This document provides information on genetic incongruity and techniques for overcoming barriers in distant plant hybridization. It defines genetic incongruity as evolutionary divergence between two taxa that results in gene incompatibility. Techniques discussed include embryo rescue, somatic hybridization, alien addition/substitution lines, and transferring small chromosome segments. Applications in crop improvement involve transferring traits like disease resistance, yield, and hybrid seed production from wild species. Challenges include sterility, incompatible crosses, and linkage of undesirable genes.

1. Hearty
WELCOME
to all….
1

2. INTRODUCTION
• Definition: Passive reproductive barrier
which is caused by isolation between the taxa.
• Incongruity is a term used by Hogenboom
(1973).
• It describes Pollen Pistil Dysfunction in wide
crosses.
• Later intercellular and intracellular interactions
were also considered.

3. Genetic Incongruity
• Passive Phenomenon which display sufficient
evolutionary divergence has occurred between
two taxa such that when brought togather as
parents in a wide cross ,some genes mismatch
and are unable to function efficiently.

4. Dysfunction
• Selection does not operate to maintain
incongruity.
• The stage of dysfunction has also changed
during a process of evolution.
Types
1. Pre-zygotic Dysfunction
2. Post-zygotic Dysfunction

5. Pre-zygotic Dysfunction
• Process which prevent fertilization.
• Expressed as cross sterility and reduced
fertility.
• Found in Carica, Papaver,Pennisetum.

6. Pre-zygotic Dysfunction
• Affects the F1 hybrid generation.
• Expressed as
Embryo death
Endosperm dysfunction
Slow seedling growth
Seedling mortality
Unusual susceptibility to disease
Abnormal organ development

7. Contd….
Chlorophyll abnormalities
Tumors development
Lack of flowering
Sterility without a cause
Seed abortion
Hybrid lethality
Hybrid sterility in F1 generation.

8. Incompatibility vs Incongruity
Incompatibility
• Disturbs the functioning
of the relationships at
intra species level.
• It is due to the
consequence of
similarity of partners for
S alleles.
Incongruity
• Disturbs the functioning
of the relationships at
inter species level
• Cause of non mismatch
of partners for the
genetic information .

9. Hybridization

10. Hybridization
• crossing between two genetically dissimilar parents is
called hybridization.
Wide Hybridization
• Interspecific Hybridization:- Crosses made between
distantly related species
• Intergeneric Hybridization:- Crosses made between
distantly related genera
Somatic hybridization (Protoplast fusion)
• Crosses made between somatic cells
Hybridization (recombination) is the third major
evolutionary process with an importance not exceeding that
of mutation and natural selection.

11. History
Thomas Fairchild (1717):
• The first authentic record of a distant hybridization for the
crop improvement is the production of a hybrid between
Carnation (Dianthus caryophyllus) and Sweet william
(Dianthus barbatus).
Karpechenko (1928):
• An interesting intergeneric hybrid, raphanobrassica, was
produced.
 Rimpu (1890):
• Produce the first intergeneric hybrid triticale which have
greater potential than raphanobrassica.

12. Introgressive hybridization
• Transference of genetic material across an
incompletely developed interspecific barrier, usually
via a partially sterile F1 hybrid, by means of repeated
backcrossing, selection of well adopted backcross
types, has been termed by Anderson and Hubricht
(1938) introgressive hybridization or introgression.

13. • Ex . partially sterile F1 hybrid between fulva
and HGC
Species A Species B
Hybrids

14. Inter-specific hybridization:
• Ex. Nerica, an upland rice for Africa
• Oryza sativa (Asian upland rice): non-
shattering, resistant to lodging, high yield
potential
• Oryza glaberrima (African rice): drought
tolerant, disease resistant, weed-suppressing
 Nerica rice combines the best of both species.

15. Triticale (intergeneric cross)
• Triticale, a new cereal created in the lab.
• Triticale, a cross (intergeneric cross) between
wheat and rye, was produced by embryo rescue
of the product of fertilization and a chemically
induced doubling of the chromosomes.
• Embryo rescue becomes necessary when fertile
offspring is never produced by an interspecific
cross.

