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

MUTATIONS/ BUD ABERRATIONS

Tetraploid types This group of bud aberrations (also known in the vernacular as “mannetjiestokke”) are characterised by the shoots appearing thicker and stockier, compared to normal grapevines, while the leaves look bigger, their appearance being slightly creased and their texture tough. The bunches are generally loose, with fewer though bigger berries throughout, that are usually subject to premature ripening. Although such grapevines may sometimes appear interesting, it has consistently been found that this group of aberrations has no commercial value, especially due to considerably lower yields – thereby branding it as a negative mutation. Because deviations within this group may occur at any time in any grapevine(s) across the entire cultivar spectrum, it remains vitally important to identify examples at an early stage; whereafter material should be destroyed, in view of the fact that vegetative propagation of negative traits is a possibility. Coulure types In some cultivars, grapevines are subject to a run-off phenomenon on an ongoing basis. In this regard abnormalities in individual bunches are associated with excessive peduncular matter, combined with far fewer berries – this situation obviously goes hand-in-hand with considerably lower yields (Photo 445). In the case of Muscat d’Alexandrie in particular, grapevines in this category are especially vigorous, with trunks assuming a noticeably thicker circumference, compared to normal grapevines. Aberrations in this group have apparently been observed in Chenin blanc, Cinsaut noir, Crouchen, Gamay, Pontac and White Muskadel among others. Currant types Aberrant types in this category correspond to run-off types to a certain extent, except that a large number of small, round seedless berries are present (Photo 446). In certain instances all the berries in the bunch – with a few exceptions – may be seedless, as with Cape Currants which are an acknowledged mutation of Red Muskadel, while Cinsaut Currants have more berries with seeds. It is commonly accepted that Greek or Zante Currants came about due to a natural mutation of a normal, seeded cultivar. Although currant types are to be found among various cultivars, including Chenin blanc, Grenache noir, Hanepoot and Pontac, so far the only mutations within this group to display any commercial importance have been Zante and Cape Currants. Despite the fact that millerandage is also associated with the incidence of smaller, often seedless berries, occurring in densely packed format

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