WINETECH Technical Yearbook 2021

TECHNICAL YEARBOOK 2021

CONTENTS

AUTHORS_ _______________________________ 3 FOREWORD_ _____________________________ 4 1. VITICULTURE______________________________ 5 2. OENOLOGY_ ____________________________54 3. PRACTICAL IN THE VINEYARD____________121 4. PRACTICAL IN THE CELLAR_ _____________149 5. GENERAL_______________________________172

IMAGES COPYRIGHT: INDIVIDUAL AUTHORS, FLICKR, PIXABAY, SHUTTERSTOCK, UNSPLASH OR WOSA LIBRARY.

DTP LAYOUT: AVANT - GARDE SOUTH AFRICA.

WINETECH TECHNICAL YEARBOOK 2021 | 2

AUTHORS

AMANDINE DEROITE: Lallemand SAS – Blagnac, France ANÉL BLIGNAUT: Blue North Sustainability (Pty) Ltd, Stellenbosch ANTOINETTE MALAN: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch ASTRID BUICA: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch BERNARD MOCKE: Private consultant BONGINKHOSI DLAMINI: Department of Conserva- tion Ecology and Entomology, Stellenbosch University, Stellenbosch CARIEN COETZEE: Basic Wine, Stellenbosch CARINA WESSELS: Blue North Sustainability (Pty) Ltd, Stellenbosch CAROLYN HOWELL: ARC Infruitec-Nietvoorbij, Stellenbosch CHARL THERON: Private consultant CODY WILLIAMS: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch DARIUSZ GOSZCZYNSKI: Plant Health and Pro- tection, Agricultural Research Council, Pretoria DIANCA YSSEL: Blue North Sustainability (Pty) Ltd, Stellenbosch ELDA BINNEMAN: Anchor Oenology EMMA CARKEEK: Vinpro, Paarl ETIENNE TERBLANCHE: Vinpro, Paarl

FLOR ETCHEBARNE: French National Institute for Agriculture, Food, and Environment (INRAE) FRANCOIS HALLEEN: ARC Infruitec-Nietvoorbij, Stellenbosch FRANCOIS VAN JAARSVELD: ARC Infruitec- Nietvoorbij, Stellenbosch GONZALO GARRIDO-BAÑUELOS: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch HANNO VAN SCHALKWYK: Vinpro, Paarl HEINRICH DU PLESSIS: ARC Infruitec-Nietvoorbij, Stellenbosch HEINRICH SCHLOMS: Vinpro, Paarl HENNIE VISSER: Vinpro, Robertson and Klein Karoo HERNÁN OJEDA: French National Institute for Agriculture, Food, and Environment (INRAE) HILARIA IIPINGE: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch JAMES DUNCAN: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch JAMES PRYKE: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch JEANNE BRAND: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch JOHAN DE JAGER: Vinpro, Paarl

JULIEN HARAN: CBGP, CIRAD, Montpellier SupAgro, INRA, IRD, University of Montpellier, France JUSTIN HOFF: ARC Infruitec-Nietvoorbij, Stellenbosch JUSTIN LASHBROOKE: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch KACHNÉ ROSS: Winetech, Paarl KAREN FREITAG: ARC Infruitec-Nietvoorbij, Stellen- bosch KARIEN O’KENNEDY: Winetech, Paarl KERRY SAYWOOD: Blue North Sustainability (Pty) Ltd, Stellenbosch KWAKU ACHIANO: ARC Infruitec-Nietvoorbij, Stellenbosch LIZÉL MOSTERT: Department of Plant Pathology, Stellenbosch University, Stellenbosch LUCINDA HEYNS: Winetech, Paarl LUCKY MOKWENA: Central Analytical Facilities (CAF), Stellenbosch University, Stellenbosch MARINUS GELDENHUYS: Department of Conserva- tion Ecology and Entomology, Stellenbosch University, Stellenbosch MARION BASTIEN: Lallemand SAS – Blagnac, France MATIJA LESKOVI Ć : South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch MESHACK MAGAGULA: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch MICHAEL SAMWAYS: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch

MICHEL MOUTOUNET: Private consultant MORNÉ KEMP: Laffort, Paarl

MPHO MAFATA: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch NEIL JOLLY: ARC Infruitec-Nietvoorbij, Stellenbosch PHILIP MYBURGH: ARC Infruitec-Nietvoorbi j, Stellenbosch PIA ADDISON: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch REMI SCHNEIDER: Oenobrands RENÉ GAIGHER: Department of Conservation Ecology and Entomology, Stellenbosch University, Stellenbosch SEBASTIAN VANNEVEL: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch TARA SOUTHEY: Centre for Geographical Analysis, Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch THIAS TAUTE: Hoedspruit Hub, Hoedspruit VALERIA PANZERI: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch VINCENT GERBAUX: IFV – Beaune, France WESSEL DU TOIT: South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University, Stellenbosch WYNAND VAN JAARSVELD: Department of Plant Pathology, Stellenbosch University, Stellenbosch

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FOREWORD

Knowledge transfer is one of Winetech’s four core functions. We use various platforms, channels and third parties to help us bring new knowledge to various industry stakeholders. One of these platforms is Winetech Technical in WineLand Magazine. Each month we publish technical articles related to viticulture, oenology and sustainability, as well as some more general articles in Afrikaans or English in the printed magazine. These articles also appear online, in English, on the WineLand website. At the end of each year we combine all the published articles in an easy to use and store interactive pdf document. Articles in this 2021 Winetech Technical Yearbook cover topics such as vineyard viruses, weevils, cultivar drought tolerance, grape breeding, pruning, smoke taint, varietal thiols, protein stability, copper in wine, yeast bio-protection and many more. We sincerely hope that the South African wine industry will continue to find the Winetech Technical Yearbook a useful resource with relevant information that can empower producers and winemakers to make informed decisions, and in doing so, to increase the profitability and sustainability of the industry as a whole.

