This describes when grafting and budding occurs:
A. Grafting for Clonal Selection and Propagation of Otherwise
Difficult-to-Clone Plants =
1. When a plant must be clonally propagated to maintain a selected
genotype (cultivar , new sport ), but is difficult to propagate
vegetatively by cuttings or other means, it is often grafted or budded. =
a. Shade tree cultivars of several difficult-to-root species are
routinely budded: =
Norway Maple (e.g. Acer platanoides 'Crimson King') =
Green Ash (e.g. Fraxinus pennsylvanica 'Marshall's Seedless') =
Honeylocust (e.g. Gleditsia triacanthos inermis 'Moraine') =
Littleleaf Linden (e.g. Tilia cordata 'Greenspire') =
b. Other ornamental cultivars =
(1) Cultivars of selected Pinaceae (Pine Family) species with unusual
growth forms =
Dwarf Pine cultivars =
Blue Spruce cultivars such as Picea pungens 'Pendens' =
(2) Bloodgood Japanese Maple (A. japonicum 'Bloodgood') =
(3) Taxus bacatta 'Repandans' =
(4) Upright Juniper cultivars =
c. Find out about these and other ornamental plants. The Nursery Web has
links to many Plant Identification websites
2. Economics - sometimes grafting is less expensive than cuttage =
This is a corollary to A.1. above, since if a selection is difficult to
root, grafting is usually cheaper than cuttage. =
a. Although labor for grafting per se is usually more costly than
cuttage (more time-consuming per unit, and more skilled), the cost of
materials and equipment may be lower if cuttage requires long periods in
a heated greenhouse, with bottom heating, mist, etc. =
b. Cost analysis: Flowering dogwood cultivars: This is the result of an
economic analysis of costs for production of flowering dogwood cultivars
by either budding or cuttings ( Badenhop, 1986). =
3. Budding for delayed self-rooting of slow-to-root species / nurse
(root) grafting (NRG) =
a. Some species are difficult to root from cuttings, because a
conventional cutting cannot stay alive long enough for rooting to occur.
Such "cuttings" may be grafted to a piece of root to keep them alive
long enough for them to become self-rooted. This is called nurse root
grafting. The graft union is planted below the soil line (unlike most
grafting), and eventually the scion becomes self rooted. Afterwards, the
rootstock can either be deliberately removed or it will die off,
especially in cases where the scion and rootstock are not closely
related, resulting in a delayed graft incompatibility. Incompatibility
is discussed in the section on Compatibility. =
In what way is the process of nurse grafting similar to layering? =
Examples: =
(1) Lilac (Syringe vulgaris), until the advent of micropropagation, was
commonly nurse root grafted to California privet (Ligustrum
ovalifolium). Both of these genera are in the Oleaceae family. =
The root piece is typically whip and tongue grafted at the bench during
winter, stored in a cool place where graft union formation occurs, and
then lined out in the field in the spring, where scion rooting occurs. =
Eventually the graft union fails due to delayed incompatibility, and the
privet root piece dies. The likelihood, overall (for any kind of plant),
of an intergeneric graft like this being a compatible scion/stock
combination is low. =
Alternatively lilacs may be nurse root grafted onto one year old root
pieces of seedling Green Ash (Fraxinus pennsylvanica, also in the
Oleaceae). =
In recent years, most lilacs are propagated by tissue culture
(micropropagation). Nurse root grafting has lost popularity because
sometimes the graft union fails before the scion becomes self rooted, or
it will not fail at all, or the rootsystem will sucker, eventually
outgrowing the lilac scion. In the image shown here, this nurse root
grafted lilac apparently did not self root, and after several years, the
lilac/privet graft union broke apart (delayed incompatibility), killing
the lilac. =
(2) Avocado. Nurse seedling graft of avocado rootstocks by the Frolich
method and modifications are described by Reuben Hofshi in the
Subtropical Fruit News, (vol. 4, no. 2, Spring, 1997). The method was
developed as a means of cloning avocado rootstock varieties. Avocado is
very difficult / slow to root from cuttings; hence, grafting. The method
involves grafting a scion, from a clone that is ultimately intended to
be used as a rootstock, onto a nurse seedling. This nurse seedling will
serve as a temporary root system for the scion of this rootstock
variety. New growth from the scion is then etiolated, and then air
layered, in order to induce its own adventitious root system. The rooted
layer is then detached from the nurse seedling and grown on.
