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Title:   Author  item
                                            Sudarshana, Mysoreitem
                                            FUCHS, MARC - Cornell University
  Submitted to: Compendium of Grape Diseases
                                    Publication Type: Book / Chapter
                                    Publication Acceptance Date: 8/15/2013
                                    Publication  Date: 8/1/2015
                                    Publication URL: http://www.apsnet.org/apsstore/shopapspress/Pages/44792.aspxCitation: Sudarshana, M.R., Fuchs, M. 2015. Grapevine red blotch. In: Wilcox, W.F., Gubler, W.D., Uyemoto, J.K., editors. Compendium of Grape Diseases. 2nd edition. St. Paul, MN: American Phytopathological Society Press. p. 122-123.Interpretive Summary:
                                Technical Abstract: Grapevine red blotch disease was first recognized in 2008 in vineyards in Napa County in California.  The name ‘red blotch' was given to distinguish disease symptoms from those caused by leafroll viruses and other graft-transmissible agents involved in graft union disorders (see pages... this compendium) on red fruited V. vinifera cultivars, as well as injuries to trunks and shoots caused by poor vineyard management practices.  In addition to North Coast vineyards in Napa and Sonoma Counties, diseased vineyards have also been found in Central Coast and San Joaquin Valley in California, in New York, and in the Ontario province of Canada. 

Symptoms
Disease symptoms generally start appearing in late August through September as irregular red blotches on leaf blades (Plate Figure 1), either between the secondary or tertiary veins or extending from the leaf margin, on basal portions of shoots.  The secondary and tertiary veins can turn partly or fully red.  Occasionally, the leaf blade reddening in the interveinal zones between secondary veins may resemble the symptoms caused by leafroll disease.  However, unlike for leafroll disease, the leaf margin does not roll downward.  Thus far, disease symptoms have been observed in vineyards planted with red grape V. vinifera cultivars such as Cabernet Franc, Cabernet Sauvignon, Malbec, Merlot, Mourvèdre, Petit Verdot, Petite Sirah, Pinot Noir, and Zinfandel.  White V. vinifera cultivars such as Chardonnay, Riesling, Semillon and Viognier are also infected but disease symptoms are unclear.  Red blotch symptoms may appear early in the season in some cultivars (e.g., Cabernet Franc and Merlot) and later in other cultivars (e.g., Cabernet Sauvignon).  Severity of red blotch symptoms may also vary from year to year. 
The most significant impact of red blotch disease is on the accumulation of total soluble solids (°Brix) which can be as much as 4 to 5 units lower than those of fruits from healthy vines of red-berried V. vinifera.  Also, affected grapevines exhibit increased acidity in fruit.  It is not established yet if red blotch disease has any effect on vigor or fruit yield. 

Causal Agent 
Red blotch symptoms do not appear to be caused by nutritional deficiencies or stress, nor by bacteria, fungi and/or nematodes.  Independent studies using rolling circle amplification and deep sequencing have found a virus, Grapevine red blotch-associated virus (GRBaV), in vines exhibiting red blotch symptoms.  GRBaV has a circular, single-stranded DNA genome and is proposed to be a member of the family Geminiviridae.  This virus was initially reported as Grapevine cabernet franc-associated virus.  It has been detected consistently in grapevines exhibiting red blotch symptoms although its definitive role in the etiology of the disease is yet to be established. 
Based on the GRBaV genome sequence information, a PCR test was developed for accurate diagnosis.  Based on PCR test results, GRBaV was shown to be present in the states of Arizona, California, Maryland, New York, North Carolina, Oregon, Pennsylvania, Texas, Virginia, and Washington, and in the province of Ontario, Canada. The distribution of the virus has been done since the summer of 2012 and its’ occurrence will likely be confirmed in many more locations in the next few years.


Disease Cycle and Epidemiology
	Grapevines of various ages (2-25 years old) can exhibit red blotch symptoms.  Disease incidence has been over 90% in several vineyards surveyed.  The primary source of inoculum appears to be the planting material and secondary spread is suspected in some vineyards although no insect vector has yet been identified.  GRBaV is graft transmissible but it is unlikely seed-borne since there is no evidence for seed transmission of any of the members of the family Geminiviridae. 

Management
	The occurrence of red blotch disease may be difficult to asse


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