WINETECH Technical Yearbook 2020

CONTENTS

1. VITICULTURE _______________________ 6 Grapevine rupestris stem pitting- associated virus ________________________ 7 With a pinch of salt …__________________ 10 Poor detection of grapevine leafroll- associated virus type 3 in rootstocks _____ 12 Responding to climate change __________ 16 Climate change in the viticulture sectors: Overview of long-term climate trends in the Western Cape (Part 1) ____________ 18 Using thermal satellite land surface temperature to supplement weather station temperatures in the Western Cape (Part 2) __________________________ 22 Seasonal weather variation within local mesoclimates explained using high resolution climate data (Part 3) __________ 25 Impact of local site and inter-seasonal weather variability on grapevine responses (Part 4)______________________ 30 The integration of multiple view points for adaptation/mitigation strategies in the context of warmer and drier future (Part 5) _______________________________ 34

Ring nematode in grapevine – a major problem for producers and researchers_ __ 38 Katydid ecology in vineyards_____________ 41 Feedback from the 11th International Workshop on Grapevine Trunk Diseases_ _____________________________ 44 Incidence and spread of aster yellows_____ 49 Indigenous leafhopper transmits aster yellows___________________________ 52 Grape flavan-3-ol evolution under altered light and temperature conditions in Cabernet Sauvignon (Part 1)_____________ 54 Grape flavan-3-ol composition under altered light and temperature conditions in Cabernet Sauvignon (Part 2)_____________ 60 Grape flavan-3-ol and anthocyanin composition under altered light and temperature conditions in Cabernet Sauvignon (Part 3)______________________ 65 Grape flavan-3-ol evolution (Part 4): Effect of sequential harvesting on the sensory properties of the wines_ _________ 70 Eutypa-like fungi associated with grapevine cankers and dieback_ _________ 74

WINETECH TECHNICAL YEARBOOK 2020 2

2. OENOLOGY_ _______________________ 77 Wine sensory benchmarking (Part 1): Why, when and how_ ___________________ 78 Wine sensory benchmarking (Part 2): _____ 80 Thiols in red wine (Part 1): Background and relevance_ _____________ 83 Thiols in red wine (Part 2): Individual thiols and levels_______________ 86 Thiols in red wine (Part 3): Thiols interaction in a Pinotage base wine_ __ 89 Thiols in red wine (Part 4): The matrix_____ 91 Volatile sulphur compounds_ ____________ 93 Manipulation of Shiraz flavour____________ 96 Wine consumers are creatures of brand habits___________________________ 99 consumers’ wine selection behaviour_ ___ 102 Yeast and its ability to release thiols_ ____ 105 Lachancea thermotolerans yeast and its role in winemaking__________________ 108 Torulaspora delbrueckii and its role in winemaking_ _______________________ 111 Metschnikowia pulcherrima yeast and its role in winemaking__________________ 113 Schizosaccharomyces pombe yeast and its role in winemaking__________________ 117 Which wine and wh(Y)? Industry perspectives on Generation Y

The conversion of sugar to alcohol_ _____ 160 The management of phenols in the vineyard and cellar_ ___________________ 162 Decreasing the cooling cost of cellars____ 164 The chemical composition of stainless steel_________________________________ 166 The phenolic compounds of white wines_ 168 The sanitation of Brett-infected barrels___ 170 Bentonite alternatives__________________ 172 The sustainability of French oak_ ________ 174 The impact of sulphur dioxide additions at crush on wine yeasts, bacteria and sensory attributes_ ____________________ 176 Winetech vine and wine innovation watch: KPA for the tartrate stabilisation of wines______________________________ 178 Winetech vine and wine innovation watch: Magnetic nanoparticles for the protein stabilisation of wines____________ 180 5. GENERAL_ ________________________ 182 Why calculate your carbon footprint? The value of knowing your carbon emissions in a global context_ __________ 183 Benchmark Report 2020 – South African Wine Grapes_____________ 186

Pichia kluyveri yeast and its role in winemaking_ _________________________ 119 The utilisation of nitrogenous compounds by commercial non- Saccharomyces yeasts________________________________ 121 New developments in protein stability_ __ 123 3. IN THE VINEYARD_ ________________ 125 Pinotage ripening – an overview_ _______ 126 Highlights of the 2019 Gen-Z cover crop demos___________________________ 129 Trellis systems in Worcester and Breedekloof_ _________________________ 137 Raise your goblet______________________ 140

Winetech vine and wine innovation watch: Fighting vineyard pathogens

with UV light__________________________ 143 Aster yellows_ ________________________ 145

4. IN THE CELLAR____________________ 148 Exploring PET and BIB as possible alternative packaging for Sauvignon blanc_ _______________________________ 149 Fine tuning flotation with potato protein___ 152 The latest developments in grape sorting technology_ ___________________ 156 Fructophilic yeasts and yeast strain choice_ _ 158

IMAGES COPYRIGHT: INDIVIDUAL AUTHORS, FLICKR, PIXABAY, SHUTTERSTOCK, UNSPLASH OR WOSA LIBRARY. DTP LAYOUT: AVANT GARDE SOUTH AFRICA.