Kind regards The Winetech Team

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1 VITICULTURE

An overview on the genetic and biological variability of viruses in vineyards ____________________________________ 6

Understanding the “terroir effect” (Part 3) _______________ 22

disease in grapevine nurseries__________________________ 33

Breeding the next Pinotage – advancements in wine grape breeding_______________________________________ 37

Weevils in vineyards – a species-rich assemblage _________ 24

TerraClim – high resolution temperature layers are available and so much more ___________________________ 11

Evaluation of the drought tolerance of 17 wine grape cultivars under dryland conditions – observations in the establishment phase __________________________________ 28

Cover crops enhance vineyard arthropod diversity ________ 41

Understanding the “terroir effect” (Part 1) _______________ 17

Entomopathogenic fungi mortality on grapevine mealybug 47

Trichoderma as possible biocontrol agent against black foot

Understanding the “terroir effect” (Part 2) _______________ 19

Minimal pruning – effects on grape aromatic composition _ 50

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VITICULTURE RESEARCH | MARCH 2021

An overview on the genetic and biological variability of viruses in vineyards

DARIUSZ GOSZCZYNSKI: Plant Health and Protection, Agricultural Research Council, Pretoria KEYWORDS: Grapevine virus detection, grapevine leafroll and rugose wood diseases.

SUBSTANTIAL INPUT OF TWO SOUTH AFRICAN LABORATORIES TO WORLDWIDE KNOWLEDGE To date, 70 virus species that can infect grapevines have been recorded (Martelli, 2017). Two groups of viruses are especially detrimental for the grapevine industry from an economic point of view. These are viruses associated with grapevine leafroll (GLRD) and rugose wood diseases (GRWD). GLRD causes degeneration of phloem cells, which prevents translocation of synthesized carbohydrates from grapevine leaves. The disease delays maturation, decreases the sugar content of berries and, ultimately, negatively influences the quality of produced wine. In GRWD-affected plants, abnormal activity of cambium cells affects graft takes of cultivars to rootstocks. This leads to reduced vigour of grapevines and, ultimately, results in lower productivity and longevity of vineyards. The diseases are

easily transmitted by pests, like mealybugs and scale, which are common in vineyards. Research has revealed many virus species of the families Closteroviridae and Betaflexiviridae (Martelli, 2017) associated with these two diseases, respectively. Each species is extensively genetically heterogenic with genome differences of up to 30% between genetic variants. The genome divergence sometimes correlates with putatively different pathogenicity to grapevines. The genetic and biological data obtained for these viruses are crucial for the reliable detection of these pathogens using molecular methods, like RT-PCR, and for the ongoing study of the aetiology of these diseases. The current scientific data on viruses associated with GLRD and GRWD is the result of many years of study in various laboratories worldwide. It all began 41 years ago, in 1979, when Namba et al. in

FIGURE 1. Grapevine cv. Shiraz and LN33 infected with severe genetic variants of Grapevine virus A (GVA) and Grapevine virus B (GVB), respectively. The grapevines are also infected with GLRaV-3.

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full genome sequence of this variant is deposited in GenBank. It is important to add that the ARC-PHP laboratory was the first to reveal the serological relation between GVA and GVB (Goszczynski, 1996). These two viruses belong to the genus Vitivirus. Recently, after introducing a new sequencing technique called next generation of sequencing (NGS) or high through-put sequencing (HTS), the number of members of this genus rose to 11 (Goszczynski, 2019). Although investigation of these viruses has only just begun, it is possible that all members of this genus, as with GVA and GVB, are associated with GRWD. It means that they may be able to deregulate the differentiation of cambium cells, which is crucial for the graft take of grapevines. In South Africa, the main problem in vineyards is the widespread presence of GLRaV-3. An intensive study of this virus began in 2004 when the full (or nearly full) genome sequence of this virus was published by a laboratory at Cornell University, USA (Ling et al ., 2004). In 2005, we used a technique called single- strand confirmation polymorphism (SSCP) which, following the brief investigation of genetic heterogeneity of GLRaV-3 sequences, revealed two clearly divergent variants of this virus (Jooste & Goszczynski,

Japan revealed the consistent presence of flexuous virus particles in GLRD- affected grapevines. This finding was quickly confirmed by a laboratory in Switzerland. The presence of serologically different viruses, named Grapevine leafroll associated viruses , GLRaV-I and-II was detected (Gugerli et al . 1984). Later, the serologically distinct GLRaV-III, -IV and -V were identified by laboratories in the USA and France (Hu et al ., 1990; Zimmermann et al ., 1990). Presently, the viruses are known as GLRaV-1, -2, -3, -4 and -5. Then, beginning in 1980, a few laboratories in Italy identified two viruses associated with GRWD, and named them Grapevine virus A (GVA) and B (GVB) (Conti et al ., 1980; Rosciglione et al ., 1983; Boscia et al ., 1993). All these new findings related to GLRD and GRWD attracted the attention of every laboratory working on grapevine viruses worldwide, including South Africa. At the Plant Protection Research Institute (PPRI), which is now named Plant Health and Protection (PHP) of the Agricultural Research Council (ARC), equipped with a new electron microscope and highly trained staff in this field, all worldwide findings regarding different species of serologically distinct viruses were confirmed. Our laboratory, however, went one step further, and were among the first whose results suggested genetic and biological

