2. Distant hybridization/ Wide
hybridization
• Interspecific crosses: Crossing between two
individuals of the two different species of the
same genus.
O. sativa x O. perennis
• Intergeneric hybridization: Crossing between
two individual of the to different genera of the
same family
T. aestivum x Secale cereale (Triticale) Rimpu
R. Sativus x B. oleracea (Raphanobrassica)
Karpechenko-1928
3. Barrier to production of distant
hybrids
1. Failure of zygote formation: Zygote is not
formed due to failure of fertilization.
Fertilization often fails because
Pollen tube is unable to reach the embro sac.
Pollen tube may burst in the style of another
species. e.g. Datura
In some cases style is longer than pollen tube
so the species with shorter style i.e. pollen
tube is unable to reach the embryo sac.
4. 2. Failure of zygote development: Fertilization does takes place
and zygote is formed but development of zygote is blocked at
different stages due to different reasons.
Lethal genes: Some species carry a lethal gene which causes
death of zygote during embryonic n case of Aegilopes
umbelullata (L1-early lehality, L2-late lethality, l- non-lethal.
Genetic disharmony b/w two parental genome.
Chromosomal elimination: Chromosomes are gradually
eliminated from the zygote. This does not prevent embryo development
but the resulting embryo and F1 plants are not true interspecific hybrid
because they do not have true parental genome. The chromosome of one
species is generally eliminated completely due to mitotic irregularities
and in extreme case chromosome of only one genome may be present in
the embryo which wwill be haploid. E.g. Wheat x Maize
Incompatible cytoplasm: The cytoplasm of the female
gamete may not be compatible with genome of the male
gamete.
5. Endosperm abortion: When endosperm
development is poor or it is completely
blocked, it is known as endosperm abortion.
Failure of hybrid seedling development:
Some distant hybrids die during seedling
development or even after initiation of
flowering. In case of Melilotus in interspecific
hybrid, chlorophyll deficient plants are fail to
survive. Failure of hybrid seedlings may be
because lethal gene, cytoplasm incompatability
& genetic imbalance.
6. Techniques for production of distant
hybrids
Sufficiently large number of flowers are
emasculated and pollinated.
By determining the barrier to the production of
hybrid embryo and then by using measures to
overcome these barriers. e.g. part of style is cut
off (maize) when it is crossed as female with
Tripsacum. Maize x Tripsacum.
Autopolyploidy also help in achieving
interspecific hybrids. e.g. B. oleracea (2n=18) x
B. campestris (2n=20). Tetraploid form produce
embryo
7. Techniques for production of distant
hybrids
Species with same ploidy level, it is easier for
hybridization.
Species with different ploidy level are crossed
hybridization b/w them are relatively difficult. In
such cases 3 approaches may be useful:
(i) Species with higher ploidy level is generally used
as female.
e.g. wild spp. Of potato x S. tuberosum
(iii)
8. Techniques for production of distant
hybrids
Use of Bridge species: Two spp. A and C are
not crossed then third spp., B is taken.
A. ventricosa (Resistance to eye spot disesase)
x T. aestivum does not produce hybrid. Third
species T. turgidum first crossed easily with A.
ventricosa and produced F1 then crossed with
T. aestivum to produce hybrid which showed
resistance against eye spot disease.
Embryo culture
9. Reason for sterility in Wild crosses
- reduced pairing of chromosome
- are of different spp. not homologous
- most of the cases pairing not occur, we get
univalent
- Distribution of chromosome is not proper in
cell division
10. Reason for sterility in Wild crosses
• Reciprocal crosses produce fertile hybrids
should be used
A x B B x A
11. • Most of the segregants have extremely new
characteristics distinct from the two
parental species
• Segregation pattern does not follow
Mendelian ratio
12. Application of Wide hybridization
Creation of new plant species is one of the major
objective of distant hybridization. e.g. Triticale
Production of Alien additition / alien substitution lines:
Alien additition / alien substitution lines are produced in
wheat, oat and tobacco.
Alien addition line carries one chr. pair from a different
species with in addition to the normal somatic chr.
complement of the parent spp.
These lines are produced to transfer disease resistance from
wild species to the recipient species. But alien chr. Carries
undesirable genes.
Alien substitution line- has one chromosomal pair from a
different spp. In place of the chr. pair of the recipient spp.
13. Application of Wide hybridization
Disease Resistance: Late blight resistant gene
has been transferred from its wild relatives
Solanum demissum.
Wider adaptability: Stability and earliness has
been transferred from its wild relatives.
Earliness has been transferred to cultivated spp.
Of Brassica and Soybean from its wild relatives.
Cold tolerance has been transferred in wheat,
onion, tomato, potato, grape & rye.
Wild relatives of wheat & pea contributes gene
for drought & heat tolerance.
14. Application of Wide hybridization
Improvement in Quality: Genes for increase
protein content has been transferred in rice,
soybean, oat and rye. Similarly, oil quality &
oil palm has been improved by gene from its
wild relatives.
Mode of Reproduction: Apomixis- Genes for
apomixis has been transferred in Maize and
Tripsacum.
Yield
15. Pre-breeding
• Pre-breeding is defined as all activities designed to identify desirable
characteristics and/or genes from unadapted plant genetic
resources(exotic and semi-exotic) that cannot be used directly in breeding
populations and transfer them to an intermediate set of materials that
plant breeder can manipulate to any kind of selection for crop
improvement.
• According to the global crop diversity trust, pre-breeding is an art of
identifying desired traits and incorporation of such traits into modern
breeding materials’.
• It is the interface of conservation of plant genetic resources (PGR) and
plant breeding.
• It is a necessary step in the “linking genetic variability to utilization” use
of diversity arising from wild relatives and other unimproved materials.
• Hence pre-breeding is referred as germplasm enhancement or
germplasm conversion.
16. Aims of pre-breeding
• To reduce genetic uniformity in crops by using a wider gene
pools of genetic material to increase yield, resistance to pests
and diseases, and other quality traits.
• Broadening the genetic bases or genetic enhancement of raw
materials which is achieved by identification of genes
controlling traits of interest or transferring desired genes
from unadapted to adapted background.
• Pre-breeding plays an important role in genetically
improving the yield potential and other economically
important traits such as abiotic and biotic stress
tolerance/resistance in the germplasm.
• To developing early maturing genotypes fit well for multiple
cropping systems.
18. Pre-breeding using Wild Cajanus species and Pigeonpea cultivars for
broadening the genetic base for pigeonpea improvement
19. Applications of pre-breeding in crop
improvement
• Broadening the genetic base to reduce vulnerability
• Identifying traits in exotic materials and moving those genes
into material more readily accessed by breeders
• Moving genes from wild species into breeding populations
when this appears to be the most effective strategy and
• Identification and transfer of novel genes from unrelated
species using genetic transformation techniques.
• The adoption of pre-breeding facilitates the efficiency and
effectiveness of crop improvement programmes by enabling
increased access to, and use of, genetic variations conserved
in gene banks.
