Winetech Technical Yearbook 2022

Anthocyanins

Colour density

MCP

TP

2016/2017

529.5 ± 33.4 a

17.04 ± 1.39 a

2089 ± 364.05 a

61.67 ± 4.0 a

384.8 ± 41.0 b

11.34 ± 1.39 b

2000 ± 74.1 a

56.24 ± 3.67 ab

412.3 ± 4.64 b

10.60 ± 0.24 b

1598 ± 144.35 b

52.08 ± 3.0 b

552.8 ± 8.17 a

17.9 ± 0.67 a

1869 ± 115 b

64.18 ± 2.90 a

413.87 ± 68.5 b

10.59 ± 3.52 b

1168 ± 169 c

47.37 ± 5.60 b

350.6 ± 5.92 b

11.70 ± 0.51 b

2472 ± 102 a

61.35 ±1.48 a

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2017/2018

411.36 ± 9.41 a

13.29 ± 1.76 a

1398.40 ± 48.95 b

46.74 ± 1.09 a

318.46 ± 5.93 b

11.04 ± 0.60 b

1567.60 ± 52.60 a

46.04 ± 0.78 ab

305.22 ± 23.78 b

10.50 ± 0.29 b

1442.48 ± 6.52 b

43.42 ± 2.05 b

showed significantly higher concentrations in wines produced from AS wines com pared to the SV wines (table 3). Despite the extended hanging time of the SVLH treatment anthocyanin and colour density did not increase significantly, except in the case of colour density in the Cabernet Sau vignon B in 2017/2018. Methyl cellulose precipitable (MCP) tannin in wine were in some cases significantly different between treatments over the two seasons (table 3), but inconclusive results were obtained to GLD response to tannins in the wine. CONCLUSIONS From this study it is clear that there is a link between the presence and/or absence of GLD on grapevine functioning. The latter is primarily linked to the shoot length, sugar accumulation, titratable acidity and the wine ethanol (% v/v). SV had consistently lower TSS and higher TA content. The GLD impact on the wine composition was variable and dependent on the cultivar, clone, site and season. Extended hanging time resulted in an increase in the TSS and % alcohol v/v. Phenolics increased in these later harvested (SVLH) fruit, but it was not consistent over the two seasons. Additional studies are needed to identify the specific influence of clone, cultivar and site on GLD grapes and the resulting wines. REFERENCES https://www.wineland.co.za/impact-of grapevine-leafroll-disease-grape-wine compos/

516.09 ± 13.09 a

16.92 ± 0.78 a

1622.37 ± 74.29 a

55.47 ± 3.84 a

372.27 ± 21.13 b

10.43 ± 0.65 c

1169.47 ± 94.29 b

43.84 ± 2.59 b

411.56 ± 23.37 b

13.93 ± 1.28 b

1764.00 ± 138.15 a

50.44 ± 2.11 a

366.22 ± 9.66 a

14.90 ± 0.90 a

1126.87 ± 122.69 a

50.13 ± 1.82 a

301.94 ± 16.11 b

11.31 ± 0.65 b

943.02 ± 70 b

40.61 ± 3.34 b

297.13 ± 28.63 b

12.17 ± 0.71 b

1188.93 ± 22.1a2

43.48 ± 2.46 b

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using Statistica, Version 13.5 (Statsoft, Tulsa, OK, U.S.A). Significant differences were judged on a 95% significance level (p≤0.05) using Fischer’s LSD test. All stat ed uncertainty is the standard deviation of

cultivar/clone (table 2). TSS was signifi cantly impacted by the vineyard, presence of the virus and the interaction between the two parameters. Juice pH was lower in SV when compared to the AS grapevines (table 2). SV had significantly higher TA than the AS grapevines in 2016/2017. A two week-extended hanging time of the symptomatic grapevines (SVLH) fruit proved to increase berry weight (table 1). Bunch numbers from the respective treat ments were not impacted by the presence or absence of GLD (table 1). The presence of GLD resulted in lower Brix levels and extended hanging time of the fruit showed to increase the Brix in SV fruit (table 2). Wine pH and TA showed in some cases significant treatment effects in both sea sons when the wines made from AS and VS were compared (table 3). In some cases longer hanging time negated these differ ences. Alcohol content (% ethanol v/v) were significantly higher in the AS treat ments than the SV treatments (table 3). SVLH wine showed to often have a higher alcohol content when compared to the SV treatment, although these levels did not reach those found in the wines made from AS vines. Anthocyanin and colour density

three replicates of one treatment. RESULTS AND DISCUSSION

A 25%, 35% and 2.5% increase in infection was noticed in the asymptomatic grape vines in the respective Cabernet Sauvignon A, Cabernet Sauvignon B and Merlot vine yards. Overall shoot length (main shoots and lateral shoots) were negatively im pacted by the presence of GLD irrespective of the vineyard or clones (table 1). Clonal differences or environmental variation appeared to have an impact on the virus response. Stomatal conductance (g s ) was significantly higher (p≤0.001) in the SV grapevines in the Cabernet Sauvignon and Merlot vineyards (table 1). No significant differences were observed in the Cabernet Sauvignon B vineyards. Grapes from the SV treatment harvested two weeks later (SVLH) showed an increase in TSS from the commercial harvest date two weeks earlier in all the cultivars. This phenom enon was observable irrespective of the

For more information, contact Erna Blancquaert at ewitbooi@sun.ac.za.

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WINETECH TECHNICAL YEARBOOK 2022