chapter 5 plant propagation part 2 – asexual propagation 1

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Chapter 5

Plant Propagation

Part 2 – Asexual Propagation

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What is Asexual Propagation?

• Plant reproduction using leaves, stems, and roots

• Also called vegetative or cutting

propagation• Cuttings are the most common

form of vegetative propagation

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Why use vegetative prop?

• Offspring are clones– Genetically identical to parents– Preserves unusual and valuable plant traits

that may not pass with seed

• Used to reproduce plants that seldom flower or are sterile

• Can be much faster than growing an equivalent plant by seed

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VEGETATIVE PROPAGATIONCuttings

• Cuttings are the most widespread vegetative propagation method.

– Vegetative plant parts such as leaves, stems & rootsthat regenerate missing parts to form new plants.

• They are cut from parent plants called stock plants.

• The environment required for growing cuttings isthe same as for germinating seeds: warmth, moisture, and a growing medium.

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VEGETATIVE PROPAGATIONCuttings

• Most parts used for vegetative propagation are taken from above-ground portions of the plant,and must regenerate roots.

– The growing medium will determine whether rootswill form, and their quality.

• The main requirement is to drain quickly to admit air to the rooting area, yet retain some moisture.– There is not one superior rooting medium.

• Many combinations of materials are used:– Sand and part peat moss, part perlite, part vermiculite.– Pure vermiculite, pure perlite, and pure sand.

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Strip trays of Oasis foam (phenolic foam) used for propagation.

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Cutting types – outdoor types

• Hardwood– May be deciduous or evergreen– Taken when plants are dormant– 6-10 inches long

• Semi-hardwood– From deciduous plants in summer– Partially matured wood– 3-6 inches long– Have leaves so must be protected from drying out

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Cutting types - outdoor

• Softwood– Taken in late spring– Most reliable type of outdoor cutting

• Herbaceous– Similar to softwood cuttings but from herbaceous plants– Can be taken and rooted at any time in growing season

• Root– Root pieces must be able to form adventitious buds– Only a few species– Must be taken in early spring while CHO loaded

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www.uvm.edu/~mstarret/plantprop/chapter10.pps (Mark C. Starrett, Associate Professor University of Vermont)

An outdoor field technique of rooting hardwood cuttings

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Semi-hardwood cutting rooted in Oasis foam

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Cutting types - indoor

• Stem tip cuttings– Most common type– 2-4 inches of a growing stem

• Leaf-bud– Lower stem sections with leaves - taken below tip

cuttings– Slower to root and grow than tip cuttings

• Stem section– Lower, leafless stem sections– 2-3 nodes and laid horizontally in rooting bed

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Cutting types - indoor

• Leaf cuttings– May include blade and petiole– Longest time to root – Must produce roots, and buds with limited

photosynthetic ability• African violet, snake plant, fibrous begonia

– Propagation procedure varies by genera.

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Leaf-bud cuttings

14www.uvm.edu/~mstarret/plantprop/chapter10.pps (Mark C. Starrett, Associate Professor University of Vermont)

Leaf cutting of tuberous begonia

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• Leaves of Africanviolet & peperomiaare picked with thepetiole attached.

The leaf is buried in the rooting medium up to the blade, and new plants form at the soil line.

Figure 5-16a African violet leaf cutting.Image copyright © 2008. Paul PostumaArs Informatica. By permission.

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Rules for cuttings

• No flowers or flower buds• At least 1 node near the base• Keep leafy cuttings moist at all times• No leaves below soil line• Remove fallen leaves and diseased cuttings or

parts regularly• Use of a rooting hormone is recommended• Reduced light and humid conditions are

required until rooting

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Rules for Cuttings

• Any leaves that will be covered after the cutting is stuck into the rooting medium should be removed.

– Left on, they rot & provide a breeding ground for disease organisms.

• Leaves that die and drop from the cuttings shouldbe removed, with whole cuttings that appear dead.

• A heat source at the bottom of the rooting chamber where the roots will be forming will increase the speed and success of rooting cuttings.

• Use of a rooting hormone can increase rooting speed and success.

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Rules for Cuttings

• Gently tug the rooting cuttings about once per week to determine whether rooting has occurred.– If it slips out easily, no anchoring roots have formed.

• The cutting should be inspected for signs of rotting and,if still healthy, can be reinserted in the medium.

– If the cutting does not pull out with gentle tugging, it may have roots already.

• The plastic lid can be opened partially to accustom the plants to normal humidity, and removed entirely after several days.– After 1 week, cuttings can be transplanted to pots.


A simple method for propagating leafy cuttings

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• A humid chamber to minimize transpiration can be made easily with a light translucent storage box.

