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

include inter alia Pinot noir and Grenache noir, notably Pinot gris and Pinot blanc in the former, and Grenache gris and Grenache blanc in the latter, being acknowledged as true berry colour mutations. Lesser known/unknown aberrations On the whole the examples mentioned above do not cover the entire spectrum of aberrations that may be propagated vegetatively and which may occur in individual or even several grapevines in a specific vineyard. Based on the economic impact of lesser known and/ or unknown aberrations, ongoing selection is strongly recommended here too – a practice that is obviously not feasible without awareness and a meticulous understanding of: (i) characteristic cultivar traits, as well as (ii) the normal morphological appearance and positioning of all organs in individual grapevines. Typical examples of aberration in this category include inter alia: (i) atypical leaves/shortened shoot growth/poor berry set (in Hárslevelü) (Photos 456 & 457); (ii) flat and double shoots/peduncles/bunch laterals/small, seedless berries (in Durif) (Photos 458 & 459); (iii) exceptionally forked shoots (in Verdelho) (Photo 460) and (iv) atypical positioning of tendrils (cultivar unknown) (Photo 461). CHIMERAS In grapevines the apical meristem of an elongating shoot (AMS) is genetically very stable – making it eminently suitable for application in tissue culture techniques. In instances where an aberration should occur in the developing tissue of the AMS (without dieback of the tissue), shoots have the amazing ability to sidestep such aberrations – in which case the principal shoot is subject to normal growth, while the aberration appears on a lateral shoot, notably as a chimera. Sometimes, however, the aberration is retained on the principal shoot. Such abnormalities do not cause the grapevines to die and are usually limited to one shoot, the prospects being that the shoots may appear normal in the subsequent growing season. Two types of chimeras that occur commonly are the so-called variegated leaf and flat shoot phenomena, the former being associated either with variable yellow and green stripes on the leaf between the veins, or by white leaves with green spots, or even by leaves of which one half is green and the other half white (Photo 462), whereas the latter is associated with broad, flat internodia – often assuming a branched appearance (Photo 463).

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