South Africa Wine Research Booklet 2023

This publication serves as a comprehensive compilation, summarising the outcomes of projects concluded in 2022 and those currently underway in 2023.

PROJECTS 2023 RESEARCH

RESEARCH, DEVELOPMENT AND INNOVATION

A DIVISION OF SOUTH AFRICA WINE

TABLE OF CONTENTS

1 FOREWORD _ ___________________________________________2

3 VITICULTURE RESEARCH _ ________________________________ 18 3.1 Grapevine protection – Insects and pests___________________19 3.2 Grapevine protection – Fungi and bacteria__________________24 3.3 Soil and water________________________________________29 3.4 Cultivation/Terroir_____________________________________36 3.5 Grapevine improvement________________________________ 39 3.6 Maintenance of critical resources_________________________49 4 OENOLOGY RESEARCH __________________________________ 52 4.1 Wine process improvement______________________________53 4.2 Wine quality improvement______________________________63 5 TECHNOLOGY TRANSFER _ _______________________________ 67 2 FLAGSHIP PROGRAMMES _________________________________4 Climate change____________________________________________6 Water efficiency ____________________________________________8 Plant breeding____________________________________________13

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1 FOREWORD

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SOUTH AFRICA WINE RESEARCH 2023

The Research, Development, and Innovation Division, formerly known as Winetech, is an integral component of the newly established wine industry body called South Africa Wine. South Africa Wine (SA Wine) operates as a non-profit company, providing vital support services across the wine and brandy industry’s value chain. The overarching goal of this initiative is to enhance the industry’s resilience, transformation, agility, and competitiveness. The primary objective of the SA Wine Research, Development, and Innovation Division (RDI) is to support the wine industry by funding academic research projects, offering specialised technical expertise, and facilitating the exchange of knowledge. These efforts are directed towards addressing pressing challenges and uncovering novel prospects within the industry. Research endeavours include vineyard management, pest and disease control, grape and wine quality enhancements, climate change adaptations, water efficiency improvements, and adopting sustainable production practices. This publication serves as a comprehensive compilation, summarising the outcomes of projects concluded in 2022 and those currently underway in 2023. The projects are organised according to the respective specialised committees overseeing them. The primary aim of this book is to promote awareness regarding the research projects initiated by South Africa Wine while also spotlighting the dedicated researchers contributing to these initiatives.

Kind regards South Africa Wine Research, Development and Innovation Team

OUR TEAM GERARD MARTIN: RDI Executive (gerard@sawine.co.za) ANEL ANDRAG: RDI Manager – Viticulture (anel@sawine.co.za) DR ADRIAAN OELOFSE: RDI Manager – Oenology (adriaan@sawine.co.za) DR KARIEN O’KENNEDY: Knowledge Transfer Manager – Oenology (karien@sawine.co.za) BRIGITTE CYSTER: Administrative Officer (brigitte@sawine.co.za)

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The South Africa Wine Research, Development, and Innovation flagship programmes are large scale, strategically focused, and highly ambitious research initiatives. They have been designed to tackle complex and significant challenges facing the South African wine industry. Within each programme, all the individual projects tie into each other to provide more comprehensive outcomes. The programmes are long-term endeavours that receive substantial financial support. Currently, three flagship programmes address climate change, water efficiency and plant breeding. These programmes aim to push the boundaries of knowledge production and innovation. They explore new and groundbreaking ideas, methodologies, and technologies, contributing to scientific progress and technological advancements. 2 FLAGSHIP PROGRAMMES

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2. FLAGSHIP PROGRAMMES CLIMATE CHANGE

CLIMATE CHANGE

Climate change has significant implications for the cultivation of grapevines for wine production. The grape-growing process is sensitive to climate conditions, and any shifts in temperature, rainfall, and extreme weather events can have positive and negative impacts on vineyards and wine production. Because of climate change, economic pressures and future water availability limitations to the agricultural sector, information about the suitability of land (soil, terrain morphology and climate) for viticulture is paramount to aid decision-making. The absence of a single, integrated data resource (database) with a user-friendly interface where viticulturists can obtain pertinent information about climate (terrain and soils) was cited as one of the main obstacles to mitigating climate change and preparing for changes in the South African wine industry. Recent advances in geospatial technologies have opened new opportunities for generating accurate climate surfaces. High-performance computing infrastructure and parallel processing allow for generating high-resolution terrain data, known as digital elevation models (DEMs). DEM derivatives are required to interpolate individual weather station records into accurate wall-to-wall climate surfaces where local climatic variations can be modelled. The Terraclim project aims to mine the geospatial database (geodatabase) for climate variability and cultivar suitability information. This goal aligns well with SA Wine’s strategy. The knowledge that will be generated is critical for the wine industry.