heterogeneity of virus species associated with GLRD and GRWD. In 1996 we mechanically transmitted GLRaV-2 to the alternative herbaceous host of this virus, Nicotiana benthamiana (Goszczynski et al ., 1996) . Although GLRaV-2 was transmitted to this herbaceous plant earlier in Canada (Monette & Godkin, 1993), our results suggested, for the first time, based on symptoms induced in N. benthamiana , the existence of the biological strains of this virus (Goszczynski et al ., 1996). The strains were sequenced at Cornell University, USA, and deposited in GenBank/EMBL database (Meng et al ., 2005). Presently, it is well known that the virus has strains with different pathogenicity to grapevines. Six groups of divergent genetic variants were identified (Angelini et al ., 2017). One of them, the strain “Redglobe” (RG) is associated with inducing stem lesions/ necrosis on various rootstocks after grafting (Angelini et al ., 2017). Analogous developments occurred with viruses GVA and GVB associated with GRWD. We confirmed that these viruses are transmissible to N. benthamiana. Moreover, our results revealed extensive genetic variability of GVA, which was correlated with different pathogenicity of variants to N. benthamiana (Goszczynski & Jooste, 2003) . Also, the resul ts

strongly suggest that members of one of the molecular groups of variants of this virus, group II, are associated with Shiraz Disease (SD) (Figure 1A) (Goszczynski, 2007). The disease is highly destructive to noble grape cultivars Shiraz and Merlot in South Africa. Among eight full genome sequences of GVA deposited in GenBank, seven are from South Africa (Goszczynski et al ., 2008). In addition, we transmitted GVB to N. benthamiana and identified and fully sequenced 3 genetic variants of this virus (Goszczynski, 2018). Four full genome sequences out of seven deposited in GenBank are from South Africa. Although the first paper that reported genetic heterogeneity of GVB originated in Australia (Shi et al ., 2004), we were the first to suggest variants with different pathogenicity to grapevines. The virus is associated with grapevine corky bark disease (GCBD). The disease induces clear cane symptoms in the LN33 hybrid, which is used as an indicator of this disease in woody indexing of grapevines. In severe cases, the disease causes LN33 to “burst” between internodes (Figure 1B). We have GVB variants associated with severe CB symptoms in our collection, but we also identified a GVB variant that is present in LN33 which consistently and over years, does not exhibit any symptoms of this disease (Goszczynski, 2010). The

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2005). Concurrently, an Italian group, also working on genetic heterogeneity of GLRaV-3 and using the same technique, published a paper on this subject (Turturo et al ., 2005). The results of our research were published the same year, although they only appeared in printed form slightly later (Jooste & Goszczynski, 2005). The ARC-PHP laboratory deposited the full genome sequences of three divergent genetic variants of GLRaV-3, named 621, 623 and PL20 in GenBank, representing I, II and III groups of this virus (Jooste et al ., 2010). Later, we identified a highly divergent genetic variant of GLRaV-3, which represented a new and yet unknown group VII of this virus (Goszczynski 2013). The full genome sequence of a variant of this group (GH24) was determined by the Vitis Laboratory, Stellenbosch University (Maree et al ., 2015). The major contribution to worldwide knowledge on GLRaV-3 is credited to the aforementioned Stellenbosch laboratory. This includes the discovery that one of the terminal parts of the genome sequence, 5’ NTR, of this virus is 737 nt and not 158 nt as was previously published (Maree et al ., 2008). The relevance of such a long genome “tail” remains unknown. It may play an important role in the biology of this virus. Moreover, the Stellenbosch University team is a leader in establishing the clarity

of the genetic heterogeneity of GLRaV-3 (Maree et al ., 2015). The excellent work of this laboratory is reflected in many solid research and review papers, beginning in 2008 (Maree et al ., 2015, 2013 & 2008; Bester et al ., 2012; Burger et al ., 2017). Currently, six groups of divergent genetic variants of this virus are known (Thompson et al ., 2019) and this number may increase. However, despite this precise GLRaV-3 sequence data, nothing is known about the biological differences between variants of this virus. In addition to GLRaV-1, -2 and -3, there is also GLRaV-4. The presence of a virus that is serologically different from GLRaV-1, -2 and -3 was noticed relatively early, in the USA, France and Switzerland (Hu et al ., 1990; Zimmerman et al ., 1990; Gugerli & Ramel, 1993). It was named as GLRaV-4, -5 and -6. Once virus genome sequence data became available from different laboratories, and the number of putative GLRaV species amounted to eight, it emerged that some of this data represented different genetic variants of a single virus species, which was named GLRaV-4 (Aboughanem-Sabanadzovic et al ., 2017). Long before the GLRaV-4 group was created, we detected a virus named “band C closterovirus”, which cross-reacted with antibodies to GLRaV-6 (Goszczynski et

al ., 1997). The virus also cross-reacted with antisera to GLRaV-4 and -5 (Goszczynski & Kasdorf, not published). This suggested a serologically related group of viruses. Our finding was basically correct. We now know that the GLRaV-4, -5 and -6 are variants of one species, GLRaV-4. The exact identity of “band C closterovirus” remains unknown. As in the case of GLRaV-3, despite the clear genetic divergence between the presently identified eight variants of GLRaV-4, nothing is known about the differences in pathogenicity to grapevines of these variants. Among viruses associated with GRWD, there is also Grapevine rupestris stem pitting associated virus (GRSPaV). This virus has a different genome organisation from members of the genus Vitivirus , like GVA and GVB, and belongs to a separate genus, Foveavirus. GRSPaV was discovered almost concurrently in two American laboratories in 1998 (Meng & Rowhani, 2017). Soon after the full genome sequence of GRSPaV was published, research data revealed that this mysterious virus is widely present in vineyards worldwide. Because it is commonly believed that this virus is not harmful to grapevines, we paid relatively little attention to it. At some point, however, an American laboratory discovered a highly divergent variant of

