Download hybridization

Maximizing productivity of wheat and barley under
dry-land systems
HYBRIDIZATION
Faddel Ismail
NCARE
June, 8-10 2015
Hybridization
Hybridization is the process of crossing two genetically
different individuals to create new genotypes (organism).
Parent 1 with BB and parent 2 with bb, produces progeny
with Bb, which is a hybrid (F1 generation).
Cross identical parents
X
X
Cross different parents
X
X
Hybridization
It is a common way of generating genetic variability.
Hybridization of plants occurs in nature through
various mechanisms.
insect-pollination (oil palm), wind-pollination (corn).
Such plants are referred to as cross-pollinated plants.
Natural hybridization is the norm in cross-pollinated
plants.
Hybridization
Hybridization: mixing (fusion) male genetic material
with female genetic material.
- Production of gametes
- Transfer of male gametes
- Mixing (merging) genetic material
- Forming zygote (new organism)
These occur in the reproduction organ The flower
Flower structure
Non-reproductive organs
 Petals – flower organs that are often
brightly colored to attract pollinators
 Corolla – group of petals
 Sepals –leaf-like organs outside the
corolla; help protect the unopened
flower bud.
 Calyx – group of sepals in a flower
female organs
 Carpel or pistil – female
reproductive organs; contains:
• Stigma – is where pollen sticks to
• Style – is the long tube that connects
stigma to ovary
• Ovary – enlarged structure at the
base of carpel/pistil where the ovules
are located; it will become the fruit.
• Ovules – contains female
gametophyte, becomes
the seed
‫ميسم‬
Ovary
‫مبيض‬
‫قلم‬
carpel
or
pistil
‫المتاع‬
male organs
 Stamen – male floral organ,
consists of:
• Anther – part of the stamen
that produces pollen
• Filament – stalk-like
structure that holds anther
• Pollen – immature male
gametophyte
‫سداة‬
‫متك‬
‫خيط‬
Plants - Flowers types
 Perfect- bisexual-hermaphrodite:
Both pistil and stamen.
 Staminate flower:
contain stamen –no pistil
 Pistillate:
contain pistil – no stamen
Flowers types - reproductive
Monoecious plant/crop:
plant has staminate and pistillate
flowers
Dioecious crop:
plants having either only male or
only female flowers
pollination
The transfer of pollen from the anther (male) to
the stigma (female)
• Self-pollination (Autogamy) :
Pollen from one flower pollinates the same
flower or other flowers of the same plant.
• Self-pollination may include
autogamy, where pollen moves to the female
part of the same flower (this).
geitonogamy, when pollen is transferred to
another flower on the same plant.
• Cross-pollination (allogamy):
Pollen from one flower pollinates flower of another plant.
• Pollinator: The agent (vector) that moves the pollen
Biotic: bees, flies, bats, moths, or birds.
Abiotic: wind, water
• Pollinizer: The plant that serves as the pollen source for
other plants.
Advantages of self pollination
• Insures seed set in absence of pollinators.
• Overcomes sterility.
• Selectively advantageous by transmitting both sets of
genes to offspring.
– Well-adapted genotypes preserved.
• Only single colonizing individual needed.
Disadvantages of self pollination
• Decreases genetic variability.
• Inability to adapt to changing conditions.
• Increases inbreeding depression.
– Reduces heterozygosity and increases homozygosity
of deleterious alleles.
– More uniform populations.
Factors affect pollination
• Perfect flowers have both male and female organs
• Cleistogamy :
Flowers never open and only capable of self-fertilization.
• Chasmogamous:
flowers that open and are then pollinated.
• Timing: Male and female organs mature at different times
Temporal separation of reproductive parts (Dichogamy)
Protandry(anther first). Protogyny
Factors affect pollination
• Biochemical:
chemical on surface of pollen and stigma/style that prevent
pollen tube germination on the same flower (Gametophytic
and Sporophytic incompatible)
Pin
• Physical separation of reproductive parts
• Morphological: Heterostyly:
Distyly (Trum and pin flowers). Tristyly
• Separation of flowers: Unisexual flowers.
Monoecious and Dioecious.
Trum
Self vs. cross
• Self compatible
• Small flowers (few)
• Unscented flowers
• Nectaries & nectar
guides absent
• Maturation of
reproductive parts
– Anthers near stigma
– Style included
• All fruits mature
• Low pollen/ovule ratio
• Self compatible and
incompatible
• Large showy flowers (many)
• Scented flowers
• Nectaries & nectar guides
present
• Differential maturation of
reproductive parts
– Anthers far from stigma
– Stigma well-exserted
• Only some fruits mature
• High pollen/ovule ratio
Pollination and Fertilization
 pollen delivered to the stigma (pollination).
