Plant Propagation Final Exam

What is grafting?

Grafting: A horticultural technique where tissues of two plants are joined so they grow as one. Typically involves joining a scion (the top part) to a rootstock (the bottom part).

What is budding

Budding: A type of grafting where a single bud (instead of a whole branch) is inserted into the rootstock.

Rootstock

The lower portion of the grafted plant. Provides the root system.

Scion

The upper portion, chosen for fruit, flower, or foliage traits.

Interstock

A stem section grafted between the scion and rootstock, often used to overcome incompatibility or manage growth characteristics.

What are some reasons for grafting and budding?

-Clone desirable traits (fruit quality, flowers)

-Disease resistance (via rootstock)

-Size control (dwarfing)

-Faster fruiting/maturity

-Combine strengths of two plants

-Repair damaged trees

-Improve cold hardiness

Benefits of the scion

-Controls traits like fruit size, color, quality

-Influences flowering and yield

Benefits of the rootstock

-Affects tree size (dwarfing/semi-dwarfing)

-Provides disease resistance

-Tolerates poor soils, drought, or cold better

What is the first stage of formation of graft union?

Wounding Response: Cut surfaces release hormones and form a protective layer.

What is the second stage of formation of graft union?

Callus Formation: Cells proliferate at the graft interface to protect and start joining.

What is the third stage of formation of graft union?

Callus Bridge Formation: Callus tissues from scion and stock grow toward each other and merge.

What is the fourth stage of formation of graft union?

Cambial Alignment: Vascular cambium lines up between both parts.

What is the fifth stage of formation of graft union?

Vascular Connection: New Xylem and Phloem develop across the union, completing graft success.

What is one type of basic repair graft?

Bridge Graft: Used to repair bark damage (e.g. from rodents) by "bridging" over the wound.

What is another type of basic repair graft?

Inarch Graft: Involves grafting new shoots or seedlings to support a damaged tree base.

What is the difference between a Bridge Graft and an Inarch Graft?

Bridge graft connects over damage;

Inarch provides support from below with a separate plant.

What are some factors influencing graft union success?

-Compatibility of scion and rootstock

-Precise cambium alignment

-Clean cuts and good technique

-Timing (dormant season usually best)

-Environmental conditions (temp, humidity)

-Prevention of desiccation

-Pest/disease control

What are some external symptoms of graft incompatibility?

-Poor or delayed growth

-Bulging or overgrowth at graft union

-Yellowing or wilting of scion

-Early leaf drop

-Premature death of scion

Are any PGR used in the commercial operation of grafting or budding?

Yes – Some PGRs (like auxins) may be used to promote callus formation and enhance rooting or healing, but usage varies based on species and commercial practices.

Whip & Tongue Graft

Use: Common in fruit trees (apple, pear)

Best for: Same diameter stock & scion

Feature: Interlocking cuts for stability and cambial contact

Visual: Looks like slanted cuts with a “tongue” slit that locks together

Cleft Graft

Use: Topworking mature trees

Best for: Joining smaller scions to large rootstocks

Feature: A deep split in rootstock, scion wedges inserted

Visual: Scions placed into a "V" cleft

Wedge Graft

Use: Topworking branches of trees

Feature: Scion shaped like a wedge fits into V-shaped cut on rootstock

Splice Graft

Use: When plant material is small and flexible

Feature: Simple slanted cuts; quick and easy, but less stable than tongue

Side-Veneer Graft

Use: Woody ornamentals, e.g. camellias

Feature: Scion fits into a small flap/cut on the side of the rootstock

What graft is most commonly used for cactus?

Cleft Graft.

What graft is commonly used in bench grafting cucurbit plants?

Splice Graft

What graft allows 2 scions, is one of the oldest methods, and is used in topworking established trees?

Cleft Graft-

One of the oldest known methods.

Allows inserting two scions into a split in a thick rootstock.

Ideal for topworking to change variety or rejuvenate old trees.

What graft requires equal diameters of rootstock and scion, and heals quickly due to good cambial contact?

Whip and Tongue Graft

In side grafts, is the shoot of the rootstock removed before or after the graft takes?

After the graft takes, this allows the rootstock to continue supporting the plant until the scion has successfully established.

Side Graft

A scion is inserted into a cut made on the side of the rootstock stem or trunk. Common in ornamentals. Visual cue: Scion inserted at an angle near the base, not the top.

Apical Graft

A scion is placed at or near the apex (top) of the rootstock. Includes whip & tongue, cleft, and wedge grafts. Visual cue: Central/top position of graft.