Figure 5-17 A rooting chamber made from a translucent storage box. Idea supplied by Janie Varley, Vanderbilt, Tex. Photo by Jennifer Finney Janssen, M.Ed., Jackson County Extension Agent—Family and Consumer Sciences, Texas AgriLife Extension Service.

Leafy cuttings wilt easily and once severely wilted are less likely to root.

Cuttings should bekept moist after cutting & before being stuck in the medium to slow water loss.

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Water rooting

• Many houseplants and some easy-to-root outdoor plants can be rooted in water– Coleus, willow

• Oxygen is usually lacking, so be careful• Stem tip cuttings are usually used• Roots do not form root hairs

– Transplanting to potting soil requires hardening- off

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Commercial propagation

• Intermittent mist benches– Time clocks or electronic leaf

• Bottom heat• Shade


Mist-a-Matic electronic leaf

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Mechanical time switches used to control intermittent mist

24-hour clock used to turn on repeating timer

Repeating timer with tabs used to turn mist on at certain intervals and for varying lengths of time

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• A root-zone heating system is often also used to warm only the bases of the cuttings to encourage faster and more reliable rooting of cuttings.

Figure 5-20 A Heat-A-Maticsuitable for use with pots or flats.Courtesy of Griffin Greenhouse& Nursery Supplies.

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Hot water tubing on propagation bench

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55% shade cloth installed over propagation area

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Natural Plant Propagation

• Crown Division• Layering• Rhizomes• Stolons/Runners• Suckers/Offsets• Bulbs, Corms, Tubers

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• Crown division is probably the most common and reliable home propagation method.

One plant is separated intotwo or more pieces, eachwith a portion of roots & crown.

Used for herbaceous perennials, shrubs, & houseplants such as ferns, asparagus ferns, Africanviolets, and spider plants.

Figure 5-21 Division of a plantain lily into several smaller crowns. Photo by George Taloumis.

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Runners of Strawberry

Simple layering

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• Suckers and offsets are young shoots that grow from the roots or stems of mature plants.

Figure 5-24 A snake plant with twoyoung offsets. Photo by Kirk Zirion.

Functionally similar to rhizomes and stolons, and found in many shrubs & houseplants such as bromeliads, succulents, and cacti.

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• Offsets on cacti are frequently produced on top of the plant and can be broken off and rooted without difficulty.

Figure 5-25 A pincushion cactuswith offsets. Photo by Rick Smith.

• Suckers from the bases of plants may or may not have developed root systems independent from the parent.– If so, they can be transplanted

directly.

– If not, they are treated ascuttings.

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Storage Organs: Bulbs, Corms, and Tubers

• Underground storage organs are produced by some herbaceous perennials.

– A repository of stored carbohydrate, botanically, theseare modified stems with nodes, buds & modified leaves.

• Lilies, gladiolas, and amaryllis.

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Storage Organs: Bulbs, Corms, and Tubers

• Their natural means of vegetative reproduction is the formation of clones of themselves (called bulbils, cormels, or tubers) around the base of the parent.– These can be broken off and planted in new locations.

• Preferably while the plant is dormant.

Figure 5-26 Removing a daughter bulb from the mother.

Blooming of storage organs may take 2 to 3 years afterthe year they are produced because a minimum sizemust be reached before flowering will occur.

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Other propagation methods

• Air layering• Grafting• Budding• Tissue Culture• Genetic Engineering – transgenic plants

– B.t.– Roundup-Ready crops

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• Choose where the new root system is desired…

Figure 5-22 Air layer. Photo by the author.

– A 1” wide strip of bark should be cut around the stem & the bark pulled off.

Girdling removes the phloem& cambium but not the xylem,which still translocates waterto the top of the plant.

– Place a handful or twoof damp sphagnummoss over the girdledarea & wrap with plastic.

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Figure 5-22 Air layer. Photo by the author.

– Use twist-ties or tape to secure both ends andseal in moisture.

– Place foil over the plasticif the air layer area will be exposed to direct sunlight.• To prevent overheating.

– In 2 to 3 months, when several roots with lengths of 2” to 3” have formed,the air layer can be cutand transplanted to itsown pot.

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Grafting and Budding• Grafting and budding are fairly complex methods of

propagation used for reproducing valuable fruit and ornamental cultivars in nurseries.

– Budding & grafting unite genetically different plants so they heal together & function as a single plant.

• An amateur who wishes to try should plan ahead andconsult reference books for more in-depth information.

• Budding transfers a bud of one plant to another plant that will function as the root system, whereas grafting attaches a small branch to another plant.

– Most frequently combining two cultivars of a speciesinto one plant that exhibits the best features of each.

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Chip budding. The scion is reduced to a single bud which is cut to fit, wrapped with grafting tape, and allowed to heal.

