This document discusses fertilization barriers in crop plants that prevent the fusion of male and female gametes. It identifies three main types of barriers - pre-fertilization barriers, post-fertilization barriers, and temporal/spatial isolation of species. Pre-fertilization barriers include failure of pollen germination or insufficient pollen tube growth. Post-fertilization barriers include failure of zygote development or hybrid sterility. The document then provides techniques to overcome each type of barrier, such as reciprocal crosses, mentor pollination, and chemical treatments. It also discusses chromosome manipulation methods that are important for distant hybridization, including haploid production, creating amphidiploids through doubling chromosomes, and inducing

1. FERTILIZATION
BARRIERS IN CROP
PLANTS

2. FERTILIZATION BARRIERS
Prevent the fusion of male and female
gametes
It limits effective utilization of the hybrids
Self Incompatibility
Very frequent in inter-specific and inter-
generic hybridization program.

3. Major Fertilization
Barriers
Temporal and
spatial isolation
of species
Pre-fertilization
barriers
Post
fertilization
barriers
“Prevent Fertilization” “Prevent Embryo
Development”

4. Temporal and spatial isolation of species
■ Non synchronous flowering of the parental species due to
different agro-ecological or geographical background.
Methods to overcome:-
1. Early/staggered sowing
2. Suitable photoperiodic treatment
3. Vernalisation

5. Pre-fertilization Barriers
1. Failure of pollen germination on stigma
2. Insufficient/slow growth of pollen tube in
style
3. Failure of male gamete to unite with
female gamete [Cross incompatibility]
“Prevent Fertilization”

6. 1.Failure of pollen germination on
stigmaA. Unilateral incompatibility (UI)
 Incompatibility operates in one direction, whereas the reciprocal
cross is successful
 The crosses show incompatible when an SI species is used as a
female parent (SI x SC)
 For active recognition of the pollen, Self-incompatibility inhibition is
necessary.
B. Inhibition on the stigma surface
 Result in the arrest of pollen germination or pollen tube entry into the
stigma..
Factors:-
Lack of effective adhesion, full hydration and pollen germination
factors.

7. Techniques to overcome…
 Effective pollination
Pollen must be transferred to the correct place and at the
correct time.
Pollen must hydrate properly
 Mentor pollination
Pollen which is fully compatible with the intended seed parent.

8. 2. Insufficient growth of pollen tube in
styleCauses:
■ The arrest of pollen tubes in the stigma.
■ Long style of flower.
 Arrested pollen tubes show abnormalities like…
• Thicker tubes.
• Excessive deposition of callose.
• Swollen tips.
• Branching of tubes
 Growing pollen tubes utilize styler nutrients. Arrested pollen tube
growth is the inability of the pollen tubes to utilize styler nutrient.

9. Techniques to overcome…
 Reciprocal crosses
 Mentor pollination
 Use of plant growth regulators
 Pollen may have to be applied in a medium
favoring germination.
 By pass stigma and style completely and apply
pollen directly to the ovule

10. 3. Failure of male gamete to unite with
female gamete [Cross incompatibility]
 Inability of the funtional pollens of one species to effect
fertilization of the female gametes of another species is
refered to as cross incompatibility.
 The failure of male and female gametes to unite to form
zygote in interspecific and intergeneric hybrids is known as cross
incompatibility.
”This is major problem in distant hybridization”

11. Post-fertilization Barriers
1. Failure of zygote development
2. Hybrid sterility
3. Hybrid breakdown in F2 or later
generation
4. Inadequate growth of Hybrid plants
“Prevent Embryo
Development”

12. 1. Failure of zygote
development
 In some wide crosses, fertilization occurs and zygote
formation also take place. But, the zygote does not grow.
 Inability of a hybrid zygote to grow into a normal embryo
under the normal conditions of developement is known as
hybrid inviability.
Causes:-
•Lethal genes
•Lack of chromosoamal homology
•Disharmony between nuclear and cytoplasmic gene
•Unfavourable interaction between embryo and endosperm

13. 2. Hybrid sterility
■ This problem is more severe in intergeneric crosses
than in interspecific crosses.
”The inability of a hybrid to produce viable
offspring.”
Causes:
•Lack of structural homology between the chromosomes of two
species turn in to non-pairing or reduce pairing.
•Structural chromosomal aberration.

