Chapter 9 - 2.1

unit twounit twoPlant Structure,Plant Structure,Chemistry, Growth, Chemistry, Growth, Development, Genetics, Development, Genetics, Biodiversity, and ProcessesBiodiversity, and Processes

6 Structure of Higher Plants

7 Plant Growth & Development

8 Plant Chemistry & Metabolism

9 Genetics & Propagation9 Genetics & Propagation

10 Cultivated Plants: Naming, Classifying, Origin, Improvement & Germplasm Diversity and Preservation

11 Photosynthesis & Respiration

12 Water Relations

13 Mineral Nutrition

© 2011, 2007, 2002, 1988 Pearson Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

Practical Horticulture 5th edition By Margaret J. McMahon, Anton M. Kofranek and Vincent E. Rubatsky

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Chapter 9 - Genetics and Propogation

• Explain how the basic concepts of genetics relate to the production and utilization of plants.

KEY LEARNING CONCEPTSKEY LEARNING CONCEPTS

• Describe the common methods of plant breeding and sexual and asexual propagation.

• Discuss how genetic engineering is used to introduce genetic traits into plants from unrelatedor distantly related organisms.

After reading this chapter, you should be able to:



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Propagation of PlantsPropagation of Plants

Propagation: The process of increasing plant numbers

• Sexual or asexual methods

• Preservation of traits



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• Line: If the plant group reproduces “true” by seed with no characteristics changed– A line is homozygous and, if self-pollinated, seed

propagation yields progeny like the original plant.– Inbred and hybrid lines



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• Heterozygous plants require vegetative propagation

• Clones: cultivars originating from a single plant or plant part



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• Control of seed source is necessary to maintain a Line

• State agencies set standard for seed quality and characteristics

– Breeder seed—produced in small amounts, under the control of the plant breeder, to produce foundation seed.

– Foundation seed—multiplied from breeder seed, available in limited amounts, planted to produce registered seed.

• Controlled by public/private foundation seed stock organizations.

– Registered seed—seed source for growers of certified seed, under the control of the registered seed producers.

• The progeny of either breeder or foundation seed.

– Certified seed—is of known genetic identity & purity, available in large quantities, sold to farmers for general crop production.



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Seed FormationSeed Formation

• A seed has three essential parts:

– The embryo, which develops into the new plant.

– Food storage material, to nourish the embryonic plant.

– Seed coverings.



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Seed Storage and Viability TestingSeed Storage and Viability Testing

• Germination test- Tests germination over a period of time



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Seed DormancySeed Dormancy

• Dormancy is an important survival mechanism for some species—a result of evolutionary development.– They have survived these factors prevent seed

germination of woody perennials in the autumn, allowing the embryonic plant in the seed to overwinter in a very cold-resistant form.• Causes for dormancy can persist indefinitely in the

seed and require specific treatments to overcome them before germination can take place.

• Dormancy can result from structural or physiological conditions in seed coverings, the embryo, or both.



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Seed DormancySeed Dormancy

• Dormancy - survival mechanism for some species– Prevents germination out of season, or in unfavorable

conditions– Can be structural (seed coat) or physiological (cold

requirement), or both.



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Seed GerminationSeed Germination

• The sequence of events during seed germination:– Imbibition of water by seeds– Activation of hormones/enzymes– Embryo growth/development



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Vegetative PropagationVegetative Propagation

• Vegetative/asexual propagation is done by mitosis.



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Mitotic cell division, produces adventitious shoots & roots and callus (parenchyma cells for healing of a wound or graft union)



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Regeneration in asexual propagation.Adventitious shoots growing from a root cutting.

Figure 9-11

Adventitious shoots shoots that appear any place other than shoot terminals or axils of leaves.



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Regeneration in asexual propagation. Adventitious roots developing from the base of a stem cutting.

Figure 9-11

Adventitious roots appear any place other than from the radicle (root tip) of the seed or its branches.



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Regeneration in asexual propagation. Callus tissue produced to give healing of a graft union.