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2. FLAGSHIP PROGRAMMES CLIMATE CHANGE

CLIMATE DATABASE AND TERRACLIM TOOL DEVELOPMENT

FShip TerraClim 2022 Dr Tara Southey, Department of Geography & Environmental Studies, Stellenbosch University Project is co-funded by the Department of Science and Innovation Start date: 2022

AIM AND INDUSTRY RELEVANCE: This project continues to build on the Terraclim project that started in 2019. The initial TerraClim project has provided an excellent foundation for research. The online Terraclim platform (www.terraclim.co.za) is a new, integrated technology tailored to the agriculture sector. It is ideal for aiding long and short-term decision-making at the farm and field level in the context of climate change in the complex terrain of the Western Cape. Terraclim provides high-resolution terrain and temperature information based on a robust climate and terrain database. The project will maintain, extend and improve the climate database and wireless logger networks. However, the initial TerraClim project also generated a wealth of data that has not yet been exploited. This new project aims to mine the geospatial database (geodatabase) for information related to climate variability and cultivar suitability. This research aims to answer the ultimate question of what actions are required to ensure a sustainable future for the wine industry. However, to answer this question, we first need to improve our understanding of climatic variations of the recent past so that we can identify trends and make predictions of how variations may play out in the near- and long-term future. With this background, we can potentially improve our understanding of how climate change may affect the wine industry, especially within the context of what has happened in the wine industry over the past few years. The continuation of the Terraclim project builds on the previous aim to improve our understanding of how the climate in the Western Cape is changing and how the grapevine/plant is responding to these changes. This knowledge is critical for the sustainable future of wine production in South Africa. This project will ultimately: 1) provide up-to-date climate situational reports for within-season decision-making 2) delineate areas most at risk of climate variability to inform new plantings 3) map terroir to understand wine character better 4) identify areas most suitable for the planting of specific cultivars 5) maintain and expand the centralised climate database.

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2. FLAGSHIP PROGRAMMES WATER EFFICIENCY

WATER EFFICIENCY

Water efficiency in viticulture is becoming increasingly important due to climate change impacts becoming evident. Consistent water scarcity is a long-term threat to grapevine production, particularly in the water-scarce South Africa. Like many other agricultural operations, vineyards can significantly impact water resources, so implementing water-efficient strategies is essential for the industry’s long-term viability and environmental stewardship. Water efficiency in viticulture requires a combination of sustainable practices, thoughtful water management, and the adoption of appropriate technologies. The commercial demonstration blocks of the Flagship Water 2 project showcase reduced water’s effect on production levels. The Flagship Water 3 project compares the reaction and potential adaptation of several cultivars and rootstocks to reduced water availability, a goal of the Water Programme. Innovative monitoring tools derived from the completed Flagship Water 1 are being incorporated and showcased to implement more effective monitoring/managing of plant water stress. Flagship Water 4 will provide a novel resource to the SA Wine Water Programme: a potted vineyard comprising 29 plant combinations (grafted and ungrafted vines). It extends and draws on the other flagship water projects (FShip Water 1-3) and will mainly support the ongoing research and showcasing of results obtained from FShip Water 3. The potted trial includes additional scion/ rootstock combinations (grafted and ungrafted) not evaluated in FShip Water 3. With the vines planted in pots, greater control can be achieved.

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2. FLAGSHIP PROGRAMMES WATER EFFICIENCY

INTEGRATED VINEYARD MONITORING SYSTEM TO IMPROVE WATER MANAGEMENT FShip Water 1 Dr Carlos Poblete-Echeverría, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University Project completed: 2022 AIM AND INDUSTRY RELEVANCE: Multiple technologies were tested for monitoring the response of vines to water deficit, considering spatial and temporal variability. The conceptual idea was to capture information at different levels by implementing five monitoring units (Unit 1 – Micrometeorological, Unit 2 – Meso and microclimate, Unit 3 in-vine monitoring, Unit 4 – In-soil monitoring and Unit 5 – Remote sensing). Field data were collected during two growing seasons (2019-20; 2020-21), and the spatial variability was analysed considering this temporal effect indicating intra-season changes as well as between the seasons. The main results were obtained under natural variability conditions (Commercially irrigated). The treatments (Dryland vs Double irrigation) were implemented only to have control conditions for testing the new methods. The experimental block was defined as homogenous, and all practices were always done evenly in all block areas. However, with the datasets collected in this project and the subsequent analysis, it was possible to implement a water stress classification of the experimental block using a geo-statistic approach. The results indicated a spatial variability higher than 30% for most analysed parameters. Three water stress classes were defined and geolocated. The statistical analysis of the proposed classification showed significant differences in fruit and wine quality parameters analysed among the water stress classes. The results of this study support with solid evidence the effects of water stress on fruit and wine quality parameters. The vines under middle and severe water stress conditions presented higher values of most quality indicators (e.g., anthocyanins, tannins, and sugar); however, the yield was highly compromised, with up to 50% decreases in the most extreme conditions. The results of this study and improvements in the methodologies (data analysis, settings and hardware) are used as a basis for future projects.

