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Chapter 5
Plant Propagation
Part 1 – Sexual Propagation
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What is Propagation?
• Plant reproduction
– Vegetative
– Sexual
• Sexual vs. Asexual propagation
Schefflera cutting
Seed of Franklin’s
Sandwort
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Seed Formation
• What causes seed formation?
– Seeds result from successful pollination and
subsequent fertilization
– Cross-pollination
– Self-pollination
• What is hybrid seed?
– Technically ‘hybrid’ can apply to any cross-pollinated
plant
– Term is reserved for plants grown from seed that is
the result of special breeding and generally superior
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Hybrid Seed
• Produces seedlings with ‘hybrid vigor’
• Is the result of controlled crossing of a dedicated
‘female line’ and a dedicated ‘male line’
– Both lines are genetically pure will have the best traits
of both parents
• Seed saved from hybrid plants will not grow into
good plants
– Only the original hybrid seed will carry the desirable
traits
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Mendelian Genetics
• Czech Monk Gregor Mendel, the original founder
of the genetic science we have today
– Original idea that offspring resemble parents
– Studied peas – flower color, seed shape, etc.
• Suspected that offspring characteristics are
dependent on specific traits that are passed by
each parent
– These traits are not blended together
• Visible manifestation of traits is called
‘phenotype’
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Mendelian Genetics
• This idea indicates that an offspring may look just like
one of the parents, even though it is a product of both
parents
• Because it is a product of both parents, the genetic
composition will not be the same as either parent.
• Mendel postulated that traits exist in pairs in each
parent
– Now called ‘genes’
– And were classified as recessive or dominant depending on
if they were manifest in the offspring
– Now we understand some genes have ‘partial dominance’
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Simplified Mendelian Cross
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Techniques of Plant Breeding
• Plants to be bred must belong to the same
genus, and almost always belong to the same
species
– Cultivars within a species usually cross-pollinate
• In rare instances do plants breed across
Genera (intergeneric hybrid)
– Fatshedera is one example (xFatshedera lizei).
• One parent is Hedera helix and the other is Fatsia
japonica
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Techniques of Plant Breeding
• Cross-pollinated seeds only make up a small
percent of seeds produced (estimated around
4%)
– The close proximity of the anther and stigma in
most flowers tends to promote self-pollination
• Dioecious plants can never self-pollinate
• How to control the pollination of flowers to be
bred depends on the type of flower
– Perfect or imperfect
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Techniques of Plant Breeding
• If exact self-pollination is desired, a small bag can
be placed over the flower just before it opens
(perfect flowers)
– When the flower opens it will encounter no other
pollen source than from it’s own anthers
• For imperfect flowers, pollen must be carefully
transferred from the desired male and put on the
desired female parent
– Often with a small brush
– This can also be done with perfect flowers when
pollen from another parent is desired instead of
allowing it to self-pollinate
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Hand pollination of watermelon, a monoecious plant
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Labeling of an eggplant flower after pollination. The flower is taped
shut after pollination to prevent contamination of the cross
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Techniques of Plant Breeding
• After successful pollination, the eggs will be
fertilized within several days and the floral parts
will fall off the flower leaving the enlarging ovary
• When seed is mature, it must be removed from
the fruit and cleaned for most uses
• Storing seeds is best in a sealed bag or jar in a
cool, dark environment
– Most seeds can be stored for long periods of time
– All experience a decrease in germination percentage
and seedling vigor as time progresses
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Wet seed extractor in the field. Used for tomatoes, melons, squash, etc.
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Three-screen seed cleaner separates
seed based on size. Can be used on
seeds from dry fruit or seeds from wet
fruit after is has been dried.
Winnowing or fanning seed with
electric fan
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Direct Seeding
• Sowing seeds outdoors is easy and practical
• Some basic rules apply to get good germination
– Plant in a area suitable for species – light, etc.
– Observe proper planting depth (usually a function of
seed size) and spacing
• 1 ½ times the seed diameter if no other info is available
–
–
–
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Ensure seed to soil contact
Keep moist
Thin plants as needed
Fertilize after true leaves appear
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Sowing seed indoors
• A popular practice to extend the growing
season
– Plants should be started 6-8 weeks ahead of
garden planting
– Timing is crucial because if started too early they
will grow too long indoors and perform poorly
outdoors later
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Sowing Seeds Indoors
• Some basic rules apply
– Provide a warm, humid environment
– Use a container that will allow water to drain away
– Growing medium must be loose, fast-draining,
and free from plant pathogens
• Commercial potting soils are usually adequate
• Commercial soils contain no actual soil
– Adequate light must be available
• Can be natural, artificial, or a combination of both
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Some commercial seed-starting kits
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Commercial seedling production
• Large-scale seedling production is often called
bedding plant production
• Specialized seed sowing equipment, trays, and
growing environment
• Seedlings can be sold wholesale to other
growers for finishing, or transplanted in-house
and sold in packs or small pots
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Drum seeder capable of seeding up to 600 trays per hour
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Damping-off
• Whether planted indoors or out, seedlings are
susceptible to a number of fungal diseases
– When a seedling or group of seedlings is infected with
a fungal disease, it is called ‘damping-off’
– It is caused by media that is too wet, excessive
humidity, very close plant spacing, and unclean media
or environment
– The fungus move fast when plants are in high
densities as in greenhouses and gardens
• Prevented with fungicides, lower humidity, more
air circulation, clean and drier media or soil
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Transplanting
• The term transplanting can be applied to moving
plants from a container into the ground, or from
one container to a larger container
• Should be done when plants crowd each other or
roots are excessively crowded
• Seedlings should be handled by leaves and not
stem
– Can survive a leaf breaking
• If roots are very dense, then cutting or separation
of the root ball is appropriate
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Transplanting
• Should be done in evening or on a cloudy day
to reduce chance of wilting
• Root ball should be moist and plants not
water-stressed
• Shading may be required
• Plants should be watered-in immediately after
planting to ensure soil-to-root ball contact
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Hardening-off
• Is the term for acclimating seedlings or adjusting them
gradually from the greenhouse or growing area to the
real world
– Idea is to gradually increase light, and wind, decrease
humidity, and adjust them to outdoor temperature and
conditions
– Placing plants outdoors in shade during the day
– Placing plants in sunny spot for a few hours a day
• After they are hardened they will not appear as soft or
succulent, have a stockier stem, and thicker leaves
• They are much less likely to wilt and die-back at
transplanting outdoors
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Spores
• Ferns produce spores instead of seeds
• These spores come from small capsules or spore
cases on the bottoms of leaves
• Ferns drop their spores on the ground which will
grow into a small, flat plant called the ‘prothallus’
• The prothallus then develops the sperm and egg
on the underneath side
– The sperm swims in the wetness at the forest floor
and hopefully some will find the eggs
– After successful fertilization a new fern will grow
under the prothallus in about a year
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Spore cases of Grape Fern
Split spore cases showing
thousands of tiny bead-like
spores
Prothallus – usually not
more that a few
centimeters or so in size
Pictures from
www.hiltonpond.org
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