Induced mutagenesis as a tool for intra-varietal improvement: increased diversity in vegetative, fruit and phenological traits in Vitis vinifera cv. Pinotage

Abstract

Climate variability and rising biotic pressure threaten global viticulture. Modern wine production depends on a limited number of grapevine cultivars, represented by multiple clones that differ slightly in their agronomic, oenological, or stress-tolerance traits. Broadening the genetic base within wine grape cultivars (identifying, conserving and deploying useful phenotypes) is therefore essential for long-term resilience. Induced mutation, using chemical or physical mutagens, could expand the intra-varietal diversity, allowing for the identification of enhanced, heritable traits.

The red-wine cultivar Pinotage is relatively young, compared to well-established cultivars such as Pinot noir, and therefore lacks clonal diversity. An intra-varietal improvement scheme was implemented using gamma irradiation to increase the diversity of current Pinotage planting materials. Gamma irradiation was applied to in vitro plantlets of three widely planted Pinotage clones (Pi7B, Pi45R and Pi48I), resulting in a collection of ~ 1400 putatively mutated plants. Asubset of 500 individuals (irradiated treatment vines and unirradiated somaclonal controls) was pre-selected and field-planted in 2021. Morpho-colourimetric analysis during the juvenile phase assessed leaf and petiole size, shape and colour, with irradiated vines displaying more extreme phenotypes than unirradiated control vines. This trend was also seen when the population bore fruit (since 2023). Phenotyping techniques (using OIV descriptors, image analysis and agronomic measurements), along with phenological scoring (using E-L scale), and ripeness monitoring, were employed to perform the initial characterisation of the fruiting putative mutant grapevines. Diverse phenotypical variation observed in the population included variation in berry skin and flesh colour and bunch compactness. Image analysis focused on differing bunch architectures and compactness, given the links with improved ripening and reduced fungal infections in less compact bunches. The population also displayed a wide range of phenological progressions and ripening periods, with increased variation in the véraison-to-harvest period. This could promote climate resilience, allow balanced phenolic accumulation, and thereby uphold wine quality. Our results on this population will be shared to highlight the potential of gamma irradiation and induced mutagenesis for increasing intra-varietal diversity in grapevine cultivars and clones.

Acknowledgements

We thank our funders, South Africa Wine and the Pinotage Association. We would also like to thank the following individuals for their technical assistance: Ms CK Bruiners, Mr T Brault, Ms R Diljee, Ms V Clayton and Dr ABerry.