Principles of Grafting and Budding

transcript

Chapter 11

Grafting & Budding Terms

Graft: Two living plants connected and growing as one

Scion: Dormant shoot, upper portion of graft

Stock: Lower portion of graft, root system

Bud: Similar to graft, but scion is reduced toa single bud

Interstock: A middle or intermediate stem piece located between scion & stock

Vascular Cambium: Meristematic tissue between xylem & phloem

VascularCambium

Grafting and Budding

• Perpetuate clones

• Rootstock effects

• Changing cultivars

• Rapid maturity– Shortens juvenility

– Used for breeding programs

• Special growth forms

• Damage repair

• Studying viruses

Seedling Rootstocks

+ Simple

+ Cheap

+ Disease free

± Better root systems

– Genetic variation

Clonal Rootstocks

• SourceStool bedsCuttingsTissue Culture

• Characteristics+ Uniformity

+ Disease Resistance

+ Growth Habit

+ Flowering Habit

– Scion rooting

– Disease potential

Rootstock benefits

• Disease resistance

• Soil tolerance

• Size control

• Fruit quality

Interstock benefits

•Overcome incompatibility

•Add additional attributes

•Dwarfing

Topworking

• Change cultivars

• Add pollinators

Topworking

• Multiple varieties on one tree

Formation of graft union

1. Line up vascular cambium

2. Wound healing responsea. Necrotic plate

3. Callus bridge formation

4. Cambium formation

5. Vascular tissue formation

1. Close Vascular Contact

• 55-90F

• Active cambium

• High humidity

• Pathogen free

• Mechanical support

• Cambium ‘matching’

2. Formation of Necrotic plate

• Cells killed when

cut is made

3. Callus Bridge Formation

• Production & Interlocking of parenchyma• Comes from phloem and immature xylem• Stock produces most callus

4. New Cambium Formation

• Adjacent callus differentiates to form cambium

• Cambium forms across bridge of callus tissue

5. New Vascular Tissue (X&P) From New Cambium

• Vascular system must be in place before bud break

GRAFT FORMATION

BUD FORMATION

Factors of graft healing

• Incompatibility

• Species or variety (cultivar)

• Temperature

• Moisture

• Oxygen

• Growth status (active vs. dormant)

• Technique or type of graft

• Disease situation

Polarity in grafting

• Distal and Proximal ends

• Reversed polarity works only for a limited time with grafts– Nurse-root grafting

• Buds can be reversed– Can cause a wide crotch angle as it grows - strong

Limits of grafting

• Generally limited to dicots & gymnosperms

• More closely related the better

• Permanent grafts in monocots are not successful– Likely has a lot to do with cambium and vascular

tissue production

• Common between same species– Apple on apple

• Harder between different Genera in same family– Tomato on potato (Solanaceae family, or Nightshade)

• Rare between families

Symptoms of Incompatibility

• High failure rate

• Yellow foliage, early defoliation

• Premature death of scion

• Differences in growth rate– Not always a sign of incompatibility

– Can be differences in genetic potential for growth rate

• Overgrowths

• Breaks at graft union

Types of Incompatibility

• Localized– At site of graft contact

• Translocated– Substances moved from the scion to rootstock or

vice-versa

• Virus present

Incompatibility

• Cause: Genetic

• Mechanism (example theories):– Chemicals found in one partner may be toxic to the

other (Cyanogenic glucoside)

– Lignification of cell walls may be inhibited

Effects of Rootstocks on the Scion

• Size and growth habit

• Fruiting

• Size, quality, and maturity of fruit

• Winter hardiness

• Disease resistance

• Timing of fruit maturity

Effects of Scion on the Rootstock

• Vigor

• Cold-hardiness

Effects of Interstock on Stock & Scion

• Reduces stock and scion size

• Direct effect, not indirect

Mechanisms of effects (theory)

• Translocation (stem)

• Absorbing ability (root system)

• Interaction of all parts

Factors influencing growth of grafted plants

• Nutrition

• Translocation

• Endogenous growth factors

Principles of Grafting and Budding

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