Transcript Propagating Plants Sexually

Horticulture Science
Lesson 15
Propagating Plants Sexually
Interest Approach
Bring 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 Objectives
•Discuss the importance of sexual
propagation of plants.
•Describe the process of seed
germination.
Student Learning Objectives
•Describe the factors involved in
planting seeds for transplanting.
•Explain how to successfully direct
seed outdoors.
Terms
•
•
•
•
•
•
•
•
•
•
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 crosspollination 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.
What is germination and what
conditions are necessary for
germination to occur in a seed?
• The environmental conditions important
for germination include moisture,
temperature, oxygen, and light or
darkness.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What is germination and what
conditions are necessary for
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.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• 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.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• 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.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• Seed is tested for percent
germination and labeled
for the consumer.
• Many state and federal
laws regulate the
shipment and sale of
seed.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• 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.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• 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.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• 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.
What factors should be considered to
successfully grow seeds indoors
from seedlings to mature plants?
• 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 the
direct 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.
What factors determine the
success of plants grown from the
direct seeding method?
• 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.
What factors determine the
success of plants grown from the
direct seeding method?
• 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.
What factors determine the
success of plants grown from the
direct seeding method?
• 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.
What factors determine the
success of plants grown from the
direct seeding method?
• 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/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?
Review/Summary
•What factors should be
considered to successfully grow
seeds indoors from seedlings to
mature plants?
Review/Summary
•What factors determine the
success of plants grown from the
direct seeding method?