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LAYERING

asexual propagation where adventitious roots are formed in a stem while attached to the parent or stock plant

HOW DOES LAYERING OCCUR NATURALLY?

takes advantage of natural ability of plants to initiate adventitious roots where they are broken or bent and touch the ground

ADVANTAGES OF LAYERING

- Avoids propagule stress
- Larger propagules can be produced
- Easier to root difficult species
- No rootstock suckering
- No graft incompatibility
- Requires minimum of facilities
- High success without sacrificing parent plant

DISADVANTAGES OF LAYERING

- Slow to develop roots
- Few propagules produced for production area required compared to many other asexual propagation techniques
- Requires skilled attention

True or False: Layering initiates adventitious roots by restricting flow of carbohydrates and auxin phloem

True

True or False: Layering constricts or girdles, roots often emerge first at node

True

WHAT ARE PRACTICES TO PROMOTE ROOT ELONGATION?

- Light exclusion for roots
- Adequate soil and atmospheric moistures
- Appropriate temperatures

What is SIMPLE LAYERING?

a low-growing stem is bent down into a hole in the soil where it takes root and the original plant goes on as two plants.

What does Simple Layering restrict?

Restricts auxin and CHO Movement

What is Compound Layering?

Similar technique to Simple Layering but used with more flexible stems

What is Mound/Stool Layering?

Using juvenile tissue to cut back heavily and mound substrate around developing stem tissue

True or False: The plant must be first wounded or girdled first prior to adding substrate for mound layering.

True

What is Trench Layering?

An advanced technique that requires the stock plants to be cut back or pinched to develop basal stems 1 to 2 years before propagation

What is air layering?

- an asexual propagation technique that is used on plants that can't bend to the ground
- A strip of bark, phloem and cambium is removed and is covered with sphagnum moss

What are the physiological keys to succcess in layering?

- Intact Xylem for nutrient, water and carbohydrate supply
- Removal or interruption of phloem where CHOs and auxins accumulate
- Light is eliminated

Runners

specialized stem that develops from the leaf axil of the plant crown - runs horiontally forming plantlets at nodes

Stolons

Horizontal stem growing at or just below the substrate surface

Offsets/plantlet separation

Lateral shoot or branch arising from base of mother plant

Suckers

Shoots arising from below ground from root tissue

Crown Division

Splitting crown making sure all propagules have both root and shoot tissue

Grafting

natural or deliberate fusion of plant parts so that vascular continuity is established between them

What are the parts to a graft?

Scion, Stock, Rootstock

Scion

a shoot piece of donor plant

Stock

plant receiving or fusing to scion

rootstock

the bottom half of a grafted plant

Grafting and Budding

Asexual propagation technique where stock and scion are fused and maintain their genetic identity

Advantages of grafting and budding

- used on plants that cannot be reproduced conveniently
- Repairs damaged trees/plants
- Hasten reproductive maturity

Limitations of grafting and budding

- Requires knowledge and skill
- Labor intensive
- Propagules can be expensive

What are factors of a successful graft?

- Compatibility
- Technique vs plant used
- Proper Environmental conditions
- Condition of stock plant
- Quality of the techniques and aftercare
- Polarity

What are symptoms of incompatibility?

- High percentage of poor take
- Leaf chlorosis, necrosis and drop
- Scion die back or deaths
- Bulging
- Cracking or breaking of graft union

What are the 4 Stages of Recovery?

- Formation of a necrotic plate
- Parenchyma cells interlock and form callus bridge
- Cells differentiate into new cambium tissue
- Cambium tissue forms xylem & phloem and the bridge is completed between scion & stock

cleft graft

Cut made into a large branch and a twig is inserted

Bark Graft

top working

splice graft

Rootstock and scion same size, Similar to whip and tongue BUT 2nd cut (tongue) not made. Used when plants have lots of pith, Wood not flexible enough to make tongue cut, plants either actively growing or dormant. Example one cotyledon graft, used with cucurbit vegetable crops, used with cucurbit vegetable crops. Splice graft Mechanized.
Example: One cotyledon graft, used with cucurbit vegetable crops.

whip and tongue graft

When the scion and stock are equal in diameter and interlock

saddle graft

Rootstock and scion same size Usually mechanized, Fast, Plant usually dormant

bridge graft

to repair damaged trunk

Inarch graft

similiar to bridge graft but can use existing sucker, shoot or watersprout

Budding techniques

Uses a single Bud and is typically done before or during growing season

T-Budding

Ex Roses involves taking buds from one plant and inserting them under the bark of the rootstock.

Chip Budding

Chip of bark removed from smooth place between nodes near base of rootstock and replaced by another chip

What are bulbs?

underground storage organs

True bulbs

Compressed stem or stem axis that form a basal plate with modified fleshy leaves attached to surrounding primordia or apical shoot

Tunicate

type of bulb with outer scales that are dry and membranous. Tunic services as protection from physical damage

Non-tunicate

Has no tunic or dry outer covering. Scales are more easily damaged

Bulblets

miniature bulbs forming on parent bulb basal plate

scooping

bulbs dug after foliage dies back

scoring

treatment applied after foliage dies down and mature bulbs lifted

Scaling

individual scales from non tunicate bulbs

corms

compressed stems with a swollen stem base that forms the basal plate

tubers

swollen underground stems that serves as a storage organ

rhizome

horizontal underground stem

True or False: Adventitious shoots arise near proximal ends

True

root cuttings

useful means of propagating species that do not come from true seed or root poorly when stem cuttings are used

True or False: New roots are near distal end

True

Where is phellogen or cork cambium located?