After it heals the stem above is removed to direct growth into the new bud

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Tissue Culture• Tissue culture, also called micropropagation, is

the propagation of plants from nearly microscopic portions of parent plants.

Figure 5-29 Tissue-cultured strawberries. Photo courtesy of Barbara M. Reed, National Clonal Germplasm Repository, Corvallis, Ore.

Importance of propagation from virus- free parent stock has come to be appreciatedrecently as the detrimental effects of unrecognizedvirus infection havebecome known.

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Tissue Culture

• The technique has two distinct advantages over traditional propagation:

– It enables mass production of a cultivar from an extremely limited amount of parent stock, in a relatively small area.

– It enables the propagator to eliminate disease-causing viruses from the parent material, unattainable through the use of pesticides.

• And to propagate numerous virus-free offspring thatare healthy and vigorous.

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Tissue Culture

• Tissue culture is not an amateur activity, because it is nearly impossible to achieve the sterile conditions necessary.

• Tissue-cultured plants still in test tubes are sold in nurseries occasionally as novelty items.

– Particularly orchids, which were the main plants tissue cultured for many years.

• The test tube is left sealed and treated as a miniature terrarium.

• When the plant outgrows the tube it sometimescan be transplanted to a pot, though theprocess is not always successful.

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Tissue Culture is the process of taking a small group of plant cells and successively getting them to grow lots of shoots, which are then further divided, and then rooted.

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GENETIC ENGINEERING

• Genetic engineering can harness the biological machinery of bacteria and viruses to…– Manufacture otherwise hard-to-obtain plant products.– Combat genetically caused diseases.– Improve tolerance of plants to adverses.– Attain other similar commendable goals.

• For plant improvement, it changes the genetic makeup of plants, without breeding or selection.

• Its main advantage is that it makes possible the transfer of genes between completely unrelated plants or bacteria.– In rare cases, even from animals to plants.

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COMMERCIAL APPLICATION OF GENETIC ENGINEERING

• In commercial horticultural production, research has centered mainly on vegetable and fruit crop genetic engineering.– With a limited amount on flowers and other

crops.

• Although genetically engineered crops are in widespread cultivation, most are not horticultural.

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• Generally, genetic engineering of horticultural crops has focused on

– Imparting disease and pest resistance.

– Imparting resistance to herbicides.

– Extending the length of product shelf life.

– Altering color.• In flowers.

– Imparting cold-temperature resistance.• In strawberries and eucalyptus trees.

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• One of the best known genetically engineered horticultural crops is the ‘Flavr Savr’ tomato.– Engineered to retain a firm texture longer than normal.

• Tomatoes destined for fresh eating must be hand-harvested to prevent bruising.

– Unlike canning tomatoes that can be harvested mechanically—a less expensive process.

• Fresh tomatoes must also be transported quickly and with careful packaging.

– To ensure that they arrive at the supermarket in an attractive condition, appealing to the buyer.

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• The ‘Flavr Savr’ inhibits expression of the genetic material that causes fruit to soften when it ripens.

– The softening part of ripening is slowed, although the flavor continues to develop.

• This allows mechanical harvesting, increased transport time, and longer fresh shelf life in the supermarket.

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• A second genetically engineered crop receiving widespread attention is a Thompson Seedless grape variety engineered to be virus resistant.– One of the most commonly cultivated table

grapes.• Also a component of blended wines.

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• Scientists hope that genetically engineered virus resistance will reduce the expense of chemicals, and their entry into the environment.

– Because it will no longerbe necessary to spray toprevent the disease.

At present, only papaya &squash have been engineered successfully for virus resistanceand put into field production.

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• Some opponents of genetic engineering fear itcould upset the ecosystem in unknown ways.

– They feel that the accelerated pace of genetic change could inundate the environment with bizarre plants, causing an unstable ecological situation.

• Some organic farmers fear a biological pesticide, which they use to control infestations of worms, will no longer be effective due to insect resistance as a result of widespread incorporation in many crops.

– Bacillus thuringiensis, is the source of geneticmaterial put into plants to cause their cells toproduce an insect poison.

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• The Environmental Protection Agency (EPA) has approved a number of genetically engineered plants.

– Over 3 million acres of genetically engineered corn, cotton, and potatoes were planted in the U.S. in 1997.

• A class-action suit has been filed against the EPA by thirty-one groups who charge that the EPA has been negligent in its approval of genetically engineered crops.

chapter 5 plant propagation part 2 – asexual propagation 1

Documents

growing cuttings

plant propagation

softwood cuttings

asexual propagation

leafbud cuttings

vegetative plant parts

tip cuttings slower

tip cuttings stem section