Bark Graft

Used on larger rootstocks. The bark is lifted or slipped, and the scion is inserted under it. Visual cue: Scion flat against exposed inner bark.

Approach Graft

Both scion and rootstock remain attached to their own root systems until the graft union forms. Often done by bringing two plants together. Visual cue: Two plants joined side by side with both still rooted.

Is slipping bark necessary for bark grafts?

Yes. The bark must be “slipping” (easily peeled away from the wood), which typically occurs during active growth in spring. It allows proper insertion of the scion.

What are the advantages of chip budding?

-Can be done when bark is not slipping

-Requires very little scion material

-More secure and less prone to desiccation

-Good for precise cambium alignment

-Can be done earlier or later in the season than T-budding

Is the scion placed upside down in an inverted T-Budding?

No. The scion is always placed right-side up, with the bud facing upward. Orientation matters—upside down won’t grow properly.

Is slipping bark needed for chip budding?

No, it is ideal when bark is not slipping.

What are the three main periods when budding is done?

1. Late Spring to Early Summer

2. Mid to Late Summer

3. Late Winter to Early Spring.

Late Spring to Early Summer

Condition: Bark is slipping

Scionwood: Current-season budwood

Buds mature but not dormant

Common for T-budding

Mid to Late Summer

Condition: Bark still slipping

Scionwood: Current-season budwood

Bud remains dormant through winter, forced next spring

Late Winter to Early Spring

Condition: Dormant season

Scionwood: Dormant budwood collected previously

Often used with chip budding since bark isn’t slipping

What are some after-graft bud-forcing methods?

Scoring: Make a small cut just above the bud to interrupt apical dominance

Bending: Physically bend the rootstock stem above the bud to reduce dominance

Heading Back: Cut back the rootstock above the bud to encourage bud break

Removing rootstock shoots: Any shoots from the rootstock are pruned to prevent competition

What are some advantages of budding over grafting?

Requires less scionwood (just a bud instead of a whole twig)

Faster and less labor-intensive than grafting

More efficient for mass production

Lower risk of drying out compared to full scions

Can be done later in the season (more flexibility)

Better cambium contact, increasing success rate

Bulb

Short stem + fleshy leaves storing nutrients. Grows underground. (Onion, Tulip)

Bulbil

a small bulblike aboveground structure, especially in the axil of a leaf or at the base of a stem, that may form a new plant. (Garlic, Tiger Lily)

Corm

Swollen underground stem; solid inside (not layered like bulbs) (Gladiolus, Crocus)

Tuber

Swollen underground stem with "eyes" (nodes) that sprout shoots

Potato

Tuberous Root

Enlarged root storing nutrients. No buds/eyes like stem tubers

Sweet potato

Tuberous Stem

Swollen stem (not root) with buds or nodes; usually aboveground parts involved too

Begonia, Cyclamen

Rhizome

Horizontal underground stem that produces shoots and roots

Ginger, Iris

Pseudobulb

Swollen stem segment above or near soil line in orchids; stores water & nutrients

Orchids (like Cattleya)

What are the three basic parts of a bulb?

Basal Plate – The short, stem-like base where roots grow

Fleshy Scales – Modified leaves that store food

Shoot/Apical Bud – The growing point at the center

2 Types of Bulbs

Tunicate Bulb:Has dry, papery covering for protection.→ Example: Onion

Scaly Bulb (Imbricate):No protective tunic; overlapping fleshy scales.→ Example: Lily

What are the propagation methods for bub-producing plants?

Division of offsets (small bulbs forming around the base)

Scaling (remove and plant individual scales)

Bulb Chipping or Scoring to induce bulbil formation

Tissue Culture (for rapid production commercially)

Propagation of Bulbs

Offsets, chipping, scaling

Propagation of Bulbil

Planting directly like a seed

Propagation of Corm

Cormels (small corms), division

Propagation of Tuber

Cut into pieces with at least one eye

Propagation of Tuberous Root

Division; each piece must have crown

Propagation of Tuberous Stem

Division at natural separation point

Propagation of Rhizome

Cut into sections with a bud

Propagation of Pseudobulb

Division (carefully cutting the orchid)

What are the two types of rhizomes?

Determinate Rhizomes – Grow horizontally for a bit, then stop (e.g., Iris)

Indeterminate Rhizomes – Continuously growing rhizomes that spread aggressively (e.g., Bermuda grass, Ginger)

What are the advantages of using clones as cultivars

Uniformity in traits (fruit, flower, size)

Maintains desirable genetic traits

Predictable performance

Can be faster to market than breeding new cultivars

What are the disadvatages of using clones as cultivars?