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2. FLAGSHIP PROGRAMMES WATER EFFICIENCY

DEMONSTRATION OF PLANT-BASED IRRIGATION ON WINE-GRAPE PERFORMANCE AND QUALITY IN THREE CLIMATICALLY DIFFERENT REGIONS

FShip Water 2 Mr Vink Lategan, Department of Soil Science, Stellenbosch University Start date: 2019

AIM AND INDUSTRY RELEVANCE: Previous research has shown that wine grapes need 250 to 350 mm irrigation water for optimum yield. However, this was primarily determined for vineyards in the coastal region under normal winter and spring rainfall conditions. Consequently, it needs to be established if these irrigation amounts will be sufficient in the warmer, drier grape growing regions, and if not, to what extent they should be adjusted. The objective of this study is to develop guidelines based on grapevine water status for wine grape irrigation. In order to apply the minimum irrigation requirement, sound irrigation scheduling practices are essential. This project will be conducted in the form of demo plots in established commercial vineyards, in three climatically different areas (Stellenbosch, Breedekloof and Olifants River). Irrigation scheduling will be done based on plant water potential values based on previous research and compared to the grower’s normal scheduling practice. The effect of the treatments on vegetative parameters, yield and water use efficiency will be evaluated. Since this project will be carried out in a number of vineyards, it is an ideal opportunity to validate remote sensing systems, e.g. satellite or drone images, for application in a variety of commercial vineyards. Experimental wines will also be made and evaluated while economic factors will also be considered. The knowledge on grape and wine responses will empower growers to save irrigation water while obtaining the best wine quality and maximum profit.

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2. FLAGSHIP PROGRAMMES WATER EFFICIENCY

PRODUCING QUALITY GRAPES WITH LIMITED WATER

FShip Water 3 Prof Melané Vivier, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University Project is co-funded by the Water Research Commission Start date: 2022

AIM AND INDUSTRY RELEVANCE: This study aims to evaluate and compare the adaptability and resilience of current commercial scion/rootstock combinations established and maintained under both optimal and sub-optimal water conditions using a holistic approach and novel techniques. The study’s main hypothesis is that grapevines (scions and rootstocks in combination) display adaptation to non-lethal water limiting conditions (through intrinsic and extrinsic factors) that can lead to their resilience to water stress conditions. From a practical point of view, this project intends to answer questions like “Can commercially planted scions/rootstocks adapt to much less water and still produce quality grapes?” and “What would be the critical aspects to consider towards such a goal?”. These seem like simple questions, but they cannot be answered without recognising the complex interaction of many factors that influence a vine’s success and resilience in a specific (natural or manipulated) environment. Therefore, they are currently largely unanswered. The Water Research Programme provided a model vineyard where grapevine water stress studies can be conducted over the lifespan of grapevines on a vineyard scale. This vineyard was designed (site selection, row layout and rootstock-scion selection) by the Water Programme Committee Workgroup and established in 2020 through a partnership between VinPro, Winetech and Stellenbosch University. The model vineyard will be a long-term resource to transfer knowledge and skills to the industry and viticulture students on the topic of grape production with limited water. It can showcase the outcomes of limiting water on a seasonal basis and over many seasons on a range of scion/rootstock combinations. The impact of innovative technologies in monitoring water stress could also be showcased.

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2. FLAGSHIP PROGRAMMES WATER EFFICIENCY

A MODEL VINEYARD IN POTS TO STUDY GRAPEVINE/ SCION RESPONSES TO WATER LIMITATION

FShip Water 4 Prof Melané Vivier, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University Start date: 2023

AIM AND INDUSTRY RELEVANCE: This research will aim to generate scenarios of water limitation on grapevines that can test the impact of the timing of and the severity of the water limitation, as well as the ability of the vines to adapt to the limitation and recuperate after successive drought scenarios. This project will provide a novel resource to the SA Wine Flagship Water Programme, namely a potted vineyard comprising a robust experimental design of 29 plant combinations (grafted and ungrafted vines), repeated nine times. It extends and draws on the other FShip Water projects (Fship 1-3) and will particularly support the ongoing research and showcasing of results obtained from Water Fship 3. The potted trial includes additional scion/rootstock combinations (grafted and ungrafted) not evaluated in FShip Water 3. With the vines planted in pots, a greater level of control can be achieved, a unique feature. When the plants experience water stress and to what level the stress will develop can be controlled. Any soil and geospatial variability are removed by using pots, and the genotype responses can be monitored with fewer confounding variables. More severe stress responses in a shorter period can be generated due to the limited soil volume, and rain can be excluded by covering the pots. Furthermore, the location and layout of the trial make it ideal for sensor and technology testing. This study will yield both academic outputs and practical information suitable to be transferred to the industry. The potted vines and the planned experiments will be ideal for showcasing the impacts of the modulated water limitations. The trial will serve as a demonstration site for indus try professionals and other stakeholders and where student engagement and training can occur.

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2. FLAGSHIP PROGRAMMES PLANT BREEDING

PLANT BREEDING

Plant breeding in viticulture is a crucial aspect of grapevine cultivation aimed at developing new grape varieties with improved traits to meet the changing demands of consumers, vineyard conditions, and winemaking practices. Plant breeding involves selecting and crossing grapevine parents with desirable traits to produce new vines, which are then evaluated and selected based on specific criteria. In this programme, we are focusing on the following: • Breeding of new, high-yielding cultivars tolerant to Botrytis, downy and powdery mildew that can deliver high-quality wines. • Implementing a molecular breeding programme for wine grapes to accelerate our transition to modern marker-assisted breeding. • Developing grapevine plant material that can withstand drought better through genome editing. • Incorporating “microvine” to reduce breeding timelines.

