P22 



W27EMLA 



B.469 



Mar1( 



B491 



P16 



0.3 



P2 



B.9 



M.26 EMLA 



M9 EMLA 



MS Pajam 1 



V.I 



M.9 Reuren 56 



M.9 NWKBT337 



M.9RN29 



MS Pajam 2 





iX; 



20 



The most planted apple 

 rootstock of the 1970's and 

 1980's, M.7, produces large 

 numbers of root suckers. 

 Growers tolerated this level of 

 suckering, because M.7 re- 

 sulted in a well-adapted, 

 productive tree that was a 

 dramatic miprovement over 

 seedling-rooted trees. 



Rootstocks which result in 

 fijily dwarf trees generally do 

 not produce root sucker to 

 anywhere near the extent that 

 M.7 does. In this trial, M.9 

 Pajam 2 and P. 16 generated 

 the greatest number of root 

 suckers, 23 and 24 per tree, 

 respectively, in seven years 

 (Table 1). Because of ex- 

 pected planting density, this 

 level suckering would be a 

 problem with P. 16, possibly 

 resuhing in as many as 5,000 

 suckers per acre per year. 

 Levels seen with other 

 rootstocks likely would not 

 present significant practical problems. 



Obviously, yield is a major consideration when 

 assessing rootstock performance. Actual yield per tree, 

 however, is misleading. In this study (Table 1) as in many 

 others, the yield per tree is more closely related to tree size 

 than to rootstock directly. The ultimate assessment would 

 be yield per acre, but that would require conducting an 

 experiment first to determine tree size then a second 

 experiment to compare rootstocks with each combination 

 planted out at an appropriate spacing relative to tree size. 

 Neither resources nor time are available to allow this 

 approach. So, it is customary to use yield efficiency to relate 

 yield to tree size. The relative differences in yield efficiency 

 among rootstocks may reflect differences in potential yield 

 per acre. Cumulative yield efficiency (1996-2000) does not 

 vary greatly in this trial (Table 1, Figure 2). Very few 

 statistically significant differences exist. It is possible to 

 suggest that trees on 0.3, B.491, and P. 1 6 are more yield 

 efficient than trees on M.26 EMLA. Also, trees on 0.3 are 

 more efficient than those on V. 1 or P. 2. Otherwise, the bulk 

 of the rootstocks result in similarly efficient trees. 



Fruit size can be affected by rootstock. In this trial 

 averaged over all cropping years, size varied from just 

 smaller than 100-count fruit (190 g) to just larger than 160- 

 count fruit ( 1 20 g). Generally, the rootstocks that would be 

 considered to have poor performance because of small fruit 



"mi 



iiii!; 





Wi'.'.'.'iV.'i i ' 



;:?3-r; 



^t^ 





40 60 80 100 120 140 160 



Average fruit weight (1996-2000) 



180 



Figure 3. Average fruit size (g) from 1996-2000 from Gala trees on several 

 rootstocks in the Massachusetts plandng of the 1994 NC- 140 Apple Rootstock 

 Trial. 



size were P.22, M.27 EMLA, B.469, Mark, B.490, and P. 1 6. 

 These are also the most dwarfing rootstocks. Generally, the 

 M.9 clones resulted in the largest fruit over the five fruiting 

 years of this study. 



This study will conclude after three more seasons, but 

 we can make some conclusions at this point: 



1 . P.22, M.27 EMLA, B.49 1 , P. 1 6, B.469, and Mark 

 result in relatively weak trees that produce small 

 fruit. It is likely that these rootstocks should be 

 avoided except with the most vigorous scion 

 cultivars. 



2. Among the remaining rootstocks, yields per acre 

 from appropriately spaced plantings will be similar. 



3. M.9 continues to be a solid performer. Yield is 

 good, and fruit size consistently is among the highest. 

 It IS important to understand differences among M.9 

 clones, however. Most of these differences relate to 

 tree vigor. Trees on the most dwarfing M.9 clone 

 (Fleuren 56) have about half the trunk cross-sectional 

 area of trees on M.26 EMLA after seven growing 

 season. Whereas, trees on the most vigorous M.9 

 clone (Pajam 2) are nearly as large as those on M.26 

 EMLA. 



ic i: ic ic ic 



Fruit Notes, Volume 63, 2000 