16. Why distant hybridization?
• Diseases and insect resistance
• Quality
• Wider adaptation
• yield
• Development of new varieties
• Production of new crop species (e.g; Triticale
hexaploid)
• Transfer of cytoplasm

17. Techniques for production of distant
hybrids
• The species with shorter style should be used as a female
parent
• A part of style may be cut off to make it shorter, eg. Part of
stigma of maize is cut off when it is crossed with tripsacum.
• Autopolyploidy: B. oleracea (cabbage) and B. campestris
(turnip rape) do not cross with each other at the diploid level,
but they produce embryos, when tetraploid species forms of
two species are crossed; embryo culture has to be used to
recover embryos.

18. Cont..
• When two species say A and C, can not be crossed
directly , a third species, e.g. B, may be used as a bridge
species.
• Transferring resistance to eye spot from Ae. ventricosa to
T. aestivum, T. turgidum is used as a bridge sp.
• Use of growth regulator e.g. IAA, 2,4-D, naphthalene
acetamide N. tabacum does not hybridize with N.
rependa, but this cross is possible when IAA applied to
pedicle of flowers in a lanoline paste.

19. Techniques to remove the crossability barriers
in distant hybridizarion :
• Embryo rescue
• Somatic hybridization
• Alien Addition lines
• Alien substitution lines
• Transfer of small chromosome segments
D B SHARMA

20. Embryo rescue :
• Embryo rescue
• When embryos fails to develop due to
endosperm degeneration, embryo culture is
used to recover hybrid plants; this is called
hybrid rescue.
• e.g; H. vulgare × Secale cereale.
• Embryo rescue generally used to overcome
endosperm degeneration.

21. Embryo rescue in barley :
Embryo Rescue
• This technique was once more efficient than
microspore culture in creating haploid barley
Hordeum vulgare Barley 2n
= 2X = 14
Hordeum bulbosum Wild
relative 2n = 2X = 14
Haploid Barley 2n = X = 7 H.
Bulbosum chromosomes
eliminated
X
D B SHARMA

22. • ’Wide’’ crossing of wheat and rye requires embryo rescue and
chemical treatments to double the no. of chromosomes triticale
Triticum durum (4X) x Secale cereale (2X)
AABB RR
ABR F1(3X): EMBRYO RESCUE
CHROMOSOME DOUBLING
HEXAPLOID TRITICALE (6X)
AABBRR

23. Limitations of embryo rescue :
• High cost of obtaining new plantlets
• Sometimes deleterious mutations may be induced during
the in vitro phase.
• A sophisticated tissue culture laboratory and a dependable
greenhouse are essential for success.
• Specialized skill for carrying out the various operations
are required.

24. SOMATIC HYBRIDIZATION :
• Development of hybrid plants through the
fusion of somatic protoplasts of two different
plant species/varieties is called somatic
hybridization

25. Somatic hybridization technique :
1. isolation of protoplast
2. Fusion of the protoplasts of desired
species/varieties
3. Identification and Selection of somatic hybrid
cells
4. Culture of the hybrid cells
5. Regeneration of hybrid plants

26. PLANT CELL
PROTOPLAST
500-800 m mol/l
SORBITOL+ 50-100 m
mol/l CaCl2
PECTINASE (0.1-1%)+
CELLULASE(1-2%)
Protoplast
 It is the cell with out cell wall created by degrading the
cell wall using enzymes

27. Protoplast Fusion
• (Fusion of protoplasts of two different
genomes)
• 1. Spontaneous Fusion : Intraspecific,
Intergeneric
• 2. Induced Fusion: Electrofusion, Mechanical
Fusion, Chemofusion

28. Induced Protoplast Fusion
• Electrofusion: A high frequency AC field is applied
between 2 electrodes immersed in the suspension of
protoplasts- this induces charges on the protoplasts and
causes them to arrange themselves in lines between the
electrodes. They are then subject to a high voltage
discharge which causes them membranes to fuse where
they are in contact.
• Polyethylene glycol (PEG): causes agglutination of
many types of small particles, including protoplasts which
fuse when centrifuged in its presence

29. Identification and Selection of somatic hybrid
cells :
• Hybrid identification- Based on difference between the
parental cells and hybrid cell with respect to –
Pigmentation
Cytoplasmic markers
Fluorochromes like FITC (Fluoroscein Isothiocyanate)
and RITC (Rhodamine Isothiocyanate) are used for
labelling of hybrid cells.
Presence of chloroplast
Nuclear staining
Heterokaryon is stained by carbol-fuschin, aceto-carmine
or aceto-orcein stain D B SHARMA

30. Regeneration of hybrid plants :
• Regeneration of hybrid plants are induced to
regenerate from hybrid calli.
• These hybrid plants must be at least partially
fertile, in addition to having some useful
property, to be of any use in breeding schemes.