Subsequently a scion of a fruiting variety is grafted onto the rootstock
clone. =
View a good video (with audio) of the Frolich method of nurse seedling
grafting of Avocado from the University of California Cooperative
Extension.
(3) In the past, apples were sometimes nurse root grafted before the use
of size controlling clonal rootstocks became common. This illustration
is from Liberty Hyde Bailey's Standard Cyclopedia of Horticulture,
written in the early part of the 20th century ( Bailey, 1924). NRG is
sometimes still used to "bulk up" (rapidly increase the numbers of)
newly selected apple rootstock selections in rootstock breeding programs
such as the one at the New York Agricultural Research Station at Geneva. =
(4) Other examples: Large-flowered Clematis hybrids, Peony, and Catalpa
cvs. =
B. Grafting for repair =
1. Grafting to repair a girdled stem - Bridge Grafting =
a. Young bridge graft =
b. Older bridge graft =
c. Bridge grafting described in an MSU Extension bulletin concerning
rodent damage and "first aid" for trees. =
d. Guy Witney, WSU Area Extension Faculty, describes the use of Bridge
Grafting to repair mouse damage (girdling) of apple trees in Washington
State. =
How is bridge grafting like double working (described in the section on
Concepts and Definitions)?
What time of year (season) is bridge grafting performed? (see Seasonal
Considerations in the section on Required for Successful Grafting and
Budding)
2. To replace a damaged (girdled) trunk base - inarching or bridge
grafting =
Inarching, an in-ground version of approach grafting, is described in
the University of Georgia Extension Web site, Propagating Deciduous
Fruit Plants Common to Georgia =
3. To replace a damaged or diseased root system - inarching =
The picture is from the cover of a 1933 extension bulletin by Thomas &
MacDaniels, which described the use of inarching to repair damage caused
by freezing. =
4. To overcome a delayed incompatibility - bridge grafting or inarching =
C. Grafting to create unusual growth forms - Highworking (see Grafting
by Position)
1. To obtain a tree-like form high working of otherwise naturally
shrubby plants several feet up on a tall straight trunk.
a. Tree (standard) Roses =
Roses that typically grow as low shrubs or climbers can be given an
arborescent (tree-like) appearance by grafting them at the top of a long
straight interstock which is in turn grafted onto a suitable rose
rootstock such as R. multiflora. This would be an example of both
highworking and double working . =
Tree Roses FAQ sheet from the Just Roses Web page =
=
b. Tree peonies =
Peonies from China Web site =
=
c. Weeping Higan Cherry (a cultivar of Prunus subhirtella)
( Picture from Edgar Joyce Nurseries) =
Prunus subhirtella is normally an arborescent (tree) form, but the
variety pendula "weeps," and would grow as a prostrate shrub. It is
grafted ~ 4 - 6' high on a P. subhirtella understock to give a "weeping
tree." =
d. Cariganna aborescens var. pendula
Picture shows high graft union (right), and root suckers from the
rootstock (left). =
=
Why are these suckers upright instead of weeping? =
e. Bonsai =
This ancient Chinese art is, perhaps, the ultimate in tree
"engineering." If the grower wants a branch in a particular location
where none exists, it can be grafted into place, as is described at the
Bonsai Primer Web page =
=
f. Living sculptures created by grafting =
One of the most unusual applications of grafting is its use to create
living sculptures such as chairs, tables, and a variety of strange
abstractions. =
The Arborsmith Studios has many examples of the work of its owner,
Richard Reams, and images of other creative designs from the past. =
D. Grafting to change fruit varieties =
Replacing an old variety on an established tree with an new one for
economic or other reasons is known as Reworking, which is a form of
topworking (see Grafting by Position spatial diagram) =
Seedling fruit trees can take 7 years or so to flower, and even grafted
nursery stock can take several years. An alternative to waiting this
long was, and still is, to a limited extent, to cleft graft a new
variety up into the crown of an established tree. This could hasten
production of the new fruit variety by several years. =
E. Grafting to put multiple scion varieties on a single tree. =
This is an example of Topworking (see Grafting by Position spatial
diagram) =
1. An enjoyable home gardening option. Examples a =
Apple with Macintosh, Granny Smith, & Red Delicious, etc. all on one
tree =
Citrus tree with orange, lemon, grapefruit all on one tree. =
Hibiscus with several cultivars differing in flower color. =
b. Cleft grafting would typically be used for this topworking objective. =
2. According to Ian Merwin, a pomologist from Cornell University,
top-working to shift from a low priced to high priced apple variety is
quite common recently, especially in Washington state. There are
professional grafters who do it relatively cheaply, with a high
percentage take. This practice creates a bearing tree relatively
rapidly, especially if the trunk is not too old. Although some experts
caution about the spread of viruses using this method, Prof. Merwin
states that virus infestations are unlikely today due to the availablity
of virus-free certified scion wood.
