Background:

Vineyard Venture Targets Genome of Pierce's Disease Microbe

Agricultural Research Service and Brazilian scientists, along with colleagues from the American Vineyard Foundation and the State of California Department of Food and Agriculture, are working out an innovative research plan to sequence the genome of the microbe that causes Pierce’s disease in vineyards.

The Brazilian scientists are with the Organization for Nucleotide Sequencing and Analysis (ONSA) in the Virtual Genomics Institute funded by the State of São Paulo Research Foundation.

Pierce's disease is caused by a bacterium, Xylella fastidiosa. It can be carried by a half-inch-long, leaf-hopping insect known as the glassy-winged sharpshooter. The pest, which is brown-to-black with ivory or yellow spots, can harbor Xylella in its gut, then move it into plants when it punctures grapevine stems--called canes--to feed on nutritious sap.

Once inside a grapevine, X. fastidiosa bacteria multiply, blocking the flow of water and nutrients. Severely infected vines die.

Pierce's disease has chronically attacked vineyards in northern California, costing growers $33 million from 1995 to 1997 alone. In southern California's Temecula Valley, about 50 miles south of Los Angeles, the disease has caused an estimated $6 million in damage to vineyards since 1997. Pierce's disease affects wine, table, and raisin grapes. Neither the insect nor the disease pose any threat to humans.

The scientists intend to discover the composition--or sequence--of all of the genes in the Xylella strain that's infecting Temecula Valley grapevines, then design new and powerful strategies to thwart it. The Brazilian researchers already sequenced the genes in a Xylella strain that causes citrus variegated chlorosis disease, or CVC.

Once a Xylella gene's sequence is known, researchers can compare it to those posted on computerized genome databases of other organisms. Because genes with the same sequence usually have the same function, the matching-up process shortens the amount of time it would otherwise take to discover a gene's function. Once scientists know a sequence and function of a Xylella gene that controls virulence, for example, they may be able to undermine it.

Edwin L. Civerolo of ARS' Crops Genetics and Pathology Research Unit in Davis, Calif., will be responsible for providing the Brazilian team with Xylella genetic material from infected Temecula Valley vines.

Andrew J. G. Simpson of the Ludwig Institute for Cancer Research at São Paulo will coordinate the Brazilian research to determine the exact sequence of the units, known as nucleotide pairs, that make up each X. fastidiosa gene. Simpson is DNA Coordinator of the Organization for Nucleotide Sequencing and Analysis at São Paulo. ONSA scientists sequenced the genome of the chlorosis-causing Xylella strain, making them the first in the world to sequence the genome of a plant pathogen.

The Napa, Calif.-based American Vineyard Foundation and the State of California Department of Food and Agriculture will each contribute $62,500 to the research, matching the planned ARS funding of $125,000. The São Paulo State Research Foundation will contribute $250,000 to the effort, which is expected to take less than a year to complete.

In addition to helping with the microbial genomics project, ARS scientists are experimenting with repellents and insecticides--including a fungus, a cinnamon extract, and a clay-based product--and are exploring tactics to boost plant resistance to the disease. In a strategy called biological control, they are searching for beneficial insects and other organisms that can attack the sharpshooters.

Contact: Marcia Wood, ARS Information, Albany, Calif., phone (510) 559-6070, fax 559-5882, mwood@asrr.arsusda.gov.