By
Marnie Aasheim
Abstract
Apple
trees can be propagated by many different means.Grafting,
budding, and layering are among the most popular and widely used methods
of propagation.Selecting the right
rootstock is an essential part of apple tree propagation.
Introduction
Apple
trees (Malus x domestica) are one of the most popular fruit trees grown
in the world today.There are thousands
of cultivars of this popular fruit tree.Methods
of propagation of the apple are numerous and can vary widely.Some
of the most popular methods of propagation are grafting and budding.Layering
is also done for apple rootstocks.Most
apple production today is from clonally propagated fruiting varieties,
which include MacIntosh, Crispin and Red Delicious, which are grafted and
budded onto clonal rootstocks.These
rootstocks are specially selected to affect the size and disease resistance
of the tree.
Methods
of Propagation
Grafting
Grafting
involves joining two pieces of genetically different living plant tissue
together so they grow together as one plant.The
lower part of the compound plant is known as the stock or rootstock.This
is the part that produces the root system.The
upper part is referred to as the scion and produces the shoot system of
the plant.For grafting, a short
piece of the tree of a desired variety is taken and placed onto a limb
of the rootstock. Grafting is usually done during the dormant season and
must be done on dormant scion and stock wood.There
are many methods of grafting, but the main objective is to unite the cambium
layers from the scion and the stock together so the plant grows as one
(California Backyard Orchard 3).
Whip-and-Tongue
Graft
The
whip-and-tongue graft is usually done on small diameter material (6-13mm)
and is one of the strongest types of grafts.High
success rates are seen with this graft because the cambium layers have
a lot of surface contact.When selecting
material for this graft, it is important to have the scion and stock of
somewhat equal diameter.A section
of scion with two or three buds should be used.Identical
cuts are made at the top of the rootstock and bottom of the scion, so the
two pieces fit together nicely.The
first cut is about 1-2.5 inches long and made at an angle with one long
and continuous motion of the knife.This
first cut should be made on the scion in the internode area below the two
or three buds.Smooth cuts are essential
so that good cambium layer contact will occur.
An
identical cut is then made on the rootstock.A
second cut is started about a third of the way down from the tip of the
first cut.This second cut should
be about half as long as the first cut and made parallel to the first.After
this second cut is made on both the scion and stock, the two pieces are
interlocked.They should fit together
perfectly, with no gaps.At this
point, it is very important that the vascular cambium layers come into
contact on one or both sides of the cuts.The
tips of the cuts should also not overlap the material they are grafted
onto to avoid callus knots.The
graft can be held together by budding rubber strips or grafting tape. To
keep the moisture in the tissues, sealing the graft with grafter’s wax
or Parafilm is sometimes done.The
grafts can also be placed in very high relative humidity until the graft
begins to take (Hartmann et al. 439). (See Figure 1 below)
Figure
1-Whip and Tongue Graft
(Source:
Reproducing Fruit Trees by Graftage, Leonard P. Stolz)
Whip
Grafting
Whip
grafts are very similar to whip-and-tongue grafts.The
only difference is that the second cut is not made when doing the whip
grafts. The first cut is again identical to the whip-and-tongue cut (smooth,
sloping and 1-2.5 inches long).The
cut is made on both the scion and stock and the two pieces are fitted together,
making sure good cambium contact occurs.The
graft is wrapped as described above.It
is common for this type of graft to be done on apple tree material with
specialized machines (Hartmann et al. 439).
Budding
Budding
is a form of grafting in which only a bud and a small piece of bark from
a stock is used.For budding to be
done, the bark on the rootstock must be “slipping”, meaning the bark can
be easily separated from the wood.When
the bark is slipping, the plant is actively growing and the cambium cells
are dividing.