Figure 9-11

Callus is a mass of undifferentiated, proliferating parenchyma cells.



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• Environmental factors can modify appearance and behavior of the plant (phenotype), so that individual plants can differ strikingly.– Mutation can also cause undesirable changes in clones.



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Disease Problems in ClonesDisease Problems in Clones

• Certification programs are established to provide nurseries with sources of true-to-name, pathogen-free propagation material.– Culture-indexed or certified cuttings



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Propagation by CuttingsPropagation by Cuttings

• Cuttings can be classified according to the part of the plant from which they are obtained:– Stem cuttings have terminal or axillary buds, but new

roots must develop before a new plant will be formed.– Leaf cuttings have no buds or roots, so both must form.– Leaf-bud cuttings have a bud at the base of the petiole,

for the new shoot system—so only new roots must form.– Root cuttings must produce a new adventitious shoot

and continue growth of the existing root piece, or develop roots from the base of the new shoot.



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Propagation by CuttingsPropagation by Cuttings

Types of cuttings:(A) Hardwood stem cutting. (B) Leafy stem cutting. (C) Leaf cutting. (D) Leaf-bud cutting. (E) Root cutting.

Figure 9-14



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Propagation by Grafting & BuddingPropagation by Grafting & Budding

• Grafting—joining parts of plants together to grow as one plant– Scion – part of the graft combination that is to become the

upper or top portion of the plant.– Rootstock lower part of the graft combination that is to

become the root system.



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Propagation by Grafting & Budding - Whip GraftingPropagation by Grafting & Budding - Whip Grafting

Whip Grafting is useful in grafting togethermaterial of about 0.25” to 0.5” diameter.



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Propagation by Grafting & Budding - Cleft GraftingPropagation by Grafting & Budding - Cleft Grafting

The cleft graft is mostly used in top-grafting, where scions of0.25” to 0.5” diameter are inserted into stubs of older limbs

3” to 4” in diameter—cut off about a foot from the trunk of the tree.



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It is important in cleft grafting to match the cambium layerof the scion as closely as possible with the cambium layer

of the stock so that the two pieces heal together.

Cleft grafting is usually done in late winter or early spring.



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Proper selection of scionwood and budwood is veryimportant in all types of grafting and budding.

Scionwood & budwood should be taken from

source trees true-to-typefor the cultivar to be

propagated.

They should be free ofknown viruses andany other diseases.



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Polarity must be observed: the scions must beinserted so that the buds point upward.

With woody plants, graftingand budding must be done

with dormant buds on the scion.



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In all types of grafting and budding, the two parts must be held together very tightly and securely by wedging, tying, nailing, or wrapping with string, rubber bands, or with plastic or cloth tape.

The graft union must also be completely covered by grafting wax to prevent the cut surfaces

from drying out.



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Propagation by Grafting & Budding - HealingPropagation by Grafting & Budding - Healing



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Propagation by Grafting & Budding - IncompatibilityPropagation by Grafting & Budding - Incompatibility

Even when grafts are compatible, grafted plants can at time be identified by a swelling where

the graft was made.

This can become a weak point, susceptible to breaking/cracking.



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Propagation by Grafting & Budding - LayeringPropagation by Grafting & Budding - Layering

Simple Layering:



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• Layering:

Tip Layering

Mound Layering



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Air Layering :



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Other Plant Structures - RunnersOther Plant Structures - Runners

Stolons:



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Other Plant Structures - SuckersOther Plant Structures - Suckers

• Suckers: adventitious shoots from the horizontal root system, which spread to form a dense thicket.



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Propagation Using Specialized Stems and RootsPropagation Using Specialized Stems and Roots

• Bulbs, corms, tubers, tuberous roots, or rhizomes can be used for propagation, too.



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Micropropagation (Tissue Culture)Micropropagation (Tissue Culture)

• Very small pieces of plant tissue grown on sterile nutrient media under aseptic conditions.– Explants are used to regenerate new shoot systems,

which can be separated for rooting & growing to full-size.

Chapter 9 - 2.1

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