Distant Hybridization and Introgression- Scope and Limitations

2.  Crossing between two genetically dissimilar parents is called hybridization.
 Distant hybridization comprises the exchange or modification of the genes due to crossing
between species from distant gene pools.
 It is a unique tool to introduce useful traits in a variety of agricultural applications
especially beneficial agronomical traits.
 Broadening the gene pool of a crop is an important plant breeding method as it can enhance
tolerance of major biotic and abiotic stresses and improve the quality characteristics of the
plant.
 Several examples demonstrate the successful transfer of useful genes from wild species to
wheat, oats, rice, cotton, Brassica, tomato, and other crop plants.
 Josef Kolrueter first study about interspecific hybridization on tobacco plant in 1760.

3. INTERSPECIFIC
HYBRIDIZATION
INTERGENERIC
HYBRIDIZATION
Crossing between two different
species of the same genus is
termed interspecific hybridization
or intra- generic hybridization.
The progeny of such cross is
called interspecific hybrid.
Eg. Dianthus barbatus х D.
caryophyllus
Crossing between two genera of
the same family is called
intergeneric hybridization.
Triticale and raphanobrassica are
outcome of intergeneric crosses.

4. WHEN TO USE…………..
Interspecific hybridization
is used when the desirable
character is not found
within the species of a crop.
It was first developed
by Thomas Fairchild
in 1717 between
Dianthus barbatus х
Dianthus
caryophyllus
Fully fertile crosses
They are the crosses
which obtained
between those species
which have complete
homology between
them
Partially fertile
crosses-they are the
crosses obtained
between those species
which differ in ploidy
level but have some
chromosomes in
common
Fully sterile crosses-
they are the crosses
which are obtained
between those species
which do not have
chromosome homology

5. • Improved Yield
Crop yields increase dramatically when hybridization is used to exceed one or more of the
parents in size and reproductive potential. For example, boysenberries (Rubus ursinus x
idaeus) were developed at Knott's Berry Farm in California.Hybrids can yield up to 100
percent more crops thanks to their resistance to disease and increased vigor.
• Longer Growing Season
Many hybrid plant varieties are bred to extend the growing season and mature faster than
non-hybrid varieties. Hybrids may also be developed to turn annual plants into perennials; for
farmers, this can increase profitability reduce some of the environmental impacts of
agriculture.
• Higher Quality
Interspecific hybrids may surpass traditional varieties in taste, shelf-life, size, texture,
nutrition, etc. Stone fruit, in particular, has a seemingly unending number of interspecific
hybrid varieties developed for their flavor and novel appearance.

6. Examples of interspecific hybridization
Oryza sativa (Asian upland rice)
Non-shattering, resistant to
lodging, high yield potential
Oryza glaberrima (African rice)
Drought tolerant, disease
resistant, weed suppressing

7. Brassica nigra(BB)
2n=16
Brassica juncea(AABB)
2n=36
Brassica carinata
(BBCC)
2n=34
Brassica
napus(AACC)
2n=38
Brassica rapa(AA)
2n=20
Brassica oleracea(CC)
2n=18

8. •
• х
Fragaria virginiana
Fragaria ananassa
Fragaria chiloensis

9. Raphanus
Raphanobrassica
Brassica

10. WHEAT
TRITICALE
RYE

11. Problems associated with wide hybridization
Temporal and spatial
isolation of species
Pre-fertilization barrier
Post-fertilization
barrier
Hybrid sterility

12. Non-
synchronous
flowering of
the parental
specie due to
different
agro-
ecological or
geographical
background
OVERCOME:
Early or staggered
sowing
Suitable photoperiodic
treatment
vernalisation

13. The main reason for pre-zygotic barrier is cross incompatibility or incogruity which is
the inability of the functional pollen grains of one species or genus to effect
fertilization in another species or genus.
Lack of pollen
germination
Insufficient growth of
pollen tube to reach
ovule
Inability of male
gamete to unite with
the egg cell
OVERCOME:
Effective pollination at correct place
correct time
Mentor pollination: pollen which is
fully compatible with the intended
see parent
OVERCOME:
Reciprocal crosses
Mentor pollination
Use of PGRs
OVERCOME:
Reciprocal crosses
Mentor pollination
Use of PGRs