WINETECH TECHNICAL YEARBOOK 2020 3

AUTHORS

ALANA SEABROOK: Laffort ALBERT STREVER: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch ANEL BLIGNAUT: Blue North Sustainability (Pty) Ltd, Stellenbosch

EMMA CARKEEK: Vinpro, Paarl ERNA BLANCQUAERT: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch ETTIENE TERBLANCHE: Vinpro, Paarl EVODIA SETATI: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch FRANCOIS HALLEEN: ARC Infruitec-Nietvoorbij, Stellenbosch GERHARD PIETERSEN: Department of Genetics, Stellenbosch University, Stellenbosch GERT ENGELBRECHT: Vinpro, Olifants River GONZALO GARRIDO-BANUELOS: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch HANNO VAN SCHALKWYK: Vinpro, Paarl HEINRICH DU PLESSIS: ARC Infruitec-Nietvoorbij, Stellenbosch HÉLÈNE NIEUWOUDT: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch ISAAC RIGAU: Laffort JEANNE BRAND: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch

JUSTIN HOFF: ARC Infruitec-Nietvoorbij, Stellenbosch KARIEN O’KENNEDY: Winetech, Paarl KERRY SAYWOOD: Blue North Sustainability (Pty) Ltd, Stellenbosch KERSTIN KRÜGER: University of Pretoria, Pretoria LEANIE LOUW: SenseLab, Oude Molen Building, Distillery Road, Stellenbosch LIZEL MOSTERT: Department of Plant Pathology, MARCE DOUBELL: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch MARET DU TOIT: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch MARIETA VAN DER RIJST: ARC Biometry, Stellenbosch MEGAN HARRIS: FABI, Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria NADIA VAN DER COLFF: Consumer Solutions, Stellenbosch Stellenbosch University, Stellenbosch LUCINDA HEYNS: Winetech, Paarl

NEIL JOLLY: ARC Infruitec-Nietvoorbij, Stellenbosch

PIA ADDISON: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch

PIERRE SNYMAN: Vinpro, Worcester

ANTOINETTE MALAN: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch

PROVIDENCE MOYO: Department of Plant Pathology, Stellenbosch University, Stellenbosch

ASTRID BUICA: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch CARIEN COETZEE: Basic Wine, Stellenbosch CHARL THERON: Private consultant CHRIS PENTZ: Department of Business Management, Stellenbosch University, Stellenbosch CLAUDIA GEVERS: Department of Viticulture and Oenology, Stellenbosch University CORINNA BAZELET: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch DARIUSZ GOSZCZYNSKI: Plant Health and Protection, Agricultural Research Council, Pretoria ELLEUNORAH ALLSOPP: ARC Infruitec- Nietvoorbij, Stellenbosch

ROLEEN CARSTENS: SAPO, Stellenbosch

SEBASTIAN VANNEVEL: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch

SHEILA STOREY: Nemlab, Klapmuts

SUSAN ERASMUS: Laffort

TARA SOUTHEY: Centre for Geographical Analysis, Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch VALERIA PANZERI: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch WESSEL DU TOIT: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch

WINETECH TECHNICAL YEARBOOK 2020 4

FOREWORD The year 2020 will forever be imprinted in the minds of people all over the world. The Covid-19 pandemic has left its seen and unseen marks on everyone. Some businesses prospered, but most suffered losses. The South African wine industry unfortunately falls in the latter category. It was all about adapting, changing, and rearranging business as usual. At Wine- tech, we also needed to change our ways of managing our day-to-day business, which included our knowledge transfer initiatives. Whilst various in-person events had to move to online, or to not at all, the Winetech Technical section published in WineLand Magazine could fortunately continue as always (albeit with a slightly trimmed budget). This yearbook com- bines all the technical articles published in WineLand during 2020 in an easy to navigate e-book. We hope that the knowl- edge provided in this book will assist the South African wine industry, even if just in a small way, to move forward and to re- cover from these crazy times. Kind regards The Winetech Team

WINETECH TECHNICAL YEARBOOK 2020 5

WINETECH TECHNICAL YEARBOOK 2020 6 Viticulture

1

Grapevine rupestris stem pitting-associated virus (GRSPaV) is the most prevalent virus in vineyards and well characterised molecularly, but still relatively unknown. Vast amounts of virus genome sequence data were accumulated recently for viruses infecting grapevines and this trend continues. The reason for this rapid accumulation of data is that the molecular analysis of virus populations in plants DARIUSZ GOSZCZYNSKI: Plant Health and Protection, Agricultural Research Council, Pretoria KEYWORDS: Grapevine rupestris stem pitting-associated virus, GRSPaV Grapevine rupestris stem pitting- associated virus JANUARY/FEBRUARY 2020

PHOTO 1. Severe RSPD symptoms in Vitis rupestris cv. St. George. GRSPaV status is unknown. (Courtesy of Tobie Oosthuizen, Vititec.)

differs between various countries: Very high (90.4%) of tested grapevines in Australia, relatively very low in countries like South Africa (14.4%), or, as in Iran, the virus is not present at all (Habili, 2015). However, these rather surprising data need careful investigation. As no insect vector was identified, it is believed that the wide presence of the virus in V. vinifera vineyards is the result of the worldwide exchange of GRSPaV-infected grapevines and transmission of this virus by grafting. All tested Iranian samples were collected from native grape cultivars that were growing from their own roots. The very

disappointed. The industry needs solid information on how harmful these viruses are to grapevines. Sometimes this information is lacking and is difficult to obtain. The classical example is grapevine rupestris stem pitting-associated virus (GRSPaV). The discovery of the virus was reported in 1998 (Meng & Rowhani, 2017). Soon investigations revealed that GRSPaV is the most widely spread virus in Vitis vinifera vineyards worldwide. Recorded infections amount to 100% of tested grapevines (Xiao et al ., 2018). Data from Waite Diagnostics, Australia, suggest that the incidence of the virus

is relatively easy. It is just a matter of purifying nucleic acids, amplifying the genome of viruses, sequencing and computer-assisted analysis of obtained sequences. This has led to the development of molecular methods, such as High- Throughput Sequencing (HTS), that precisely evaluate the virus status of investigated grapevines. Although this is a great achievement from a scientific perspective, the application of these techniques, and revealing that virus infections of grapevines are common in vineyards, cause the average grapevine farmer to become confused and somewhat

