Apple rootstock evaluation in the Witzenberg Valley

The objective of this study was to evaluate new dwarfing, semi-dwarfing and semi-vigorous rootstocks from the GENEVA® range against the South African industry standard rootstocks.

‘Rosy Glow’ scions grafted on G222, CG3007, Cepiland, Lancep, M793, M7, MM106, M9 RN29, MM109/M9 rootstocks were planted in 5 blocks at 4 x 1.25 m spacing as the “dwarfing site” while scions grafted on G222, G.228, G778, CG934, M25, M793, Maruba and MM109 rootstocks were planted in 6 blocks at 4 x 1.5 m spacing as the adjacent “semi-vigorous site” in the Witzenberg Valley. The scions on M793 and G222 rootstocks 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.

The trees on CG3007 and M.9 Nic29 rootstocks were the biggest while the trees on G222 and M793 trees were the smallest at planting. The trees on M9 RN29 rootstocks were the most dwarfing trees. On vigorous site, the trees on Maruba rootstocks were the biggest followed by the trees on G778 and G.228 rootstocks. The trees on the G222, M793 and MM109 rootstocks were much smaller. The trees on M25 and CG934 rootstocks were amongst the tallest at planting. In 2013, the Cornel Geneva® rootstocks produced better yields than the industry standard rootstocks at both sites (dwarfing and vigorous). During the 2014 harvest season, the greatest yield efficiency was with trees on CG3007, M9 RN29 rootstocks while the lowest yield efficiency was with trees on M793, MM106 and M7 rootstocks. During the 2015 harvest season, the trees on G778, M9 RN29, and MM109/M9 rootstocks yielded more efficient than expected from their expected size. Both trees on M9 RN29 and MM109/M9 rootstocks performed better than other dwarfing rootstocks during the 2015 season. The trees on M9 RN29, MM109/M9, and G778 rootstocks were precocious and yield efficient during the 2016 season. The trees on M9 RN29, MM109/M9, and G778 rootstocks appeared to be more yield efficient than expected from their size. Trees on Lancep rootstocks yielded efficiently but seem stunted with smaller average fruit size compared to other M9 clones. During the 2017 season, the trees on G778, M9 RN29, and MM109/M9 outperformed all the rootstocks and yielded more efficient than the other rootstocks.

The trees on M9 RN29, MM109/M9, and G778 rootstocks were precocious, productive and yield efficient than the South African standard rootstocks (M7, M25, M793, and MM109). Therefore, the G778 rootstock has potential to replace the current vigorous industry standard M793 and MM109 rootstocks.