14. 3. Hybrid breakdown in F2 or later
generation
■ In this f1 plants are vigorous and fertile but become
sterile or weak in f2 or later generation.
Causes:-
Gene combination: Unfavorable combinations of dominant and
recessive genes breakdown due to segregation and recombination
Structural differences: Structural differences in the chromosomes,
gametes with deletion and duplication

15. 4. Insufficient growth of Hybrid plants
■ Flower shedding
■ Delayed maturity of fruits
■ Chlorophyll deficient
■ Seed abortion
■ Due to unfavourable interactions between Genes of two species

16. Techniques to overcome…
1. Choice of parents…
 Which are crossing competible
 Having chromosomal similarity or homology (so that
atleast fertility can be restored)
 Choose the parent from…
1. Primary gene pool
2. Secondary gene pool
3. Tertiary gene pool

17. 2. Reciprocal cross:
■ The interspecific cross of black gram as
female and green gram as male was not
successfully reported but the reciprocal
cross was found successful.

18. 3. Modification of ploidy levels:
Ex:
■ If Parent A having 2n=24 chromosome number & Parent B having 2n=12
cromosome number than first,
Parent B (2n=12)
2n= 24
Then after cross between both are carried out.
In some cases haploid is produced.
Or
In some cases the semisterile f1’s chromosome is doubled for restoration of fertility.
Doubling of chromosome

19. 4. Modification of pistil:
■ Use short styled species as female
If,
Maize♀ × Tripsacum ♂
Because of the pollen tube of Tripsacum have not enough growth to reach
due to long style of maize.

20. 5. Mentor pollination
• The pollen which has been purposefully treated is
called mentor pollen.
• “The compatible pollen is treat…
 To improve its fertilization ability
 To retain power to stimulate incompatible pollen to
accomplish fertilization”.

21. 6. Bridge species
■ Example : If there was two genotype A
and C can not directly cross then
genotype B which can cross with both
A and C is used as bridge species.
A × B
Product × C
Desired F1
N. Sylvestris x N. repanda
x N.
tabacum
T. Turgidum x Ae. Ventricosa
x T. aestivum
amphidiploid
amphidiploid

22. 7.Chemical treatment of the pistil or
pollen:
Eg.
• N. tabacum does not hybridize with N. rependa.
But this cross is possible when IAA applied to pedicle of flowers in a lanoline
paste
- It cause More rapid pollen tube growth
- Longer pistil viability
• Vigna radiata x Vigna ambellate
EACA (immunosuppressant) applied before pollination
• Interspecific crosses in cotton
IAA, NAA and GA3 applied to crossed buds to Prevent shedding and
Use of growth regulator.

23. 8. Embryo
Culture :
■ Isolation & growth of an immature or mature embryo
in vitro, with the goal of obtaining a viable plant.
■ The first attempt to grow the embryos of angiosperms
was made by Hannig (1904) from two Crucifers
Cochleria & Raphanus.

24. 9. Protoplast fusion or somatic
hybridization
■ Development of hybrid plants
through the fusion of somatic
protoplasts of two different plant
species/varieties is called somatic
hybridization.

25. 10. Grafting
■ Carried out in horticultural crops.
■ In which stock and scion is used.

26. CHROMOSOME
MANIPULATION IN DISTANT
HYBRIDIZATION

27. Chromosomal Manipulation
■The term chromosome manipulation
describes process or technologies in
which chromosomes are manipulated
to change their mode of genetic
inheritance.