T-Budding
T-budding
is usually done on rootstocks that range from 6 to 25 mm in diameter.The
first cut on the rootstock is a vertical cut through the cambium and just
into the wood tissue, about 5 to 25 cm above the soil level.Then
a horizontal cut just above the vertical cut is made to form a “T” in the
bark.The knife is twisted when
this horizontal cut is made to slightly open up the “T” so the flaps formed
can be peeled back.Removing a bud
on the scion is done by making an upward slicing cut about 13 mm below
the bud and then cutting upward to about 2.5 cm above the bud.The
bud is removed then by a horizontal cut about 1.3 to 1.9 cm above the bud.This
bud “shield” is then inserted into the T-shaped cut flaps and slid under
the bark flaps until the top edges are even.The
bud union area is then wrapped with budding rubbers or wrapping tape, being
careful not to cover the actual bud itself.It
is important to not tie the tape or budding rubbers too tight or too loose.The
top part of the seedling rootstock is removed after growth from the bud
occurs (Hartmann et al. 491). (See Figure 2 below)
Figure
2- T-Bud
(Source:
Propagation of Woody Ornamentals by Grafting and Budding, David Hamilton)
Chip
Budding
Chip
budding is done on 13 to 25 mm in diameter material.For
this type of budding, a small chip of bark is cut out from the rootstock
near the base and an identical size and shape chip from the scion is put
back in its place.Identical procedures
for cuts are used for both the scion bud removing and the rootstock chip
removing.A 30-45 degree angle
is cut below the bud and into the wood about ¼ of the way.Then
another cut is made about 1 inch above the bud and sloping downward, cutting
behind the bud.This cut is made
all the way down until it reaches the first cut, thereby completely removing
the bud “chip” from the scion.As
stated previously, identical cuts are made on the rootstock.So
the chip from the scion can then be inserted onto the area of the rootstock
where the chip was removed.Again,
care must be taken to insure the cambium layers from the rootstock and
the scion chip are meeting in the graft area.Contact
is better if the cambium layers meet on both sides, but contact on only
one side is really needed.Wrapping
the chip bud with nursery adhesive tape or transparent plastic tape holds
the two pieces together firmly and keeps the moisture in the bud area.
The tape is cut when the bud start to grow and the top of the rootstock
is removed when the graft has taken, meaning the union is complete (Hartmann
et al. 487). (See figure 3 below)
Figure
3-Chip Bud
(Source:
Reproducing Fruit Trees by Graftage, Leonard Stoltz)
Mound
Layering
Mound
layering is used to propagate apple clonal rootstocks. In this method,
soil is mounded around shoots that have been cut back, thereby stimulating
roots to grow at the base of the shoots.A
year before propagation begins, eight to ten millimeter diameter stock
plants are planted in rows and then cut back to 45-60 cm.They
are then grown for one year.In the
spring, the plants are again cut back, this time to 2.5 cm above the ground.
New shoots gradually form and more soil and bark is added in mounds around
the plants. This cycle may continue on through the growing season (Hartmann
et al. 509). Then the shoots are harvested by cutting close to the bases.The
mother stool beds are then left exposed until further growth of the new
shoots has occurred and another cycle of hilling begins (Hartmann et al.
510).
Rootstocks
When
propagating apple trees, a great deal of attention is put on the roots,
probably more than any other species.Rootstocks
are used for grafting and propagation of apple scion varieties (Apple Tree
Rootstocks 1).
Seed
Rootstocks
When
rootstocks grown from seed are used, the resulting trees are often large,
slow developing and susceptible to dying because of not being able to adapt
to the soil or climate in the orchard (California Backyard Orchard 4).Some
cultivars such as ‘Golden Delicious’, ‘McIntosh’, ‘Winesap’, ‘Yellow Newtown’
and ‘Delicious’ have actually been quite successful though, producing uniform
apples and no incompatibilities.In
the Dakotas and Minnesota, where winters are cold and harsh, the Siberian
crab apple (Malus baccata) and the cultivar ‘Antonovka’ are widely used.Some
example of apples not recommended for use as seedling rootstocks include
‘Arkansas’, “Bramley’s Seedling’, ‘Jonagold’, ‘Tompkins King’, and ‘Mutsu’.All
these are triploid cultivars and have low viability (Hartmann et al. 640).
Clonal
Rootstocks
Clonal
rootstocks are widely used today to get around adaptability problems.Clonal
rootstocks are rootstocks that are grafted onto rootstocks that are genetically
identical clones of a parent rootstock.These
rootstocks are special because they have certain desirable characteristics
including tolerance to winter cold, poorly drained soil, heavy clay or
salty soil, or very dry soil.The
ultimate tree size can be controlled by the rootstock also.Apple
rootstocks are available for dwarf trees all the way through gigantic trees.By
selecting the right rootstock for the conditions in the area, the grower
greatly enhances productivity of the apple trees(Apple
Tree Rootstocks 2).
In
the 1900s, the East Malling Research Station in England started classifying
apple rootstocks based on size.Researchers,
or specifically pomologists, gathered and characterized the clonal rootstocks
that had been used for hundreds of years in Europe by farmers.For
each clone, they assigned a number.Rootstocks
have now been created by breeding, or hybridizing, these clones with other
species and varieties of apples.As
a result, these “Malling” rootstocks are compatible with most apple cultivars
around the world.In later years,
a “Malling-Merton” series of rootstocks was developed to provide resistance
to wooly aphids and a wider range of vigor.Both
the Malling-Merton and Malling rootstock have high yield and excellent
propagation qualities (Hartmann et al. 640).
