Evaluating more yield efficient dwarfing, semi-dwarfing and semi-vigorous rootstocks for the South African apple industry

摘要

South African apple growers utilise the vigorous M793, MM109 and M7 rootstocks due to the perception that dwarfing rootstock are poorly adapted to their harsh Mediterranean-type climate (32-34°S latitude). Also, apple trees express pronounced basal dominance under South African low chill conditions while soils are generally poor and extremely variable. Due to increasing production costs, variability on the tree and to remain internationally competitive, there is a need to migrate to more precociousand yield efficient rootstocks that are tolerant to marginal soils and warm climatic conditions. The objective of this study was to evaluate new dwarfing, semi-dwarfing and semi-vigorous rootstocks from the GENEVA~R range against the South African industry standard rootstocks. 'Rosy Glow' on G222, CG3007, Cepiland, Lancep, M793, M7, MM106, MM109 with an M9 interstem, and M9 RN29 were planted in 5 blocks at 4x1.25 m spacing as the "dwarfing site" while G222, G228, G778, CG934, M25, M793, Maruba and MM109were planted in 6 blocks at 4x1.5 m spacing as the adjacent "semi-vigorous site" in the Witzenberg Valley. M793 and G222 were included in both plantings for comparison. Both plantings were made in 2010 on a fumigated site previously planted to apple. Trees were managed according to industry recommendations and assessed for vegetative and reproductive performance. As expected, tree size generally correlated negatively with yield efficiency. Trees on M9 RN29, MM109/M9 and G778 in particular are proving considerably more yield efficient than expected from their size. Lancep trees are also very yield efficient but seem stunted with smaller average fruit size compared to other M9 clones. The yield performance of M9 RN29 and MM109/M9 for high density plantings and G778 for weaker sites and at lower density is very encouraging.