Technical Yearbook 2024

JULY

RESEARCH UPDATE

The quest for new Pinotage clones

(mutations for berry colour and leaf hairiness) and the Chasselas group (mutations for leaf shape, berry colour and aroma compounds). Clonal selection programmes are typically employed to enhance a cultivar’s diversity by identifying and testing unique characteristics that offer subtle and desired diversity. Given the predominance of relatively few Vitis vinifera cultivars grown globally, clonal selection has been central to plant improvement strategies for wine grapes for years. Gamma irradiance can enhance the rate of somaclonal mutations and the likelihood of observing potentially valuable changes that could enrich the cultivar in the form of unique clones. This technique has been widely used to generate variation in various plant species. The Pinotage Diversity Project A project was initiated under the leadership of Phyllis Burger (ARC Infruitec-Nietvoorbij) and Prof Melané Vivier (SAGWRI – South African Grape and Wine Research Institute) to attempt to enhance clonal diversity in Pinotage by accelerating mutations that typically lead to clonal diversity. The first phase of this multiphase project, conducted from 2017 to 2018, was dedicated to optimising the methodology to create mutations in three existing Pinotage clones. This established a gamma-irradiated Pinotage collection of approximately 1 500 plants with potential mutations. The second phase of the project lasted from 2019 to 2023. This phase involved characterising the collection of plants that originated from irradiation and comparing them to the three original Pinotage clones. A subset of the plants was chosen to establish in a field trial of 500 plants, including controls. The collection was successfully planted in 2021 and evaluated over two seasons already. The residual plants were also planted in the field in 2022 for further analysis. The results from this phase of the project were presented to the Pinotage Association, requesting their input in the selection of desired traits in clones going forward. The third phase, which started in 2024, aims to build on the previous work and conduct viticultural and oenological analyses on chosen subsets of the vines to identify potential material for new clonal selection of Pinotage. An overview of the project phases and the evaluations that form part of each of the stages are outlined in Figure 1. Results of the project so far The study’s main findings were as follows: • In general, a tendency for a decreased rate of phenological development of irradiated grapevines

Pinotage was developed in South Africa in 1924/1925 and planted commercially since the 1950s. Few commercial clones of Pinotage are available for planting, and their viticultural and oenological properties are quite similar. Given the importance of Pinotage for South Africa, the existence of only a few commercial clones is a limitation. The potential for a more diverse set of clones is desirable and crucial for this cultivar’s continued success and growth. How clones occur The occurrence of naturally varying traits within a cultivar is rooted in environmental influences, particularly light quantity and quality, which could induce somatic mutations over time. This process leads to noticeable differences from the original vine, such as yield, vine architecture, phenological progression, etc. These variations can also be reflected in the wine, affecting factors like phenolic content, sugar-acid ratios, aroma components, etc. When these mutations lead to pronounced differences, such as changes in berry colour and/or leaf shapes, the plant material is usually considered a new cultivar. More subtle variations in traits, for example, looser clusters or earlier/later ripening, would lead to potential new clones. Clones and sometimes new cultivars typically arise in especially very old cultivars widely grown under diverse conditions. Well-known examples are the Pinot group South Africa Wine research projects P04000060 and P04000060-2019: Evaluation of induced mutation methods to increase the genetic variability of Pinotage and testing Pinotage mutation plants. P04000060-2024: Analysing induced diversity in a collection of Pinotage plants after gamma irradiance. Project leaders Melané Vivier and Phyllis Burger.

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TECHNICAL YEARBOOK 2024