134
Table 2. Average fruit weight of ‘Gala’ apple on 10 dwarfing rootstocks at British Columbia for three seasons. Values are least-squares means, adjusted for missing observations and crop density (CD). In 2003 there was a significant rootstock by CD interaction, so least squares means were compared at three CDs (3.0, 5.6, and 7.0 fruit·cm⁻² TCA).
| 2001 | 2002 | 2003 | |||
| Stock | CD = 3.0 | CD = 5.6 | CD = 7.0 | ||
| M.9 EMLA | 190 a | 177 b | 142 b | 151 ab | 156 a |
| M.26 EMLA | 194 a | 180 ab | 169 ab | 143 b | 129 b |
| M.9RN29 | 202 a | 197 a | 156 ab | 159 a | 161 a |
| M.9 Pajam1 | 197 a | 187 ab | 180 a | 161 a | 151 a |
| M.9 Pajam2 | 195 a | 189 ab | 166 ab | 157 a | 153 a |
| B.9 | 194 a | 185 ab | 153 b | 154 ab | 155 a |
| O.3 | 196 a | 181 ab | 169 ab | 162 a | 158 a |
| V.1 | 196 a | 187 ab | 165 ab | 152 a | 144 ab |
| Mark | 161 b | 137 c | 122 c | 129 b | 134 b |
| M.9T337 | 203 a | 197 a | 165 ab | 161 a | 159 a |
2 LSmeans within columns were compared with PDIFF, P=0.05.
designs, scion cultivars, rootstocks and statistical methods may vary. This is the second trial with ‘Gala’ where trees on B.9 produced relatively large fruit. However, these results also contradict those of the previous trial (14), where trees on Mark produced intermediate sized fruit and trees on M.26 EMLA consistently produced small fruit. The positive relationships between FW and CD, as indicated by the positive slopes, were unexpected because there are many reports of a negative relationship between these two variables (1, 9, 12, 20). There are several possible explanations for these unexpected results. 1) Some cooperators may have thinned trees too late in the season to substantially improve fruit size. 2) The number of replications may have been too low to obtain the true relationship because unusual observations can be highly influential when there are few replicates. 3) The unexpected results most likely resulted from the narrow range of crop loads. In most thinning experiments, treatments are selected that will produce a wide range of crop loads. However in rootstock studies, cooperators use various fruit thinning techniques to obtain crop loads that would encourage good fruit size and adequate return bloom. For these reasons, typical rootstock trials and orchard observations may not be appropriate for evaluating the influence of rootstocks on fruit size. Perhaps the influence of crop load on FW is relatively minor and inconsistent when trees are thinned adequately. Ideally, experiments should be designed specifically to evaluate the influence of rootstock and cultural practices on fruit size. Such experiments would involve wide ranges in CD and overlapping CDs for all rootstocks or treatments. NC-140 cooperators are currently conducting a study to evaluate the effects of rootstock on FW over a wide range of CDs and results from that study may help explain previous inconsistent results.
orchard observations may not be appropriate for evaluating the influence of rootstocks on fruit size. Perhaps the influence of crop load on FW is relatively minor and inconsistent when trees are thinned adequately. Ideally, experiments should be designed specifically to evaluate the influence of rootstock and cultural practices on fruit size. Such experiments would involve wide ranges in CD and overlapping CDs for all rootstocks or treatments. NC-140 cooperators are currently conducting a study to evaluate the effects of rootstock on FW over a wide range of CDs and results from that study may help explain previous inconsistent results.