Effects of dwarfing and semi-dwarfing apple rootstocks on the growth and yield of 'Gala', 'Fuji' and 'York' apples

A field trial consisting of three apple cultivars (‘Red Yorking’, ‘Rising Sun Fuji’, and ‘Buckeye Gala’) grown on eight to ten dwarfing and semi-dwarfing rootstocks (G.16, G.41, G.935, G.11, G.30, B. 9, M.9 Nic 29, M.26, M.7 and/or MM.111) was established on a research farm (AHS, Jr. AREC, Winchester, VA, USA) in 2011. This trial investigated the effects of rootstocks on tree growth (e.g., trunk cross sectional area (cm²), TCSA), fruit drop, cumulative yield (2013-2017), and cumulative yield efficiency of the scion cultivars. Trees were planted in a 3.6×6.7 m tree spacing and distributed in four randomized blocks (with two trees per experimental unit) for each cultivar. Analysis of the seven-year data set showed significant differences among rootstocks, particularly on tree vigor; with B.9 and G.41 exhibiting the lowest TCSA values; whereas MM.111 and M.26 show the highest TCSA values. Because of their dwarfing effects on the grafted scions, both B.9 and G.41 resulted in the highest cumulative yield efficiency for all three scion varieties. However, in terms of the cumulative yield, B.9 showed the lowest values (55.0 and 87.9 kg tree^‑1) for ‘Gala’ and ‘Fuji’, respectively. The highest cumulative yield for ‘Gala’ and ‘Fuji’ (167.8 and 203.1 kg tree^‑1) was obtained when trees were on G.30 and M.26, respectively. For ‘York’, values of the cumulative yield were not significant between dwarfing (e.g., B.9 and G.41 and more-vigorous (e.g., M.7 and MM.111) rootstocks. ‘Fuji’ and ‘Gala’ trees on G.935 also showed high cumulative yields comparable to those on G.30, but were less vigorous. Taking into consideration the suitability for high-density planting systems, cumulative yield, and reported resistance to fire blight, our results would recommend G.41, B.9 or G.30 for ‘Red Yorking’; and G.41, G.935 or G.30 for ‘Rising Sun Fuji’, and ‘Buckeye Gala’.