this virus in grapevines affected by so- called Syrah decline (Sd) (Lima et al ., 2006). Although a high divergence between genetic variants of grapevine viruses is common, the media fuelled the suggestion that the newly-identified GRSPaV variant is associated with this disease. Sd severely affects graft of certain clones of cv. Syrah to rootstocks. Sd was identified in France and some French Syrah clones were imported to South Africa. Initially, a few mother blocks of these clones were established but, shortly after the report of Sd, propagation of these grapevines was stopped. An extensive survey conducted by the ARC- PHP revealed that none of the divergent genetic variants of GRSPaV is associated with Sd-affected grapevines in South Africa (Goszczynski, 2010). Sd is now considered a genetic disorder and not associated with any grapevine pathogen. Currently eight genetic variants of GRSPaV are known, but the pathogenicity of variants to grapevines remains a mystery (Meng & Rowhani, 2017; Goszczynski, 2020). Despite the fact that the virus is associated with grapevine rupestris stem pitting disease (GRSPD), the variants inducing symptoms of this disease in Rupestris St George grapevine have not been clearly identified (Goszczynski, 2020).

Genetic variability data is crucial for the precise detection of viruses. Currently,

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the most sensitive method of detection of grapevine viruses is RT-PCR. The technique requires a profound knowledge of targeted virus sequences to ensure rel iable detection. Equally valuable as sequence data is biological data on grapevine viruses. We must bear in mind that from a strictly scientific perspective, the viral aetiology of GLRD and GRWD has not been firmly confirmed. The third Koch’s postulate, which states that isolation of a pathogen and re-infection of a host with a pure culture of that pathogen, and which must be followed with the development of disease symptoms, has not been fulfilled. The reason for this lapse in knowledge is the fact that grapevines are usually infected with a mixture of various virus species and different genetic variants of a single virus species, and separation of them is not possible. Although some viruses, like GVA, GVB and GLRaV-2, were isolated in alternative herbaceous host N. benthamiana , transmission of them back to Vitis is impossible using current techniques. The only way to obtain a pure culture of grapevine viruses is to construct biologically active cDNA clones of these viruses in the laboratory (Goszczynski, 2018). The cDNA clones for the following GLRD- and GRWD-associated viruses were constructed: GVA, GVB, GRSPaV, GLRaV-2 and -3 (Galiakparov et al ., 1999; Sardarelli,

2000; Meng et al ., 2013; Kurth et al ., 2012; Jarugula et al ., 2012). In the ARC- PHP laboratory, biologically active cDNA clones were constructed to GVA and GVB (Goszczynski, 2015). Currently, the full data on virus infection of grapevines using cDNA clones has only been established for GLRaV-2 by a laboratory in the USA (Kurth et al ., 2012). Soon we can expect other research papers to confirm the successful infection of grapevines using cDNA clones of viruses. Recently an Italian laboratory published a paper on successful fulfilment of Koch’s third postulate for a member of the family Betaflexiviridae , Grapevine Pinot gris virus (GPGV), which is known to be associated with stunting, chlorotic mottling and leaf deformation of some grapevines (Tarquini et al ., 2018). SUMMARY About 40 years of intensive research of grapevine leafroll (GLRD) and grapevine rugose wood (GRWD) diseases has revealed that many virus species of the two virus families, Closteroviridae and Betaflexiviridae , are associated with these diseases. Results have also revealed that each virus species is composed of a large number of divergent genetic variants, some of them with putative different pathogenicity to grapevines. Accumulated data is crucial for the accurate detection

and further study of these important viruses. Two South African laboratories, ARC- Plant Health and Vitis Laboratory of Stellenbosch University, have played a significant role in creating this worldwide knowledge. ACKNOWLEDGEMENTS All the research described in this article was made possible by the financial support of Winetech, South Africa, and with the aid of institutions such as KWV, nurseries Vititec and Ernita, and with further help from people like J.H. Booysen, A. Andrag, R. Carstens, G. Kriel, N. Spreeth, T. Oosthuizen, J. Wiid and the late Prof. P. Goussard. REFERENCES Martelli, 2017. In: Meng B, Martelli GP, Go- lino DE, Fuchs M, (eds). Grapevine viruses: molecular biology, diagnostics and manage- ment. Springer, Cham, 31-46. Namba et al ., 1979. Annals of the Phyto­ pathological Society of Japan 45, 497-502. Gugerli et al . 1984. Revue Suisse de Viti­ culture, Arboriculture et Horticulture . 16, 299-304. Hu et al ., 1990. Journal of Phytopathology . 128, 1-14 Zimmermann et al., 1990. Journal of Phyto­ pathology . 130, 205-218

Conti et al ., 1980. Phytopathology 70, 394- 399. Rosciglione et al ., 1983. Vitis 22, 331-347. Boscia et al ., 1993. Archives of Virology 130, 109-120. Goszczynski et al ., 1996. Vitis 35, 133-135. Monette & Godkin, 1993. Plant Pathology ( Trends in Agriculture Science ) 1, 7-12. Meng et al ., 2005. Virus Genes 31, 31-41. Angelini et al ., 2017. In: Meng B, Martelli GP, Golino DE, Fuchs M, eds. Grapevine viruses: molecular biology, diagnostics and manage- ment. Springer, Cham, 141-165. Goszczynski & Jooste, 2003. European Jour­ nal of Plant Pathology 109, 397-403. Goszczynski, 2007. Plant Pathology 56, 755- 762. Goszczynski et al ., 2008. Virus Research 138, 105-110. Goszczynski, 2018. Journal of Plant Pathol­ ogy 100, 105-109. Shi et al ., 2004. Virus Genes 29, 279-285. Goszczynski, 2010. Virus Genes 41, 273- 281. Goszczynski, 1996. Journal of Phytopathol­ ogy 144, 581-583. Goszczynski, 2019. Wineland , November 2019. Ling et al ., 2004. Journal of General Virolo­ gy 85, 2099-2102.