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2. FLAGSHIP PROGRAMMES PLANT BREEDING

BREEDING WINE GRAPES RESISTANT TO POWDERY AND DOWNY MILDEW

P04000058 Ms Phyllis Burger, ARC Infruitec-Nietvoorbij, Stellenbosch Start date: 2014

AIM AND INDUSTRY RELEVANCE: The aim, ultimately, is to breed new, high yielding cultivars, that will produce high quality V. vinifera type wine and have tolerance to downy and/or powdery mildew and/or to Botrytis under local conditions. In this project crosses are made to develop cultivars with disease tolerance and good crop and wine making characteristics. OBJECTIVES OF THE PROJECT INCLUDE: • Screening of seedlings obtained from crosses for tolerance to downy and powdery mildew; • Identifying potential parents with disease tolerance and suitable qualities to be used in crosses; • Making crosses, stratifying and germinating seeds; • Developing and establishing seedlings in tunnels and older plants in vineyards; • Identifying and importing cultivars with tolerance to fungal diseases, if possible.

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2. FLAGSHIP PROGRAMMES PLANT BREEDING

INITIATION OF MOLECULAR BREEDING: TOWARDS NOVEL AFRICAN WINE GRAPE CULTIVARS FShip Breeding Dr Justin Lashbrooke and Prof Melané Vivier, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University and Ms Phyllis Burger, ARC Infruitec-Nietvoorbij, Stellenbosch Project is co-funded by the Department of Science and Innovation Start date: 2019 AIM AND INDUSTRY RELEVANCE: The early stages of this project involve the establishment and implementation of specific methods and workflows (e.g. genotyping and phenotyping platforms) so that marker assisted selection could be implemented in our local grapevine breeding programme. This will give breeders the ability to select for the desired characteristics at a significantly earlier stage in the breeding cycle and in a much more directed way (i.e. evaluating seedlings for the presence of resistance genes, or combinations of genes, without having to grow mature plants). The platforms will also be used to accurately profile (genetically and phenotypically) the existing breeding materials in South Africa, allowing for future crosses to be made with concrete genetic knowledge, and more predictable (phenotypic) outcomes. This project is therefore the first foundational activity towards implementing a molecular breeding programme for wine grapes in South Africa, and will significantly strengthen the existing breeding programme conducted by Phyllis Burger at the ARC (refer to Project number: P04000058). In order to optimally and efficiently accelerate our transition to modern marker assisted breeding, there will be a focus on implementing the latest relevant technologies essential to this approach. Moreover, international collaborations with partner institutions already successfully involved in this sphere, will allow for the exchange of knowledge, but also access to valuable breeding materials with known increased resistances and other valuable characteristics, relevant to our local industry.

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2. FLAGSHIP PROGRAMMES PLANT BREEDING

GRAPEVINE CRISPR-2: INTRODUCING DROUGHT TOLERANCE IN GRAPEVINE CULTIVARS

FShip GenUS 21-01 Prof Melané Vivier, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University and Prof Johan Burger, Department of Genetics, Stellenbosch University Project is co-funded by the Department of Science and Innovation Start date: 2021 AIM AND INDUSTRY RELEVANCE: This project aims to provide proof of the principle of gene manipulation, specifically genome editing, as an approach to developing grapevine plant material (both scion and rootstock) that can withstand drought better. Grapevine drought tolerance is a critically important aim toward sustainable production of quality grapes and derived products. Still, it is a difficult scientific quest due to the multitude of plant and environmental factors that interact and ultimately shape the response of a given rootstock and scion variety to limiting water conditions. When selecting rootstocks, one of the first parameters considered is drought tolerance. The information gained from studying the modulating effect of the below-ground rootstock on the above-ground scion’s water response, however, presents a complicated picture that shows that the scion also contributes to local responses, specifically in aspects of stomatal opening and closure. This project emphasises developing the first practical applications for the CRISPR technology established in the grapevine recently. In response to industry needs, researchers decided to concentrate on drought tolerance in both scion and rootstock cultivars since it is one of the most serious conditions impacting negatively on grapevine production in South Africa. In a best-case scenario, the efficacy of CRISPR technology to address these real-life issues will be demonstrated, albeit still as a proof-of-concept, and it will contribute to future research in this field.

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2. FLAGSHIP PROGRAMMES PLANT BREEDING

SPEED BREEDING VIA THE CREATION OF SHORT LIFE CYCLE MICROVINE PLANTS

FShip GenUS JL 23-01 Dr Justin Lashbrooke and Prof Johan Burger, Department of Genetics, Stellenbosch University Start date: 2023

AIM AND INDUSTRY RELEVANCE: Extracted from the research proposal presented by Dr Lashbrooke and Prof Burger: Grapevine breeding is time-consuming, largely because the species is a woody perennial with a long-life cycle. The time from seed to seed typically ranges from five to seven years. One way to overcome this problem is the incorporation of “microvine” into breeding programmes. Microvine is a grapevine mutant that has a seed-to-seed cycle of about six months. Incorporating microvine will allow the ongoing breeding programme to dramatically reduce timelines while building on the knowledge generated in previously funded Winetech projects. Cultivars generated through this approach can be used to dramatically reduce breeding times, accelerating our efforts and bene fiting the industry with novel cultivars in a shorter time. Importantly, novel cultivars bred using this approach will contain no transgenic material and can be considered non-GMO.

