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

Leafroll associated viirus particles.

Anatomical and physiological changes/reactions Issuing from characterisation analyses of leafroll infected Cabernet Sauvignon grapevines (Goussard & Underhay, 2004/5), phloem degeneration was observed in petioles. Such anatomical changes were especially characterised by a wavy appearance of the cambium and obliteration (compression), deforming and necrosis of sieve-cells – a situation which proved to be more intense in the petioles of visually heavily infected vs. visually lightly infected grapevines (based on the degree of intensity of leaf discolourations) (Photo 207). With regard to physiological reactions in terms of grape composition, sugar and anthocyanin concentrations especially were significantly lower in the visually heavily infected grapevines. Based on the above-mentioned results/observations, it is possible to explain, as clearly as possible, the effect(s) of such changes/reactions – individually, as well as communally – on grapevine size, leaf and bunch characteristics, shoot mass and root systems.

PHOTO 179. An electron microscopic depiction of particles representative of leafroll associated virus type 3 (GLRaV-3).

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