Polyploidy refers to organisms that have more than two complete sets of chromosomes. It occurs naturally in plants through processes like autopolyploidy, where multiple chromosome sets are from the same species, and allopolyploidy, where chromosome sets are from different species. Polyploidy provides benefits like increased size, vigor and fertility restoration in some cases. It has played an important role in crop evolution, with many important crops being polyploid like potato, banana and coffee. Polyploidy can be artificially induced using techniques like colchicine treatment which inhibits chromosome separation. This has applications in crop improvement through creating new varieties and restoring fertility in interspecific crosses.

1. Polyploidy in Plant Breeding
Dr. NAVEENKUMAR K.L
Assistant Professor
Dept. of GPB

2. Introduction
 Most of the crop species have diploid chromosome
number.
 The chromosome number remains constant over the
generation
 but because of irregularities during cell division, there
may be change in chromosome number.
 These chromosomal aberrations also contribute to
crop evolution and improvement.

3. Types of changes in Chromosome number
 Haploid (n):an individual with half of the somatic chromosome number.
 Gametic chromosome number is – n
 Basic chromosome number - x
 Monoploid (x):an individual with basic of a species.
 Somatic chromosome number is designated by -2n (It may be diploid or
polyploid)
 x = Genome or chromosome complement In a diploid species n=x
 Diploid species has 2 copies of a genome 2x
 Triploid species has 3 copies of a genome 3x
 Tetraploid species has 4 copies of a genome 4x But all are designated as 2n

4. Haploid vs Monoploid
 The monoploid chromosome set is the basic set
of chromosomes multiplied in a ploidy series.
Monoploids have one genome-x.
 The haploid chromosome set is the set of
chromosomes present in a gamete.
 Polyploid -More than one copy of genome

7.  Heteroploidy – The change in chromosome number from diploid (2x,
but not 2n).
 Heteroploids – Individuals with chromosome number other than
diploid number (2x).
 Aneuploidy – The change in chromosome number involving one or
few chromosomes of a genome.
 Aneuploid changes are determined in relation to the somatic chromosome number –
2n
 Aneuploid – One or few chromosomes extra or missing 2n ± few
missing from 2n
 Nullisomic :One chromosome pair absent 2n-2
 Monosomic :One chromosome absent 2n-1
 Double monosomic :One chromosome from each of two different
chromosome pairs absent 2n-1-1
 Trisomic :One chromosome extra 2n+1
 Double trisomic :One chromosome from each of two different
chromosome pairs extra
 2n+1+1
 Tetrasomic :One chromosome pair extra 2n+2

8. Polyploidy
An organism or individual having more than two
basic sets or monoploid sets of chromosomes is
called polyploid and such condition is known as
polyploidy.
One third species of flowering plants
In wild species of grass family polyploidy has
been reported upto 70 % .
In animals polyploidy is rare because of its lethal
effects.

9. History
• The first polyploidy was reported in
Oenothera, the gigas mutant, an
autotetraploid.

10. Characteristics of polyploids
1. Polyploids have larger cell size than the
diploids.
2. Guard cells of stomata are larger and number
of stomata is lower in polyploids than in diploids.
3. They have larger and thicker leaves, larger
flowers and fruits.
4. Generally there is an increase in vigour and
vegetative growth.

13. Autopolyploidy
Polyploids which originate by multiplication of the
chromosome of a single species-autopolyploidy or
Situation in which additional sets of
chromosomes arise from the same species.

14. Autopolyploid: Genomes identical with each other
Types Ploidy Example
Autotriploid Three copies of a
genome
3x Banana, sugarcane, apple,
watermelon
Autotetraploid Four copies of a
genome
4x Rye, grapes, alfalfa, potato,
coffee, groundnut

15. Autopolyploidy
Origin and Production
1. Spontaneous:
Chromosome doubling occurs occasionally in somatic tissues and
unreduced gametes are also produced in low frequencies.
•Ex: Potato
2. Production of Adventitious buds:
In some solanaceae species decapitation leads to callus formation at the
cut end of stem. Such callus has some polyploid cells and buds
regenerated from the callus may be polyploid. Application of 1% IAA
increases the frequency of callus formation and polyploid buds.
•Ex: Tomato
3. Physical agents:
Heat or cold treatments, X-ray or gamma-ray irradiation produce
polyploids at low frequency. Heat treatment has been successfully used in
barley, wheat, rye and other crop species.

16. 4.Regeneration in vitro:
Some of the plants regenerated from callus and
suspension cultures may be polyploids.
• Ex: Rice, Tobacco, Datura, Carrot etc
5.Colchicine treatment:
It is most effective and the most widely used treatment for
chromosome doubling. It blocks spindle formation and thus
inhibits the movement of sister chromatids to opposite
poles.
• Ex: Tomato, Sorghum
6.Other chemicals: Not commonly used
These include, Ethyl-mercury chloride, Sulfanilamide,
Acenaphthene, 8-hydroxyquinoline, Chloral hydrate,
hexachloride, Cyclohexane etc.

