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PARC
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Growth of Buckeye Gala
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Royal Gala Trunk Cross-section
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Performance of Golden Delicious
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Trunk Cross-section Golden Delicious
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Performance of Aurora Golden Gala
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Trunk Cross-section Aurora Golden Gala
In B.C., growers are chiefly interested in dwarf and semi-dwarf trees to suit high density plantings such as super spindle orchards. Ideally, we want a rootstock with all the good traits of M.9 (rootstock), but with more resistance to fire blight and apple replant syndrome, and ideally greater winter hardiness.
The Agriculture and Agri-Food Canada research centre at Summerland, B.C., has long been a participant in the USDA NC-140 series of collaborative uniform trials of tree fruit rootstocks (www.nc140.org). These trials are a useful way of acquiring new rootstocks to try, and generating practical site-specific data on performance. There are many locations in the trials, each with its own set of production challenges, which helps to identify rootstock strengths and weaknesses more quickly. A recent example is the detection of brittle graft unions with some rootstocks, when high winds associated with a passing hurricane hit some trial sites in the southeastern USA. Certain locations have frequent episodes of fire blight or winter damage, and their reports yield useful information to the whole group.
Here we report the findings from the Summerland site for the NC-140 apple trials planted in 2002 and 2003. In addition, a small independent rootstock trial is described: a trial of four Vineland rootstocks (bred at AAFC in Vineland, ON many years ago).
The 2002 NC-140 trial had ‘Buckeye Gala’ as the scion on 10 rootstocks, and the 2003 trial tested 18 rootstocks with ‘Golden Delicious’ as the scion. In both of these trials, the trees were trained as vertical axes, supported by a post-and-wire trellis. Irrigation and sprays followed local commercial practices. The trees were de-fruited in their second leaf to encourage tree growth and prevent stunting. In later years, the trees were spray thinned at bloom or (in some years) at the young fruitlet stage. Follow-up hand thinning was done to achieve a suitable crop load, generally spaced as one fruit every 6 inches (15 cm) of branch length, in single-fruit clusters. Thinning was normally completed by early July. Root suckers were counted every year in August and then removed (the cumulative number is shown in the tables.) The fruit from each tree was counted during harvest, then weighed, to get yield per tree and average fruit size. The yields were summed over all 8 cropping years. Cumulative yield divided by trunk girth (cumulative yield efficiency) is a measure of the production of fruit relative to the size of the tree.
The rootstocks in these trials were sourced from a variety of countries, including the USA (Cornell-Geneva rootstocks, indicated by “G” or “CG”), Germany (“Pi Au” and Supporter rootstocks), Poland (“P” rootstocks), Russia (Budagovsky (B.) rootstocks), the Czech Republic (“J-TE-” series) and Japan (Morioka rootstocks, or “JM”). Standards were M.9 and M.26. Sub-clones of M.9, M.26 and B.9 from different source nurseries or programs were also tested to see if they differed significantly. The final results (after 10 growing seasons) from these trials are shown in Tables 1 and 2.
The small trial of Vineland (“V.”) rootstocks was planted in 2003. It was managed in the same way as the two NC-140 plantings, but we propagated the trees in our own nursery, and the scion was ‘8S6923’ (fruit trade name Aurora Golden Gala™). The Vineland rootstock trial was ended after 8 growing seasons, and the results are shown in Table 3.
The Summerland results for the three completed trials are summarized below by vigor category. The trunk cross-sectional area (TCSA) is generally used as an indication of aboveground tree size. Note that rootstock performance varies quite a lot from location to location. The results from other test sites can be viewed at the NC-140 web site (www.nc140.org). For commercial use, it is always wise to do one’s own small test planting when trying a new rootstock, before making a significant investment. Management and site factors can affect the rootstock performance profoundly in ways that are not always easy to predict.
Rootstocks more vigorous than M.26
Trees on Pi 56-83, Pi 51-4, JM.2, P.14 and V.4 were significantly larger than trees on M.26. Supporter 4 may also be in this category. Average trunk cross-sectional area (TCSA) of Supporter 4 was bigger than M.26 but the difference was not statistically significant. All these rootstocks had low cumulative yield efficiency (CYE), which indicates they had low production relative to tree size. Trees on both Pi stocks and JM.2 had good survival, low suckering, and good fruit size. With P.14 and Supporter 4, suckering was also low and fruit size was good, but greater rates of tree mortality occurred. P.14 was also slow to come into bearing (low precocity). Tree survival on V.4 was good, but these trees also had low precocity, moderate suckering, and smaller fruit size. Trees more vigorous than M.26 are typically not used for high density plantings like super spindle.