In old roots

Where are pericycle located?

In young roots just inside the endodermis

What are leaf cuttings?

Leaf bud cuttings are not "true" leaf cuttings

What is a limiting factor to leaf cuttings?

Formation of adventitious stem tissue

What are advantages of leaf cuttings?

- Little expertise needed
- No need for elaborate facilities
- High humidity better than mist
- Well drained substrate required

What are the disadvantages of leaf cuttings?

- Doesn't work with chimeras
- Small propagules produced
- Auxin may inhibit adventitious shoots

What are Leaf Cutting Types?

- Whole leaf
- Leaf Section
- Vein removal

these two seed tissues may require special preconditioning to overcome a dormancy and germinate

embryo and seed coat

how is stratification usually completed?

exposing seed to a period of low temperature

what is not a technique for seed scarification?

exposing the seed to UV Light

what does 2,3,5 TTC detect showing a seed is viable?

carbon dioxide from respiration

why should seed be thinly sown when planting in a row?

allow air movement, allow ease of transplanting, reduce competition between developing seedlings

why are small seeded plant species not covered with substrate?

often require light for germination

True or False: uniformity of plant material is essential for his or her production cycle. Meeting seed dormancies is critical to prevent different size and age seedlings producing a uniform crop

true

when treating a hard seed coat dormancy, leaving the seed concentrated in sulfuric acid too long can damage the embryo reducing seed viability

true

what is a method of determining percent seed germination?

rag doll test, petri dish test, soil germination test

a seed package gives a published germination percentage 90%. what does this mean?

percent of germination will be below the published germination %

Propagators should neve use both scarification and stratification to overcome dormancy

False

a hammer can be used on large seeded species as a means of scarification

true

Propagation of plants is a

fundamental occupation of civilizations

the origins of plant propagation

date back thousands of years, when hunter and gatherers began to cultivate plants and domesticate animals

what is the primary reason for early plant propagation?

plant selection for stable food supply

what are the fundamental activities involved in agriculture?

1. plant selection and breeding for specific traits
2. plant propagation to maintain traits
3. crop production, maximimizing yields
4. crop handling and storage
5. food technology - preserving harvest

what was the first system of plant cataloguing?

binomial nomenclature by Carl von Linne

what is the Morrill Act?

an act of Congress in 1862 that established land grant universities for scientific study and teaching of agriculture and mechanical arts

what is the importance of plant propagation industry today?

preservation of rare and endangered species of plants

Early Greeks, Romans, and Chinese knew and used various techiniques of plant propagation. What are some of these?

Rooting cuttings, air layering, grafting

Knowledge of plant growth hormones, in particular which endogenous growth regulator inducing root initiation was a major milestone in plant propagation development?

IAA which is part of the hormone group auxins.

Various methods are used to propagate plants, but ultimately, the methodology used depends on what?

whether a plant is desired to be genetically identical to the original

sexual processes result in propagation by seed. seed propagation is a major part of which plant production industries?

-vegetable transplants, bedding plants, and nursery industries

What are asexual propagation techniques that are discussed throughout this course?

division, stem, root and leaf cuttings, budding/grafting

do stem cuttings produce adventitious roots?

yes - cells form tissues, tissues form organs

what is the nucleus of a plant cell?

the nucleus is the location of chromosomes, DNA - genetic coding for all cell functions (totipotency), differentiation of organism's cells, and reproduction

what is the plasma membrane?

a semi permeable barrior between outside and inside of the cell

What are the functions of the plasma membrane?

regulates movement of chemicals and molecules in and out of the cell "gate keeper"; also site for synthesis of cellulose

what is the cell wall?

gives the cell a definite shape and structure

what are the functions of the cell wall?

reduces water loss, prevents cell from rupturing due to turgor pressure, difference betwen plant and animal cells

what are the parts of a cell wall?

Primary cell wall - cellulose, hemicellulose, pectin; Middle lamella - "glue" that holds cells together, contains high pectin levels

What is the function of plasmodesmata?

connects cells and cytoplasm

in what ways to plant parts differ from one another?

shape, size; vegetative tissues vs reproductive tissues; differentiation

what are the three basic cell types?

parenchyma, collenchyma, sclerenchyma

what are parenchyma cells?

thin primary cell walls that contain a nuclei and functioning protoplast - undifferentiated and can resume meristematic activity

collenchyma

specialized plant cell that provides support; found in young stems and leaf petioles

sclerenchyma

mechanical support and water conduction; major plant organs (vessel elements, tracheids, and fibers)

what are epidural plant tissues?

outer layer of stems, roots and leaves.