Marubakaido is highly susceptible.
Furthermore, Japanese nurserymen gave up propagating M.9
rootstocks by the stooling method.Thus the M.26 introduced as ACLSV virus free has been
mainly used as an interstock for growing dwarfing nursery trees.M.26 has not been
recommended recently for Fuji apples because deeply planted interstem trees on M.26/
Marubakaido are too big for the spacing of 2 m x 4 m (6.5 x 13 feet) to 3 m x 5 m (9.8 x 16 feet).
In addition, M.26 tends to develop many burrknots and trees on M.26 with burrknots are less
productive if planted with the M.26 interstem exposed above ground.Instead of M.26, M.9 has
been recommended for the last 10 years.Several clones of M.9 such as M.9A, M.9 EMLA and
M.9 NAGANO are commercially used in Japan and new clones such as NAKB, FL56, M.9B,
Pajam 1 and Pajam 2 introduced from Europe are being tested in Nagano Fruit Tree Experiment
Station.
M.9 NAGANO which had
been called M.9- (minus) is a selected ACLSV virus-free clone named by the Nagano Fruit Tree
Experiment Station in 1997.It originated from M.9 which was introduced from East Malling
Research Station in England before 1960.Trees on M.9 NAGANO seem to be smaller than
other clones such as M.9A and M.9 EMLA in Japan.Therefore, M.9 NAGANO rootstock
propagated by the stooling method has been recommended for growing small trees adapted for
higher density planting.M.27, CG.10 and CG.80, which have been tested in Nagano, are not
good for Fuji because fruit on M.27 is too small, trees on CG.10 produce many burrknots and
fruit of trees on CG.80 is small and less juicy.It is thought from our experience that rootstocks
which are more dwarfing than M.9 are suitable for Fuji planted closer than 1.5 to 2 m x 4 m (4.9
to 6.5 feet x 13 feet) spacing in hedgerow systems (Table 12).M.9 NAKB (T337), M.9 Pajam 1,
P.16, M.20, G.65, JTE, JM.5, JM.7, JM.8 and some other clones of M.9 rootstocks are
considered to be worthy of further trials in Japan.
ROOTSTOCK ANDPLANTING STUDIES
The rootstock studies in Nagano Fruit Tree Experiment Station have been conducted to select the
best dwarfing rootstocks and establish high density planting systems.
Fuji on M.9 NAGANO during 9 years showed smaller tree size and higher efficiency than those
on M.26.It is concluded that fruit growers should use more dwarfing rootstocks such as
M.9 NAGANO for high density planting of Fuji because M.26 is too vigorous (Table 12).
There is quite a difference in a 20-year study between shallow and deeply planted M.26
interstem trees.Shallow planted trees on M.26/Marubakaido showed weaker tree vigor.In
contrast, deeply planted trees with an M.26 interstem grew too vigorously and attained a tree size
too large for the 1.5 to 2 m x 4 m planting distance.Trees on M.9 NAGANO were smaller than
those on M.26 and showed the best yield efficiency (Table 13).It is also observed that mean
fruit size of trees on M.9 NAGANO were larger than those on others.In conclusion, we
determined that M.9 NAGANO is a promising rootstock for Fuji if trees are planted at spacing of
1.5 to 2 m x 4 m.
Studies were carried out to determine optimum canopy structure and tree growth indices of Fuji
apple trees on dwarfing rootstocks planted in 1.5 to 2.0 m x 4 m spacing.From the results, it is
This study showed that Fuji needed at least 30% relative light intensity (% of full sun) for
production of colored fruit and promotion of flower bud differentiation (Fig. 4).It is also
considered that ground area covered by hedgerow canopy (hedge occupied area, HOA), leaf area
index (LAI, total leaf area per orchard area), shoot length, number of shoots, ratio of growth
terminated shoots (GTS) and leaf color are important indices for tree growth and high quality
fruit production.Optimum HOA and LAI for producing commercially valuable fruit in Japan
are thought to be about 60% for HOA and 1.8 to 2.2 for LAI in mature orchards which have been
planted 1.5 to 2.0 m x 4 m spacing (Tables 14, 15).Fruit quality will be worse as LAI increases
because of higher light interception and lower light penetration.Average shoot length and % of
growth terminated shoots show high correlation to % of poor colored fruit and brix of fruit
(Tables 16, 17).
spacing is 6,000 to 8,000, when LAI is 2.0. In these conditions, trees can bear 100 to 110 fruits
and a yield of 30 to 35 kg is expected. As a result, yield per hectare reaches 40 to 50 tons.
mean shoot length of about 20 cm (8 inches) in early July, ratio of growth terminated shoots is
90 to 95% in mid-June, leaf color as determined by Minolta-SPAD50is 29 to 31 in mid-May and
45 to 55 in mid-June (Table 18).By keeping these optimum indices, it is possible to keep
optimum tree size for above spacing and quality fruit each year.For keeping good tree growth,
selection of dwarf rootstocks such as M.9 NAGANO is most important.If trees are rather
vigorous for the given space, removing every second tree to provide enough space is most
important.