Rootstocks with vigor similar to M.26 or slightly smaller
The rootstocks CG.6210, J-TE-H, CG.5935, Pi 51-11, V.1 and V.2 all produced trees similar in size to those on M.26. Some (but not all) of the individual trees on CG.6210, CG.5935, Pi 51-11 and J-TE-H produced quite a few suckers. CG.5935 had very good yield and yield efficiency, being significantly better than M.26 in these respects. This rootstock has been commercially released as Geneva 935. It is said to be resistant to woolly apple aphids and fire blight, tolerant to replant and crown/root rot, and cold hardy. V.1 and V.2 reduced fruit size slightly, but they had low suckering and otherwise performed well in our trial. The Vineland rootstocks are also reported to be more cold-hardy than M.9 and resistant to fire blight. They can be difficult to obtain commercially.
JM.7 and JM.8 trees were intermediate between M.9 and M.26 in vigor. JM.8 cannot be recommended due to poor survival, and survival was only moderate for JM.7.
Rootstocks with vigor similar to M.9
Rootstocks producing trees similar in size to trees on M.9 included CG.3041, G.16, B.62396, V.3, B.9 and M.9 sub-clones. The best new ones (aside from sub-clones) in our experience were CG.3041 and B.62396, which had good survival, high efficiency and possibly fewer root suckers than trees on M.9-T337, which is the M.9 sub-clone in most common use in the Okanagan Valley. CG.3041 has been commercially released as Geneva 41. It is said to be resistant to woolly apple aphids and fire blight, tolerant to replant and to crown/root rot, and cold hardy. V.3 was also good in most respects but it reduced fruit size slightly. Trees on G.16 had greater losses from tree mortality, and they also had smaller fruit, lower CYE and more suckering than M.9 in some cases. Geneva 16 is also commercially available. Trees on the M.9 sub-clones Pajam 2 and Nic 29 had an undesirable degree of suckering, but they were otherwise similar to M.9-T337 in performance. (These two had larger trees on average than T337, but the difference was not statistically significant.)
Although our trees on B.9 had high CYE, they became stunted, with insufficient new growth and a trend to smaller fruit size and lower cumulative yield. The problem was not a lack of water, because all trees were irrigated. We have had variable results with B.9 in trials over the past couple of decades at the Summerland research station. On good soil, the trees can be slightly larger than those on M.9, but on coarse soils, they seem to lack sufficient extension growth and are liable to “runt out”. A few ‘Gala’ trees on B.9 snapped off at the bud union in a big windstorm one year.
Rootstocks with less vigor than M.9
Rootstocks JM.1 and J-TE-G both produced trees significantly smaller than M.9, and too small to be of commercial interest to most growers in the Okanagan. Although trees on J-TE-G were too dwarfed (similar to trees on M.27 in size), they had virtually no suckering, and their survival and CYE were both superior to trees on JM.1. M.27 is known for inducing smaller fruit size on the scion than M.9, but J-TE-G had good fruit size. It would be worthy of testing if a very small tree was desired.
Sub-clones of M.9, B.9 and M.26
The two sub-clones of B.9 were statistically similar to each other in all respects, except that those on B.9 Europe seemed to produce more suckers. Likewise the two M.26 sub-clones were not different from each other. Among the M.9 sub-clones, performance did not differ greatly. Nic 29 and Burgmer 756 may produce slightly larger trees than M.9-T337, and Nic 29 and Pajam 2 had a greater propensity for suckering. All had good CYE, fruit size and yield.
PARC
We are currently participating in another NC-140 apple rootstock trial, which was planted in 2010, with ‘Honeycrisp’ as the scion. It is too early for conclusions from this trial, but it includes some new Geneva rootstocks and quite a few new rootstocks from the Russian Budagovsky series (the same program that produced B.9). We also have a small trial with some new rootstocks from Agriculture Canada in Quebec. Results from these trials will be available in future. ■
