Propagation by Grafting

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Propagation by Grafting
MODULE 4
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Grafting

• Grafting is an all embracing term which covers a
  range of carpentry techniques
• It includes the SCION which forms the above
  ground part of the grafted plant
• AND the ROOTSTOCK which is the lower portion of
  the grafted plant which provides the root system
  for the new plant

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Grafting

• An INTERSTOCK or intermediate rootstock may be
  used with some fruit trees where a degree of
  incompatibility occurs
• Interstocks are not normally needed with
  ornamental plants
• Grafting with interstocks is referred to as
  DOUBLE WORKING

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Grafting

• The aim of grafting is to make clean cuts in the
  tissue of the two pieces so that the CAMBIUM
  tissues can be matched together
• Cambium is the main layer of meristematic tissue
  in woody plants
• It is located as a thin layer of tissue
  immediately under the bark in stem and roots

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The botanical limits of grafting

• Grafting within species
• Grafting of species within the same genus
• Grafting of different genera within the same
  family
• Grafting between families

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Reasons for grafting plants

• To propagate plants which cannot be economically
  propagated by other techniques
• Eg. Cultivars of ornamental shrubs and trees

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Reasons for grafting plants

• To control the growth and performance of trees
• Eg. Apple and pear orchards
• Malling series rootstocks
• Malling 27, 26, 9

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Reasons for grafting plants

• To confer resistance to pathogens to the grafted
  plant
• Eg. Waxflowers
• Eg. Avocados
• Eg. Grapes
• Eg. Tomatoes

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Grafting practice with students
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Reasons for grafting plants

• To bring fruiting plants into fruit production
  earlier in the life of the plant
• All fruit crops which are commercially grafted
• Fruit at 2-3 years

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Reasons for grafting plants

• Grafting to obtain special effects in plants
• Eg. Weeping standards
• Eg. 2 citrus fruits on the same tree
• Eg. Multicoloured rose plants

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Reasons for grafting plants

• Grafting as an orchard management technique
• Eg. Top working of fruit trees to change
  varieties
• Eg. Frame working of fruit trees to assist
  pollination

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Factors of importance in the healing of a graft
union

• Time of year
• Scion material at correct stage of growth
• Standard of carpentry
• Tying of the graft
• Growing environment

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Polarity in grafting

• Correct polar differentiation of stock and scion
  must be maintained
• The PROXIMAL end of the scion is fitted to the
  DISTAL end of the stock

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Incompatibility in grafting

• Graft compatibility implies that when two closely
  related plants are grafted together, there is no
  physiological or morphological reason why a union
  should not form

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Incompatibility in grafting

• Graft incompatibility occurs when, for
  morphological or physiological reasons a closely
  related rootstock / scion combination will not
  develop a strong union

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Incompatibility in grafting

• Incompatibility is not common with ornamental
  plants as most rootstocks selected for grafting
  are botanically closely related to the scion

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Systems of grafting

• There are two basic systems
• Field Grafting the traditional system where
  rootstocks are grown and grafted in the field

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Selection of suitable rootstocks

• With woody ornamentals, most rootstocks used are
  closely related species to the scion
• Many are seed propagated
• Easy to propagate and fast growing

• The vigour characteristics of the rootstock
  usually determine the size and vigour of the
  grafted plant
• This means that many grafted shrubs grow to a
  large size

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Systems of grafting

• Bench grafting
• The rootstocks are grown in containers
• When they are large enough, grafting is carried
  out sitting down in the work shed

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Methods of Grafting
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Systems of grafting

• A Budding
• B Top grafting
• C Side grafting
• D Approach grafting

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A. Budding

• Budding is a contraction of BUD GRAFTING
• The scion used consists of a single bud
• Simple to learn
• Fast to do
• High success rates
• 95-100 common

• Budding produces a strong union
• It is economical in the use of scion material
• This is important with new varieties when
  material is in short supply
• The number 1 option for the grafter

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A. Budding

• T-budding
• Inverted T-budding
• Chip budding
• Patch budding

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A. Plants which are Budded

• Deciduous fruit trees
• Stone fruits
• Nut trees
• Citrus
• Subtropical fruits
• Climbing fruits
• Roses
• Ornamental trees

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B Top grafting

• In top grafting the top is removed from the
  rootstock and the scion shoot is grafted in to
  the top end of the rootstock stem
• Used both in the field and in bench grafting

• Top grafting is much slower to perform than
  budding
• Many styles are complicated to carry out
• Often used in spring when t-budding is not
  possible

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B Top grafting

• Examples of plants top grafted
• Avocado
• Feijoa
• Grape
• Passionfruit
• Pecan
• Grevillea

Pecan
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C Side grafting

• There are a number of species which do not
  respond well to top grafting
• It appears that once the top is removed from the
  rootstock, uptake of water and mineral nutrients
  is restricted
• This prevents a graft union from forming

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C Side grafting

• In side grafting the scion is grafted onto the
  side of the stem of the rootstock
• This enables the top to be retained on the
  rootstock to assist in moisture and nutrient
  uptake

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C Side grafting

• Side grafting is only carried out on container
  grown rootstocks
• This means the grafted rootstocks can be grown on
  in a warm greenhouse

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C Side grafting

• With many fruit trees, side grafting is carried
  out in early spring
• The dormant scion material is collected in winter
  and cold stored until use

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C Side grafting

• With side grafting of waxflower, it can be
  carried out almost all year round
• The rootstocks should be in active growth
• The scions can also be in soft, active growth

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Examples of side grafting

• Conifers
• Cedars
• Cypress
• Junipers
• Spruce
• Pines
• Taxus

• Broadleaved
• Maples
• Azaleas
• Birch
• Camellias
• Euc ficifolia
• Magnolias
• Oaks
• Viburnums

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D Approach grafting

• Usually considered to be the last resort in
  grafting
• The other grafting systems are examples of
  DETACHED SCION GRAFTING
• In approach grafting the scion remains attached
  to the mother plant until after the graft union
  has formed

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D Approach grafting

• Approach grafting is often considered to be an
  old fashioned horticultural curiosity
• However, it is now often used in north Queensland
  in the grafting of exotic tropical fruits
• It is also used in the grafting of European
  tomato varieties onto disease resistant
  rootstocks

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Cutting grafts

• Grafting onto unrooted cuttings is an innovation
  designed to eliminate the production period of
  the rootstock

• The development of a root system on the unrooted
  cutting occurs simultaneously with the healing of
  the graft union
• Both processes need the same greenhouse
  environment

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Grafting machines

• A number of grafting machines have been developed
  to speed up the grafting process
• It also enables the grafting to be carried out by
  less skilled staff
• Careful grading of grafting material is required
  so that the scions and rootstocks are matched in
  diameter

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Tying materials for grafting

• A number of tying materials are available for
  securing the graft union
• The choice depends on the grafting technique and
  the post-grafting environment to be used
• The main aim in tying the union is to keep
  moisture from entering the graft union

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Tying materials for grafting

• With t-budding, simple rubber budding patches are
  often used
• The rubber is biodegradable and they will
  disintegrate within 4-6 weeks
• PVC budding tape is widely used but must be cut
  off after the graft union has formed

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Tying materials for grafting

• At UQ Gatton we use the medical laboratory tape
  PARAFILM
• This is a thin, stretchable tape which seals the
  graft union very effectively against the entry of
  water
• It also degrades rapidly so it does not need to
  be removed