31. Uses for protoplast fusion
• Used for combining the two complete genomes
• Exchange single or few traits between species
• The transfer of mitochondria or chloroplasts
between species
• Protoplast fusion between male sterile cabbage
and normal cabbage was done, and cybrids were
selected that contained the radish mitochondria
and the cabbage chloroplast

32. Advantages of somatic hybridization
• Symmetric hybrids can be produced between species
which can not be hybridized sexually.
• Cytoplasm can be transfer in one year ,while
backcrossing may take 5-6 years.
• Mitochondria of one species can be combined with
protoplast of another.
• Production of novel interspecific and intergenic hybrid.
i.e. Pomato (Hybrid of potato and tomato).
• Production of fertile diploids and polypoids from
sexually sterile haploids, triploids and aneuploids

33. Cont…
• Production of heterozygous lines in the single
species which cannot be propagated by
vegetative means
• Studies on the fate of plasma gene
• Production of unique hybrids of nucleus and
cytoplasm.
• Transfer gene for disease resistance, abiotic
stress resistance, herbicide resistance and
many other quality characters

34. Limitations of somatic hybridizations
• Poor regeneration of hybrid plants
• Non-viability of fused products
• Not successful in all plants.
• Production of unfavorable hybrids
• Lack of an efficient method for selection of
hybrids
• No confirmation of expression of particular
trait in somatic hybrids

35. Alien addition lines :
• These lines carries one chromosome pair from a different
species in addition to the normal somatic chromosome
complement of the parent species
• When only one chromosome from another species is
present, it is known as alien addition monosome.
• The main purpose of alien addition is the transfer of
disease resistance from related wild species.
• e.g. transfer of mosaic resistance from Nicotiana
glutinosa to N. tabacum.

36. • The alien addition lines have been developed in case
of wheat, oats, tobacco and several other species.
• Alien addition lines are of still agricultural
importance since the alien chromosome generally
carries many undesirable genes.

37. Alien substitution lines :
• This line has one chromosome from a different species in place of
the chromosome pair of the recipient species.
• When a single chromosome (not a pair) from different species in
place of a single chromosome of the recipient species.
• Alien –substitution lines have been developed in wheat, cotton,
tobacco, oats.
• The alien substitution show more undesirable effects than alien
additions and more useful in agriculture.

38. Transfer of small chromosome
segments
• Transfer of small chromosome segments carrying
specific desirable gene has been widely used in
crop improvement programme.
• It would be ideal to transfer only the desired gene
from the related alien species, since the gene
under transfer may be linked with other
undesirable genes.
• Transfer of black arm resistance from G.
barbadense(Egyptian cotton) to G. hirsutum
(American upland cotton).

39. Applications of wide hybridization in crop
improvement:
• Production of alien addition lines and substitution lines
• Transfer of chromosomal segments carrying specific desirable genes
which has been widely used in crop improvement programmes
• By transferring wild species quality has been improved e.g. gene for
increased protein content in rice, soybean, oats, rye.
• Incompatibility alleles from wild species can be transferred to
cultivated species for hybrid seed production. E.g. brassica
• Increased yield through introgression of yield genes from a related
wild species into cultivated species. E.g. Oats.
• Transfer of cytoplasm is done by repeated back crossing mainly
used for transferring male sterility into the cultivated species.
• Development of new crop species. E.g. Raphanobrassica, Triticale.

40. Limitation of distant hybridization
• Incompatible crosses
• F1 sterility
• Problems in creating new species
• Lack of homeology between chromosome of the parental
species
• Undesirable linkage
• Problems in the transfer of recessive oligogenes and
quantitative traits
• Lack of flowering in F1
• Problems in using improved varieties in distant
hybridization
• Dormancy

41. References
• Genetic basis and methods of plant breeding-
Sultan Singh & I.A. Pawar.
• Principles of plant breeding- R.W. Allard
• General plant breeding-A.R. Dabholkar
• Principles and Practice of Plant Breeding -J.R
Sharma
• Advances in Agronomy
• Principles of genetics and plant breeding –
George Aquah
• Cytogenetics- P.K. Gupta.

42. Thank you
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Your aim is yours so don’t change it for others, but your character is not yours so
Change it for others – Swami Vivekananda