WINETECH TECHNICAL YEARBOOK 2020 7

high percentage of GRSPaV infections in vineyards is confusing the grapevine industry. If the GRSPaV infections are common, the intriguing question is, what is the pathogenicity of this virus to grapevines? Should the industry be concerned about this virus? GRSPaV is regarded as being associated with rupestris stem pitting disease (RSPD), which is one of the rugose wood complex diseases (RWD) of grapevines (Meng & Rowhani, 2017). When tissue of a grapevine infected with GRSPaV is grafted to Vitis rupestris cv. St. George plant, symptoms of modified wood (pitting), like that shown in Figure 1, may appear on the woody cylinder of this grapevine. The problem is that the modification of wood is clearly visible only in grapevine V. rupestris cv. St. George, which is especially sensitive to RSPD and is used as an indicator of this disease. In other grapevines GRSPaV infections are latent. So what does this mean? Does it mean that the virus does not induce any pathogenic effect in grapevines of these cultivars, but co-exist in peaceful relation with these plants? There are only two papers in which authors address this important question. An Italian laboratory reports that GRSPaV infection triggers various physiological changes in V. vinifera , but it seems these changes would have no negative influence on the productivity of a vineyard (Gambino et al .,

2012). The authors suggest that GRSPaV evolved to peacefully co-exist in grapevines. Similar conclusion regarding influence of GRSPaV on grapevine productivity has been reported from Canada (Reynolds et al ., 1997). However, in both studies little or no attention is given to a detailed characterisation of population of genetic variants of GRSPaV infecting grapevines used in the study. It is well known that not all GRSPaV-infected grapevines grafted to St. George induce RSPD symptoms in this indicator (Meng & Rowhani, 2017). It is believed that the lack of inducing RSPD symptoms in some cases is because of the presence of mild or not pathogenic strains of GRSPaV. Presently eight groups of genetically divergent variants of GRSPaV have been identified (Meng & Rowhani, 2017). The groups are named as GRSPaV-1, -ML, -JF, -PN, -SY, -BS, -SG1 and -SLS. Clear divergence of genome sequences and encoded proteins between members of different groups of GRSPaV suggest that these are different biological strains of this virus, with different pathogenicity to the grapevine host. And this may be true. The laboratory led by Dr. Meng, soon after the discovery of GRSPaV, also discovered that the St. George they used as an indicator of RSPD was already infected with GRSPaV (Meng & Rowhani, 2017). Later they determined that this was a genetic variant GRSPaV-

industries. These grapevines have precise data from RT-PCR testing and woody indexing, and would be excellent for the study. Of special value is the biological data. Genetic heterogeneity of GRSPaV population present in these grapevines could be determined in just a few weeks. Regarding the second option, although the construction of the cDNA clone of GRSPaV is a relatively easy and quick way to obtain a pure culture of any genetic variant of GRSPaV, knowledge of precise events occurring during infection of grapevines by viruses is, in general, still insufficient. To induce the disease, the virus has to successfully infect grapevine cells, increase its titer and systemically spread in a plant. The construction of the cDNA clone of GRSPaV was reported six years ago, in 2013 (Meng & Rowhani, 2017). Although it was shown that the clone is infectious to grapevines, the virus was hardly detectable in successfully infected plants. We are still awaiting the report that the GRSPaV originating from such infection is increasing its titer and spreading in grapevine. It may merely be a matter of time since for woody plants, unlike herbaceous hosts, it takes months or years to develop virus infections. Of concern, however, is the fact that the clone is a DNA copy of genetic variant GRSPaV- GG closely related to -SG1 variant, which is putative not pathogenic to grapevines (Meng & Rowhani, 2017). Presently a

SG1, classified as being not pathogenic to grapevines. Surprisingly, this is the only solid information on pathogenicity of GRSPaV. There is no data on putative severe genetic variants of GRSPaV. In addition, somewhat also surprising is that 22 years after the discovery of GRSPaV, and numerous statements that this virus is associated with RSPD, very little is known about populations of GRSPaV variants inducing clear, severe RSPD symptoms in St. George indicator. Such data, generated in different laboratories, could point to putative severe strains of GRSPaV, which are urgently needed for progress to be made in the study of pathogenicity of this virus in grapevines. Basically, there are two ways to investigate GRSPaV pathogenicity in controlled laboratory conditions: 1. Using various natural single infection of grapevines with GRSPaV; or 2. produce cDNA clone of this ssRNA virus and infect virus-free grapevines using the clone. Regarding the first option, finding a grapevine infected only with GRSPaV in vineyards may be a serious challenge. However, as the virus is relatively very difficult to eliminate from grapevines, the author believes that single GRSPaV infections can be quickly found in collections of nucleus material of grapevine