17. Morphological and Cytological features of
autopolyploids
• Autopolyploids have larger cell size, number of
stomata per unit area.
• Large sized pollen grains.
• Slow growth rate and delayed flowering.
• Large and thick leaves, large sized flowers and fruits
but less in number.
• Generally increase in vigour and vegetative growth.
• Increase in vigour and growth may not be represented
in increased dry matter.
• Show reduced fertility as compared to diploid.

18. The cytological features vary with the level of ploids
Triploids
Trivalents Bivalents Univalents
Trisomic Double Trisomic
Autotetrapolids
Quadrivalents Trivalents Bivalents Univalents
Ex: Triploids
Ex: Autotetraploids -
Metaphase I

19. Role of Autopolyploidy in Evolution
• Autotetraploids are more successful as crops
than other forms of autopoyploids.
• Autopolyploid crop species,
– Potato (4x),
– Groundnut (4x),
– Coffee (4x),
– Alfalfa (4x),
– Banana (3x),
– Sweet potato (6x)

20. Applications of autopolyploidy in crop
improvement
Triploids :
 Triploids are produced by crossing tetraploids
and diploid strains.
 They are highly sterile, except few cases.
 This feature is useful in production of seedless
watermelon.
 Triploids are more vigorous than normal diploids
e.g.,sugarbeets

21. Tetraploids
 Useful in breeding: In banana (Musa
sapientum) autotetraploids are having weak
leaves and increased fertility so they are
inferior to triploid banana.
 But they are used in breeding for disease
resistance in banana by crossing tetraploid
banana with diploid disease resistant parent.
The resultant progeny are yet to be used as
varieties

22. Other uses of autotetraploids: They are useful in
–Improving quality
–: Tetraploid maize has 43% more carotenoid pigment & vit A than
diploid
–Overcoming self-incompatibility
–: Ex. Tobacco and White clover
–Distant crosses are not successful at diploid level
:Ex. 2x Brassica oleracea x B. chinesis -not succssful
4x Brassica oleracea x B. chinesis - succssful
–Variety
–Ex. Forage and ornomental crops
(Tetraploid red clover, ryegrass)

23. Limitations of Autopolyploidy
1. The larger size of autopolyploids is generally
accompanied with a higher water content
2. Show high sterility and poor seed set.
3. Due to the complex segregation in autotetraploids
progress under selection is slow.
4. Triploids cannot be maintained except through clonal
propogation.
5. New polyploids can rarely be used directly in crop
production.
6. Effects of autopolyploidy cannot be predicted.

24. Allopolyploidy
A polyploid organism which originates by
combining complete chromosome sets from two or
more species is known as allopolyploid or alloploid
and such condition is referred to as allopolyploidy.
Also known as hybrid polyploids or bispecies or
multispecies polyploids.
An allopolyploid which arises by combining
genomes of two diploid species- allotetraploid or
amphidiploid.

25. It can be developed by interspecific crosses
and fertility is restored by chromosome
doubling with colchicine treatment.
allopolyploidy has played greater role in crop
evolution than autopolyploidy, because
allopolyploidy is found in about 50 % of crop
plants.

26. • Allopolyploid : Two or more distinct genomes
(Generally each genome has wo copies)
– Allotetrapolid: Two distinct genomes 2x1+2x2
– Allohexaploid: Three distinct genomes
2x1+2x2+2x3
- Allooctaploid: Four distinct genomes
2x1+2x2+2x3+2x4

27. ORIGIN AND PRODUCTON OF ANEUPLOIDS
1. Spontaneous:
Originate spontaneously in experimental populations due to meiotic irregularities,
leading formation of n+1 and n-1 gametes. Ultimately progenies with 2n+1 and 2n-1
chromosomes.
2. Autotriploid Plants:
In triploid plants irregular distribution of chromosomes during meiotic anaphase leads
to production of aneuploids for different chromosomes
3. Asynaptic and Desynaptic Plants:
In asynaptic and desynaptic plants few to all chromosomes are present as univalents
at metaphase I of meiosis. In the progeny of such plants relatively high frequency of
aneuploids are obtained
4. Translocation heterozygotes:
A 3:1 disjunction of the ring or chain of four chromosomes in a translocation
heterozygote would produce n+1 and n-1 gametes and aneuploid progenies.
5. Tetrasomic plants:
When the tetrasomics (2n+2) are crossed with normal disomic (2n) plants,
high frequency of trisomics are produced

28. Colchicine
 a poisonous chemical isolated from seeds (0.2 – 0.8 %) and
bulbs (0.1 – 0.5%) of autumn crocus (Colchicum
autumnale).
Effect of Colchicine
 It block spindle formation and thus inhibits the movement of
sister chromatids to the opposite poles.
 The resulting nucleus includes all the chromatides & as a
result, the chromosome number of the cell is doubled .
 colchicine affects only dividing cells

29. Colchicine treatment:
Freshly prepared aqueous solutions of
colchicine (0.2% is more common) is used.
Seeds are generally soaked: A small
cotton wool piece may be placed at the
shoot tip in plants, which is daily soaked with
colchicine solution.

