White root tip dynamics of bearing apple trees in a Mediterranean climate, South Africa

White root growth peaks have been reported on numerous occasions in the northern hemisphere (NH) for deciduous crops and forest plantings. Variation from the bimodal seasonal pattern was reported, but apple trees usually conformed to this pattern. Only a few papers on this subject reported on findings in Australia (1972) and no information is available on new cultivars and rootstocks that were planted thereafter. A CID root scanner was used in existing orchards in the Elgin area to quantify average white root tip dynamics non-destructively for three growing seasons. White root tip production dynamics showed similar bimodal seasonal pattern for bearing 'Golden Delicious', 'Cripps Pink' and 'Fuji' orchards, with peaks in summer and autumn/winter. This was irrespective of rootstock, soil type or management practices. The occurrence of a summer root growth peak agreed with existing literature, except that it started later mid-November, than in the NH. The summer peaks were smaller compared to the respective postharvest peaks and agree with literature. The unusual long root growth peak in June started shortly after harvest, and continued through winter until the end of August, and may be due to relative high soil temperatures in this area. This is unique to local conditions and may impact on the tree carbohydrate and nutrient reserve status.