WINETECH TECHNICAL YEARBOOK 2020 8

Xiao, H., Shabanian, M., Moore, C., Li, C. & Meng, B., 2018. Survey for major viruses in commercial Vitis vinifera wine grapes in Ontario. Virology Journal 15, 127. Habili, N., 2015. Failure to detect grapevine rupestris stem pitting-associated virus in Iran may give a clue to the origin of this virus. Proceedings of the 18th Congress of ICVG, Ankara, Turkey, 7-11 September 2015, pp. 93-94. Gambino, G., Cuozzo, D., Fasoli, M., Pagli- arani, C., Vitali, M., Boccacci, P., Pezzotti, M. & Mannini, F., 2012. Co-evolution be- tween grapevine rupestris stem pitting-as- sociated virus and Vitis vinifera L. leads to decreased defence responses and increased

cDNA clone of another variant, related to GRSPaV-SY, was constructed in the same laboratory. But again, due to insufficient information on the genetic structure of populations of GRSPaV, mentioned earlier in this article, we do not know if the chosen variant is the most likely to be inducing RSPD in St. George. SUMMARY Grapevine rupestris stem pitting-associated virus (GRSPaV) is the most prevalent virus in vineyards worldwide. Recorded infections of GRSPaV amount to 100% of tested grapevines. Despite that the virus is well known molecularly, we still do not know much about its pathogenicity to grapevines. It is commonly believed that GRSPaV is

transcription of genes related to photosyn- thesis. Journal of Experimental Botany 63, 5919-5933. Reynolds, A.G., Lanterman, W.S. &Wardle, D.A., 1997. Yield and berry composition of five vitis cultivars as affected by rupestris stem-pitting virus. American Journal of Enology and Viticulture 48, 449-458.

a latent pathogen. However, do we really have enough data on putative severe strains of the virus that allow us to make such a statement? The author believes strongly that the industry should invest in further study of this still mysterious virus. ACKNOWLEDGEMENT The author thanks Winetech, South Africa for the financial support. REFERENCES Meng, B. & Rowhani, A., 2017. Grapevine rupestris stem pitting-associated virus. In: Grapevine viruses: Molecular biology, diagnostics and management. Meng, B., Martelli, G.P., Golino, D.E. & Fuchs, M. (eds). Springer, Cham., pp. 257-287.

For more information, contact Dariusz Goszczynski at GoszczynskiD@arc.agric.za.

WINETECH TECHNICAL YEARBOOK 2020 9

With a pinch of salt…

OBJECTIVES AND RATIONALE The main questions were related to the primary origin of the salinity/sodicity, cation and anion concentrations occurring in the grapevine, the cation and anion content of the grape juice and wine, the different cation and anion measurement techniques locally and overseas, as well as the practices implemented for the management of salinity/sodicity. In addition to this, anecdotal evidence suggested that some wines with higher mineral contents may also have positive style attributes. The potential sensory impact of salts in wine therefore had to be considered. TABLE 1. Tank samples of some wines exhibiting high sodium and chloride levels (mg/L). Cl Na 13/701 49.6 43.54 13/702 53.2 39.35 13/703 46.1 50.03 13/704 58.5 86.00 13/705 90.4 152.81 13/706 129 227.54 13/707 42.5 58.05 13/708 489 324.24 13/709 128 142.39 13/710 347 262.83

through persistent droughts. Cation and anion analysis in the leaves, petioles and grape components is essential for the prevention of the negative effects it may have on grapevine physiology, the grape juice and also the wines made from it. The OIV resolution (Oeno 6/91) with regard to sodium states that: “When wine contains excess sodium (excess sodium is equal to the content of sodium ions less the content of chloride ions expressed as sodium), it is generally less than 60 mg/L, a limit which may be exceeded in exceptional cases…”. As a result of these restrictions, some wines may even be rejected from the export market. High concentrations NaCl also have an effect on the sensorial quality of wine, and may as a result be described as flat, dull, soap, seawater-like and saline. Some local wine tank samples were found to exceed the stated OIV limit, as well as the local beverage limit, of 100 mg/L significantly in some cases (see table 1). Australia already in 1997 published an article (Leske et al. , 1997) to create awareness of sodium levels in Australian wines. In Australia, for example, the sodium content may not exceed 1 000 mg/L in wine, as the country has a high occurrence of saline and sodic soils. It seems that some regulators do not even consider chloride levels as recommended in the OIV legislation, which makes a huge difference in interpretation.

APRIL 2020

ALBERT STREVER: Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KEYWORDS: Salt, cations, anions, wine, grapevines

and 10. Grapevines should grow normally at values below 2.5 dS/m, resistance over 300 Ohm, and at soil pH levels between 5 and 7.5. Grapevines are known to be moderately sensitive to salinity, but salinity and sodicity can have an adverse effect on plant growth, whether directly or indirectly. These conditions also affect the grapevine’s physiological responses, causing yield reduction, decrease in shoot growth and increase in cation and anion concentrations in the fruit and final wine. It may also affect the biochemical pathways, leading to toxicities, deficiencies and mineral imbalances in the plant. The most important cations associated with salinity are Na + , Ca 2+ and Mg 2+ , whereas the most important anions are Cl - , SO 4 2- and HCO 3 . They may occur naturally in the soil, but more commonly are added to the soil through irrigation, also exacerbated

Although salinity or sodicity may be localised to certain production areas, the study aimed to provide insight into the potential impact of cations and anions in wine and its origins, from a positive, as well as potentially negative perspective. INTRODUCTION Soil salinity and sodicity occurs mostly in arid and semi-arid environments. Saline soils have high concentrations of soluble salts (e.g. NaCl) in the soil solum/regolith with electrical conductivity values of over 4 dS/m and resistance of less than 300 Ohm, an exchangeable sodium percentage of lower than 15 and pH lower than 8,5. Sodic soils in turn have a high concentration of sodium ions compared to other cations, with electrical conductivity values of lower than 4 dS/m, sodium adsorption ratio of over 13, an exchangeable sodium percentage of over 15 and pH between 8,5

