Project title: Investigation of the impact of grapevine red blotch-associated virus (GRBaV) on
grapevine health and subsequent grape and wine composition and style (2016-1953).
Principal Investigator: Dr. Anita Oberholster
Since 2014, we have been investigating the impact of Red Blotch disease in Chardonnay, Cabernet Sauvignon and Merlot grapes with the support of American Vineyard Foundation (AVF) funding. The 2014 and 2015 season demonstrated that RB disease can impact both the basic chemical and phenolic composition of grapes and the resulting wines, which was reflected in wine sensory
properties. Due to vine removal, new Cabernet Sauvignon and Merlot vineyards in respectively
Oakville and Paso Robles were utilized in 2016 in addition to a third season at our Chardonnay
vineyard. Our findings from the 2016 season both supported previous results as well as added to
our body of knowledge. Slower sugar accumulation and higher titratable (TA) acidity were
consistent characteristics of grapes from symptomatic grapevines (RB (+)) when compared to
asymptomatic grapevines (RB (-)). The impact on phenol composition was less clear with some
differences in anthocyanin, tannin and polymeric pigment concentrations in grapes at harvest and
in the final wines depending on variety and site. In addition, wines made from RB (+) grapes
consistently had lower ethanol concentrations and mostly an increased pH compared to RB (-)
wines. In addition, we employed sequential harvesting in 2016 and processed RB (+) grapes that
was harvested at a similar Brix as RB (-) referred to as (RB (+) 2H). The resulting wines were
more similar in composition to those made from RB (-) grapes. Interestingly, this was not always
reflected in grape composition, indicating that longer hang time had an impact on extractability.
Similarities in wine composition were reflected in the sensory properties of the wines. Sensory
descriptive analysis showed that wine attributes such as ‘astringency’, ‘hot mouthfeel’, ‘color’ and ‘bitterness’ were significantly impacted when RB (+) and RB (-) wines were compared.
Descriptive analysis (DA) demonstrated that judges are able to discriminate among RB (-), RB (+) and RB (+) 2H wines although there were more similarities between RB (-) and RB (+) 2H wines when compared to RB (+) wines. This research enhanced our knowledge base regarding the impact of RB disease on grape and wine composition and quality and is needed so that informed recommendations can be made to the grape and wine industry regarding the management of RB disease in the vineyard and winery.