Principles of Grafting and Budding Chapter 11 Grafting

Principles of Grafting and Budding 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

Grafting & Budding Terms Bud: Similar to graft, but scion is reduced to a single bud

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

Grafting & Budding Terms Vascular Cambium: Meristematic tissue between xylem & phloem Vascular Cambium X P

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 • Source Ø Stool beds Ø Cuttings Ø Tissue 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 response a. Necrotic plate 3. Callus bridge formation 4. Cambium formation 5. Vascular tissue formation

1. Close Vascular Contact • • • 55 -90 F 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