30. Application in crop improvement
 Useful to study the effects of loss or gain of
chromosome on the phenotype of an individual.
 Useful in locating a linkage group and gene to a
particular chromosome.
Nullisomic analysis
Monosomic analysis
Trisomic analysis
 Study of homoeology between different genomes in a
allopolyploid plant species.
 Useful in identification of chromosomes involved in
translocations.
 Useful in production of substitution lines. Which can be
used for studying effects of individual chromosomes.

31. Black mustard
Chinese cabbage, Bok Choi
Cauliflower, broccoli, kale
QuickTime™ and a
TIFF (Uncompres sed) decompres sor
are needed to see this picture.
rape seed
Indian mustard
Canola-type oil seeds
Collard green,
good for cold
climates
biodiesel
Brassica nigra
Brassica rapa
Brassica olarecea
Brassica carinata Brassica juncea
N=8
N=9 N=10
N=10+8
N=10+9
Brassica napus
BB
AABB
AA
BBCC
AACC
N=9+8
CC
The cabbage family: “Triangle of U”

32. Morphological & Cytological features of
Allopolyploids
1. In general allopolyploids are more vigours than
diploids.
2. Adaptability differs and hardier than diploid parents.
3. Many of them are Apomictic.
4. Allopolyploids developed from related species, have
more homeology between the chromosomes,
resulting in formation of quadrivalents and sterility.
5. Less the homeology, regular pairing of
chromosomes, bivalents and fertility.

33. Natural allopolyploid:
Evolution of wheat
Evolution of Nicotiana tabacum
Evolution of Gossypium hirsutum
Amphidiploid Brassica spp.
Oat
Artificial allopolyploid:
Raphanobrassica
Triticale

34. Polyploidy and Evolution: Hexaploid Wheat
(amphidiploid)
hexaploid
(Chromosome doubling)
(Chromosome doubling)

35. Amphidiploidy in Brassica
3rd parental species
2 parental species

36. Tobacco

37. 1. Evolution of cultivated tetraploid spp
Gossypium barbadense
G.herbaceum x G.raimondii
F1 sterile- AD
AADD Gossypium barbadense
( allotetraploid American cotton)

38. 2. Evolution of Gossypium hirsutum
Old world diploid cotton x Gossypium thurberi
F1 sterile – AD
`
Gossypium hirsutum (AADD)

39. Applications of allopolyploidy in crop improvement
1. Utilization as bridging species: Amphidiploids serve as bridging
species in the transfer of characters from one species to another
species.
Why bridging species?
Most of the times interspecific hybrid is sterile.
Ex. The F1 obtained from cross Nicotiana tabacum x N. sylvestris is
sterile. Chromrosome doubling of this hybrid resulted in a
synthetic hexaploid called N.digluta which is relatively fertile
and is backcrossed to the N.tabacum to produce a pentaploid.
The pentaploid is fertile and is backcrossed to N.tabacum and in
the progeny N.tabacum -like plants resistant to TMV are
selected

40. 2. Creation of new species.
Ex. 1. Triticale(wheat x rye) Commercially cultivated in
Poland, Germany, Canada and France
Desirable features of triticales: they yielding ability and
quality grains like wheat and abiotic stress tolerance like
rye.
2. Raphanobrassica is a triploid from Brassica napus x B.
compestris
3. Widening the base of existing polyploids Ex. B napus which
has less natural variability. Synthesize new amphidiploid B.
napus (AACC, n=19)from the parental diploids- B.
compestris (n=10, AA) x B. oleraceae (n=9, CC)

41. 4. Polyploid is one of the sources for variation and
thus helps in evolution and polyploid played a
key role in natural evolution of number of
plants like wheat, cotton, galeopsis and primula
etc
5. Allopolyploid is one of the effective mechanism
for maintaining hybrid vigour in successive
generation, because as a result of allopolyploidy,
different genomes are brought together and are
passed from one generation to another.

42. Limitations
1. Effect can’t be predicted
2. Many defect associated with allopolyploid like
Low fertility, cytogenetic and genetic instability
Synthetic allopolyploids have to be improved through
extensive breeding at polyploidy level Only small
proportions are promising