Canopy Growth, Yield, and Fruit Quality of 'Royal Gala' Apple Trees Grown for Eight Years in Five Tree Training Systems

In 1993, a planting of virus-free 'Royal Gala' apple (Malus ×domestica Borkh.) on 'M.9' rootstock was established at Summerland, B.C., Canada, to determine whether angled-canopy training systems could improve orchard tree performance relative to slender spindles. The trees were trained in one of five ways: slender spindle (SS), Geneva Y-trellis (GY), a modified Solen training we called 'Solen Y-trellis' (SY), or V-trellis (LDV), all at the same spacing (1.2 m × 2.8 m), giving a planting density of 2976 trees/ha. In addition, a higher density (7143 trees/ha) version of the V-trellis (HDV) was planted to gauge the performance of this system at densities approaching those of local super spindle orchards. The plots were drip-irrigated and hand-thinned. No summer pruning was done. After 8 years, differences among training systems at the same density and spacing were small and few. The two Y-shaped training systems had 11% to 14% greater cumulative yield/ha than the SS, but did not intercept significantly more light at maturity. No consistent differences occurred in fruit size or the percentage of fruit with delayed color development among the four training systems at the same density. Relative to the LDV, the HDV yielded less per tree, but far more per hectare, particularly in the first 3 years. After 8 years, the cumulative yield/ha was still 65% greater than with LDV. Yield efficiency was unaffected by tree density. Fruit size on HDV ranked lowest among the systems nearly every year, but was still commercially acceptable. The HDV intercepted more light (73%) than SS (53%). The percentage of fruit with delayed color development in HDV was not significantly different from that for LDV in most years. The trees in HDV were difficult to contain within their allotted space without summer pruning. The substantially similar performance of all the training systems (at a given density, and with minimal pruning) suggests that cost and ease of management should be the decisive factors when choosing a tree training method. scion leaf area, tree size, and vigor, and they impact yield by affecting the relative parti- tioning of photosynthate into fruit growth (Palmer, 1999b). A tree training system is a method of ma- nipulating tree planting arrangement and canopy geometry to improve the interception and distribution of PAR, for the purpose of optimizing fruit quality and yield. Many com- parisons of training systems have been re- ported in the past two decades, and some researchers have purported to find more effi- cient systems. However, the best-performing systems have usually been the ones with the greatest tree density, or the most efficient rootstock. The contribution of the training system in the absence of these confounding factors is unclear. Very few studies offer a direct comparison of training systems with identical tree density, spacing and rootstock. Clayton-Greene (1993) reported on the growth and yield of 'Granny Smith' and 'Starking Delicious' trees trained eight different ways. After 7 years, the training system had only minor effects on performance compared with density. At a given density, he found no evidence for differences in leaf area index or yield among systems, but systems did vary in fruit size and color, the incidence of certain fruit defects, and in yield efficiency. Fruit quality effects were associated with differences in light and wind exposure (Clayton-Greene, 1993; Ferree et al., 1993). Unfortunately no fruit thinning was done in this experiment. Robinson (1992) found that early fruit yields were primarily a function of density, but after 6 years, the cumulative yield (CY) was higher on the Geneva Y-trellis than on central leader trees, provided the angle of the Y-trellis was between 50° and 70°. CY after 8 years on the Y-trellis was 8% to 15% greater than with slender spindle or vertical axis training (Robinson, 1997). The Y-trellis intercepted more light and had higher partitioning effi- ciency. In a separate trial, trees trained as vertical axes or on a Y-trellis differed in nei- ther interception nor yield by year six, if the vertical axis was grown to an optimal height: alley width ratio (Robinson, 1997). In a study of density and training system at constant rectangularity, trees trained as Y-trellis, slen- der spindle, or modified vertical axis showed no differences in interception, yield, yield efficiency, trunk girth, or canopy spread for the first 5 years (Hampson et al., 1997, 1998). Thereafter the Y-trellis intercepted more light and slightly out yielded the other two systems (unpublished data). No direct comparisons involving V trellises could be located in the literature. All these authors remarked on the striking similarity in performance among very different tree shapes and training strategies when other factors were held constant and