WINETECH TECHNICAL YEARBOOK 2020 10

MATERIALS AND METHODS Areas with soil salinity and sodicity were selected in Chenin blanc and Pinotage vineyards from two farms in an arid area of the Western Cape with hot and dry summers. The plots, of which one was rain- fed and one irrigated, were divided into ‘high’ and ‘low vigour’ according to salinity and sodicity levels and aerial imagery. Soil analysis was conducted at three depths to confirm the presence of high cation and anion concentrations. Meso-climate loggers were installed on both farms in order to analyse the climatic effects on the grapevine. Vegetative and reproductive measurements were conducted including trunk circumference measurements, shoot measurements, destructive leaf area measurements, berry sampling and harvest measurements. The cation and anion concentrations in the soil, different grapevine parts (leaves, petioles and canes), grape berry parts (juice, homogenised grapes, skins and the sediment after juice settling), and in the subsequent wines were also assessed and the sensory profile of the wines were determined. RESULTS AND DISCUSSION Soil samples confirmed the presence of salinity/sodicity in the plots, which affected the growth (as measured through shoot

juice sediment, stressing the importance of judicious skin contact. Wines made from high cation content juice did not always show high levels of cations and anions, warranting further investigation. Sensory analysis showed that at certain concentrations sensory factors could be affected positively or negatively by high salt content in wine. Analysis methods differed between laboratories, and there is a need for standardisation of methods and calibration between the labs. REFERENCES Leske, P.A., Sas, A.N., Coulter, A.D., Stockley, C.S. & Lee, T.H., 1997. The composition of Australian grape juice: Chloride, sodium and sulphate ions. Australian Journal of Grape and Wine Research 3, 26-30. Muller, K., 2017. Grapevine cation and anion transfer: A perspective from the soil to wine chemical and sensory properties. MSc(Agric) Thesis, Stellenbosch University, March 2017.

levels of cations and anions, which needs further investigation. Sensory analysis has indicated that, at certain concentrations, sensory factors could be affected positively or negatively, however, this was dependent on the concentrations of the cations and anions. Considering that we found different interpretations in accepted limits, as well as considerable differences in analysis results between laboratories on the same samples, we recommend clear guidelines to be set for accepted limits, as well as analysis methods. SUMMARY Wines wi th high cat ion and anion concentrations can be found in many wine grape-growing regions across the world, and this have also been reported for some South African wines, originating from grapes grown on soils with high levels of salinity or sodicity. Questions arose concerning the origin of the salinity/ sodicity, cation and anion concentrations occurring in the grapevine, as well as the grape juice and wine, different measu­ rement techniques, as well as the practices implemented for the management of salt content in wines. The sensory impact was also investigated. The study confirmed ion transfer from soil to vine to grape and into the wine, and showed high concentrations of certain cations in the

growth, trunk circumference and leaf area), as well as yield per vine. Shoot, petiole and leaf analysis showed high levels of sodium, reaching values greater than 1 500 mg/L. The juice cation and anion analysis showed high levels of sodium for some plots, however, chloride levels were found to be below harmful limits. There were differences between juice, sediment, skin and homogenised sample analysis, confirming that the sediment contained the highest cation and anion content. Some marked differences were reported between analyses of the different laboratories. Descriptive sensory analysis showed no significant differences in terms of saltiness, however, some wines exhibited significant differences between aroma and taste descriptors. The high salt content in the wine may also have had a positive effect on the taste of the wine. At low salt concentrations wines may appear to be sweeter, or less bitter. CONCLUSIONS The study confirmed ion transfer from soil to vine to grape and into the wine, and also showed how high concentrations of certain cations can exist in the juice sediment. This could affect wines that undergo skin/lees contact for long periods of time. The wines made from the high cation content juice surprisingly had lower

For more details on this project, please refer to Muller (2017) and for more information, contact Albert Strever at aestr@sun.ac.za.

WINETECH TECHNICAL YEARBOOK 2020 11

Poor detection of grapevine leafroll-associated virus type 3 in rootstocks

Adding complexity to certification schemes, scions of V. vinifera are grafted (Photo 4) onto a number of American Vitis species rootstocks in countries, such as South Africa, where phylloxera ( Daktulosphaira vitifoliae ) occurs. This is required as V. vinifera vines on their own roots are attacked by this aphid-like insect. Many rootstocks are asymptomatic hosts of GLD (photo 5) and require virus spe- cific laboratory-based detection methods to test for virus infection. The reliability of detection of GLRaV-3 in rootstocks in certification schemes by PCR has, however, not been fully assessed anywhere. In this study, we assessed the detection by the very sensitive laboratory technique, reverse-transcriptase polymerase chain react ion (RT-PCR) of GLRaV-3 in individual vines of the most widely utilised rootstocks in South Africa compared with their corresponding scions (photo 6). Most of the initial work was done on Richter 99 ( Vitis berlandieri X Vitis rupestris) and most of the information presented here refers to this rootstock. We also compare the variants of GLRaV-3 found in both Richter 99 rootstocks and scions of selected individual vines and we determine the presence of other leafroll-associated viruses in Richter 99.