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3 VITICULTURE RESEARCH

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3. VITICULTURE RESEARCH NEW PROJECT

3.1 GRAPEVINE PROTECTION – INSECTS AND PESTS ESTABLISHING A BARCODING DATABASE OF LOCAL PESTS OF DECIDUOUS FRUIT

SU-EE PA 23-01 Prof Pia Addison, Department of Conservation Ecology and Entomology, Stellenbosch University Start date: 2023

AIM AND INDUSTRY RELEVANCE: This project aims to develop new knowledge regarding South African pests and to have an ac curate, repeatable and rapid identification method for such pests to ensure market access and good management. Morphological identifications of insects can be problematic when dealing with immature stages or species complexes, such as with the banded fruit weevil complex and fruit flies ( Ceratitis rosa and Ceratitis quilicii ). Immature insects (e.g. fruit-fly larvae) must be reared first since morphological identifications can only be made with adult insects. With validated sequencing, where pest insects are identified by taxonomists and sequenced molecularly, it will be possible to establish a reference database for South African pest insects, especially those that are local and barcoding sequences are not available. South Africa is experiencing a shortage of taxonomists for various insect groups, which means there will be no experts available for morphological insect identifications in the future, as very few people are being trained to take over. Accurate insect identifications significantly impact the management of pests, specifically those of quarantine significance, since incorrect identifications lead to loss of access and financial implications for growers. The outcome of this project will allow for easier identifications by people not trained as Entomol ogists. It is critical, however, to establish a good morphological base on which to make these sequences available.

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3. VITICULTURE RESEARCH PROJECT IN PROGRESS

THE ECOLOGY OF LOBESIA VANILLANA IN WINE GRAPE VINEYARDS, WITH EMPHASIS ON MANAGEMENT OPTIONS

US ENT 17-A3 Prof Pia Addison, Department Conservation Ecology and Entomology, Stellenbosch University Start date: 2016

AIM AND INDUSTRY RELEVANCE: Lobesia vanillana is a pest species that was recently confirmed to attack wine grapes in the Western Cape. Grapes have not been listed as a host for this pest, therefore we know nothing of its ecology in vineyards. Preliminary observations have indicated that this could be a severe, direct pest that appears to be expanding its host and geographic range. The project aims to address the following questions: 1) What are the most efficient trapping systems to use for monitoring Lobesia , 2) what chemical and biological management practices could be applied to control its populations and, 3) what is the basic life cycle and ecology of L.vanillana in South African vineyards. Apart from taxonomic literature and one host list, excluding samples from the Western Cape, no information is available for L. vanillana . The aim of this study is therefore to obtain data on basic ecology and possible management, with focus on biological control, to develop an initial management strategy.

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3. VITICULTURE RESEARCH COMPLETED PROJECT

IDENTIFICATION AND CHARACTERISATION OF NATURALLY SUPPRESSIVE SOILS SPECIFIC TO RING NEMATODES (Criconemoides xenoplax)

P04000280 Dr Rinus Knoetze, ARC Infruitec-Nietvoorbij, Stellenbosch Project completed: 2022

AIM AND INDUSTRY RELEVANCE: Ring nematodes are one of the most common and abundant nematode species in vineyards. Understanding the crop management practices that modulate the suppressive activity of the soil microbiome towards plant parasitic nematodes (PPN) will lead to long-lasting and cost-effective crop production. This study aimed to detect, identify and characterise soils that maintain specific suppressiveness to ring nematodes. Sites that showed suppression, as determined by the lab assays and pot trials, also had high to very high numbers of ring nematodes, which seems to result from a density-dependant biological component in these soils. Ring nematode numbers and relative suppression are also associated with higher levels of P and Ca, although these correlations were weak and not statistically significant. Ring nematode numbers were negatively correlated with soil enzyme activity, indicating lower numbers of nematodes at higher levels of these soil enzymes. It seems that increased microbial activity in the soil, associated with higher levels of these soil enzymes, could inhibit the reproduction of ring nematodes in these soils. High ring nematode numbers were positively correlated with the nematode-based index, EI, which parallels the intensity of nutrient enrichment in the soil. High values of EI indicate equivalent levels of food availability, which leads to an increase in the ring nematode population. Management practices should be targeted towards the inducement of nematode suppression in vineyards. Many factors stimulate or create suppressive conditions against PPN, such as microbiota activities, organic matter amount, chemical composition and physical constitution. The presence of nematophagous fungi in soils with high ring nematode numbers was not able to suppress the ring nematode population in those soils, but healthy soils have increased microbial activity, which has a suppressive effect on ring nematodes. Therefore, practices aimed at enhancing these microbes in the soil could lead to lower levels of ring nematodes. However, certain practices, like the overuse of inorganic fertiliser and the indiscriminate use of organic amendments, could have adverse effects, increasing the number of ring nematodes in the soil.