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Jarugula et al ., 2012. In: Proceedings of the 17th Congress of ICVG, Davis, California, 2012, pp. 70-71. Goszczynski, 2015. SpringerPlus 4: 739 (DOI 10.1186/s40064-015-1517-2). Tarquini et al . , 2018. PLoS ONE 14: e0214010.

viruses: molecular biology, diagnostics and management. Springer, Cham, 257-287. Lima et al ., 2006. Archives of Virology 151, 1889-1894. Goszczynski, 2010. Archives of Virology 155, 1463-1469. Goszczynski, 2020. Wineland , January 2020. Goszczynski, 2018. Wineland , June 2018. Galiakparov et al ., 1999. Virus Genes 19, 235-242. Sardarelli, 2000. Archives of Virology 145, 397-405. Meng et al ., 2013. Virology 435, 453-462. Kurth et al ., 2012. Journal of Virology 86, 6002-6009.

Jooste & Goszczynski, 2005. Vitis 44, 39-43. Turturo et al ., 2005. Journal of General Vi­ rology 86, 217-224. Jooste et al ., 2010. Archives of Virology 155, 1997-2006. Goszczynski 2013. Journal of Phytopatholo­ gy 161, 874-879. Maree et al ., 2015. PLoS ONE 10: e0126819. Maree et al ., 2008. Archives of Virology 153, 755-757. Bester et al ., 2012. Archives of Virology 157, 1815-1819. Maree et al ., 2013. Frontiers in Microbiology 4 (doi:10.3389/fmicb.2013.00082). Burger et al ., 2017. In: Meng B, Martelli GP, Golino DE, Fuchs M (eds). Grapevine viruses:

molecular biology, diagnostics and manage- ment. Springer, Cham, 167-195. (Rev). Thompson et al., 2019. Plant Disease 103, 509-518. Gugerl i & Ramel , 1993. In: Extend- ed abstracts of the 11th meeting of ICVG, Montreux, Switzerland, 23-24. Aboughanem-Sabanadzovic et al ., 2017. In: Meng B, Martelli GP, Golino DE, Fuchs M (eds). Grapevine viruses: molecular biolo- gy, diagnostics and management. Springer, Cham,197-219. (GL4 group). Goszczynski et al ., 1997. In: P.L. Monette (ed) Filamentous viruses of woody plants, Re- search Signpost, Trivandrum, India, 49-59. Meng & Rowhani, 2017. In: Meng B, Martelli GP, Golino DE, Fuchs M (eds). Grapevine

For more information, contact Dariusz Goszczynski at Plant Health and Protection, Agricultural Research Council – GoszczynskiD@arc.agric.za.

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VITICULTURE RESEARCH | APRIL 2021

TerraClim – high resolution temperature layers are available and so much more TARA SOUTHEY: Centre for Geographical Analysis, Department of Geography and Environmental Studies, Stellenbosch University, Stellenbosch KEYWORDS: Climate, terrain, GIS, innovation, suitability.

The integrated data resources are displayed through a user-friendly interface (www. terraclim.co.za), thereby addressing the limited accessibility to climate/terrain information experienced by the agriculture sector. The results from the TerraClim research and development is novel and new to the Western Cape and continue to ensure improved accuracy of temperature layers created to aid effective decision making. Technical transfer of the TerraClim platform to industry and potential user pay clients continues to return positive feedback. Some key results in 2020 include: • Finalisation of the central climate database ingestion procedures. • Improvements to www.terraclim.co.za reporting functionality. • Application of regional climate surface interpolation. • High density temperature and relative humidity logger network extension. • Suitability analysis using vineyard planting database.

climate change at regional, farm and vineyard level. The integrated geospatial database (geodatabase) is suitable for dynamic mapping, statistical interrogation, data mining, machine learning and climate change analyses. This is of great value to the producer in the Western Cape, due to the highly complex climate (ranging from semi-arid to mediterranean) and topography (mountainous to planar) and in the context of increased seasonal variability, understanding trends over space and time at farm and field level would contribute to economically sustainable decision making. TerraClim solves the problem of data inaccessibility by providing highly detailed, up-to-date, field-specific climate data at regional scales. This data is ideal for generating historic and current climatic and physical (terroir) profiles for each individual field, orchard or vineyard.

Calculated hourly threshold maps as hours above 18°C and 30°C for each growing season over five years (2015-2019).

TERRACLIM TO ADAPT, strategise, leverage change and building resilience in the face of great uncertainty. The TerraClim project is one of Winetech’s flagship projects that aims to improve the understanding of climate change in the Western Cape and how the grapevine/ plant responds to these changes. Specific

objectives include building a comprehensive climate and terrain database, using new research and technologies to spatialise climate, terrain and vineyard information. TerraClim uses automated functionality to collate, improve, spatialise and disseminate climate data, empowering the farmer and researcher to better analyse and mitigate

