnosis procedure, is with a real-time
PCR instrument. Thus, research providing needed information for practical disease control is
made feasible with molecular technology.
Status | Finished |
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Effective start/end date | 7/1/02 → 6/30/05 |
Funding
- Cornell University: $25,000.00
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