 Pollen sticks to the stigma, starts growing a pollen tube
 Fertilization begins when tube begins to grow toward
the egg
 Double fertilization.
Pollen
contains TWO
nuclei: a
sperm
nucleus and
tube nucleus
•Sperm
nucleus is
protected in
gametophyte
tissue
Double Fertilization
• Double fertilization occurs: One sperm nucleus (1n)
•
•
fertilizes the egg, producing a zygote (2n)  which
becomes the plant embryo inside the seed
Another sperm nucleus fuses with the polar nuclei,
resulting in a triploid endosperm (3n)
Endosperm is a source of food for the young embryo.
Endosperm
Hybridization
It is a common way of generating genetic variability.
As an example of the power of hybridization in creating variability,
• Cross between hypothetical wheat varieties differing by only 21
genes
• Capable of producing more than 10,000,000,000 different genotypes
in F2
• More than 100,000 dunum (10cm*10cm) would be required to grow
them.
• Majority of F2 are heterozygous genotypes for one or more traits
• Statistically it is possible that 2,097,152 different homozygous
genotypes can occur, each potentially a new pure-line variety.
• These illustrate the importance of efficient techniques in managing
hybrid populations.
Hybridization technique.
Pollinate the female parent flower with pollens from the
required male parent and prevent any other source of
pollens.
• Easiest in dioecious crops.
• Moderate in monoecious.
• Could be very hard in plants with perfect flowers.
o The techniques require skilled hands.
o First step in hybridization is to ensure that no pollination
takes place before done artificially.
o The process involves the bringing of the stigma and pollen
of different plants together. They should be combatable and
at proper stage of maturity.
o Selected parents should be combatable.
Hybridization technique.
• Emasculation of perfect flower and used as female flower:
• Artificial Pollination:
• Rising of hybrids:
Emasculation of perfect flower:
• Physical removal of the anthers in self- pollinated plants.
• The female flower is ready
As a rough guide, an experienced person takes a good ten
minutes to remove all the anthers from wheat spike.
Bagging: After emasculation, female flowers are enclosed in
bags to avoid getting pollens from undesired sources.
Bagging is done with special paper or polyethylene
Labeling properly the emasculated flowers.
Artificial Pollination:
• Pollens from the selected male plants are collected in
suitable containers (paper bags, tubes or dishes)
• Dusted with a fine brush, on to the receptive stigma of the
female parent.
• Or Direct contact between mature anthers and stigma
• Female flower is securely sealed in a bag till the time of
seed setting.
Rising of hybrids:
Seeds are collected from the fertilized plants (F1 seeds)
Handel the F1 seeds
• Sell
• Produce pure line
• ……..
Emasculation:
No emasculation
• Male sterility
• Self incompatible
• Monoecious
• Dioecious
Emasculation:
Where physical removal of anthers is not possible.
• Genetic Male Sterility.
• Cytoplasmic genetic male sterility.
Male sterility is controlled by the interaction of a genetic factor
(S) present in the cytoplasm and nuclear gene (s).
• Environment-sensitive genetic male sterility.
Male sterility is controlled by nuclear gene expression, which is
influenced by environmental factors such as temperature.
eg. Dipping panicle in hot water (50°c) for 10 minutes.
practiced in Sorghum
• Chemically induced male sterility
Male sterility is induced by some chemicals
eg. dichlorophenoxy acetic acid maleic hydrazide in wheat
Timing:
Hybridization involves the bringing of the stigma and pollen of
different plants together.
Synchronize flowering
•Plant a set of parents at different times
•photoperiod in photoperiod sensitive species. Delay, Advance
•Manipulation of temperature
•Plant density
•Irrigation
•Removal of old flowers, induce new flush of flowers
•Pinching. To induce tillering or branching with new flowers.
•Store of pollin grains
Emasculation and pollination movies:
00001.mtc
GRU Information Resource 1- Guide to how to cross peas.wmv‬
GRU Information Resource 2- Guide to how to emasculate wheat florets.wmv‬
GRU Information Resource 3- Guide to how to pollinate wheat florets.wmv‬
‫شك ار لحسن استماعكم‬
HYBRIDIZATION
Faddel Ismail
NCARE
June, 8-10 2015