A Guide to Grapevine Abnormalities in South Africa - P.G. GOUSSARD

PART 7

GENETIC DEVIATIONS 7

A part from the high degree of diversity associated with it, the occurrence of genetic deviations can be considered to be wellknown phenomena in the SA wine industry. Overall the occurrence of such deviations/mutations can be seen as resulting from sudden changes in the genes (carriers of genetic traits) – a situation(s) which may at any time and in any cell or plant tissue give rise to the establishment of new characteristics. In this way red berries can suddenly occur in a white grape cultivar, or in cases of otherwise normal vines either seedless berry types or run-off bunches can be produced. In addition to the fact that existing traits may gradually, based on heredity regarding mutations, either be improved or weakened, it is important to remain up to date with identification procedures in this regard and obtaining expert advice in confirmation is advised – especially in cases where there may be confusion as to other causes. In light of the fact that certain deviations as are specifically ascribed to mutations can be vegetatively reproduced, the value of overall, continuous and careful intra-cultivar selection, including especially foundation and mother blocks, cannot be overemphasized. On this basis negative mutations can be eliminated before further propagation, while positive traits – in terms of their heredity – can be subjected to further investigations with the application of clone selection. In addition to this, awareness of chimeras and to what extent they differ from real/permanent mutations is encouraged.

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