F. To provide a pollinizer branch for self-incompatible fruit tree
species =
1. Apples, cherries and some other fruit tree species are
self-incompatible within a clone. =
e.g. Macintosh apple will not self-pollinate, but it will
cross-pollinate with another domestic apple or a crabapple. =
2. In commercial apple production, one pollinizer (often crabapple) tree
is usually planted at the end of each row, but grafting a pollinizer
branch of another variety may be practical (and fun) in the home fruit =
garden. =
G. Grafting to Influence Growth Phase =
1. Grafting to avoid rejuvenation =
a. Generally a grafted tree will come into bearing sooner than a
seedling.
(1) This is because the (adult) growth phase of the scion tends to be
maintained; whereas, a seedling is naturally rejuvenated by the process
of embryogenesis (seed formation) compared to the seed-bearing parent
tree. =
(2) Furthermore, dwarfing rootstocks tend to induce scion precocity,
i.e. they cause a scion to come into flowering one or more years sooner
than it would on its own roots or grafted onto a non-(or less) dwarfing
rootstock. =
b. This avoidance of rejuvenation is exploited by tree fruit growers, to
avoid the long delay (several years) associated with orchard
establishment from seedlings.
e.g. Avocado would come acceptably true-to-type from seed, but several
years of bearing would be lost. Hence top wedge grafting of a scion from
a mature bearing tree onto a seedling understock is commonly practiced
in the nursery production of this tropical crop. =
See autotutorial slide set on Top Wedge grafting of avocado. =
e.g. Many Citrus varieties would come true-to-type from apomictic seed,
since apomixis is a natural form of asexual propagation. Apomictic
seedlings, however, like zygotic seedlings, are juvenile, and flowering
would be delayed for several years, as explained above. Hence, one
reason for T -budding citrus is to avoid seedling rejuvenation. =
see autotutorial slide set on T-budding of citrus. =
It should not be inferred that avoidance of rejuvenation is the only or
even the principal reason for grafting fruit trees. Grafting is also
practiced simply because many fruit tree species (e.g. apple, avocado,
etc.) are difficult to root from cuttings (described above), and in
order to take advantage of specific rootstock effects (described below) =
2. Grafting for scion rejuvenation to facilitate subsequent rooting of
cuttings ( Serial Grafting) =
a. Ease of rooting is a general property of juvenile compared to adult
growth. =
b. Even though a scion from a mature tree tends to retain its adult
growth phase. =
As pointed out in the previous section, an adult scion will be slightly
rejuvenated by grafting onto a juvenile (seedling) understock. Because
this rejuvenating effect is only slight a scion may have to be
sequentially regrafted onto a series of juvenile rootstocks before a
useful degree of rejuvenation has been achieved. Cuttings taken from
this rejuvenated growth tend to root more easily than from mature
growth.
c. This rootstock-influenced gradual rejuvenation of the scion is called
serial grafting. =
d. Serial grafting is an extreme (last resort) method for facilitating
the rooting of cuttings from the mature wood of extremely
difficult-to-root species such as 100 year-old Sequoia ( Tranvan, et
al., 1991). =
H. Grafting for Virus Detection (Graft indexing) =
1. Essentially, all viruses are graft transmissible. This is, of course,
a disadvantage of grafting unless the objective is viral detection via
graft indexing (see below).