In 1992, we established a trial of rootstocks including M.9 clones and JM.7 (Japan Morioka
rootstock) using Fuji as a scion variety.M.9 VF157 produced the smallest tree followed by M.9
Pajam l, M.9 Pajam 2 and M.9 NAGANO.Trees on JM.7 and M.9 NAGANO/Marubakaido
produced larger trees and showed lower yield efficiency than those on other rootstocks.
Significant difference in tree size is not recognized among trees on other rootstocks based on
these early results for 5 years (Table 19).
M.9 NAGANO/Marubakaido was also established in 1992.The training systems slender spindle
bush and Y-trellis are compared (Table 20).Based on the results for 5 years, trees on Seirin-spur
Fuji on M.9 NAGANO produced smaller trees than standard Fuji but had almost the same yield
efficiency.There are large differences in shoot length and % of spurs per tree between
Seirin-spur Fuji and Fuji.Total shoot length for Seirin-spur Fuji was about half that of Fuji in
the slender spindle bush trees and about one-third of Fuji in Y-trellis trees.Trees trained as
Y-trellis had lower bearing height than those trained as the slender spindle bush, but had similar
TCA and yield efficiency for each variety (Table 20).It is observed that Seirin-spur Fuji has
somewhat stronger alternative bearing habit than Fuji.In conclusion, further studies will be
necessary to adequately evaluate the performance of Seirin-spur Fuji and the Y-trellis training
system.
TRAINING HIGH DENSITY FUJI APPLES
During the 1970s, apple growing in Japan became more intensified.The Dutch slender spindle
system was adopted at that time for mainly M.26 interstem trees on Marubakaido understock.
shaped tree form within its narrow space.The system involved limb bending, a zigzag-shaped
central leader, renewal of upper limbs and shortening the permanent lower scaffold limbs.
Contrary to our expectation, M.26 interstem Fuji apple trees at maturity have generally grown
too vigorously.Mature Fuji apple trees on M.26/Marubakaido tended to change their form
naturally to the forms of a free spindle or vertical axis which have a lower layer of strong frame
branches.Furthermore, removal of every second tree and tree form improvement toward the free
spindle bush are recommended for almost all mature Fuji trees on M.26/Marubakaido planted at
spacing of 2 m x 4 m in Nagano.Enough spacing for canopy volume and light pruning are
important to maintain optimum tree growth.Training of free spindle bush, Hybrid Tree Cone,
Vertical axis and Y-trellis for Fuji trees on M.9 NAGANO rootstock are now under testing in
Nagano Fruit Tree Experiment Station.
The most important first step to form a cone-shaped tree is planting well-feathered 1-year-old
nursery trees or 2-year-old “knip”(cut) trees.Heading back or cutting the central leader has
been done only in the planting year to avoid induction of greater vegetative growth of leader.
Narrow crotch-angled branches which have a diameter more than half of the leader are pruned
off.Branches with narrow crotch angles are bent into a horizontal or a somewhat downward
position in late winter without a heading cut to promote flower bud formation or reduce the
vigor.Upright strong shoots (sprouts) on limbs which have been bent to the horizontal position
are removed.The strong branches on the upper part of leader are removed to maintain the
conical shape.Weeping tips of the fruiting branch are cut back to the flattened position to keep
the fruiting zone close to the central leader by maintaining the balance between fruiting and
reproductive growth.A strong heading cut (bench cut) with a limb is not recommended because
this pruning cut usually causes strong localized shoot growth and abnormal fruit growth with
mineral disorders of fruit such as bitter pit (low calcium).
coloring for varieties such as Fuji which have the characteristic of poor coloring.In general,
Fuji apples color well at 30% or more full sun exposure in growing regions of Nagano.The size
and brix of fruit are also highly related to light exposure.It is generally said that summer
pruning suppresses tree vigor and causes dwarfing by reducing the leaves or rootlets.However,
it is often the cause of an unexpected burst of growth from terminated spurs or axillary buds
below the pruning cut, resulting in poor flower buds when it is done during early summer
(Table 21).Ogata et al. (1986) have shown that flowers of secondary shoots and spurs occurring
after summer pruning tend to bloom late the following spring and produce abnormal-shaped
fruit.The bourse of these flower clusters showed a strange extension growth.In general, branch
bending which enhances the development of vigorous upright shoots (water shoots) has been
recommended in spindle bush training.These upright shoots on horizontal or downward facing
limbs should be thinned out with summer pruning once or twice during the summer in Nagano.
PROPAGATION OF ROOTSTOCKS AND NURSERYTREE QUALITY
It is clear from several experiments over 20 years that mature M.26/Marubakaido interstem Fuji
trees grow too large for their allotted space at 1.5 to 2 m x 4 m spacing.Therefore, stooling
techniques for propagating M.9 NAGANO, which improve dwarfness and efficiency, are being
recommended to permit higher density plantings of Fuji apples.Studies on stooling techniques
of M.9 NAGANO undertaken at the Nagano Fruit Tree Experiment Station show that etiolation
by covering with 3 to 4 cm (2 inch) layer of peat-soil mixture is effective for improving the
![[made with GoClick]](imgs/goclick.gif)
