Table grape rootstocks in South Africa

Successful grafting in the nursery is an essential step in the production of table grapevines. Reports of several problems relating to the grafting of vines in the nursery and with vines that die after vineyard establishment have increased in recent years. The problem is sometimes referred to as incompatibility and sometimes as poor affinity. Compatibility refers to the ability of the rootstock and scion cultivar to combine anatomically and physiologically after grafting (i.e. to unify successfully), thereby producing a strongly growing, grafted vine. Affinity refers to the long-term productive capacity of the graft combination. Therefore, although a rootstock and scion cultivar can be compatible, poor affinity could cause the graft combination to deteriorate after a few years and eventually die. Problems with compatibility are expressed within the same year as when the grafting was done (in the nursery following bench grafting or the vineyard after aerial grafting). Affinity is expressed after establishment in the vineyard, two or more years after grafting or one or more years after planting. Unsuccessful grafting has a major negative impact on both the nursery and producer. A scarcity of grafted plant material of a specific scion-rootstock combination causes these vines to be more expensive than abundant combinations. This situation leads to producers using scion-rootstock combinations that are merely available and not necessarily the best combination for a relevant vineyard site. Unsuccessful grafting inevitably influences the availability of certain scion-rootstock combinations of new and newly imported scion cultivars. In establishing six semi-commercial trials with Merbein Seedless and Sultanina H4 on different rootstocks, the graft success rate for Merbein Seedless and Sultanina was 20.7% and 21.2%, respectively. Two clones of 143 B Mgt were grafted with Merbein Seedless as scion cultivar, with a success rate of 20.7% and 47.4%, respectively. The graft success rate of both the above scion cultivars with Ramsey as rootstock was 50%. Reasons for such failures of Merbein Seedless and Sultanina with 143 B Mgt as a rootstock are largely unclear. Poor graft success rates are often attributed 2 Compatibility and affinity of scion-rootstock combinations

to the quality of the graft material, the graft technique used, callus formation and environmental factors.

COMPATIBILITY is expressed within the same year in which grafting was performed (in the nursery through bench grafting or in the vineyard after aerial grafting).

AFFINITY is expressed after establishment in the vineyard, two or more years after grafting or one or more years after planting.

Compatibility Table 2 and Figure 7 provide information on the compatibility of various table grape scion-rootstock graft combinations. This table and figure have been compiled from information collected from vine nurseries over five years (2012-2016). The graft success rates of certified vines in nurseries (bench grafting) were calculated and used as a benchmark for compatibility. Table 2 and Figures 7, 8, 9 and 10 show that many differences were present between rootstocks, cultivars and clones. Not one of the scion cultivars showed equally good compatibility with all rootstocks (e.g. P 1103 – 38.9%, Ramsey – 40.7%, R 110 – 36.2%, US 8-7 – 38% and R 99 – 36.3%, data not shown). Not one specific rootstock showed equally good compatibility with all the scion cultivars (e.g. Sultanina H5 – 40.1%, Prime – 42.2%, Crimson Seedless – 49.4%, data not shown). It seems as if rootstock choice has a greater influence than scion cultivar on compatibility. There are clear differences in the compatibility of clones of scion cultivars and rootstock. The average graft success rate over all scion cultivars showed that the compatibility for all rootstocks is less than 50%. Figure 7 shows that the best compatibility is obtained with R 110 and P 1103 and the poorest with Ramsey and R 99.

18 Table Grape Rootstocks in South Africa