2. In a given crop species, a virus may or may not cause obvious disease
symptoms. Those virus-infected plants which are asymptomatic have no
apparent symptoms may still exhibit decreased vigor and yield. =
3. Graft Indexing. Grafting a scion from a tree of an asymptomatic
species suspected of harboring a virus onto a more sensitive
(symptomatic) indicator species will result in viral transmission from
asymptotic scion to susceptible stock, which will then develop visible
symptoms (mottling, streaking). =
Why is it important that the indicator is used as understock, not as
the scion? =
Note: for many viruses there are other newer, more specific and/or more
sensitive virus indexing techniques such as ELISA (enzyme linked immuno
sorbant assay). Hence, graft indexing tends to be used less frequently. =
a. Examples: =
(1) Strawberry - petiole wedge graft - terminal leaflet of trifoliate
leaf removed, and small split made, where rachis of suspect terminal
leaflet is inserted. =
(2) Prunus subhirtella is used as an indicator for cherry, plum, etc. -
compatible union doesn't even form, but virus is transmitted, and
detection can be made. =
I. Grafting to achieve independent optimization of component genotypes -
Specific Rootstock / Interstock Benefits =
1. Grafted Plants are Compound Genetic Systems =
a. The rootsystem and the shoot system of a plant exist in different
environments. Each has a different role in plant development and each
makes a different contribution to agricultural productivity. Given the
long generation time of trees (years), it could take a very long time,
using standard plant breeding methods, to breed a tree to genetically
optimize both the root and the shoot systems. Grafting, on the other
hand, has allowed agriculturists to mix and match different genotypes in
the root and shoot systems, resulting in a genetically compound plant
that performs better overall than either genotype alone. =
b. Of course, in modern times, genetic engineering, is another way to
"construct" a plant with genes from more than one organism. However
promising, genetic engineering is still in its infancy with respect to
"designer" trees. =
Do you think genetic engineering will ever make traditional grafting
obsolete? =
2. What is the Difference Between "Specific" Rootstock Effects and
Non-Specific Rootstock Effects? =
a. "Specific" rootstock (or scion, or interstock) benefits, in the
context of this discussion, are advantages gained by grafting that are
due to the specific genotype of stock or interstock. For example:
Grafting Macintosh apple (scion) onto an M9 (dwarfing) rootstock,
results in size control (dwarfing) of the scion because hormonal or
other aspects of M9, under genetic control, are translated to the scion,
affecting its vigor. Size control and other specific rootstock benefits
in apples discussed in the section on Clonal Apple Rootstocks. =
Grafting Arabica Coffee (Coffea arabica, higher quality but nematode
susceptible) onto another species of coffee, C. robusta, which is
nematode resistant. =
b. Non-specific rootstock effects would be grafting to achieve an
objective that could be achieved by any compatible rootstock, regardless
of its genotype. This includes many of the reasons for grafting &
budding stated above such as the following examples in which the scion
but the rootstock genotype is important: =
Grafting onto a seedling rootstock merely to propagate a
difficult-to-root clone. =
Grafting onto a seedling rootstock to produce a plant with an unusual
growth form, such as a weeping cherry. =
What are some other non-specific rootstock effects? =
3. A List of Specific Rootstock Benefits =
a. Size control of the scion. =
"Size control" in this context refers to some degree of dwarfing (or in
some cases invigoration) of the scion by the rootstock, especially in
the case of fruit trees. =
Apple - the use of clonal rootstocks for size control (and other
reasons) is a major part of modern apple production. The Malling and
Malling-Merton apple rootstocks, introduced in the early 20th century,
revolutionized apple production. Progress has been made since then by a
number of other apple rootstock breeding programs around the world.
Since apple is perhaps the best example of crop improvement through
selection of clonal rootstocks, this topic is discussed at length in the
section on Clonal Rootstocks.
Pears are sometimes dwarfed by grafting them onto quince rootstocks
b. Effects of rootstock on precocity (early flowering) of scion =
Flowering and fruiting of an adult phase scion occurs more rapidly
(precociously) when grafted on some rootstock genotypes than on others.
