Impacts of Grapevine Leafroll Disease on Fruit Yield and Grape and Wine Chemistry in a Wine Grape (Vitis vinifera L.) Cultivar

Abstract

Grapevine leafroll disease (GLD) is an economically important virus disease affecting wine grapes (Vitis vinifera L.), but little is known about its effect on wine chemistry and sensory composition of wines. In this study, impacts of GLD on fruit yield, berry quality and wine chemistry and sensory features were investigated in a red wine grape cultivar planted in a commercial vineyard. Own-rooted Merlot vines showing GLD symptoms and tested positive for Grapevine leafroll-associated virus 3 and adjacent non-symptomatic vines that tested negative for the virus were compared during three consecutive seasons. Number and total weight of clusters per vine were significantly less in symptomatic relative to non-symptomatic vines. In contrast to previous studies, a time-course analysis of juice from grapes harvested at different stages of berry development from symptomatic and non-symptomatic vines indicated more prominent negative impacts of GLD on total soluble solids (TSS) and berry skin anthocyanins than in juice pH and titratable acidity. Differences in TSS between grapes of symptomatic and non-symptomatic vines were more pronounced after the onset of véraison, with significantly lower concentrations of TSS in grapes from symptomatic vines throughout berry ripening until harvest. Wines made from grapes of GLD-affected vines had significantly lower alcohol, polymeric pigments, and anthocyanins compared to corresponding wines from grapes of non-symptomatic vines. Sensory descriptive analysis of 2010 wines indicated significant differences in color, aroma and astringency between wines made from grapes harvested from GLD-affected and unaffected vines. The impacts of GLD on yield and fruit and wine quality traits were variable between the seasons, with greater impacts observed during a cooler season, suggesting the influence of host plant × environment interactions on overall impacts of the disease.

Fig 1. Symptoms of grapevine leafroll disease (GLD) in cv. Merlot.

Merlot vines with (right) and without (left) GLD symptoms. Symptomatic vines were positive for GLRaV-3 and showed less vigorous growth and lower fruit yield compared to non-symptomatic vines.

Fig 2. Impacts of grapevine leafroll disease (GLD) on fruit quality.

Time-course analyses of impacts of GLD on fruit maturity indices (total soluble solids, pH, titratable acidity and total anthocyanins) in own-rooted wine grape cv. Merlot during (A) 2009, (B) 2010 and (C) 2011 seasons. Line drawings with open circles represent samples from non-symptomatic (healthy) vines while line drawings with colored circles represent samples from symptomatic (infected) vines. Each data point represents means of five replicates per treatment. Approximate date of véraison in each season is denoted by the grey diamond. Statistical significance was determined by one-way ANOVA: (* = p ≤ 0.05; ** = p ≤ 0.001).

Fig 3. Sensory analysis of wine.

Principal component analysis (PCA) plots displaying confidence intervals for each replicate of wines produced from grapes harvested from symptomatic (infected) and non-symptomatic (healthy) vines at 95% confidence according to multivariate Hottelling test.

Fig 4. Sensory evaluation of wine.

Forced-choice triangular test conducted on triplicate wines produced from non- symptomatic (healthy) and symptomatic (infected) own-rooted cv. Merlot vines. Thirty-three panelists (17 males and 16 females) evaluated wines presented in transparent and black tulip-shaped glasses for overall differences in color, aroma and astringency attributes. Sixteen panelists are required to correctly distinguish between the wine treatments in order to achieve statistical significance (p ≤ 0.05) [34]. Actual numbers of panelists able or unable to distinguish between wines from non-symptomatic and symptomatic vines are indicated on each bar.