Evaluation of induced mutation methods in Pinotage to increase genetic variability

By Phyllis Burger

Current Winetech funded project: This project aims to develop a method to increase the genetic diversity of Pinotage. Pinotage, South Africa’s locally bred cultivar, is considered the country’s flagship red cultivar, however very few clones are available to the industry. Pinotage was only bred in the twentieth century (1925) and can be regarded as a “young” cultivar. This means it has had limited time to give rise to mutations compared to other cultivars that have been around for centuries.

Traditional breeding involves crossing two parent cultivars and since grapevine is a heterozygous crop, their off-spring are unique individuals with characteristics varying from both parent cultivars and from its siblings. Thus traditional cross-breeding is not suited to improve or alter single or limited characteristics of an existing cultivar. Genetic modification provides an ideal solution since specific genes can be inserted into an existing cultivar, but there is a lot of controversy and consumer resistance against this technique. Evidence exists that spontaneous bud-mutations result in the formation of new cultivars and clones while induced mutation has been successfully used to develop new cultivars in a number of crops. Induced mutation alters characteristics at random, but allows for the generation of a large number of variations that can be used for possible selection.

Mutations  in  grapes  have  been  induced  by  gamma irradiation of buds, after which plants are established on own  roots  from  the  buds,  or  by  grafting  single-bud cuttings   onto   rootstocks.   Once   the   plants   are established, potential mutants can be selected based on phenotypic differences. The sensitivity of cultivars to irradiation differ, some withstanding higher doses than others.

The   current   pilot   study   explores   irradiation-based mutagenesis of Pinotage by evaluating irradiation doses   and length of exposure to mutagenic agents on different tissues (bud wood, in vitro micro buds and somatic embryos or embryogenic callus).

The results provided three main outcomes: (i) Information was obtained to establish a protocol of the irradiance conditions that are sub-lethal to the materials; (ii) a large collection of irradiated nodal cuttings were obtained for three clones of Pinotage that can now be tested   further   for   possible   mutations   (ARC   and   IWBT);   and (iii) embryogenic callus lines that could be regenerated into plantlets to evaluate the impact of irradiance and somatic embryogenesis in the likelihood to induce mutations (IWBT).

Researchers: Phyllis Burger and Melané Vivier

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