14. Absence of seed germination
Ploidy difference between the parents are the main cause for this and can be
overcomed by embryo rescue technique
Hybrid breakdown
When F1 hybrid plant of an interspecific crosses are vigorous and fertile but their F2
progeny is weak and sterile is called hybrid breakdown.
This is due to the structural difference of chromosomes or problems in gene
combinations.
Lack of growth vigor
It is correlated with low chloroplast content.
Incompatibility between parental genome and formation of non-functional protein
Hybrid albinism
Incompatibility between the plastome and nuclear genome inhibits chloroplast
development and chlorophyll formation and can be overcomed by backcross method

15. This is the inability of the hybrid to produce viable offspring. It is more prominent in case of
intergeneric crosses
The major reason is the lack of structural homology between the chromosomes of the two
species.
This leads to the meiotic abnormalities like chromosome scattering, chromosome
extension, lagging of chromosome in the anaphase, formation of anaphase bridge,
development of chromosome rings and chains and irregular and unequal anaphase
separation
OVERCOME
Mitotic
chromosome
doubling
Meiotic
chromosome
doubling
Protoplast
fusion
Embryo
rescue

17. WHEN TO USE…….

19. PARTULARS INTERSPECIFIC HYBRIDIZATION INTERGENERIC HYBRIDIZATION
Parents involved Involves two different species of
the same genes
Involves two different genera of
the same family
Fertility Such hybrids vary from completely
fertile to completely sterile
Hybrids are always sterile
Seed setting More than intergeneric crosses low
Use in crop
improvement
More than intergeneric crosses Less than interspecific crosses
Release of hybrid
varieties
Possible in some crops Not possible
Evolution of new
crops
Not possible, but evolution of new
species is sometimes possible
Sometimes possible, example is
Triticale

20. Main features of Distant hybridization
It is use when the desirable
character is not found within
the species of a crop.
It is an effective method of
transferring gene into cutivated
plants from their related
cultivated or wild species
It is more successful in
vegetatively propagated species
like sugarcane and potato than
in seed propagated species.
It gives rice to three types of
crosses viz. a) fully fertile b)
partially fertile c) fully sterile in
different crop species
It leads to the introgression
which refers to transfer of some
genes from one species into
genome of another species

21. Distant hybridization: A tool for interspecific chromosome
manipulation
1. Incorporation of single chromosome or chromosome fragment
from a wild species also called alien species) into an existing crop in
order to enhance crop genetic diversity. The resulting alien
chromosome substitution, addition or translocation lines help
breeders to transfer beneficial characteristics from wild and weedy
plants into cultivated crop species
2. Incorporation of all the alien chromosome for chromosome
doubling in order to produce amphidiploid. This amphidipld can be
used for the development of a new crop. The man-made Triticale is
an amphidiploid between wheat and rye.
3. Elimination of all alien chromosomes in order to induce crop
haploid. Haploid is very useful in double-haploid breeding of a true-
breeding crop like wheat and rice since it can quickly fix genetic
recombination and enhance breeding efficiency or facilitate genetic
analysis
The chromosomes can be manipulated in three different ways…..

22. 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 (not a
pair of 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
eg. Transfer of mosaic
resistance from
Nicotiana glutinosa to
Nicotiana tabacum.
The alien addition
lines have been
developed in case of
wheat, oats , tobacco,
rice cotton and
brassicas
Alien addition lines
are of little
agricultural
importance since the
alien chromosome
generally carries
many undesirable
genes eg. Reduced
growth and short,
broad leaves in
addition to mosaic
resistance.

23. This line has one chromosome pair 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
chromosme of the recipient species is used then it is known as alien-substitution
monosome.
Alien-substitution line have been developed in wheat, cotton, tobacco, oats, etc
In case of tobacco, mosaic resistance gene N was tranferred from the N. glutinosa
to N. tabacum line ha 23 pairs of N. tabacum chromosome and one
pair(chromosme H) of N. glutinosa chromosomes.
The alien substitution show more undesirable effects than alien additions and as
a consequence are of no direct use in agriculture

24. Crosses between
species of same or
different genera
contributed
immensely to crop
improvement, gene
and genome
mapping,
understanding of
chromosome
behaviour and
evolution in crops
like rice, wheat,
maize, cotton
tomato
The ultimate goal
of distant
hybridization is to
transfer one or few
genes from alien
species into
cultivated species.
It is responsible for
species evolution
and speciation of a
species.
Wide crosses are
generally used to
improve crop
varieties for
disease, pest
resistance , stress
resistance , quality,
adaptation, yield,
etc.
So, introgression is the transfer of genetic information from one species to another
as a result of hybridization between them and repeated backcrossing

25. Crop Domestication and introgression
 The occurrence of beneficial gene flow from locally adapted wild relatives to
crop during their expansion following domestication is called adaptive
introgression.
It has three components:
1. hybridization between differentiated taxa
2. backcrossing to one of the parents
3. selection on recombinant genotype with progressively diminished
linkage drag
In domesticated species adaptive introgression would consist of crop wild hybrid
backcrossing to a crop followed by increase in frequency of adaptive wild
alleles in the crop an selection against undesirable wild background
Recently developed methods have been applied to high density marker data to
detect genome wide patterns of introgression, granting novel insights into the
prevalence of adaptive introgression in crop histories.

