Grapevine Red Blotch associated Virus (GRBaV)

California Pest Rating for

Grapevine Red Blotch associated Virus (GRBaV)

Pest Rating: B

PEST RATING PROFILE

Initiating Event:

None.

History & Status:

Background: The origin of Grapevine red blotch does not appear to be recent. For long the disease escaped the attention of vineyard growers because of its close resemblance to leafroll disease symptoms. Nevertheless, in 2008, an emerging grapevine disease – later termed red blotch disease, was first recognized in a Cabernet Sauvignon vineyard in Napa Valley, California. The disease was typified by leaf reddening and delayed fruit maturity in red cultivars of grapevine and initially confused with grapevine leafroll due to the late-season symptom of leaf reddening. However, some symptomatic leafroll grapevine cultivars were found to be free of leafroll viruses and DNA sequencing analysis revealed the presence of a single stranded DNA virus that was named, Grapevine red blotch associated virus (Al Rwahnih et al., 2012, 2013). In 2010, severe decline of grapevine cultivar ‘Cabernet franc’ was discovered in a vineyard in New York. As in California, the disease was initially described as leafroll but following nucleic acid analysis, was found to be free of leafroll viruses, and found to have a single stranded DNA that, on sequence analysis, resembled members of the virus family Geminiviridae. This virus was tentatively named, Grapevine cabernet franc-associated virus (GCFaV). Subsequently, both GRBaV and GCFaV were found to be the same virus and the name, Grapevine red blotch associated virus was used for the causal organism of the associated grapevine red blotch disease to distinguish the symptoms from those caused by leafroll viruses and other graft-transmissible agents (Krenz et al., 2014). Grapevine red blotch associated virus is a newly identified virus of grapevines and a putative member of a new genus within the family Geminiviridae (Sudarshana et al., 2015). In 2013, in Washington State vineyards, a disease similar to grapevine red blotch was reported to be caused by Grapevine red leaf-associated virus, which was determined to be genetically identical to GRBaV (Poojari et al., 2013).

Since its initial discovery in 2008, GRBaV has been detected in several regions of California (see ‘California Distribution’). Furthermore, through surveys, the disease was found to be widely distributed in North America. Grapevine red blotch has not been reported outside of North America. Studies conducted in the National Clonal Germplasm Repository (NCGR) located near Winters, California, revealed that grapevine accessions originating from 33 countries and five continents outside North America tested positive for the virus. However, it was not concluded from those studies that the virus occurs in those countries (Rwahnih et al., 2015).

Hosts: Vitis vinifera (grapevine) red cultivars: Cabernet Franc, Cabernet Sauvignon, Malbec, Merlot, Mourvèdre, Petite Sirah, Petit Verdot, Pinot Noir, and Zinfandel; white V. vinifera cultivars such as Chardonnay, Riesling, Semillon, and Viognier; also, table and raisin grapes and some root stocks. GRBaV has been detected in grapevine collections, nursery stock and established vineyards (EPPO, 2015).

Symptoms: Symptoms have been observed in grapevines of various ages in young (first leaf) and mature (5-20 yr old vineyards. Generally, symptoms appear in late August through September as red blotches on leaf blades on basal portions of shoots either between secondary or tertiary veins or extending from the leaf margin with the veins turning partly or fully red (Sudarshana & Fuchs, 2015). Foliar symptoms in white cultivars are less conspicuous and usually involve irregular chlorotic areas that may become necrotic late in season (Sudarshana et al., 2015). Certain white cultivars, such as Sauvignon Blanc may remain asymptomatic (EPPO, 2015). Symptoms of red blotch are very similar to those caused by leafroll disease in that leaves, primarily at the base of shoots, turn red during early fall. However, unlike leafroll, red blotch affected leaves have pink or red veins on the underside of leaves without the margins rolling downwards.

Damage Potential: GRBaV reduces fruit quality and ripening of grape. The most significant impact of red blotch disease is the reduction of sugar levels (°Brix), up to 4-5 times lower, in fruit of diseased grapes than in fruit of healthy grapes thereby, causing delayed harvests. This is of particular concern to wine grape growers who must achieve a certain sugar level in their wine grapes before the latter are acceptable for wine production. Also, fruit of diseased grapevines have increased acidity. The effect of red blotch disease on fruit yield or vine longevity is not known.