A number of viruses have been reported from vines with grapevine leafroll disease (GLD) and are known as grapevine leafroll-associated viruses. Amongst these, grapevine leafroll-associated virus 3 (GLRaV-3) appears to be the most prevalent and widespread virus and this certainly is the case in South Africa. Commercial grapes are primarily cultivars of Vitis vinifera , V. labrusca , Muscadinia rotundifolia , V. amurensis and several interspecific hybrids. Worldwide, grape­ vines are prone to various virus diseases of which GLD is the most common and widespread (photo 1). It is economically important as it reduces plant vigour and longevity, fruit yield and quality. GLD can be successfully controlled using an integrated control strategy which includes producing and planting certified, virus- tested propagation material, vector number and dispersal management, and roguing of infected vines. Detection of GLD for these purposes is easily achieved in a number of red cultivars where symptoms of GLD are obvious in autumn and infected plants easily identified (photo 2). This is more difficult in white cultivars, where symptoms are not obvious (photo 3) and where laboratory- based virus detection techniques have to be employed to detect the viruses associated with the disease.

APRIL 2020

GERHARD PIETERSEN 2 & MEGAN HARRIS 1 : 1, FABI, Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria; 2 Department of Genetics, University of Stellenbosch, Stellenbosch KEYWORDS: Grapevine leafroll virus (GLD) detection, reverse- transcriptase polymerase chain reaction (RT-PCR)

WINETECH TECHNICAL YEARBOOK 2020 12

PHOTO 2. Obvious symptoms of leafroll disease in a number of red cultivars of Vitis vinifera (Merlot, Cabernet Sauvignon, Shiraz and Pinotage), in this case autumn 2017, on Vergelegen in a vineyard where infected vines are rogued annually.

PHOTO 1. Prevalence of grapevine leafroll disease in many vineyards in South Africa and inter- nationally.

Samples were processed by removing the outer bark and preparing phloem shavings separately of the scion and rootstock mate- rial of each vine and then extracting RNA from these. RT-PCR was then performed separately on the scion and rootstock. Clear

usually pruned in practice, such plants were relatively rare, but 69 such vines with Richter 99 rootstocks were collected over three seasons. In this regard, we were fortunate to have had access to an abandoned vineyard (photo 8).

and Stellenbosch during 2014, 2015 and 2016. Specimens were selected based on the occurrence of clear GLD symptoms on the scions. Only vines with sizeable lignified Richter 99 canes were selected for sampling. As rootstock suckers are

Cane material was collected separately (photo 7) from both the scion and rootstock individual vines grafted on Richter 99 ( Vitis berlandieri X Vitis rupestris). These were from two commercial wine estates and two trial sites in Wellington

WINETECH TECHNICAL YEARBOOK 2020 13

PHOTO 7. Collect lignified cane material sep- arately from the scion and rootstock of lea- froll-infected vines, perform RNA extraction on the phloem tissue and test for GLRaV-3 by RT-PCR separately in both components.

PHOTO 3. Grapevine leafroll disease is diffi- cult to detect in white cultivars. In the picture above, Chardonnay, which is one of the white cultivars that shows the disease best, displays the symptoms which gave grapevine leafroll disease its name.

PHOTO 6. Vines were selected where the sci- on (red cultivars) displayed clear symptoms of grapevine leafroll disease, but where vigorous, lignified Richter 99 rootstocks were present.

PHOTO 4. Grafting of the Vitis vinifera sci- on onto a rootstock via omega grafting, as a means of managing the effect of phylloxera.

PHOTO 8. An abandoned vineyard where the Richter 99 rootstock had not been removed over a number of seasons.

PHOTO 5. Rootstocks do not show symptoms of grapevine leafroll disease.

WINETECH TECHNICAL YEARBOOK 2020 14

It remains unknown whether: 1) GLRaV-3 is generally present in Richter 99 when the scion is infected, but at titers sub-detect- able to the detection methods employed, 2) GLRaV-3 has an uneven distribution in Richter 99 resulting in poor detection, 3) if GLRaV-3 has variants or genome components selected for in the Richter 99 rootstock which are less efficiently detected by PCR, or 4) the V. berlandieri X V. rupes- tris interspecific hybrid produces inhibitors to the PCR reaction. Also, it is not known in instances where GLRaV-3 is at detect- able levels, whether it is a) either due to “resistance breaking” variants capable of partially overcoming the Richter 99 de- fence mechanisms, or b) genetic variation amongst various clones Richter 99, some of which may allow replication of GLRaV-3. Any of these possibilities or combinations of them may account for the differences in GLRaV-3 status observed amongst sci- on and Richter 99 rootstocks and further studies to assess these possibilities need to be conducted.

differences in GLRaV-3 infection status were observed between the Vitis vinifera scion and the V. berlandieri X V. rupestris Richter 99 rootstocks of individual leafroll disease-infected vines (figure 1). The scion material of all 69 vines analysed contained GLRaV-3. GLRaV-3 could not be detected by RT-PCR in 66% of Richter 99 rootstocks from these, despite the fact that the cor- responding scions were positive for GL- RaV-3, displayed obvious GLD symptoms, and were a constant source of GLRaV-3 inoculum to the rootstock. Of the 23 Richter 99 samples that did contain GLRaV-3, only five yielded levels of amplicons in end-point PCR reactions comparable to that of the scions, while the remainder all yielded considerably less, yielding only very faint bands in agarose electrophoresis gels. Using next generation sequencing, we found only minor differences in the GL - RaV-3 variant composition of Richter 99 and corresponding scions in those instanc- es where GLRaV-3 was found in the root- stock. We also demonstrated that Richter 99 can also be infected with GLRaV-1, GL- RaV-2, grapevine virus A (GVA), grapevine virus B (GVB) and grapevine rupestris stem pitting-associated virus (GRSPaV).