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3. VITICULTURE RESEARCH COMPLETED PROJECT

POLYPHAGOUS SHOT HOLE BORER (PSHB) AND ITS FUNGUS IN SOUTH AFRICAN VINEYARDS

US FR 20-01 Prof Francois Roets, Department Conservation Ecology and Entomology,

Stellenbosch University Project completed: 2022

AIM AND INDUSTRY RELEVANCE: Polyphagous Shot Hole Borer Beetle (PSHB) is a devastating pest that carries the wilt fungus Fusarium euwallaceae, which can cause significant economic damage. This project aimed to characterise the pathogenicity of F. euwallaceae to grapevine and assess its effect on grapevine health in the Western Cape Province. The researchers tested the pathogenicity of the fungus on Vitis vinifera cvs. Merlot and Cabernet Sauvignon on the Nietvoorbij experimental farm in Stellenbosch using a modified inoculation technique that mimics beetle activity on more than 100 individual vines of each cultivar. The effect of the application of plant fertiliser on fungal growth was also determined. Lesion development around inoculation points in grapevine consisted of dark staining penetrating no more than 2 mm into the xylem. The fungus never presented any significant lesion development, and after three months, no further lesion development was observed, and the fungus could not be re-isolated, indicating that the fungus could not survive within these tissues for prolonged periods. Therefore, the fungus and PSHB do not seem to pose any immediate threat to grapevines. However, South Africa is host to more than one genotype of the beetle and likely a different Fusarium species. This allows these organisms to evolve virulence and cause future outbreaks on non-usual hosts. New genetic material may also continuously enter the country due to limited support for goods inspections at borders. Therefore, continuous monitoring for possible infestations should be conducted to determine if the beetle is present at a site and whether it can successfully infest grapevines. This has become more crucial since the first discovery of PSHB colonisation attempts in a vineyard in Somerset West in February 2022.

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3. VITICULTURE RESEARCH COMPLETED PROJECT

GENETIC DIVERSITY OF GRAPEVINE MITES IN SA

GenUS BvA 18-01 Dr Barbara van Asch, Department of Genetics, Stellenbosch University Project completed: 2022

AIM AND INDUSTRY RELEVANCE: The diversity of eriophyid grapevine mites needs to be better understood in South Africa and worldwide. This study assessed the species diversity of eriophyid grapevine mites found in bud and leaf blisters in the Western Cape using a combination of DNA-based and electron microscopy analyses. Genetic diversity was assessed using Sanger sequencing and a novel species-specific multiplex Polymerase chain reaction (PCR) method. Morphological diversity was evaluated using cryo-scanning electron microscopy (cryo-SEM). The results showed that grapevine mites in South Africa and worldwide comprise at least five species that can be distinguished genetically but is not morphologically distinguishable by light or electron microscopy. However, the researchers did not find exclusive associations between a given species and a particular plant symptom; this means that a causation effect species-symptom could not be clarified. Different genetic groups are often co-present in the same plant tissue. Some associations (but not exclusive) between genetic groups and plant symptoms were found. Knowledge of the biology of these organisms is minimal, and the results set the foundation for new studies. Designing a Real-Time PCR test for detecting grapevine mites will be possible. Still, two difficulties remain, the tiny amount of DNA and the potential existence of more species in the worldwide distribution of grapevine mites in addition to the five species discovered by the researchers. The importance for producers is that until now, they have assumed that there is only one type of mite that causes bud symptoms and galls and another type that causes symptoms of leaf curling and blisters on the grapevine leaves. Therefore, the general advice was to treat these separately as caused by different strains. However, the researchers’ genetic studies show that although there are indeed different types of mites, they are not limited to specific parts (leaves or buds) of a grapevine. If producers only spray when they see bud symptoms but ignore blisters on leaves, those same mites could reappear in the buds the following season.

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3. VITICULTURE RESEARCH NEW PROJECT

3.2 GRAPEVINE PROTECTION – FUNGI AND BACTERIA

THE PRACTICAL IMPACT OF SEXUAL REPRODUCTION OF GRAPEVINE POWDERY MILDEW ON REDUCED FUNGICIDE SENSITIVITY

P04000325 Dr Minette Havenga, ARC Infruitec-Nietvoorbij, Stellenbosch Start date: 2023

AIM AND INDUSTRY RELEVANCE: This project will develop new knowledge regarding the primary inoculum, dominant reproductive strategy and basic biology of the powdery mildew fungus. Factors that will be evaluated include environmental requirements, the level of reduced sensitivity to DMI and QoI fungicides in South African vineyards and the effect of post-harvest application on chasmothecia development. Powdery mildew causes serious economic damage in all grape-growing regions. Only a few sexual structures (chasmothecia) were observed in 1996-1999 in Stellenbosch. Since 2015, high num bers of chasmothecia have been common on leaves at the later stages of the growing season in Western Cape vineyards. Sexual reproduction may lead to better-adapted individuals that are less responsive to fungicides. Due to climate change, Western Cape springs are becoming wetter. During bud break, conditions are now more favourable for releasing sexual spores. Asexual and sexual reproduction require different conditions, yet the primary inoculum for the infection is unknown. Therefore, disease models cannot effectively predict fungicide timing. In dustry experts suspect reduced sensitivity to QoI and DMIs. The project aims to determine the primary inoculum source, the level of reduced sensitivity and the effect of sexual reproduction on reduced sensitivity. The project aims not to determine whether specific products have a reduced efficacy but to evaluate biological factors contributing to decreased management. The results will provide information to calibrate prediction models accurately to the environmental requirements of the dominant reproductive system, which will increase the efficacy of fungicide spray programmes and reduce overall fungicide use.