Transmission: GRBaV is graft transmissible. The primary source of spread of the pathogen is through infected planting material. There is no evidence for seed transmission (similar to other members of Geminiviridae). While the role of an insect vector in transmitting GRBaV in vineyards has not been confirmed, greenhouse experiments have shown that the Virginia creeper leafhopper (Erythroneura aicazc) is involved in spreading the virus from vine to vine in the greenhouse. The role of this leafhopper in vineyards and how plant-to-plant spread of GRBaV occurs under field conditions are not yet known (Rwahnih et al., 2015; Sudarshana & Fuchs, 2015).

Worldwide Distribution: North America: USA (Arizona, Arkansas, California, Georgia, Idaho, Maryland, New Jersey, New York, North Carolina, Oregon, Pennsylvania, Texas, Virginia, and Washington) and Canada (British Columbia and Ontario) (EPPO, 2015; McFadden-Smith, 2013; Sudarshana & Fuchs, 2015).

Official Control: Grapevine red blotch associated virus is on the “2015 Alert list” of the European and Mediterranean Plant Protection Organization (EPPO, 2015). Currently, it is a Q-rated quarantine pathogen in California.

California Distribution: Red blotch disease has been found in Napa and Sonoma Counties, as well as in the central coast (San Luis Obispo County) and San Joaquin Valley (Fresno County) regions of the State (Al Rwahnih et al., 2013; Sudarshana & Fuchs, 2015).

California Interceptions: There are no records of detection of GRBaV in quarantine shipments of plant material intercepted in California.

The risk Grapevine red blotch associated virus would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Evaluate if the pest would have suitable hosts and climate to establish in California. Score:

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.
– Medium (2) may be able to establish in a larger but limited part of California.
– High (3) likely to establish a widespread distribution in California.

Risk is High (3) –.Grapevine red blotch associated virus has already spread to certain grape growing counties in California’s northern, central and San Joaquin Valley regions. If left unchecked, the pathogen is likely to establish a widespread distribution in grape producing regions of the State.

2) Known Pest Host Range: Evaluate the host range of the pest. Score:

– Low (1) has a very limited host range.
– Medium (2) has a moderate host range.
– High (3) has a wide host range.

Risk is Low (1) – Grapevine red blotch associated virus has been identified in nine Vitis vinifera red cultivars: Cabernet Franc, Cabernet Sauvignon, Malbec, Merlot, Mourvèdre, Petite Sirah, Petit Verdot, Pinot Noir, and Zinfandel; and white cultivars V. vinifera cultivars such as Chardonnay, Riesling, Semillon, and Viognier; also, table and raisin grapes and some root stocks. Although the pathogen has a limited host range, Grape production is a major enterprise and grapevine is cultivated over significant acreage in California.

3) Pest Dispersal Potential: Evaluate the natural and artificial dispersal potential of the pest. Score:

– Low (1) does not have high reproductive or dispersal potential.
– Medium (2) has either high reproductive or dispersal potential.
– High (3) has both high reproduction and dispersal potential.

Risk is High (3) – Grapevine red blotch associated virus is graft transmissible. The primary source of spread of the pathogen to vineyards is through infected planting material. The role of an insect vector in vineyards and plant-to-plant spread of GRBaV under field conditions are not yet known.

4) Economic Impact: Evaluate the economic impact of the pest to California using the criteria below. Score:

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

– Low (1) causes 0 or 1 of these impacts.
– Medium (2) causes 2 of these impacts.
– High (3) causes 3 or more of these impacts.

Risk is Medium (2) – The effect of red blotch disease on fruit yield or vine longevity is not known. However, Grapevine red blotch associated virus reduces fruit quality and ripening of grape resulting in lowered crop value, loss of markets and is likely to negatively change normal cultural practices including removal of diseased vines and replant of vineyards since there is no cure once the virus is present in a vineyard (UCDavis News & information, 2013). The most significant impact of red blotch disease is the reduction of sugar levels (°Brix), up to 4-5 times lower, in fruit of diseased grapes than in fruit of healthy grapes thereby, causing delayed harvests. This is of particular concern to wine grape growers who must achieve a certain sugar level in their wine grapes before the latter are acceptable for wine production. Also, fruit of diseased grapevines have increased acidity. The involvement of an insect vector in spreading the virus under field conditions is not known.

5) Environmental Impact: Evaluate the environmental impact of the pest on California using the criteria below.

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Score the pest for Environmental Impact. Score:

– Low (1) causes none of the above to occur.
– Medium (2) causes one of the above to occur.
– High (3) causes two or more of the above to occur.

