Project number
P04000060-2019
Project leader
Burger, P
Institution
ARC Infruitec-Nietvoorbij, Stellenbosch and South African Grape and Wine Research Institute, Department of Viticulture and Oenology, Stellenbosch University
Start date
2019
EXECUTIVE SUMMARY
Objectives and Rationale
The ultimate goal of this project was to generate more Pinotage clones, given that only very few commercial clones are available for this important cultivar and that the available clones did not display prominent variation in viticultural and oenological traits. In the first part of this multi-phase project (2017-2018), three widely used Pinotage clones were subjected to gamma irradiance, whereas this second phase aimed to screen the resulting population, select some individuals for field testing and provide a first analysis of vegetative and reproductive traits observed in the population.
Methods
In the previous funding cycle, gamma irradiation was used to stimulate somatic mutations in in vitro cultured plants of three Pinotage clones. Over the course of this project, the resulting plants were hardened off and grown in tunnels where vegetative traits were scored. The population of approximately 1500 plants exhibited a diverse collection of traits, and a sub-population was selected for field evaluation and characterisation. A detailed characterisation of the diversity observed in the vegetative characteristics of 500 plants in a field trial was completed using morphometrics, and the first scoring of grape cluster and berry characteristics was possible for a subset of vines that yielded some bunches in the last year of this phase of the project.
Key Results
The initial similarity and dissimilarity scoring of the 1500 plants allowed the selection of 90 controls (30 per clone, based on similarity with the unirradiated controls), and the rest of the irradiated plants that exhibited dissimilar features (to the controls). Phenological progression of the field trial population indicated that budding time and onset of senescence were altered in many of the population of plants (earlier and later). Moreover, the morphometrics of leaves and petioles confirmed that the irradiance caused increased variation in most of the observed traits. The description of the growth habits (plant architecture) and initial bunch and berry characteristics in the mutant population during the final study year also provided confirmation that the population contained individuals with altered phenotypes, compared to the controls.
Key Conclusion of Discussion
The phenotyping of the mutant population indicated that increased diversity was achieved in several parameters analysed, confirming the potential of gamma irradiance to induce variation. The altered phenological development rates, with some vines displaying earlier or later ripening compared to existing clones holds potential as a parameter in further selection criteria in the population. Similarly, the wide diversity in bunch architecture, berry size, and skin and flesh colours observed is interesting and needs to be studied in more depth in the population. The broad range of canopy sizes and growth habits observed, from very bushy to upright, also warrants further investigation and confirms that the irradiance caused more diverse phenotypes regarding these parameters compared to the controls.
Take Home Message for Industry
This project concludes with successfully demonstrating the efficacy of gamma irradiance to induce plant phenotypic variation in several important vegetative and reproductive traits that could support clonal diversification for Pinotage. The progress made in characterising the mutant population in this project provides the base for the next steps in the project, which would be the preselection of some candidate plants for further evaluation in a clonal selection process.