For more information, contact Gerhard Pietersen at gpietersen@sun.ac.za.

FIGURE 1. Results of a RT-PCR reaction for GLRaV-3 on electrophoresis gel. The presence of the white bands above is clear in the scion of any vine, but not in its corresponding Richter 99 rootstock (each red rectangle represents a single vine).

WINETECH TECHNICAL YEARBOOK 2020 15

Climate change, increased seasonal varia­ bility and limitation of available water resources, have increased pressure on the production of table wines, and could continue without effective adaptive strategies. The question is how exactly is climate in the Western Cape changing, how do grape­ vines respond and how can producers adapt? To shed light on these questions, Winetech funded a PhD study by Dr Tara Southey which integrated remote sensing, climate and grapevine responses over six localities and four years. The study included extreme climatic conditions by selecting sites over a climatic band, and multiple factor analysis was used to evaluate the interaction of climate with grapevine expression to isolate possible driving factors that can be used in future climatic modelling. Results from the study indicated that the grapevine is responding to climate change through altered phenology, growth and ripening responses. Despite differences on vineyard and site level, the grapevine’s performance is affected by environmental parameters. Integrating these multiple environmental factors into site selection models in the near future for the Western Cape study area, would allow for informed decision making regarding site suitability within the context of climate change.

Responding to climate change

MARCH 2020

TARA SOUTHEY: Centre for Geographical Analysis, Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch KEYWORDS: Climate change, Terraclim

WINETECH TECHNICAL YEARBOOK 2020 16

TERRACLIM This PhD study was undertaken to integrate remote sensing, climate and phenological data. The results highlighted the reality of climate change and that grapevines respond to a changing climate. Another outcome of the project was the realisation that access to climate data is extremely limited. Based on this, Winetech commissioned a survey among industry members to identify what they need to aid decision making in the context of climate change. The feedback from the industry was that having a user-friendly platform where climate data and GIS information can be integrated, would be of immense value to aid short and long-term decision making and to help producers adapt to climate change. This led to the development of the TerraClim platform. For more information about Terraclim, visit www.terraclim.co.za or you can also watch this video: https://www.youtube.com/watch?v=RMeqGnLeIzM&t=4s.

Keep an eye out for this icon to follow this article series.

PART 1: CLIMATE CHANGE IN THE VITICULTURE SECTORS: OVERVIEW OF LONG TERM CLIMATE TRENDS IN THE WESTERN CAPE

PART 5: THE INTEGRATION OF

PART 2: USING THERMAL SATELLITE LAND SURFACE TEMPERATURE TO SUPPLEMENT WEATHER STATION TEMPERATURES IN THE WESTERN CAPE

MULTIPLE VIEW POINTS FOR ADAPTATION/MITIGATION STRATEGIES IN THE CONTEXT OF WARMER AND DRIER FUTURE

PART 3: SEASONAL WEATHER VARIATION WITHIN LOCAL MESOCLIMATES EXPLAINED USING HIGH RESOLUTION CLIMATE DATA

PART 4: IMPACT OF LOCAL SITE AND INTER SEASONAL WEATHER VARIABILITY ON GRAPEVINE RESPONSES

More details about this PhD study and the results from the study will be published in a five part article series over the next few months in the Winetech Technical. Above graph indicates the topics that will be discussed in each article in this series.

WINETECH TECHNICAL YEARBOOK 2020 17

Climate change in the viticulture sectors: Overview of long-term

This article summarises extensive statistical climatic analysis into normalised bar graphs, graphics that better highlight increases and decreases in weather over regions and months. Land and ocean surface temperatures, continue to increase above the average 132-year record held within the world meteorological organisation. The average surface temperature of the earth has risen by about 0.9°C since the late 19th century, a change driven largely by increased carbon dioxide into the atmosphere. The five warmest years on record taking place since 2010, 2016 being the hottest on record, followed by 2019, 2018, 2017 and 2014 respectively. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year (January to September, with the exception of June) the warmest on record for those respective months. January 2016 was the hottest January ever recorded, and recently in 2019 June, July and September was the hottest ever recorded for those months. This is globally and locally alarming. The period April 2018 to March 2019 was the warmest 12 month period on record for Europe. Australia recently had its warmest March on record. Africa is one of the continents most vulnerable to climate change, and regions at lower latitudes are especially vulnerable as they already suffer from intense heat. Climate change on a South African scale

based on the annual average temperatures from1901-2018 highlights the warming that is of concern (#knowyourstripes). Scientists continue to highlight the alarming warming trend that stands out from the noise of natural variation that sceptics tend to push on weather phenomenons like El Nino, but still we are warmer today than in the 1900s. In view of climate change, economic pres- sures and future limitation of water avail- ability to the agricultural sector, informed decisions regarding the suitability of envi- ronments for viticulture are paramount lo- cally and globally. Every local environment has unique diurnal temperature variations due to the inland penetration of the sea breeze and other local effects, such as wind, topography, coastline orientation, slope angle and aspect. Continuous monitoring of extreme environments is hampered by the sparse and/or irregular distribution of meteorological stations, the difficulties in accessing data from government data custodians, the quality of the data is not assured, and data is costly. Our under- standing of climate is meteorological vari- ables in a given region over a long period, usually over a 30-year interval, as opposed to weather which is a particular condition at a particular place over a short period of time within years or over years. This article uses two spatial networks of long-term climate data for the average period of 1980-2014, see figure 1.

climate trends in the Western Cape (PART 1)

APRIL 2020

TARA SOUTHEY: Centre for Geographical Analysis, Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch KEYWORDS: Climate, Western Cape, climate change

WARMING STRIPES FOR SOUTH AFRICA W FROM 1901 - 2018 WW

#showyourstripes

Annual average temperatures for South Africa from 1901-2018. Each stripe highlights the annual temperature difference compared to the long term mean (the first stripe is 1901 and the last stripe is 2018). (Source of graphic: Ed Hawkins. Data source: Berkeley Earth, NOAA, UK Met Office, MeteoSwiss, DWD.)