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1. TerraClim is driven by a robust central climate database. Such a central database does not currently exist for the Western Cape, and portions of existing climate data amongst various custodians are highly variable in completeness, accuracy and structure. TerraClim climate layers are based on a standardised, long-term, live climate database of hourly, daily and monthly t empora l r eso l ut i ons . Aut oma t ed workflows have been developed for ingesting multiple climate datasets into one standardised climate database, the central climate database incorporates standardised, gap fills ingested data from over 600 weather stations in the Western Cape. The interpolated wall-to-wall climate surfaces, terrain derivatives and industry- specific bioclimatic indices at a vineyard level are disseminated through a user- friendly interface (www.terraclim.co.za) to aid infield decision making. 2. The TerraClim platform has developed a comprehensive infield viewing and reporting functionality driven by industry user feedback. Effective data dissemination was a strong focus in 2020. A modular dashboard has

been added to the TerraClim platform allowing the user to select, view and interact with their climatic or terrain variables of choice at field level (figure 1). Selecting a field of interest populates the online dashboard with selected information for that specific field and generates a comprehensive report viewable online or downloadable as a pdf. The report generated has been populated with climate and terrain information at field level, including context for the interpretation of maps and graphs represented within the report. The continued aim of the report is to develop as a guide to aid user interpretation of the graphs and maps within the context of climate change and industry standards. The website www. terraclim.co.za is currently in the final beta version, improving continuously as we acquire new user feedback (contact tara@ sun.ac.za for feedback). FIGURE 1. Examples of the dashboard and reporting functionality, top and bottom right temperature displays at field and regional level. Bottom left is an example of climatic variables in reporting documentations: (A) Mean daily temperature for multiple seasons (2017-2019), (B) mean, minimum and maximum monthly average temperature for the period 2016- 2019, and (C) example of mean, minimum and maximum daily temperature.

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3. The appl ication of regional climate surface interpolation improves the accuracy and processing time. The regional interpolat ion method development for surface temperature was a major milestone in 2020 (see story map https://arcg.is/1q0mTn0). Regionality research was undertaken by delineating and interpolat ing the temperature surfaces on subsections (wine regions) of the Western Cape, resulting in an improved understanding of the topographic differences driving temperature changes. In some areas temperature is strongly affected by covariates, such as distance to coast, elevation, solar radiation, etcetera. The regional interpolation improves the final merged output by allowing the incorporation of locally-tailored covariate relationships per region, compared to applying the same, generalised covariate relationships to all regions (figure 2). The regionality results has allowed for the study area to be expanded to cover 33% of the Western Cape and 97.9% of wine grape vineyards (figure 3). The research results rendered improved accuracies, faster run times, scalable methodology and valuable recommendations for future weather station density and region size (figure 4) for more accurate temperature FIGURE 1. Examples of the dashbo rd and reporting functionality, top and bottom right temperature displays at field and regional level. Bottom left is an example of climatic variables in reporting documentations: (A) Mean daily temperature for multiple seasons (2017 - 2019), (B) mean, minimum and maximum monthly average temperature for the period 2016 - 2019, and (C) example of mean, minimum and maximum daily temperature.

FIGURE 2. A Visual comparison of final temperature surface layers using the regional interpolation (A) compared to standard interpolation without regionalisation (B). The image on the left (A) captures the regional variation with greater accuracy (more very red and very blue areas), compared to the over-generalised output of the standard interpolation (B). FIGURE 2. A Visual comparison of final temperature surface layers using the regional interpolation (A) compared to standard interpolation without regionalisation (B). The image on the left (A) captures the regional variation with greater accuracy (more very red and very blue areas), compared to the over-gen ralised output of the standard interpolation (B).

layers in the future. The spatial distribution of accuracy per region is described in figure 4a, areas in red are greater concern than areas in green. Certain regions identified as “error hotspots” as they have higher RMSE values, i.e. region 1 (Gansbaai) and region 3 (Constantia), highlighting the need for more weather stations to improve accuracy.

FIGURE 3. Shows the current TerraClim study area (left) and updated TerraClim extent (right) as an outcome from the regionality study, the new area covers 33% of the Western Cape and 97.9% of wine grape vineyards.

n the report. The continued aim of the report uide the aid user interpre ation of the graphs the context of climate change and industry bsite www.terraclim.co.za is currently in the mproving continuously as we acquire new user ara@sun.ac.za for feedback).

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TION OF REGIONAL CLIMATE ERPOLATION IMPROVES THE

4. To further the understanding of temperature and terrain, a high density wireless logger (50) network has been installed in the Banghoek/Jonkershoek Valley. This resource will be used to interpolate very high resolution climate surfaces, which will be compared against the regional interpolations, thereby providing new information for improved understanding of climate and terrain dynamics and improving spatial interpolation methods in the future. 5. TerraClim project has advanced even further in 2020 with re- search and development, creating a grapevine suitability tool within TerraClim that can recommend future plantings and utilise the integrated geodatabase. This new and novel suitability tool developed within TerraClim, can be tailored to any crop type based on the input data for analysis. Extensive council with viticulturists, consultants and researchers rendered the best source for suitability analysis to be an existing database of currently planted vineyards in the Western Cape. The suitability analysis is based on a data-mining approach, using a test database of actual vineyards (seven wine

FIGURE 4. Shows the regional delineation selected for TerraClim processing, area extent covers approximately 97.9% of vineyards in the Western Cape. The image on the left shows the RMSE per region for study area, areas highlighted in red are of greater concern than areas in green. On the right is an example of merged daily average temperature (14 February 2019) symbolised using a natural breaks stretch (left) and quantile classification (right).

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grape cultivars, namely Cabernet Sauvignon, Merlot, Chardonnay, Chenin blanc, Shiraz, Sauvignon blanc and Pinotage) planted in the three regions (figure 6) as an initial analysis for the development of a robust tool. A random forest machine learning classification performed on 42 data sources/layers within the geodatabase resulting in a feature importance list. The analysis showed digital elevation model, solar radiation, slope, distance from coast, aspect, wind speed, growing degree days, growing season temperature, rootstock, trellis system and soil depth, respectively, to be the top eleven layers (each with a feature importance weighting) that drive cultivar selection/recommendation. The suitability tool has three main functions that return a suitability recommendation. The user can draw a new polygon/field, select a previously drawn polygon/field or compare two previously drawn polygons/fields with each other (figure 6). KEY TAKE-HOME MESSAGE TerraClim products can be viewed, interrogated and downloaded through a user-friendly web application. Reports on the historical and current climatic and topographic characteristics of a particular agricultural field, orchard or vineyard can be generated and printed/ downloaded. While the web application facilitates a business-to- consumer data service, the climatic layers can also be made accessible to other mobile and web-based applications through an application programming interface (API), thereby enabling business-to-business data services. Use TerraClim to adapt, strategise, leverage change and build resilience in the face of seasonal uncertainty. View the web interface at www. terraclim.co.za and provide feedback to tara@sun.ac.za. We endeavour to improve the tool based on your feedback. Watch this space for more information as we grow in knowledge.

