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Grapes ripening on a vine. Click the image for additional information about it.
Grape genes for resistance to Pierce's disease are the focus of some ARS studies in Parlier, California.  Click the image for additional information about it.

What Genes Help Grapevines Battle Pierce's Disease?

By Marcia Wood
November 28, 2003

Thanks to their genes, some grape plants are better able than others to shrug off attack by disease-causing microbes. Agricultural Research Service scientists and their university colleagues are systematically hunting for genes that enable grapevines to fight a devastating microbe called Xylella fastidiosa.

This microbe causes Pierce's disease of grapes. Infected vines can easily weaken and die. X. fastidiosa makes that happen by accumulating in clumps that block the normal flow of water and nutrients inside the plant.

Plant physiologist Hong Lin of the ARS San Joaquin Valley Agricultural Sciences Center in Parlier, Calif., is doing the gene-hunting experiments. He's working with M. Andrew Walker of the University of California, Davis and David W. Ramming, an ARS research horticulturist and grape breeder at Parlier.

In the confines of a research greenhouse, the scientists are infecting hundreds of grapevines with X. fastidiosa, then are looking for those that are either highly resistant or highly vulnerable to X. fastidiosa. Next, they're comparing the natural, gene-derived compounds that the vines produce over time and in response to the infection. For these comparisons, they're analyzing leaves and other plant parts.

From the tests, the scientists hope to pinpoint compounds that play a key role in equipping the resistant plants to successfully battle the microbe. Ideally, the genes that direct the plants to produce these protective compounds could be put into rootstocks to arm grapevines of the future. A rootstock is the lower, rooted portion of a grapevine, to which the upper, grape-bearing portion--called the scion--is grafted or attached.

The strategy may protect tomorrow's raisin, fresh-market and wine grapes alike from Pierce's disease. In the last decade, an outbreak of Pierce's disease in southern California killed 50 to 90 percent of all infected grapevines on thousands of acres. The disease remains a threat.

ARS is the U.S. Department of Agriculture's chief scientific research agency.