Horticulture Science Lesson 15 Propagating Plants Sexually

Horticulture Science Lesson 15

Propagating Plants Sexually

Horticulture Science Lesson 15

Propagating Plants Sexually

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Interest ApproachInterest ApproachBring to class several varieties of blooming plants such as geraniums and petunias. If plants are not available, use a flowering plant seed catalog that contains color pictures of plant varieties. Ask students about the significance of variety. How does it happen? How has genetic variation impacted our world food resources? Show students a variety of bean seeds. What do the seeds have in common? What is different about them? How does germination unlock the “secret” within each seed?


Student Learning ObjectivesStudent Learning Objectives• Discuss the importance of sexual propagation of plants.

• Describe the process of seed germination.


Student Learning ObjectivesStudent Learning Objectives

• Describe the factors involved in planting seeds for transplanting.

• Explain how to successfully direct seed outdoors.


TermsTerms• direct seeding• germination• indirect seeding• medium• planting date• scarification• stratification• turgor• viability• vigor


How does the ability to sexually produce seeds benefit a plant?• Many important

horticultural crops are grown from seed, including bedding plants, perennials, vegetables, and woody plants.

• Most of the flower and plant varieties used in the floriculture industry today are the result of cross-pollination by plant breeders.


How does the ability to sexually produce seeds benefit a plant?• Plant breeders select plants for

outstanding characteristics, such as flower color and disease resistance.

• Then, they collect pollen from one plant and transfer it to the flower of another.

• Their hope is to have the outstanding characteristics expressed in the offspring.

• This process is called hybridization.


How does the ability to sexually produce seeds benefit a plant?

• The offspring of two plants of the same or related species that differ genetically is said to be a hybrid.

• The advantage of hybridizing is that desired traits of different parent plants can be combined in the offspring.


How does the ability to sexually produce seeds benefit a plant?• In the

landscape/nursery industry, many trees and shrubs are produced from seed.

• Seeds are collected from trees and shrubs that exhibit outstanding characteristics.

• These are sown and grown for sale.


How does the ability to sexually produce seeds benefit a plant?• Sowing vast numbers of seeds also allows

breeders to select exceptional offspring. • The exceptional plants are propagated

asexually to maintain genetic makeup.


What is germination and what conditions are necessary for

germination to occur in a seed?• The beginning of plant growth from seed is

called germination. • Germination is a complex process that begins when favorable conditions exist for the survival of the developing seedling plant.



germination to occur in a seed?• The environmental conditions important

for germination include moisture, temperature, oxygen, and light or darkness.



germination to occur in a seed?• The first important step in germination is

usually the absorption of water. • Water enters the seed by diffusion. • The moisture triggers several important

processes.

• Water also causes the seed to expand and creates pressure within the seed.



germination to occur in a seed?• This pressure, known as turgor, causes

the seed coat to rupture. • The primary root, or radicle, emerges

through the rupture and forms the root system of the plant.



germination to occur in a seed?• Water also stimulates the production of

plant hormones that begin the process of converting stored food into energy for the developing embryo.

• In addition, plant hormones cause cells of the radicle to divide, allowing it to emerge from the seed to absorb water and nutrients for the embryo.



germination to occur in a seed?• Seeds germinate at a wide range of

temperatures. • Some plants require very warm

germination temperatures, and other plants must have cool temperatures.

• The temperature range is from 32° to 104°F, with the optimum range for most seeds being between 65° and 80°F.



germination to occur in a seed?• All seeds need oxygen to

germinate. • The oxygen is necessary for the

cellular respiration. • Through cellular respiration,

chemical energy held in the starches is released for the growth and development of the embryo.



germination to occur in a seed?• Without sufficient oxygen,

the embryo cannot develop.

• Wet soil that prevents oxygen from reaching the seed can cause the death of an embryo or seedling.



germination to occur in a seed?• Seeds of some plants need exposure to

light before they will germinate. • Some plant seeds require darkness. • Other plants are unaffected by light or

darkness.




germination to occur in a seed?• Some plants produce seeds that germinate

immediately; others produce seeds that remain dormant, perhaps for years, until the conditions are likely to result in the survival of the seedlings.

• Internal seed mechanisms are sometimes responsible for preventing seed germination even when environmental factors appear optimal for germination.



germination to occur in a seed?• One mechanism is stratification, which is

a required period of cold temperature before germination.

• This is especially important for plants that produce their fruit in the fall.



germination to occur in a seed?• In a natural setting, these types of plants

receive the cold period during the winter months.