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SOUTH AFRICA WINE RESEARCH 2023

3. VITICULTURE RESEARCH NEW PROJECT

NEW PRUNING WOUND PROTECTION STRATEGIES AGAINST TRUNK PATHOGENS IN ROOTSTOCK MOTHER VINES

P04000333 Prof Francois Halleen, ARC Infruitec-Nietvoorbij, Stellenbosch Start date: 2023

AIM AND INDUSTRY RELEVANCE: A previous project (P04000108) concluded that rootstock mother vine pruning wounds remained susceptible to Phaeomoniella chlamydospora infections for up to 42 days after pruning. Although several chemical, biological and chemical + biological treatments reduced P. chlamydospora inci dences in artificially inoculated Ramsey and 101-14 Mgt. pruning wounds, the study recommended that more pathogens and rootstock varieties be investigated. Fungicide mixtures will also have to be evaluated to broaden the efficacy of treatments to protect vines against the onslaught of several pathogen groups that all differ in their sensitivity towards fungicides. The use, availability and range of fungicides are under increased pressure worldwide. The search for alternative or biological control agents is crucial to securing sustainable grape production and market access. The study aims to evaluate chemical and biological control agents in various combinations to provide effective pruning wound protection against a range of grapevine trunk pathogens to pro duce high-quality propagation material. There is no published literature on the use of chemicals or biological control agents on rootstock (Vitis spp.) pruning wounds. All previous studies were done on wounds in vineyards (Vitis vinifera) and were not always tested against a wide range of grapevine trunk disease pathogens. The duration of rootstock wound susceptibility across a wide range of grapevine trunk disease pathogens is unknown in SA and worldwide. The benefit of the project to the industry will be a significant contribution towards producing high-quality grapevine propagation material that will contribute to higher take percentages in grapevine nurseries and better establishment of young vines in new vineyards.

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3. VITICULTURE RESEARCH PROJECT IN PROGRESS

FORMULATION AND EVALUATION OF MICROBIAL CONSORTIA FOR BIOLOGICAL CONTROL OF GRAPEVINE FUNGAL PATHOGENS SAGWRI ES 22-01 Prof Evodia Setati, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University Project is co-funded by the Department of Science and Innovation (DSI) and the National Research Foundation (NRF). Start date: 2022 AIM AND INDUSTRY RELEVANCE: The study’s main objective is to construct yeast-bacterial consortia that have antifungal activity against grey rot and mildew disease agents in grapevines and can be used as biocontrol agents. Existing biocontrol agents are mainly single species formulations which are sometimes ineffective under varying environmental conditions. Globally, there is growing interest in reducing the number of chemical fungicides used to control grapevine pathogens such as Botrytis cinerea , Plasmopara viticola and Erysiphe necator . Alternative biological formulations comprising microbial strains are commercially available for use in vineyards. However, not all of them work effectively and consistently under varying field conditions. Consequently, further research is necessary to identify new biological agents with higher efficacy. In the current study, we aim to generate multi-species microbial consortia for the biological control of bunch rot, powdery mildew and downy mildew. Existing biological control agents are based on single microbial species. We believe that multi-species consortia comprising strains with different modes of action that grow optimally under different environmental conditions will offer more efficacy in field conditions. By selecting organisms that do not negatively affect wine fermentation and are tolerant to chemical fungicides currently in use, we believe we can generate biological control agents that can complement existing fungicide spray programs and reduce chemical fungicide use.

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3. VITICULTURE RESEARCH PROJECT IN PROGRESS

DETERMINING FACTORS THAT MAY REDUCE/SHORTEN THE PRODUCTIVE LIFESPAN OF ROOTSTOCK MOTHER PLANTATIONS

P04000235 Prof Francois Halleen, ARC Infruitec-Nietvoorbij, Stellenbosch Start date: 2019

AIM AND INDUSTRY RELEVANCE: The aim of this project is to identify factors that may reduce or shorten the productive lifespan of rootstock mother blocks. In this study, physical, physiological and pathogenic detail will be considered on the same mother material. This approach has not been followed before and may provide answers that are hitherto unknown. Accumulation of pathogen infections inside rootstock mother vines will occur over time through pruning wounds. Currently the risks associated with ageing rootstock mother blocks are unknown as most of these infected rootstock canes will visually appear as healthy. In practice it is unknown at what age mother blocks require replacement. Results from this project can provide local grapevine nurseries, rootstock mother block owners and the Plant Improvement Scheme with scientifically based information and guidelines on how the productive lifespan of rootstock mother blocks can be managed. This allows for proper planning for replacement of such mother blocks in order to ensure sustainability at farm level. It could potentially make a positive contribution towards higher take percentages in nurseries. However, more importantly it will improve the phytosanitary status of grafted vines which will lead to better establishment success and healthier vines with a longer productive lifespan for the wine industry.