28. Types of Chromosome manipulation
 Incorporation of fragments of chromosome from a wild
into the existing crops to enhance the genetic diversity.
 Incorporation of an alien chromosome by
chromosomes doubling in order to produce
amphidiploids.
 Elimination of an alien chromosome in order to induce
haploids.

29. Chromosomal Manipulation in crop
improvement
 Chromosomes elimination
and haploid crops
■ Chromosome elimination is the
degeneration of one parental
chromosomes in F1 hybrid due
to inactivation of kinetochore
function.
Zygote
Embryogenesis and elimination
of bulbosum chromosomes (B)
Haploid of H. vulgare
(x=7)
Hordeum bulbosum x Hordeum
vulgare
7 bulbosum + 7
vulgare chromosomes
(2x= 14, BB) (2x= 14 VV)
F1

30.  Chromosomes doubling
and amphidiploids
■ Chromosome doubling can
be carried out through the
treatment with anti-
microtubule drugs &
Colchicine.
F1
AABBRR
(6x)
Triticum aestivum x Secale cereale
AABB (4x) RR (2x)
Hexaploid Triticale
ABR (3x)
Chromosome doubling

31.  Homeologous chromosomes
pairing
■ The manipulation of Ph1 gene
can relieve the restriction of
homoeologous chromosome
pairing and thus improve the
efficiency of alien translocation
development.

32. ■ Chromosomes manipulation techniques change the
mode of genetic inheritance.
■ It is useful in the development of various varieties and
lines of crops with desirable traits (transfer from wild to
cultivated crops).
■ It is an important technique to create genetic diversity
in crops species (which is the basic for crop
improvement and breeding).

33. Haploids:-
■ Types of haploids production:-
 In vitro techniques
 In vivo techniques
A cell, tissue or organism possessing the gametic number (n)
of chromosomes is called haploid.

34. In vitro techniques:-
•Anther culture
(anderogenesis)
•Ovule culture
(Gynogenesis)

35. 1.Parthenogenesis and
Apogamy
 The term parthenogenesis is used for the development of embryo from ovum / egg cell
without fertilization, whereas the term apogamy is used for the development of embryo
from the vegetative cells without fertilization.
 The hapoids arising from the maternal cells in the embryo sac are called ‘gynogenetic
haploids’ whereas, those arising from the male (sperm) nucleus in the embryo sac are
called ‘androgenetic haploids’
In vivo techniques:-

36. 2. Somatic
Reduction
Somatic reduction:
• It is the phenomenon which results in the reduction of somatic chromosome complements
and involves the segregation of whole genomes. It involves the abnormalities such as
multipolar spindle formations. Give rise to haploid cells during the parasexual cycle of
certain fungi.
• It can be induced by certain chemicals, in different plants e.g. by chloramphenicol in barley
root tips, by parafluorophenylalanine (pFPA) in grape

37. 3. Chromosome
elimination
 In certain plants, interspecific or intergeneric
hybridization leads to the gradual
elimination of chromosomes of one of the
parental genomes resulting in the production
of haploids.
 The mechanism of elimination may involve
failure of chromosome congression at
metaphase leading to chromosome lagging
at anaphase and formation of micronuclei.
This process may also lead to the production
of androgenetic haploids.
Zygote
Embryogenesis and elimination
of bulbosum chromosomes (B)
Haploid of H. vulgare
(x=7)
Hordeum bulbosum x Hordeum
vulgare
7 bulbosum + 7
vulgare chromosomes
(2x= 14, BB) (2x= 14 VV)
F1

38. Uses & Advantages
■ Development of homozygous lines and pure cultivars.
■ Selection of genotypes that contain favorable genes.
■ Short breeding cycle
■ For mutation research
■ For evolutionary studies
■ Genetic studies
■ To obtain information on the ancestry of species
■ No masking effects because of high homogeneity.

39. THANK YOU…