• If the seeds of these plants germinated immediately, they would die with the onset of cold winter temperatures.



germination to occur in a seed?• Scarification is a mechanism that

prevents germination until the seed coat has been physically broken down.

• A tough, protective seed coat prevents diffusion of both water and oxygen into the seed.

• The seed coat must be broken before germination can begin.



germination to occur in a seed?• Plants have developed many interesting

methods to accomplish this task. • The seed coat can be damaged or broken

by the acid produced in an animal’s stomach, by soil microorganisms, by repeated freezing and thawing, by mechanical stress from being ground in the gizzard of birds, and by being stepped upon or chewed.



What factors should be considered to successfully grow seeds indoors from seedlings to mature plants?

• Seeds can be planted indoors until they grow into seedlings that are then transplanted into larger containers or to a permanent location outdoors.

• This is called indirect seeding.



• The quality of seed used is very important. • Seed quality includes both viability and

vigor.– Viability is the ability of seeds to

germinate under optimum conditions. • Quality seed should have high viability, with

a germination rate of more than 75 percent.– Vigor is the ability of seeds to germinate

under less than optimal conditions and still produce healthy seedlings.



• Seeds are stored in cool, dry conditions to maintain seed viability and vigor.

• Most seed is stored at temperatures around 40°F and at a relative humidity between 20 and 40 percent.

• No matter how well seed is stored, its quality decreases over time.



• Seed is tested for percent germination and labeled for the consumer.

• Many state and federal laws regulate the shipment and sale of seed.



• Seeds can be planted indoors to increase the length of the growing season, to increase production, and for economy of space.– 1. Seeds may be planted in flats or

containers of germinating medium. – Medium is the material in which plants are

grown. – Start with clean containers with drainage

holes.


What factors should be considered to successfully grow seeds indoors from seedlings to mature plants?– 2. A good germinating medium is fine

textured, has good water-holding capabilities, is well aerated, and provides support for the growing plant.

– 3. Sow the seed in rows to reduce the spread of disease. • When using flats, the rows should be about

2 inches apart. • Plant the seeds close together at the

approved depth and, if recommended, cover the seeds with medium.


What factors should be considered to successfully grow seeds indoors from seedlings to mature plants?– 4. Label each flat with the seed variety and

the date the seed was sown.– 5. Maintain the proper temperature.

• The recommended temperature for most seed germination is between 65° and 80°F.



• 6. Water seed flats lightly from the top using a sprayer or mister.

• Cover seed flats with poly or glass to maintain moisture level and humidity.

• Remove the covering once the seeds start to germinate.

• 7. Since developing seedlings require higher amounts of oxygen, avoid overwatering the seed flats.

• Over-watering and lack of proper drainage reduce the oxygen level by filling the air spaces with water.




• Seedlings should be transplanted when the first true leaves are fully developed.

• 1. When transplanting, care should be used in handling seedlings.

• Seedlings should be held only by their leaves and not by their stems.



• 2. Make a hole with a dibble, stick, or forefinger in the new location.

• Place the seedling in the hole at a depth slightly below the former depth.

• 3. After transplanting, the seedlings should be watered and placed in the shade to help prevent wilting.

• In a few days, move the plants to receive proper light intensity and water them to promote good root growth.


What factors determine the success of plants grown from

thedirect seeding method?

• Many flowers, vegetables, and grass seeds are planted directly into the soil outdoors in their permanent location.

• In the greenhouse, seeds are sometimes planted right into the finish pot.

• These methods are called direct seeding. • Factors that should be considered when

direct seeding are site selection, seedbed preparation, planting date, planting depth and spacing, and care of the seedlings.




• The site should have sufficient light for the plants to grow.

• The seedbed should be prepared so that it is loose and fine textured, allowing for adequate moisture and aeration.




• The planting date is the date to plant seeds.

• It is determined by the soil temperature required by the seeds for successful germination.

• Planting date is also influenced by the time of maturity, harvest dates of vegetables, and peak bloom dates of flowers.




• Seeds should be sown at recommended planting depths and spacing.

• A general rule, if the planting depth is unknown, is to plant seeds at a depth of three to four times their greatest thickness.

• Spacing between seeds is also important to prevent overcrowding.




• The seedbed should be kept uniformly moist until the seedlings are established.

• It is also important to control weeds that compete for light, nutrients, and water.


Review/SummaryReview/Summary

• How does the ability to sexually produce seeds benefit a plant?

• What is germination and what conditions are necessary for germination to occur in a seed?



• What factors should be considered to successfully grow seeds indoors from seedlings to mature plants?



• What factors determine the success of plants grown from the direct seeding method?


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Horticulture Science Lesson 15 Propagating Plants Sexually