WINETECH TECHNICAL YEARBOOK 2020 18

regions considering temperature and rain- fall only. The topography and distance from the ocean seemed to drive regional shifts over the three decades (1984-2015), with a more pronounced effect on temperature in the coastal region, some regions being more prone to change, emphasising the need for finer scale demarcation when cli - mate aspects are considered. The analysis highlights the need for regional and month- ly review in the context of climate change to be focused on maximum and minimum temperature, as when averages are used, the meaning of the data is masked. Figure 2 explains what has happened in the dif- ferent wine-producing regions over the last 10 years compared to the long-term mean. For example the Breede River Valley is seeing increases in maximum temperatures and decreases in minimum temperatures, this could mean that the region could expect more heatwaves or higher summer temperatures along with cooler winters/ spring temperatures that could manifest in the form of frost. The incidence of frost has increased in some areas within the Breede River Valley the past few seasons, having a significant impact on the crop load at harvest. The increases in rainfall in the Breede River Valley could have positive or negative impacts, very much dependent on the timing of rainfall. Figure 2 can be used to aid decision making in the context of a changing climate, some

regions more prone to increased/decreased temperatures and other more prone to changes in rainfall, this knowledge could aid viticulture management strategies. Climatic indices used to summate the seasonal growing temperatures have showed significant increases. This trend is continuing and is shifting the climate zone demarcations for viticulture. However, in the context of climate change, seasonal summations are not enough to quantify the impact of temperature shifts on the grapevine. A higher temporal resolution of weather conditions is required, and highlights that the seasonal summations are driven by warmer than normal months later in the season, specifically driven by increases in temperatures in the months of December, January and March (figure 3). The growing season is warming and demarcated areas linked to specific production and cultivar targets need to be reviewed. Monthly temperature shifts, rather than regional temperatures, better illustrated the fluctuations of temperatures across the decades. The most significant shift to warmer temperatures was noted in December, January and March, with increasing rainfall in January and March, insights that could affect the grapevine’s growth and especially ripening. Cooler minimum temperatures in September could affect budburst and the cooling temperatures in November, along with

The data clearly highlighted: a general warming trend within the extent of the Western Cape over the last 30 years, regions and months responding differently. The results showed significant differences in the warming and cooling over decades (10 years), half decades (five years), years, regions and months. There was a significant climatic trend of warming for the 30-year period, with a similar trend across the different wine regions of South Africa. Over all temperature elements, there was a warming trend from 1984-2015, maximum temperatures showed the most increase of between 1-2°C and minimum temperature increases were observed over all

the regions, but with less intensity (<0.6°C). Temperatures in the Western Cape are projected to increase by as much as 1.5°C along the coast and 3°C inland by 2050. Rainfall was not well explained by specific long-term trends, but regional and monthly changes of annual increases and decreases over decades, with a general trend of rainfall shifting more into the summer season of the Western Cape. The 30-year long-term temperature and rainfall averages for each wine producing region are described in Table 1, highlight- ing the cooler and warmer production ar- eas. Figure 2 highlights the climate change impacts on the different wine-producing

WINETECH TECHNICAL YEARBOOK 2020 19

more rainfall in October/November, could delay phenology, or promote vegetative growth of the grapevine, increasing vigour. Winter months are key for chill unit calculations and efficient budburst for an even and timeous start to the growing season. April, May and July showed increasing maximum temperatures and decreasing minimum temperatures. Rainfall is decreasing overall in the winter months with the exception of increases in June for the last decade. The shifts of rainfall out of the post-harvest and winter periods, could have an impact on the soil moisture and temperature profile, this would impact the traditional irrigation strategies. The results highlighted that the climate in the Western Cape wine growing area is changing, with a general trend of warming that was more pronounced in some regions and for some months. South Africa’s wine grape growing regions are characterised by diversity in climate, topography, soil type, etcetera. This diversity is a key for effective adaptive strategies, it allows for more complexity in the management of climate change. Changes in the areas of suitability for certain cultivars could be of major importance for the regional economy. Adaptation, change in production practices and development of new wine regions are the keys to surviving climate change. The South African wine industry has already shown considerable flexibility in shifting geographically to new production areas that are characterised by cooler climatic conditions, but this may come at a cost with regard to less favourable conditions, such as more summer rainfall, changes in wind during critical growth and ripening stages. The study emphasised the need for more climate monitoring sites, especially in the complex terrain of the Western Cape. Spatial and temporal data sources need to be integrated to create new spatial and temporal layers of

WESTERN CAPE: LONG TERM WEATHER STATION DATASETS

FIGURE 1. Two spatial networks of long-term climate data for the average period of 1980-2014. (Data source: ISCW-ARC.)

WINETECH TECHNICAL YEARBOOK 2020 20