FIGURE 5. Image of the spatial distribution of a high density wireless logger (50) network installed in the Banghoek/ Jonkershoek Valley, to further the understanding of temperature and terrain dynamics.

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SUMMARY TerraClim provides spatially-explicit, up-to-date climatic data that is critical for informing agricultural decision making in the Western Cape. The TerraClim extent has expanded to cover 33% of the Western Cape and 97.9% of wine grape vineyards based on novel regionality research, with results that ensure improved accuracies and significantly faster processing times per hectare. TerraClim hosts multiple data resources into a central database with a user-friendly interface that allows users to obtain pertinent information about climate, terrain and soil to aid long- and short-term agricultural decision making, building resilience in the face of climate uncertainty in the Western Cape. A range of data products are provided. For example, air temperature is measured at hundreds of weather stations and converted to temperature maps (climatic layers) covering several agricultural regions in the province. These maps, generated at a spatial resolution of up to two metres, are frequently (e.g. hourly) updated. Various value-added climatic products, including growing degree days, accumulated cold units and extreme temperature events, are continuously generated. These products can be viewed, interrogated and downloaded through a user-friendly web application. Reports on the historical and current climatic and topographic characteristics of a particular agricultural field, orchard or vineyard can be generated and printed/downloaded. ACKNOWLEDGEMENT Centre for Geographical Analysis (CGA), namely Prof. Van Niekerk, G. Stephenson, C. Theron, A. Prins, T. Pauw and Z. Mouton.

FIGURE 6. Shows an example of the new suitability tool developed, the main window of the website displays the suitability study extent (left), the tool has three main functions that return a suitability recommendation. The user can draw a new polygon/field, select a previously drawn polygon/field (middle) or compare two previously drawn polygons/fields with each other (right), which provides a list of recommended cultivars with a summary table (quick summary values of the most important variables driving the cultivar recommendation).

For more information, contact Tara Southey at tara@sun.ac.za or visit www.terraclim.co.za.

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VITICULTURE RESEARCH | MAY 2021

Understanding the “terroir effect” (PART 1)

BERNARD MOCKE: Private consultant KEYWORDS: Terroir, aromatic grape and wine compounds.

THE TASTE OF ANY GIVEN WINE, regard- less of cultivar, is inextricably linked to its origin. Environmental factors, such as soil and climate, influence organoleptic charac - ters and by deconstructing measurable soil and climate parameters, this influence on a wine’s typicity can be better understood. In Part 1 of this two-article series, a brief introduction on the effect of terroir on wine aroma and an overview of the main families of aromatic grape and wine compounds are given. Part 2 of this series will focus on specifically how terroir shapes grape and wine aroma expression, and the prediction and management of aroma typicity relating to terroir. INTRODUCTION It has long been acknowledged that wine typicity, or style and quality in other words, depends heavily on where vines grow. Local soil and climate conditions are major

influences on wine sensory qualities. It is up to the winegrower to harness optimal plant material and vineyard management practices adapted to site, and the wine­ maker to use appropriate winemaking techniques according to berry composition, in order to fully shape the terroir effect. But to go further than merely a descriptive link between wine typicity, soil and climate, these need to be broken down into measurable parameters. Simply put, the effect of climate can be assessed through the measurement of air temperatures, radiation and rainfall. Similarly, the role of soil can be assessed through the measurement of soil water-holding capacity and nitrogen status. GRAPE AND WINE AROMAS Wine aromas can be classified as primary (produced during grape ripening) , secondary (produced during fermentation)

and tertiary (produced during wine ageing), and it follows that their expression is of key importance. Odorous primary aroma compounds are either free (volatile) or bound (conjugated) to other molecules present in grapes and can be liberated during fermentation or ageing. Ester compounds (secondary aroma compounds) are rather abundant depending on wine composition. The hundreds of aromatic compounds that have been identified in wine can be further grouped into specific families. GREEN AND PEPPERY FLAVOURS Major contributors to green aromas are methoxypyrazines, particularly 2-me- thoxy-3-isobutylpyrazine (IBMP), which is responsible for green (bell) pepper aroma. C6 compounds also contribute to green aromas and their abundance in wine is modulated by the winemaking protocol fol-

lowed, but there is not a lot of information available in literature about the impact of environmental factors on their presence in grapes and wines. 1,8-Cineole, a monoter- pene, imparts minty flavours to wine and (-)-rotundone, a sesquiterpene, notably contributes peppery aromas to Syrah and other cultivars.