28. INSECT TOLERANCE CROP WILD RELATIVES PUTATIVE CAUSE OF
RESISTANCE/TOLERANCE
Tolerance to armyworm
(Spodoptera frugiperda)
Z. mays subsp. parviglumis Leaf toughness and leaf
trichome
Z. diploperennis Chemical composition of
leaves
Z. mays spp. parviglumis Higher expression of wip1,
RP1 and chitinase genes
Tolerance to Maize spotted
stalk borer
Z. mays ssp. mexicana Higher concentration of
benzoazinoids
Z. mays spp. mexicana Emission of (E)-4,8-Dimethl-
1,3,7-nonatriene resulted
from the egg ovipostion of
thre maize spotted stalk borer
that attracts egg and larval
parasitooides
Z. mays spp. parviglumis
Z. perennis
Tolerance to western corn
rootworm
Teosinte Emission of (E)-β-
caryophyllene by root
herbivory that attracts the
entomogenic nematode
Kumar et al., 2011

29. DISEASE TOLERANCE CROP WILD RELATIVES
Gray leaf spot disease Z. Mays subsp. parviglumis
Corn smut disease resitance Teosinte
Maize chlorotic dwarf virus resistance Z.diploperennis
Maize chlorotic mottle virus resistance Z. diploperennis
Maize streak virus resistance Z. diploperennis
Maize bushy stunt mycoplasma
resistance
Z. diploperennis
Rust resistance Eastern gamagrass
Corn leaf spot disease resistance Z. diploperennis
Kumar et al., 2011

30. Tolerance to abiotic
stresses
Crop wild relative Putative cause of
resistance/ tolerance
Drought tolerance Eastern gamagrass Deeply penetrating root
system
Acid soil and aluminium
tolerance
Eastern gamagrass unknown
Salinity tolerance Eastern gamagrass Ability to conserve sodium
in the leaves lowering
water potential of leaves,
maintaining the turgor
pressure required for
vegetative growth and
lowering the shoot/root
rate
Water logging tolerance Z. nicaraguensis Ability to develop a barrier
to radial oxygen loss in
basal areas of adventitious
roots under stagnant
deoxygenated conditions
Kumar et al., 2011

32. INSECT TOLERANCE CROP WILD RELATIIVE AND RESPECTIVE
GENOME
Brown plant hopper resistance
O. nivara (AA)
O. punctata (BB/BBCC)
O. longistaminata (AA)
O. barthi (AA)
O. rufipogon (AA)
O. officinalis (CC)
O. minuta (BBCC)
O. latifolia (CCDD)
O. glaberimma (AA)
Kumar et al., 2011

33. Kumar et al., 2011

34. Tolerance to abiotic stress Crop wild relative an respective
genomes
Drought and heat tolerance
O. glaberrima (AA)
O. barthi (AA)
O. meridionalis (AA)
O. australiensis (AA)
O. longistaminata (AA)
Acid soil and aluminium tolerance O. rufipogon (AA)
Salinity tolerance Porteresia coarctata
Cold tolerance O. rufipogon (AA)
Kumar et al., 2011

36. INSECT TOLERANCE CROP WILD RELATIVE PUTATIVE CAUSE OF
RESISTANCE/TOLERANCE
Helicoverpas spp. G. somalense Smooth leaf type
Tolerance to jassids
G. barbadense Hairiness trait controlled by
genes, designated by H1
and H6
G. hirsutum Low tannin/high phenol
content
Tolerance to fleahopper G. hirsutum Pilose trait and square
structure impacting stylet
penetration
Tolerance to thrips G. tomentosum unknown
Nectariless G. sturtianum Cotton plant without the
extrafloral and floral nectary
glands do not attract insects
Kumar et al., 2011

37. Diseasse tolerance Crop wild relative
Bacterial blight resistance G. arboreum
Rust resistance G. anomalum
Cotton leaf curl virus resistance
G. stocksii
G. herbaceum
Fusarium wilt resistance
G. austral
G. sturtianum
G. darwinii
Verticillium wilt resistance G. austral
G. thurberi
Kumar et al., 2011

