Pollination

1
Pollination Fertilization

• The Birds the Bees, or
• The Bees the Wind!

2
Objectives

• Learn how pollination fertilization occur in
  plants
• Learn factors the affect successful pollination
  fertilization
• Consider ways horticulturists increase the
  likelihood of successful pollination
  fertilization

3
Pollination Fertilization

• Critical processes in fruit and seed production
  (2nd 3rd steps) (remember flowering was the
  1st step)
• Note
• seed development triggers fruit
  development!

4
Steps in the Process
1.Anthesis (pollen shed)
Pollen grain of carnation
5
Anthesis

• Pollen produced in great excess
• Example apple flower
• 20 anthers
• 3,500 pollen grains / anther
• 70,000 pollen grains / flower
• 5 stigmas / flower each with 2 ovules
• Approx. 7,000 pollen grains / ovule

6
Steps in the Process
2.Pollination (pollen transfer to a stigma)
to other flowers
1.Anthesis (pollen shed)
Stigma of carnation
Pollen on stigma
7
Pollination (pollen transfer)

• Within same flower or same plant - self
  pollination
• Examples tomato, peach, pea
• Between differing plants - cross pollination
• Examples apple, sweet cherry

8
Cross Pollination - Vectors

• Wind
• Examples many trees (walnut, pecan, hazelnut,
  birch) grasses (sweet corn) - not showy flowers
• Extreme excess pollen production
• Hazelnut 250,000 pollen grains / ovule (remember
  apple - 7,000 / ovule)
• For seed production - 1 mile isolation needed
• Examples beet, corn, spinach

9
Cross Pollination - Vectors

• Insects
• Examples most fruits and vegetables - showy
  flowers, scent, nectar to attract insects
• A honeybees work is nectar and pollen collection
  as food, and moving pollen for the plant is
  unintentional
• For seed production - 1/4 mile isolation needed

10
Steps in the Process
2.Pollination (pollen transfer to a stigma)
to other flowers
1.Anthesis (pollen shed)
3.Pollen germination (on stigma)
Germinating pollen on carnation stigma
11
Pollen Germination

• Pollen grain is hydrated (moistened) on the
  stigmatic surface
• Pollen grain contains
• One nucleus that is the tube nucleus
• One nucleus that will divide as the tube grows
• Germ tube begins to grow toward ovary

12
Pollen Germination
Germinating pollen on a stigma
Germinating pollen with germ tube and nuclei
apparent
13
Steps in the Process
2.Pollination (pollen transfer to a stigma)
to other flowers
1.Anthesis (pollen shed)
3.Pollen germination (on stigma)
4.Growth of germ tube to ovary
14
Germ tube growth

• Tube grows between ( through) style cells
• Style tissue secretes compounds that influence
  tube growth (faster/slower)
• Nuclear division occurs
• Generative nucleus divides as tube grows and
  becomes two sperm nuclei that will fuse with
  different parts of the ovule

15
Steps in the Process
2.Pollination (pollen transfer to a stigma)
to other flowers
1.Anthesis (pollen shed)
3.Pollen germination (on stigma)
4.Growth of germ tube to ovary
5.Fertilization of ovule
16
Fertilization
1

• Germ tube enters embryo sac
• One sperm nucleus fuses with egg to become
  embryo, other fuses with polar nuclei to
  become endosperm (food storage)

3
2
Embryo sac
3
2
1
Second sperm nucleus
17
What Can Go Wrong?

• Achieve pollination but failure of fertilization
• Failure to achieve pollination

18
Failure of Fertilization even with Successful
Pollination

• Self-incompatibility (self-sterility)
• A plant may be an obligate outcrosser
• Thus, its own pollen will not achieve
  fertilization
• How is fertilization prevented? Chemical
  interaction between pollen and pistil.
• Pollen doesnt germinate on stigma
• Germ tube grows some and stops part way
• Germ tube grows too slow

19
Failure of Pollination/Fert.

• Temperature
• Freeze during flowering can kill flowers
• Low temperature slows insect pollinators
• Low temperature slows germ tube growth
• Wind
• Reduces bee flight

20
Failure of Pollination/Fert.

• Rain
• Can prevent pollen shed, or movement, especially
  in wind pollinated species
• Reduces bee flight
• Washes off stigmatic secretions - can reduce
  pollen adherance to stigma and pollen germination

21
Failure of Pollination

• Low population of pollinators
• Natural insect populations may be too low
• Habitat destruction
• Disease, pests (mites)
• Fruit and vegetable growers often bring in hives
  of honeybees during crop flowering
• Competition for insects from other flowers
• Avoid weediness

22
A Horticultural Example

• P F is a critical aspect of fruit production
• In Indiana and many areas in the temperate
  region, a major fruit crop is apples.
• P F in orchards may determine whether a grower
  has a profitable year or a not so profitable one.

23
Apple orchard pollination

• Apples require cross pollination
• Careful selection of pollen provider trees is
  necessary
• Pollen providers called pollenizers
• Not all apple cultivars produce pollen that will
  fertilize all other apple cultivars
• Example Winesap pollen is sterile

24
Pollenizer Selection

• Bloom time of pollenizer must overlap bloom time
  of crop producer
• Other apple cultivars as pollenizers allow for
  harvestable yield
• Crabapples sometimes used as pollenizers

25
Pollenizer Location

• Every third tree of every third row
• X X X X X X X X X X X X X X
• X P X X P X X P X X P X X P
• X X X X X X X X X X X X X X
• X X X X X X X X X X X X X X
• X P X X P X X P X X P X X P
• X X X X X X X X X X X X X X
• X X X X X X X X X X X X X X
• X P X X P X X P X X P X X P

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Pollenizer Location

• Alternate rows, alternate double rows
• Every fifth row

MacIntosh MacIntosh Red Delicious Red
Delicious MacIntosh MacIntosh Red Delicious Red
Delicious
Red Delicious Red Delicious Red Delicious Red
Delicious Red Delicious MacIntosh Red
Delicious Red Delicious
27
Summary

• Pollenization fertilization are multi-step,
  complex processes, affected by many internal
  externals factors.
• Understanding the factors allows horticulturists
  to influence P F.
• Reading for next lecture
• pp11-16, 58, 148-149