Lack of genetic diversity → high vulnerability to disease/pests

Accumulation of mutations over time

Can’t adapt to changing environments

Some traits can degenerate over time without fresh selection

What is the criteria for successful exploitation of a bud-sport

Bud-sport must be:

Genetically stable (not just temporary)

Clearly different from parent

Desirable/marketable

Capable of being propagated clonally

Clonal Selection:

Choosing superior individuals from a clone population for propagation.

Bud-Sport

A spontaneous genetic mutation in a bud that results in a plant part (fruit, flower, leaf) that's different from the rest

Chimera

A plant with two or more genetically distinct tissues growing together in the same plant.

Anticlinal Cell Division

Cell walls divide perpendicular to the surface → expands circumference

Periclinal Cell Division

Cell walls divide parallel to the surface → adds thickness/layers(More relevant for chimera layer structure)

Periclinal Chimera

One distinct genetic layer surrounded by another (most stable)

Mericlinal Chimera

Mutation affects only part of one layer, not stable

Sectorial Chimera

Mutation affects a full sector across multiple layers

Acceptable propagation of periclinal chimeras:

Yes:

Grafting

Cutting propagation (if it includes the mutated layer)

Tissue culture (sometimes, depending on layer structure)

No:

Root cuttings ❌ (roots don’t contain all shoot layers)

Leaf cuttings ❌ (usually from one layer only)

How is a graft chimera formed?

When tissues from two genetically different plants form a single shoot at the graft union. Not the same as normal grafting—this is a blended tissue chimera, not just a scion-rootstock combo.

What casues phenotypic variation within clones?

Bud mutations (e.g. bud-sports)

Epigenetic changes

Environmental influence on expression

Pathogen infection (especially viruses)

True to Name

The plant is correctly identified by name/label.

True to Type

The plant is correctly identified by name/label.

How to eliminate pathogens in clonal propagation

Heat therapy (thermotherapy)

Meristem culture (tiny shoot tips are often virus-free)

Indexing and selection (test and only propagate clean stock)

Sources of clonal propagules

Foundation stock plants (clean, verified material)

Certified nurseries

Breeding programs

Tissue culture labs

Virus-indexed mother plants

Advantages & Applications of Plant Tissue Culture

Mass propagation of clones (fast, consistent production)

Virus-free plants via meristem culture

Off-season production

Propagation of rare or endangered species

Genetic modification / biotech applications

Rapid multiplication of new varieties

Limitations of Plant Tissue Culture

High cost (equipment + media)

Requires specialized skills & facilities

Contamination risk is high

Some species are difficult to culture

Can result in somaclonal variation (genetic instability)

What is the fundamental ability of plant cells behind tissue culture?

Totipotency – the ability of a single plant cell to regenerate into an entire plant under the right conditions(This is what makes tissue culture even possible!)

Organogenisis

Formation of organs (shoots/roots) from explant

Explant source: Leaf, stem, root, cotyledon

Higher propagation ratio (PR) than embryogenesis

somatic embryogenesis

Development of a new sponge from fragments or aggregates of cells

higher PR is better in commercial micropropagation—means more plants from less material.

TRUE

What is stage one of micropropagation?

Establishment

Goal: Get the explant sterile and growing

How: Surface sterilization, placing explant in nutrient medium

What is stage two of micropropagation?

Multiplication

Goal: Produce multiple shoots or callus

How: Add cytokinins to promote shoot development; subculture regularly

What is stage three of micropropagation

Rooting (Pre-transplant)

Goal: Develop roots on shoots

How: Use auxins like IBA or NAA in the medium

What is stage four of micropropagation?

Acclimatization

Goal: Transition plantlets from sterile lab to real-world conditions

How: Gradually expose to lower humidity, more light, soil media

What are the three major categories of ingredients in micropropagation medium?

1. Inorganic Nutrients

2. Organic Supplements

3. Gelling Agent

Inorganic nutrients

Macro elements (N, P, K, Ca, Mg, S)

Micro elements (Fe, Mn, Zn, Cu, B, Mo)

Organic Supplements

Carbon source: usually sucrose

Vitamins: thiamine, nicotinic acid, pyridoxine

Amino acids (optional)

Growth regulators: auxins, cytokinins, sometimes gibberellins

Gelling Agent

Agar or gellan gum to solidify the medium

What are the laboratory ingredients used in Tissue Culture?

Laminar flow hood (sterile workspace)

Autoclave (sterilizes media, tools)

Culture room (controlled light, temp, humidity)

Growth chambers (for specific developmental conditions)

Microscope (monitor development)

Media preparation area (with balances, pH meter, etc.)