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3. VITICULTURE RESEARCH PROJECT IN PROGRESS

EFFECT OF MECHANICAL PRUNING ON GRAPEVINE TRUNK DISEASES

P04000236 Prof Francois Halleen, ARC Infruitec-Nietvoorbij, Stellenbosch Start date: 2019

AIM AND INDUSTRY RELEVANCE: The objective of this research project is to study the effect of mechanical pruning (MP) on the incidence and severity of grapevine foliar, fruit and trunk diseases compared to conventional pruning. Locally, a lot of research has been done on MP however, the effect on the incidence and severity of major leaf, fruit and trunk diseases, especially the long-term effect in terms of sustainable production, is unknown. The project will compare the incidence and severity of the following, in MP versus hand pruned vines: • Foliar and fruit diseases (powdery and downy mildew, botrytis and Phomopsis); • Leafroll virus and mealybugs; • Pruning wound infections. Researchers will also identify and determine the incidence of inoculum (fungal fruiting bodies) on wood, canes and leaves of MP vs hand pruned vines. The study aims to provide the local grapevine industry with new information on the risks and benefits associated with MP and to make recommendations to prevent inoculum build-up and wound infections. Potentially these recommendations can help to increase the lifespan of such vineyards in order to complement other benefits of MP like reduced labour costs, increased production and acceptable or increased wine quality.

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SOUTH AFRICA WINE RESEARCH 2023

3. VITICULTURE RESEARCH NEW PROJECT

3.3 SOIL AND WATER

MEASURING THE EFFECT OF COVER CROPS ON SOIL AND VINE HEALTH, AND GRAPE QUALITY

EXPCo G32-22 Dr Annika Pienaar, Experico, Stellenbosch Start date: 2023

AIM AND INDUSTRY RELEVANCE: This project aims to build on existing knowledge and investigate the effect of cover crop mixes on soil health and grapevines. With increased interest in more sustainable farming practices, more research is being done on using cover crops in agricultural systems. Local cover crop trials have recently been conducted in vineyards, focusing on cover crop mixes and their success, cover crop biomass and weed suppression. Using the right cover crop mix can increase soil moisture, improve soil structure, suppress weeds and pests, increase plant-available nutrients and improve crop resilience. This, in turn, reduces irrigation, pesticide, and fertiliser costs. In this project, the viability of growing cover crops under the vine and growing permanent cover crops will also be investigated. Analysis of nematode communities will add to the knowledge base of nematode host status of cover crop species. Care will be taken to include cover crops that will have a suppressive effect on inoculum and infestation levels of pathogens and/or pests. This project aims to provide the industry with crucial information to fill the knowledge gaps about selecting cover crops to improve the properties and ecology of soil in vineyards.

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3. VITICULTURE RESEARCH NEW PROJECT

SOIL HEALTH MANAGEMENT FOR SUSTAINABLE VITICULTURE: A FRAMEWORK FOR RESEARCH AND ON-FARM PRACTICE

SAGWRI ES 23-01 Prof Evodia Setati, South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University Start date: 2023

AIM AND INDUSTRY RELEVANCE: This project aims to identify key soil health indicators and threshold values to generate guidelines on best practices for analysing soil health in South African viticulture and draft a report highlighting common soil health indicators relevant to the wine industry and a Soil Health Research framework to aid producers with decision-making around soil health interventions. In viticulture, healthy soil is crucial to support grapevine growth and the production of good-quality grapes. For this purpose, the soil must have balanced physical, chemical and biological attributes. To assess this, regular testing is conducted. A suite of physical, chemical and biological indicators is measured and interpreted against known threshold values. However, critical soil values for some biological indicators were adapted from orchards and therefore are not specific to grapevines. Furthermore, biological indicators, such as soil microbial biomass, measure the total size of the microbial population but not its composition or functional potential. Consequently, existing criteria and guidelines for interpreting soil health assessment data and how to best use the outcomes to sustain economically feasible and effective grape production do not always adequately facilitate decision-making. Existing threshold values can be refined to generate more viticulture realistic target values. Several outputs will be generated from the study. These include: A draft framework for soil health research and measurement in viticulture and wine production An infographic will be created to be used as a reference tool for soil health and with other tools for training workshops or webinars.

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3. VITICULTURE RESEARCH PROJECT IN PROGRESS

A NOVEL METHOD THAT TURNS WINE INDUSTRY EFFLUENT INTO VALUABLE PRODUCT STREAMS

UWC BB 20-01 Prof Ben Bladergroen, South African Institute for Advanced Materials Chemistry Energy

Storage and Fluid Treatment Centre, University of the Western Cape Project is co-funded by The Department of Science and Innovation Start date: 2020

AIM AND INDUSTRY RELEVANCE: In this project, an unconventional, unprecedented, inventive, ground-breaking and robust technology will be tested on winery effluent. Previous research has shown it is a promising alternative to current available technology. Costs associated with both water consumption and waste water treatment form an ever increasing portion of the operational budget of many wineries, exacerbated by reduced rainfall and more stringent municipal regulations around effluent discharge. Re-use of winery wastewater for irrigation purposes without treatment is often not recommended as the Chemical Oxygen Demand (COD) and Total Dissolved Solids (TDS) levels cause the water to be an unfit source. The potential for water re-use in the wine industry is great but currently the cost of water treatment plants is too high, specifically for many small to medium scale wineries. This new technology aims to address major shortcomings of current treatment systems and other challenges. These include cost efficiency of wastewater treatment and reducing the suspended solids, COD and TDS levels of effluent, making the treated effluent more compatible as a source for irrigation water.

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