Dwarfing
Clonal Rootstocks
‘Malling
27’
The
greatest dwarfing affect occurs with this stock.One
and one half to two meter tall trees are the average size for this stock.This
stock can be used as an interstock between the scion and another rootstock
for dwarfing.
‘Malling
9’ (‘Juane de Metz’)
This
is a popular variety in North America, producing small, dwarfed trees ideal
for small areas.Trees wont grow
over 3 meters usually and can be planted relatively close together. After
planting, these trees will produce fruit within one or two years.This
rootstock needs fertile soil and support with staking and trellising.The
roots are thick, brittle, fleshy, and sensitive to cold temperatures. Crown
gall, fire blight, mildew and wooly apple aphid can be a problem with this
rootstock.It can be used as an
interstock and is usually propagated by stooling.
‘Malling
26’
This
is also a popular variety in North America, with better anchorage and ultimate
larger size than the ‘Malling 9’.It
is a cross between ‘Malling 16’ and ‘Malling 9’.Methods
of propagation include softwood cuttings and hardwood cuttings.This
stock usually needs staking and is relatively winter-hardy.Poorly
drained or heavy soils can be a problem in this rootstock, as well as fire
blight and collar rot (Hartmann et al. 641).
Semi-dwarfing
Clonal Rootstocks
‘Malling
7a’
Trees
on this stock are larger than ‘Malling 26’ trees.The
original ‘Malling 7’ was the first of this type, and then a clonal selection,
‘Malling 7a’, was produced to be free of certain viruses that were in ‘Malling
7’.The root system of ‘Malling
7a’ is deeper and stronger than ‘Malling 9’.The
tree produced with ‘Malling 7a’ is semi-dwarfed and bears fruit early.Good
anchorage and tolerance to excessive moisture are advantages of this stock.But
it is susceptible to crown gall, tends to produce numerous suckers and
is not very winter hardy.Propagation
methods of ‘Malling 7a’ included stooling or leaf cuttings.
‘Malling-Merton
106’
This
stock is the result of crossing ‘Northern Spy’ and ‘Malling 1’.Some
advantages of this stock include good anchorage, limited sucker production
and resistance to fire blight.Crown
rot problems have limited the use of this stock, as well as susceptibility
to collar rot.It is also not resistant
to early fall freezes.Propagation
methods of this stock include hardwood cuttings, softwood cuttings and
stooling.
Vigorous
Clonal Rootstocks
‘Malling-Merton
111’
This
stock came from a cross of ‘Northern Spy’ and “Merton 793’.An
advantage of this stock is that it does well on most soil types and is
resistant to wooly aphid and collar rot.It
is susceptible to mildew.Stooling,
hardwood cuttings and softwood cuttings are all propagation methods (Hartmann
et al. 641).
Future
Work Needed
Future
work is needed in developing even more disease resistant rootstocks and
cultivars of apple.With recent advances
in biotechnology and breeding, new genetically modified cultivars will
likely soon be developed.A great
deal of research will need to be done on these genetically altered apple
cultivars, making sure they are safe for food consumption.These
genetic alterations may not happen until years down the road, but I think
future work in propagation of apple trees will likely revolve around genetics.I
think a lot of research will also be needed on developing disease resistant
cultivars, possibly also by genetic engineering.
Works
Cited
“Apple
Tree Rootstocks-Gardening Resources, Cornell College of Agriculture and
LifeSciences.” 14.
Apr. 2002<http://www.hort.cornell.edu/gardening/fctsheet/egfactsh/rootstoc.html>
Hamilton,
David F. and James T. Midcap.“Propagation
of Woody Ornamentals by
Grafting
and Budding.” 21.
Apr. 2002 < http://edis.ifas.ufl.edu/EP031>
Hartmann,
Hudson T., et al. Plant Propagation: Principles and Practices. New
Jersey:
Prentice
Hall, 1997.
Stoltz,
Leonard and John Strang. “Reproducing Fruit Trees by Graftage.” 21.
Apr. 2002
<
http://www.ca.uky.edu/agc/pubs/ho/ho39/ho39.htm>
“The
California Backyard Orchard: A University of California Resource for Fruit
and Nut Crops.” 24. Mar. 2002
<http://homeorchard.ucdavis.edu/general-prop.shtml
- grafting-budding>