Winetech Technical Yearbook 2022

TABLE 3. Wine chemical analysis in the study.

Vineyard

Treatment

pH

TA

Ethanol

2016/2017

AS

3.74 ± 0.12 a

6.26 ± 0.36 b

14.93 ± 0.15 a

Cabernet Sauvignon A

SV

3.52 ± 0.04 b

7.03 ± 0.05 a

13.54 ± 0.21 b

SVLH

3.61± 0.08 b

6.71 ± 0.17 ab

13.10 ± 0.48 b

AS

3.63 ± 0.04 ab

6.8 ± 0.12 b

16.02 ± 0.20 a

Cabernet Sauvignon B

SV

3.66 ± 0.02 a

6.24 ± 0.20 c

13.00 ± 0.60 b

SVLH

3.45 ± 0.15 b

8.24 ± 0.34 a

13.97 ± 0.35 c

Cabernet Sauvignon A

*

*

**

p-value

Cabernet Sauvignon B

*

***

***

2017/2018

AS

3.56 ± 0.21

5.67 ± 0.29 b

13.78 ± 1.14

Cabernet Sauvignon A

SV

3.40 ± 0.062

6.08 ± 0.07 a

13.64 ± 0.40

SVLH

3.54 ± 0.05

6.27 ± 0.06 a

14.49 ± 0.27

AS

3.43 ± 0.01 a

5.93 ± 0.11

14.21 ± 0.24 a

Cabernet Sauvignon B

SV

3.32 ± 0.02 b

6.02 ± 0.08

12.28 ± 0.28 c

SVLH

3.42 ± 0.01 a

5.93 ± 0.02

13.45 ± 0.27 b

Merlot noir

AS

3.56 ± 0.007 a

5.34 ± 0.07 a

14.11 ± 0.04 a

SV

3.48 ± 0.03 b

5.56 ± 0.10 b

12.78 ± 0.21 c

SVLH

3.51 ± 0.03 ab

5.46 ± 0.07 ab

13.35 ± 0.41 b

Cabernet Sauvignon A

ns

**

ns

p-value

Cabernet Sauvignon B

***

ns

***

Merlot noir

*

*

**

ANOVA was used to compare data. Asymptomatic vine – AV; Symptomatic vines – SV; and Symptomatic vine late harvest – SVLH. Mean followed by significant letters in a row are significant at p<0.05 (Fischers LSD). The standard deviation of three replicates per treatment was determined. Significance of one-way ANOVA for virus presence. Significance (*, ** and *** indicate significance at p≤0.05, 0.01 and 0.001 respectively; ns: not significant).

MATERIALS AND METHODS The study was conducted during the 2016/2017 and 2017/2018 growing seasons in two commercial Cabernet Sauvignon vineyards (hereinafter Cabernet Sauvignon A – clone CS 12/R110 and Cabernet Sauvignon B – clone CS 45/101 14 Mgt) with a north-south and east-west row orientation in the Stellenbosch wine region. In 2017/2018 a commercial Merlot noir vineyard (clone MO343/R99) in the Constantia wine region was also evaluated. Vineyards were visually evaluated for typical GLD symptoms. Thirty symptomatic (SV) and 30 non-symptomatic (AS) grapevines were selected in each vineyard. An additional 30 symptomatic vines were selected which were harvested two weeks later than the commercial harvest date (SVLH). The 2016/2017 season was aimed at identifying SV- and AS-infected grapevines in commercial vineyards through virus di agnosis. Grape berries were sampled at the commercial harvest date and subjected to

result in the downward rolling leaves and become brittle. 8 Red cultivars express red spotting which turn red purple colour and a green vein-banding symptom and inter veinal yellowing of leaves and leafrolling in white cultivars. 2,8 Previous studies on GLD in red grape varieties reported significant losses in both yield and fruit quality. 9-13 The wine proper ties were also impacted by the presence of GLD. Wines made from non-symptomatic vines were perceived as being more purple in colour, with less brown and with a more saturated colour. 11 The aim of this study was to: (i) evaluate the occurrence of GLD and non-GLD-infected grapevines in commercial vineyards, (ii) monitor GLD infection rate in a commercial vineyard over a two season period, (iii) grapevine physiological responses to GLD, and (iv) evaluate the impact of fruit and wine chemistry.

classical analysis, total soluble solids (TSS), pH and titratable acidity (TA). The bunch number and bunch weights were record ed. Wines were made from the harvested grapes according to the experimental cellar protocol from the Department of Viticulture and Oenology, Stellenbosch University. In 2017/2018 the same grapevines which were used in 2016/2017 were sub jected to virus diagnosis to ensure that the AS were not infected during the course of the season. Destructive shoot mea surements were performed at pea-size. Stomatal conductance was recorded and grape ripening was monitored throughout the season from véraison until commercial harvest and post commercial harvest for the SVLH treatment. The same harvesting and winemaking protocols followed in 2016/2017 were repeated 2017/2018. STATISTICAL ANALYSIS One-way and two-way analyses of vari ance (ANOVA) were performed on the grape chemical and wine chemical data

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WINETECH TECHNICAL YEARBOOK 2022