Technical Yearbook 2023

MAY

Winetech funds research towards improved Vitis planting material for

the wine industry By Gerhard Pietersen, Katie Usher & Mmapula Lesailane

The aim of the two studies* presented were: 1) to assess the usefulness of commercial ELISA kits against local grapevine fleck virus (GFkV) isolates, validate it for routine use in the certification scheme, and submit recommendations to Department of Agriculture, Land Reform and Rural Development (DALRDD); and 2) to determine whether an emerging exotic virus, grapevine pinot gris virus (GPGV), occurs in South Africa.

Introduction Vegetative propagation is the process of increasing the number of plants of a particular species or cultivar via asexual means. Many plants reproduce this way naturally (e.g., potatoes via tubers, or strawberries via stolons), but vegetative propagation can also be utilised by humankind. Modern viticulture is based primarily on the vegetative propagation of planting material derived from a mother plant of desirable properties using cuttings. The main advantage of vegetative propagation methods is that the new vines contain the genetic material of only the parent from which they were derived, so they are essentially clones of the parent plant. This means that, once you have a vine with desirable traits, you can reproduce the same

FIGURE 1. Steps in certification schemes to produce Vitis plants free of specific viruses. 1) Selection of specific Vitis cultivar maintained at 30°C for three months in vector-free phytotrons (heat therapy). 2) Cutting of a 0.24 mm section of the meristem of the heat-treated vine. 3) Growth of the meristem tissue and regeneration of new plantlets. 4) Establishment of the vine in insect-free greenhouses, called nuclear blocks. 5) Tests to confirm the absence of specific viruses. 6) Establishment of so-called foundation blocks, isolated from other vineyards from which mother blocks and nursery material are propagated for use in industry.

* These studies were conducted during Gerhard Pietersen’s employment at Stellenbosch University and formed the basis of the MSc. studies of Katie Usher and Mmapula Lesailane.

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TECHNICAL YEARBOOK 2023