of ancient genome duplications shared by many
species.• Polyploid plants can arise spontaneously in nature, by
several mechanisms, including meiotic or mitotic
failures, and fusion of unreduced (2n) gametes.
• Both autopolyploids (e.g., potato) and allopolyploids
(e.g., Canola, wheat, cotton) can be found among both
wild and domesticated plant species.
• Most polyploids display heterosis relative to their
parental species, and may display novel variation or
morphologies that may contribute to the processes of
speciation and eco-niche exploitation.
• The mechanisms leading to novel variation in newly
formed allopolyploids may include gene dosage
effects (resulting from more numerous copies of
genome content), the reunion of divergent gene
regulatory hierarchies, chromosomal rearrangements,
and epigenetic remodelling, all of which affect gene
content and/or expression levels.
• Many of these rapid changes may contribute to
reproductive isolation and speciation.
• Lomatia tasmanica is an extremely rare Tasmanian
shrub which is triploid and sterile, and reproduction
is entirely vegetative with all plants having the same
genetic structure.
• There are few naturally occurring polyploid conifers.
One example is the giant tree Sequoia sempervirens
or Coast Redwood, which is a hexaploid (6x) with 66
chromosomes (2n = 6x = 66), although the origin
is unclear.
Polyploid crops
• Polyploid plants tend to be larger and better at
flourishing in early succession habitats, such as
farm fields.
• In the breeding of crops, the tallest and best thriving
plants are selected.
• Thus, many crops (and agricultural weeds) may have
unintentionally been bred to a higher level of ploidy.
• The induction of polyploidy is a common technique
to overcome the sterility of a hybrid species during
plant breeding.
• Triticale is the hybrid of wheat (Triticum aestivum)
and rye (Secale cereale). It combines sought-after
characteristics of the parents, but the initial hybrids
are sterile.
• After polyploidization, the hybrid becomes fertile
and can thus be further propagated to become
Triticale.
• In some situations polyploid crops are preferred
because they are sterile. For example many seedless
fruit varieties are seedless as a result of polyploidy.
• Polyploid crops are propagated using asexual
techniques such as grafting.examples of polyploid crops
• Triploid crops : banana, apple, ginger, watermelon,
citrus.
• Tetraploid crops : durum or macaroni wheat, maize,
cotton, potato, cabbage, leek, tobacco, peanut.
• Hexaploid crops : Chrysanthemum, bread wheat,
Triticale, oat, kiwifruit.
• Octaploid crops : strawberry, dahlia, pansies,
sugarcane.
• Some crops are found in a variety of ploidy. Apples,
tulips and lilies are commonly found as both diploid
and as triploid.
• Daylilies cultivars are available as either diploid or
tetraploid and kinnows can be tetraploid, diploid, or
triploid.
features of polyploids
• Enlargement of vegetative and reproductive parts
(i.e., gigantism).
• Due to increase in cell size, water content is increased
which leads to decrease in osmotic pressure,
Hence, cold and frost resistance are decreased in
polyploids.
• Slower growth rate, due to decreased rate of cell
division.
• Delayed flowering.
• Sterility and poor seed setting.
• Death occurs at higher ploidy levels.types of polyploidy
Polyploidy is of 3 types:
(i) Autopolyploidy,
(ii) Allopolyploidy, and
(iii) Segmental polyploidy or autoallopolyploidy.(i) autopolyploidy
• Here, there is multiplication of same basic set of
chromosomes. For example :