Risk is Medium (2) – Grapevine red blotch associated virus could significantly impact cultural practices, home/urban plantings of disease infected grapevines and trigger official or private treatment programs.

Consequences of Introduction to California for Grapevine red blotch associated virus

Add up the total score and include it here. (Score)

-Low = 5-8 points
–Medium = 9-12 points
-High = 13-15 points

Total points obtained on evaluation of consequences of introduction of GRBaV to California = Medium (11).

6) Post Entry Distribution and Survey Information: Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included. (Score)

-Not established (0) Pest never detected in California, or known only from incursions.
-Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).
–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.
-High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Evaluation is Medium (-2). Presently, Grapevine red blotch associated virus has been reported from Napa and Sonoma Counties, as well as in the central coast (San Luis Obispo County) and San Joaquin Valley (Fresno County) regions in California.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: (Score)

Final Score: Score of Consequences of Introduction – Score of Post Entry Distribution and Survey Information = 9.

Uncertainty:

The means by which GRBaV spreads in vineyards is not known and is a current focused study of researchers. Virus spread is suspected via a vector but this has yet to be identified. Knowledge gained in this area may further the distribution of the virus than what is reported here.

Conclusion and Rating Justification:

Based on the evidence provided above the proposed rating for Grapevine red blotch associated virus is B.

References:

Al Rwahnih, M., A. Dave, M. Anderson, J. K. Uyemoto, and M. R. Sudarshana. 2012. Association of a circular DNA virus in grapevine affected by red blotch disease in California. Proceedings of the 17^th Congress of ICVG, Davis, California, USA. October 7-14, 2012.

Al Rwahnih, M., M. R. Sudarshana, and J. Wolpert. 2013. Red Blotch Disease. Viticulture Information, University of California Integrated Viticulture: http://iv.ucdavis.edu/Viticultural_Information/?uid=284&ds=351.

Al Rwahnih, M., A. Dave, M. M. Anderson, A. Rowhani, J. K. Uyemoto, and M. R. Sudarshana. 2013. Association of a DNA virus with grapevines affected by red blotch disease in California. Phytopathology 103:1069-1076.

Al Rwahnih, A. Rowhani, D. A. Golino, C. M. Islas, J. E. Preece, and M A. Sudarshana. 2015. Detection and genetic diversity of Grapevine red blotch-associated virus isolated in table grape accessions in the National Clonal Germplasm Repository in California. Canadian Journal of Plant Pathology, 37:130-135. http://dx.doi.org/10.1080/07060661.2014.999705.

EPPO. 2015. Grapevine red blotch-associated virus. European and Mediterranean Plant Protection Organization: http://www.eppo.int/QUARANTINE/Alert_List/viruses/GRBAV0.htm.

Krenz, B., J. R. Thompson, H. L. McLane, M. Fuchs, and K. L. Perry. 2014. Grapevine red blotch-associated virus is widespread in the United States. Phytopathology 104:1232-1240.

McFadden-Smith, W. 2013. Grapevine red blotch associated virus: A newly identified disease in vineyards. Ontario Ministry of Agriculture, Food and Rural Affairs: http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2013/22hrt13a1.htm.

Poojari S, O. J. Alabi, V. Y. Fofanov, and R. A. Naidu RA. 2013. A leafhopper transmissible DNA virus with novel evolutionary lineage in the family Geminiviridae implicated in grapevine redleaf disease by next-generation sequencing. PLoS One. 8:e64194. doi:10.1371/journal.pone.0064194.

Sudarshana M., and M. Fuchs. 2015. Grapevine Red Blotch. In Compendium of Grape Diseases, Disorders, and Pests, Second Edition, Edited by W. F. Wilcox, W. D. Gubler, and J. K. Uyemoto. The American Phytopathological Society, St. Paul, Minnesota. 122-123 pp.

Sudarshana, M. R., K. L. Perry, and M. F. Fuchs. 2015. Grapevine red blotch associated virus, an emerging threat to the grapevine industry. Phytopathology, 105:1026-1032. http://dx.doi.org/10.1094/PHYTO-12-14-0369-FI.

UCDavis News and Information. 2015. New technology offers hope for solving grapevine red blotch disease problem. http://news.ucdavis.edu/search/news_detail.lasso?id=10499.

Responsible Party:

John J. Chitambar, Primary Plant Pathologist/Nematologist, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, CA 95832. Phone: 916-262-1110, plant.health[@]cdfa.ca.gov.

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