Table grape rootstocks in South Africa

5 Guidelines for rootstock selection The presence of nematodes in the soil is the primary consideration when selecting a rootstock for table grapes. However, phylloxera should not be disregarded. Currently, the five most widely used rootstocks for table grape production, viz . Ramsey, R 110, P 1103, R 99 and US 8-7 show good to high tolerance against root-knot nematodes and very good to excellent tolerance against

phylloxera. Two rootstocks which performed well in trials and have high potential for use with table grapes, namely Dog Ridge and SO4, are very good to excellent and good to very good in terms of resistance against root-knot nematodes, respectively. Both rootstocks also have good resistance to phylloxera. All table grapes in South Africa are cultivated in medium to high potential soils. Optimal cultivation practices are applied, including establishment, cultivation, fertilisation and irrigation. Correction of soil acidity (pH) and nutrient deficiencies (e.g. P and K levels) are done during soil preparation. Consequently, new vineyards that are developed are established under highly favourable conditions, resulting in vineyards with well developed root systems. These particularly favourable conditions, along with the inherently strong vigour of “newly” imported and other cultivars, together with the use of Ramsey as rootstock, often result in excessively vigorous vines. It can increase canopy management costs, adversely affects the grape quality pre-harvest as well as during cold storage and the decreases fertility of the vines. Excessive growth of grafted vines is one of the most critical viticultural challenges that table grape growers deal with. Rootstocks often influence vine vigour, but rootstock alone cannot resolve the problem of excessive growth. Site characteristics (e.g. overhead protection such as hail nets or plastic covering), environmental conditions (climate and specifically soil quality) and available water (irrigation and rainfall) may also significantly influence rootstock performance of table grape vineyards.

A Ramsey bunch (Photo: Jan Avenant)

For selecting the correct rootstock, specific steps should be followed: STEP 1: Eliminate less suitable poor rootstocks Eliminate rootstocks or specific rootstock clones that have poor compatibility and/or poor affinity with the chosen scion cultivar. STEP 2: Classify the potentially best rootstocks GROUP 1 Rootstocks with strong vigour: Ramsey and Dog Ridge These rootstocks may induce rapid and vigorous growth, depending on the inherent vigour of the scion cultivar. Vines can, therefore, be fully developed within the season of establishment. Most scion cultivars produce good to excellent quality table grapes, with good berry size on these rootstocks.

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