Overview of Apple Rootstocks in South Africa

There are currently around 21,000 ha of apples grown in South Africa. High soil temperatures and high solar radiation in summer, insufficient winter chilling, variable, poor and shallow soils, replant problems and virulent Woolly Apple Aphid (WAA) strains place specific demands on rootstock choice. Merton 793 was established as the standard rootstock in South Africa during the late 1960s, yet the use of seedling rootstock also found wide application until fairly recently. From results of rootstock trials conducted from 1967 to 2004 in the main producing regions with a range of scion cultivars, M.793 was confirmed to be the best standard sized rootstock available, while M.7, which is susceptible to WAA and suckering and MM.106, susceptible to Phytophthora, were conditionally recommended as semi-dwarfing stocks, while MM.109, a high vigour stock, was recommended for soils of low fertility and spur types. There is thus a need for an improved range of rootstocks which is more dwarfing, precocious, yield efficient, resistant to major pests and diseases and which are adapted to various soil types and conditions. Hence a range of Geneva rootstocks was imported and a trial established in 2000 in order to find alternatives more suited to modern and sustainable apple planting systems.