In particular, the more dwarfing caused by the rootstock, the sooner the
scion will flower and "come into bearing" from the standpoint of fruit
production. =
c. Pathogen resistance =
Many rootstocks have been selected for disease or pest resistance but in
most cases the resistance is not transmitted to the scion (in contrast
to dwarfing). For example:
(1) Fungal pathogens =
Fusarium sp. =
Fusarium causes a wilting disease of many species, caused by fungal
plugging of host xylem. =
e.g. Passion fruit (Passiflora edulis), purple-fruited hybrid varieties
that are Fusarium wilt-sensitive, are grafted onto resistant seedlings
of P. edulis forma flavicarpa =
Phytophthora root rot =
Resistance to root rot is one of the major selection criteria for the
apple rootstock breeding program at the NY Agriculture Experiment
Station at Geneva, NY. =
=
(2) Bacterial pathogens =
Fire blight (Erwinia amylovora) =
A disease of pear, apple, etc. Rosaceous fruits (link to Plant Pathology
Online, by Phil Arneson, Cornell University) =
Fireblight resistance is one of several selection criteria in modern
apple rootstock breeding program at the NY Agriculture Experiment
Station =
Characteristics of Apple Rootstocks and Interstem Combinations by Paul
Domoto (including resistance to fireblight) is part of the NC-140
Regional rootstock breeding program Web site. =
=
(3) Viral pathogens =
Tristeza virus =
Tristeza causes greening disease in citrus which is a serious problem in
Africa and other parts of the world. =
Resistance to tristeza is conferred by rough lemon rootstock. A table
of citrus rootstock resistance to Tristeza and other diseases is
presented by the Florida Agricultural Information Retrieval System. =
=
d. Pest resistance =
(1) Insect pests =
Wooly aphid (WA) (Eriosoma lanigerum) is an insect pest of apple. The
Malling-Merton series rootstocks were developed by crossing wooly
aphid-susceptible East Malling selections with WA-resistant Northern Spy
apple (Information sheet from UC Davis IPM Pest Management project). =
Phylloxera, described in an Information sheet from Univ. of California
Integrated Pest Management project, is an aphid-like sucking insect pest
of grape which parasitizes the root system. Phylloxera infestation in
the wine regions of France in the 19th century virtually destroyed
production of European (wines) grapes (Vitus vinifera) until they began
grafting them onto resistant American grape rootstocks (Vitus
lambrusca). =
=
(2) Nematodes =
Nematodes are microscopic "eel worms" which parasitize the root systems
of many agricultural crops =
Almond (Prunus amygdala) scions are grafted on Mariana plum 2624
rootstocks which are nematode-resistant. ( Information sheet from
University of California IPM Pest Management Project) =
Arabian coffee (Coffea arabica) produces a higher grade of coffee than
Canefera coffee (Coffea robusta, the kind used to make instant coffee),
but the former is nematode-susceptible while the latter is resistant.
Scions from seedlings of C. arabica are grafted onto seedling
understocks of C. robusta for coffee plantations in Guatemala and other
parts of Latin America. =
=
(3) Rodents - the cultivar 'Novole' crabapple rootstock, selected at the
NY Agriculture Experiment Station at Geneva, inhibits meadow voles from
feeding on the bark during the winter. =
e. Cold hardiness =
(1) Trifoliate orange (Poncris trifoliata) is deciduous (unlike the
citrus species cultivated as fruit crops) citrus species. It is
sometimes used as a rootstock for citrus. Orange or other citrus grafted
on trifoliate rootstock are better suited for more northerly Florida
growing conditions because of the cold hardiness of the trifoliate
orange. This is one of the few examples of evergreen/deciduous grafting. =
(2) Apple - for a summary of apple rootstock (cold) hardiness consult
Paul Domoto's Characteristics of Apple Rootstocks table.
For what (other) reason is it surprising that Poncris trifoliata is
used as a rootstock for Citrus sp. (hint, check the section on
Requirements for Successful Grafting and Budding)? =
f. Tolerance of specific soil types =
(1) The apple rootstock M7 is tolerant of wet soil conditions;
conversely MM104 is tolerant of dry soil conditions. For a summary of
apple rootstock soil adaptability consult Paul Domoto's Characteristics
of Apple Rootstocks table.
4. Specific Interstock Benefits =
Just as single working (scion/understock grafting) allows the grafter to
combine the best possible scion genotype with the best possible
rootstock genotype, double working (scion/interstock/understock
grafting) allows for further optimization of each of the three
components of a tree - root system (nutrition, anchorage, dwarfing,
etc.), trunk (support), canopy (fruit). See Grafting by Position =
a. Size control =
(1) A genotype that causes dwarfing when used as a rootstock has a
similar dwarfing effect (but to a lesser extent) when used as an
interstock.
(2) In addition, the degree of dwarfing by a given interstock genotype
is proportional to the length of the interstock, i.e. a relatively long
section of M9 used as an interstock has a greater dwarfing effect than a
shorter section of the same genotype. =
Why use an interstock for size control of a double worked tree rather
than using the same genotype as a rootstock in a single worked tree?
(Hint: see Apple Grafting autotutorial slide set)
b. To achieve an arborescent growth form of an otherwise shrubby scion
variety (see Grafting to achieve special growth forms in this section,
above)
c. Avoid incompatibility of an otherwise incompatible stock / scion
combination by inserting a mutually compatible interstock. (see
discussion of Bradford pear/Quince incompatibility in the section on
Compatibility) =
5. Summaries of Specific Rootstock Characteristics for Specific Crops =
a. Apple
b. Stone fruits =
J
-- =
Celestial Habitats by J. Kolenovsky
2003 Honorable Mention Award, Keep Houston Beautiful
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