38. Abiotic stress Crop wild relative
Drought tolerance
G. tomentosum
G. herbaceum
G. darwinii
Salt tolerance G. tomentosum
G. davidsoni
G. aridum
Heat tolerance G.tomentosum
Kumar et al., 2011

40. Kumar et al., 2011

41. Kumar et al., 2011

42. Kumar et al., 2011

43. Case studies

44. Objectives:
1. Broadening the base of pigeon pea cultivar
2. Developing improved plant types having high level of resistance to various biotic and
abiotic stress

45. Sharma and Upadhyaya, 2016

46. Sharma and Upadhyaya, 2016

47. Sharma and Upadhyaya, 2016

48. CONCLUSION:
 Wild species harvor many useful genes and can be utilized effectively to create
enormous genetic variability following wide hybridization.
 At ICRISAT, utilization of wild Cajanus species has contributed significantly
through the development of CMS system for pigeonpea improvement.
 Development of pre-breeeding population using pigeonpea cultivar as recipient and
wild Cajanus species as donor has resulted in enriching the variability for different
traits in the primary gene pool.
 Introgression lines having good agronomic performance and high level of resistance
against important biotic stress have been identified, which can be utilized in
breeding programme to develop new cultivars with broad genetic base.
 Overall, these pre-breeding activities have led to the genetic enhancement by
increasing the extend of useful diversity in the primary gene pool for further used
by the breeder.

49. Comparison of two comprehensive approach for the achievement of wide hybridization
between C. annum and C. baccatum by using 1) genetic bridge using C. chinense and C.
frutescens as bridge species. 2) direct hybridization between C. annum and C. baccatum in
combination with embryo rescue.

50. Results and discussion
Manzur et al., 2015

51. Manzur et al., 2015

52. Manzur et al., 2015

53. Manzur et al., 2015

54. Manzur et al., 2015

55. Manzur et al., 2015

56. • C. baccatum has been reported as a source of variation for many different traits to improve
common pepper but strong interspecific barrier exist between them.
• So, wide hybridization approaches for introgressing C baccatum gene into C. annuum was
performed through use of genetic bridge method and in vitro embryo rescue method.
• According to the results wide hybridization between C annuum and C. baccatum is possible
using both GB (genetic bridge) and ER ( embryo rescue) approach, although the degree of
success is highly dependent on the genotype to obtain interspecific hybrids and subsequent
generations.
• The best crossing scheme to obtain successful hybridization and introgression from C.
baccatum to C. annuum have been identified and the genotypes with best performance in
these experiments are good candidates for introgression breeding from C. baccatum to C.
annuum.
• Ultimately, these results provide breeders with relevant infromation on wide hybridization
approaches and on appropriate plant material to be used for successfully incorporate the C.
baccatum gene pool as a source of variation for introgression breeeding in C. annuum
breeding programmes.

57. Incompatible crosses, Dormancy, F2 segregation
sterility of F1 hybrid, Lack of flowering in F1
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
Problem in using improved variety

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

60. References:
Kumar, S. I., Imtiaz, M.G. and Pratap, A. 2011. Distant hybridization and alien gene introgression .
Biology and breeding of food legumes, 81-110
Hancock, G.W. Tallury, S.P. Isleib, T.G., Chu, Y. Ozias-Akins, P. and Stalker, H.T. 2019. Introgression
analysis and morphological characterization of an Arachis hypogaea х A. diogoi interspecific hybrid
derived population. Crop science Society of america,59:640-649.
Harrison G.R. and Larson E.L., 2014, Hybridization, introgression and the nature of species boundaries.
The american genetic association . 105:795-809.
Liu, D., Zhang, H., Zhang , L., Yuan, H.M, and Zheng, Y. 2014. Distant hybridization: a tool for
interspecific manipulation of chromosomes 25-42
Manzur, J.P., Fita, A., Prohens, J. and Rodriguez-burruezo, A.2015. Successful wide hybridization and
introgression breeding in a diverse set of common pepper ( Capsicum annum) using different
cultivated Aji (C. baccatum) accessions as donor parents.journal pone . 1-18
Sharma, S. and Upadhyaya, H.D. 2016. Pre- breeding to expand primary genepool through introgression of
genes from wild Cajanus species for pigeonpea improvement. Legume perspectives.17-20
Janzen, G.M., Wang L. and Hufford, M.B. 2018. The extent of adaptive wild introgression in crops.
Peer J Preprints, 1-25.
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