Evaluation of plum rootstocks

The main objectives for this project are: to evaluate high potential imported and local rootstocks on different soil types and climatic conditions and to make recommendations that can complement yield and fruit quality of plum cultivars.

All experimental trees were planted in a randomised complete-block design with 10 replications (only Sonskyn 5 replications and 3 trees/plot) and form part of a bigger commercial orchard. All cultivation practises were the same as recommended for the commercial orchard.

Sandy soils with fluctuating water tables and high numbers of ring nematodes are a high risk for planting plum trees especially on Marianna. Stress situations occur that predisposed trees to bacterial and fungal infestation/development and dieback. Effective drainage systems are the only way to solve the problem. After being drained results showed that ˈAfrican Delightˈ trees on several rootstocks can be recommended for these reclaimed soils. On 90% sandy, high pH soil (KCl of 7.6) and high ring nematode numbers (more than 1000/300 cm³ soil) in Robertson region, ˈAfrican Delightˈ plum trees on the rootstocks Cadaman and Atlas performed well. Forty plus tons per hectare might be the optimal tree potential to assure good fruit weight. Fruit weight of trees on rootstocks like Marianna, Flordaguard, Maridon and Tsukuba 5 are negatively affected by high numbers of ring nematodes whilst fruit of trees on SAPO 778 (cuttings and seedlings) and Flordaguard are negatively affected by the high pH. The rootstock Garnem was not available for this trial.

On less sandy soil (75% sand) with moderate high pH (KCl 7.2) and ring nematode number of less than 400/300 cm³ soil in the Robertson region, trees on GF 677, Atlas and Marianna performed well. Trees on Marianna showed symptoms of iron deficiency, but no effect on yield and fruit weight.

On high clay soils (31% clay) and high numbers of ring nematodes, trees on the rootstocks, Maridon, SAPO 778 (cuttings and seedling) as well as trees on Viking performed well. Dieback occurs when trees are under stress. The peach x almond rootstocks are very sensitive and not recommended for high clay soils.

On drained low-lying sandy soils with fluctuating water tables, Maridon can be recommended because it is less sensitive to bacterial canker, but ring nematodes must be controlled. SAPO 778 is tolerant to ring nematodes, but not suitable for early cultivars and low chilling areas. Atlas will be a good choice because it can handle the sandy soil and tolerate the effects of ring nematodes. On calcareous sandy soil with high numbers of ring nematodes trees on GF 677, Atlas and Cadaman perform the best. On high potential soil with moderate numbers of several nematodes, trees on GF 677, Viking, Atlas and Marianna performed well in terms of yield, fruit weight and yield efficiency. On heavier clay soils (31%) trees on SAPO 778, Viking and Atlas performed well. Maridon can be recommended if ring nematodes are controlled.