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- Polyploidy is pervasive in plants and some estimates suggest that 30-80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy (paleopolyploidy) in their genomes.
- Huge explosions in angiosperm species diversity appear to have coincided with the timing of ancient genome duplications shared by many species.
- It has been established that 15% of angiosperm and 31% of fern speciation events are accompanied by ploidy increase.
- Polyploid plants can arise spontaneously in nature by several mechanisms, including meiotic or mitotic failures, and fusion of unreduced (2n) gametes.
- Both autopolyploids (eg. potato]) and allopolyploids (e.g. Okra, 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 remodeling, 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 Coast Redwood (Sequoia sempervirens) 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 for.
- 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.
- For example, Triticale is the hybrid of wheat (Triticum turgidum) andrye (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. Such crops are propagated using asexual techniques such as grafting.
- Polyploidy in crop plants is most commonly induced by treating seeds with the chemical colchicine.
Examples of polyploid crops
- Triploid crops: banana, apple, ginger seedless watermelon, citrus
- Tetraploid crops: durum or macaroni wheat, cotton, potato, cabbage, leek, tobacco, peanut, kinnow, Pelargonium
- Hexaploid crops: chrysanthemum,bread wheat, triticale, oat, kiwifruit and sweet potato
- 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 (Hemerocallis) cultivars are available as either diploid or tetraploid. Kinnows can be tetraploid, diploid, or triploid.
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