Grapevine phytoplasma diseases

Grapevine Phytoplasma Diseases

Phytoplasmas are microscopic plant pathogens, similar to bacteria, but much smaller and lacking cell walls. They live in the vascular system of plants and are spread by sap-feeding insects, including leafhoppers and planthoppers. There are several diseases of grapevine caused by phytoplasmas:

Flavescence dorée
Bois noir (black wood, vergilbungskrankheit)
Grapevine yellows

These diseases are not established in Canada.

	Flavescence doree symptoms on Chardonnay, including downward leaf rolling and shrivelling of berry clusters. Photo courtesy INRA, France
	Bois noir symptoms on Grenache clonal 70 on rootstock 3309 clonal 143. Photo courtesy CFIA

Flavescence dorée is the most important and destructive phytoplasma disease of grapevines. It is known to occur only in France, Italy and Spain. Bois noir occurs in France and Germany, but is less serious due to a slower rate of spread. Diseases similar to bois noir have also been reported in Switzerland, Italy, Greece, Hungary, Israel, and are suspected to occur in Chile and South Africa. Phytoplasma diseases of grape elsewhere in the world are referred to as grapevine yellows, including an American grapevine yellows that occurs in New York and Virginia, and an Australian grapevine yellows.

Impacts

Flavescence dorée has been called “catastrophic” in France. Impacts include reduced vitality of vines, yield reductions, and reduced wine quality due to high acid and low sugar contents of fruit from infected plants. Without control measures, the disease spreads rapidly, affecting up to 80-100% of vines within a few years. Flavescence dorée has destroyed large viticultural areas in France and Corsica. It is still spreading despite mandatory control programs.

Popular cultivars such as Chardonnay, Cabernet Sauvignon, Pinot noir, Riesling, Sauvignon blanc, and Sémillon are highly susceptible to flavescence dorée. Some cultivars such as Sangiovese and Garganega are extremely susceptible and are killed quickly.

Symptoms

All grapevine yellows diseases have similar symptoms, including growth reduction, leaf discolouration, downward rolling of leaves, and reduced quality and quantity of fruit. Symptoms are not uniform, and may appear on some or all shoots of infected vines. A few rootstock varieties are tolerant to flavescence dorée, and can be symptomless carriers of the disease.


Bois noir infected leaves on Sylvaner x Riesling in Mosel, Germany. Photo courtesy Clemson University, Plant Virus Slide Series; photo credit W. Gartel.	Flavescence doree infected Baco 22A grapevine, Armagnac, France. Photo courtesy Clemson University, Plant Virus Slide Series; photo credit W. Gartel.

Flavescence doree symptoms on Cabernet Sauvignon, including shrivelled berries and reddish leaf discolouration. Photo courtesy INRA, France	Bois noir symptoms on Pinot Noir. Photo courtesy INRA, France

Leaf symptoms in white cultivars appear as small, yellow spots along the main veins. These spots enlarge to form yellow bands along the veins, which gradually extend over large parts of the leaf. Red cultivars develop a similar pattern on the leaves, but the discolorations are reddish.

Infected shoots often fail to lignify, and appear thin and rubbery. They later become brittle, sometimes with bud necrosis. Affected branches blacken and die during the winter. Numerous small black pustules form along the diseased branches of susceptible cultivars.

Fruit set is reduced on grapevines infected early in the season, as the inflorescences dry out and fall off. In later infections, bunches become brown and shriveled. Premature berry drop occurs in some cultivars.


American grape vine yellows - healthy and diseased clusters of DeChaunac. Photo courtesy Clemson University, Plant Virus Slide Series; photo credit J.K. Uyemoto.	Bois noir - black pustules on shoot. Photo courtesy Clemson University, Plant Virus Slide Series; photo credit W. Gartel.

Disease Cycle

Flavescence dorée is spread by the leafhopper Scaphoideus titanus, which is native to eastern North America. It is known to occur in Canada from the Maritimes through to Saskatchewan, but it has not yet been detected in British Columbia.

S. titanus spends its whole life cycle on grapevines. It is a highly mobile and efficient vector that is largely responsible for the epidemic spread of flavescence dorée. Both nymphs and adults are able to acquire the phytoplasma while feeding. After a latent period they are able to transmit the disease until they die. This leafhopper overwinters as eggs which are inserted (laid) into the bark of grapevines.

Bois Noir has a different vector, the planthopper Hyalesthes obsoletus. This insect is not known to occur in Canada. It prefers herbaceous weeds over grapevines. Bindweed (Convolvulus arvensis) is an important reservoir of bois noir in Europe. Since the vector only feeds incidentally on grape, bois noir is a much slower spreading disease than flavescence dorée.

Both Phytoplasmas and leafhoppers can be spread with propagation material. Flavescence dorée is symptomless in some cultivars, and it also has a long (up to 3 year) latent period before symptoms can be seen. Thus even apparently healthy vines may be carrying grapevine yellows diseases. A few rootstock varieties are symptomless carriers that have been responsible for spread of flavescence dorée in Europe.

Control

Control of phytoplasma diseases involves scouting and removal of infected or symptomatic vines, as well as control of the vector with insecticide sprays.

In France, flavescence dorée is a regulated disease. Compulsory control measures for both the disease and the vector were strengthened in 2003. When an infected grapevine is found, a quarantine area is delimited around it for a minimum of 2 years. All infected plants must be destroyed, and control of the vector with several insecticide sprays is required in that zone.

Prevention

Use only planting material from reliable, approved sources and produced in areas where phytoplasma diseases are not present.

Canada has grapevine import regulations that help to protect grape growers from the introduction and spread of diseases and other pests which are not yet established in British Columbia. Selected grapevine varieties/clones and rootstocks from Canadian-approved nurseries in France and Germany are currently approved for importation into Canada. Under this program, tests for regulated pests and diseases are carried out both in the exporting country and in Canada, prior to the approval for the importation of any grapevine variety or rootstock.

Note that the requirements for importation from France and Germany were changed in December 2005 due to the increased prevalence of flavescence dorée and bois noir in France. Import requirements were further strengthened in 2006. Contact the Canadian Food Inspection Agency (CFIA) for more information.

Import Requirements for Grapevines from France and Germany for 2007 and Beyond:

An Import Permit and Phytosanitary Certificate are required for all imports.

Grapevine material must be sourced from approved nurseries and clones.
Grapevine material grown within French Flavescence Dorée Control Zones is prohibited.
Hot Water Treatment (HWT) at 50⁰ Celsius for a minimum period of 35 minutes.
EITHER
A. Imported grapevine material from France and Germany will receive HWT prior to export. The National Plant Protection Organizations of France and Germany must supervise the treatments and certify them on the phytosanitary certificate.
OR
B. HWT may be performed in Canada prior to planting. Canadian facilities may apply to CFIA for approval as HWT Facilities to perform HWT on imported grapevine materials immediately prior to planting. CFIA will audit these facilities to ensure compliance.
Prior to the issuance of an import permit authorizing HWT in Canada, the importer must have access to a HWT Facility approved by CFIA. The grapevine materials will remain under the care, control and responsibility of the import permit holder until the HWT is carried out.
Grapevine material that has received HWT will not be subject to post-entry monitoring conditions.

Vines imported from France or Germany in 2006 that are under post-entry quarantine must be monitored for symptoms over the next several years. Report any suspicious vines to CFIA or the BC Ministry of Agriculture and Lands so they can be tested for phytoplasma diseases.

Photos and More Information on Grapevine Phytoplasma Diseases:

November 2006

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