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OTHER MONOTERPENES Terpenes can be found as free or glycosylated forms in grapes. They are important contributors to Muscat aromas in grapevine cultivars such as Muscat,

also a C 13 -norisoprenoid, smells of spices and tobacco, and is often referred to as “tabanone”. DRIED FRUIT AROMAS Massoia lactone, γ-nonalactone and furaneol , 3-methyl-2,4-nonanedione (MND), and (Z)-1,5-octadien-3-one have recently been identified as compounds contributing to dried fruit aromas in must and red wines. This family of compounds are specifically associated with over- ripening of grapes and are expressed in Several studies have demonstrated the sen- sory impact of substituted esters on fruity expression in red wines, even when these compounds were present at concentrations below their detection thresholds. These esters increase the perception of fruity aromas due to numerous synergistic effects between fruity compounds. OTHER AROMA COMPOUNDS AND COMPLEMENTARY OBSERVATIONS Dimethyl sulphide (DMS) in wine has a varying aroma impact, depending on its wines made from such grapes. SUBSTITUTED ESTERS AND QUALITATIVE FRUIT AROMAS

concentration. At low concentrations it imparts blackcurrant aroma, at medium concentration truffle or undergrowth, and at high concentration green olive or asparagus. It should be noted that there is a positive link between DMS concentration and the ageing bouquet complexity of the most iconic Bordeaux red wines. DMS does not impart fruit aromas, but it does have an indirect impact on fruity aroma expression, enhancing blackcurrant aromas at low concentrations. Aromatic N,S-heterocycles, a large family of wine aromatic compounds, contribute a broad spectrum of aromas ranging from meat to cooked potatoes, roasted coffee or hazelnut. O-aminoacetophenone (AAP) is associated with the untypical ageing character of white wines, particularly in Riesling. Wines showing high levels of AAP reminisce of naphthalene, floor polish, acacia blossom or mothballs and display a metallic bitterness on the palate. CONCLUSION It is known that volatile aromatic com­ pounds are not specific to a cultivar, but rather that their concentration varies depending on cultivars. One example of

this is Riesling wine that contains more TDN than Chardonnay or Gewürztraminer. Aroma compounds i n wi ne va r y considerably with environmental factors such as soil or climate – the influence of cultivar, soil and climatic conditions on a wine’s taste is known as the “terroir effect”. Part 2 of this series of articles will focus on measurable parameters, such as air temperature and vine water status (to name but a few), and how they impact wine typicity. REFERENCE Van Leeuwen, C., Barbe, J., Darriet, P., Geffroy, O., Gomès, E., Guillaumie, S., Helwi, P., Laboyrie, J., Lytra, G., Le Menn, N., Marchand, S., Picard, M., Pons, A., Schüttler, A. & Thibon, C., 2020. Recent advancements in understanding the terroir effect on aromas in grapes and wines. OENO One 4, 985-1006.

Gewürztraminer and Riesling. VOLATILE THIOLS AND C 13 - NORISOPRENOIDS

Although the volatile thiols aroma family was first identified in Sauvignon blanc, it is present in numerous other cultivars. They are present in grapes as non- odorous glutathione or cysteine bound precursors and are released, and thereby becoming aromatic, during alcoholic fermentation by yeast. Important volatile thiols are 3-mercaptohexanol (3MH – grapefruit), 3-mercaptohexanol acetate (3MHA – passion fruit) and 4-mercapto-4- methylpentan-2-one (4MMP – boxwood). C 13 -norisoprenoids, a family of important wi ne a roma compounds , i nc l ude β-damascenone, described by fruity-flowery or baked apple notes and 1,1,6-trimethyl- 1,2-dihydronaphtalene (TDN), which imparts kerosene-like notes. The latter compound is characteristically found in older Riesling wines. Megastigmatrienone,

For more information, contact Bernard Mocke at bmocke@gmail.com.

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VITICULTURE RESEARCH | JUNE 2021

Understanding the “terroir effect” (PART 2)

BERNARD MOCKE: Private consultant KEYWORDS: Terroir, grape and wine aroma.

AIR TEMPERATURE Green and peppery flavours

THE TASTE OF ANY GIVEN WINE, regard- less of cultivar, is inextricably linked to its origin. Environmental factors, such as soil and climate, influence organoleptic charac - ters and by deconstructing measurable soil and climate parameters, this influence on a wine’s typicity can be better understood. Part 1 of this expanded three article series introduced the terroir effect on wine aroma and gave an overview of the main families of aromatic grape and wine compounds. Part 2 focuses on specifically how terroir shapes grape and wine aroma expression, and Part 3 gives insights on the prediction and management of aroma typicity relating to terroir. INTRODUCTION Much is known about the role of climate and soil on wine typicity and by measuring air temperature, radiation, rainfall, soil water holding capacity, and vine nitrogen

status, the link with each other becomes clearer. Comprehensive databases are available on all of the relevant parameters, and these can be spatialised and quantified at vineyard scale. The winemaker’s role in shaping a wine’s future by reacting to berry composition is of vital importance. Of equal importance is the viticulturist, who also has a major influence on the terroir effect by suitably reacting to the above-mentioned soil and climate conditions. THE EFFECT OF MAJOR TERROIR FACTORS AND GRAPE AND WINE AROMA Due to the large amount of information, the terroir effect on aroma cannot be fully discussed – the reader is encouraged to study the “Recent advancements in understanding the terroir effect on aromas in grapes and wines” ( OENO one 4, 985- 1006) article for more information.

Methoxypyrazines, IBMP in particular, decrease in grapes undergoing maturation wi th an increase in temperature . An increase in IBMP is seen in higher altitude vineyards, attributed to lower temperatures. Cooler vintages result in a marked increase in (-)-rotundone levels, a peppery flavour in Syrah. Volatile thiols and C 13 -norisoprenoids It seems that 4MMP decreases under high temperatures in wines from Sauvignon blanc and it has been shown that cool climate Riesling (Germany) contained less TDN than warm climate Riesling (South Africa). Dried fruit aromas There is a clear effect of higher temperature and the development of dried fruit

aromas in grapes. Must and wine samples marked by this aroma has higher levels of γ-nonalactone, massoia lactone, furaneol or MND (3-methyl-2,4-nonanedione – dried fruit aromas such as dried prune). Other aroma compounds Particularly high levels of DMS (dimethyl sulphide – enhances blackcurrant aromas

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