Published on: Mar 4, 2016
Transcripts - Polyploidy breeding
Polyploidy and It’s
Application in plant breeding
Reg. no.: 04-2690-
Polyploidy involves three or more sets of chromosomes ,
and may occur naturally or by induction.
Nearly all plants and animals probably have some polyploid
i. Plant endosperm is triploid.
ii. Liver of mammals (and perhaps other vertebrates) is
iii. Wheat is hexaploid (6N) and the strawberry is
Origin of polyploids
There are various modes for the origin of polyploids. These
mainly include mechanisms such as
1. Somatic doubling during mitosis,
2. Non-reduction in meiosis leading to the production of
3. Polyspermaty (fertilization of the egg by two male
4. Endoreplication (replication of the DNA but no
somatic doubling during mitosis,
Chromosome doubling can occur either in the zygote to
produce a completely polyploid individual or locally in
some apical meristem to give polyploid chimeras.
In somatic doubling the main cause is mitotic non-
disjunction. This doubling may occur in purely vegetative
tissues (as in root nodules of some leguminous plants) or
at times in a branch that may produce flowers or in early
embryos (and may therefore be carried further down).
Non-reduction in meiosis leading
to the production of unreduced
Non reduction could be due to meiotic non-
disjunction (failure of the chromosome to separate
and subsequent reduction in chromosome
number), failure of cell wall formation or formation
of gametes by mitosis instead of meiosis. The
classic example, Raphanobrassica, originated by a
one step process of fusion of two non- reduced
Polyspermaty (fertilization of the egg by two male
Polyspermy is observed in many plants but its
contribution as a mechanism for polyploid formation is
rather rare except perhaps in some orchids .
Endoreplication (replication of the DNA but no
Endoreduplication is a form of nuclear polyploidization
resulting in multiple uniform copies of chromosomes. It
has been known to occur in the endosperm and the
cotyledons of developing seeds, leaves and stems of
There are a number of other factors favoring polyploidy
The mode of reproduction
The mode of fertilization
The breeding system present
The growth habit of the plant
Size of chromosomes etc.
Types of polyploids
doubling of the same
chromosome set .
derived from within a
is the product of inter-
allopolyploids arise via
An allopolyploid resulting due to chromosome doubling in a sterile
hybrid derived from hybridization between two unrelated diploid
species is also called as “ amphidiploid”. If the parental species are
polyploids, the derivative will be called as “ amphipolyploid”.
One of the early examples of a natural polyploid was one of
original mutations of Oenothera lamarckiana (Hindi
:Dheriani, English : Evening Primerose).
The first example of an artificial polyploid was by Winkler
(1916) who in fact introduced the term polyploidy. Winkler
was working on vegetative grafts and chimeras of Solanum
nigrum and found that callus regenerating from cut surfaces
of stem explants were teratploid.
Artificial or synthetic allopolyploids have been
synthesized in some crops with two main objectives,
1)Either to study the origin of naturally available
2) To explore the possibilities of creating new species.
sativus, n = 9)
oleracea, n = 9)
(4n = 36)
Some Terminology of Heteroplody
Heteroplody : Individuals carrying chromosome number
other than the diploid.
Aneuploidy : change in one or few chromosome of the
1. Nullisomic : one chromosome pair missing (2n-2)
2. Monosomic : one chromosome missing (2n-1)
3. Double monosomic : one chromosome from each of two
diff. chromosome pair missing (2n-1-1)
4. Trisomic : one extra chromosome (2n+1)
5. Tetrasomic : one extra pair of chromosome (2n+2)
Euploid : Involve one or more complete genome.
1. Monoploid : one copy of a single genome (x)
2. Haploid : Gametic chromosome complement
Polyploid : More than 2 copy of genome
Autopolyploid : Genome identical with each other
1. Autotriploid : Three copies of one genome (3x)
2. Autotetraploid : four copies of one genome (4x)
Allopolyploid : two or more distinct genome
Allohexaploid : Three distinct genome(2x1 +2x2+2x3)
Breeding of Autopolyploids
Cells/individuals having autopolyploid (doubled)
chromosome numbers may originate in one of the
following several ways:
(2) Due to treatment with physical agents
(3) Regeneration in vitro
(4) Colchicine treatment
(5) Other chemical agents.
Chromosome doubling occurs occasionally in
somatic tissues and unreduced gametes are also
produced in low frequencies.
Production of Adventitious buds:
Decapitation in some plants leads to callus
development at the cut end of stem. Such a callus has
some polyploid cells, and some of the Shoot buds
regenerated from the callus may be polyploid. This is of
common occurrence in Solanaceae where 6-36 per cent
of adventitious shoot buds are reported to be tetraploid.
Heat or cold treatments, centrifugation and X-ray or
gamma ray irradiation may produce polyploids in low
frequencies. Tetraploid branches were produced in
Datura in response to cold treatment.
Regeneration in Vitro:
Polyploidy is a common feature of the cells cultured
in vitro. Plants of various ploidy have been regenerated
from callus cultures of Nicotiana, Datura, rice and several
Colchicine Treatments :
Colchicine treatment is the most effective and the
most widely used treatment for chromosome doubling. At
any given time, only a small proportion of the cells would
be in division; therefore, repeated treatments should be
given at brief intervals to double the chromosome number
in a large number of cells of the shoot apex. The polyploid
and diploid cells present in a shoot-tip compete with each
other and diploid cells may often out compete the polyploid
Application of Allopolyploidy in Crop
1. Bridging cross: Amphidiploids can be used
as a bridge where direct cross between two
species is not possible due to sterility in F1.
2.Creation of new crop species: Alloploidy
sometimes helps in creation of new crop
species. Such as Triticale, Raphanobrassica,
triploid (AAC), tetraploids .
3.Interspecific Gene Transfer: In case of
unavailability the desirable characters within
the species, it is transferred from the related
4.Tracing the origin of crop species:
Alloploidy study is used to identify the origin of
natural alloploidy plants.
With knowledge of the origins, variations and
characteristics of different types of polyploids,
there are many opportunities for developing and
utilizing polyploids in plant improvement
Significant opportunities include developing sterile
cultivars, overcoming barriers to hybridization,
restoring fertility in wide hybrids, enhancing flower
size, increasing heterosis and vigor, and improving
pest resistance and tolerance to environmental