Did you ever wonder how do we get seedless fruit? To find out, we need to take a step back to high school biology class and the study of genetics.
What is Polyploidy?
Molecules of DNA determine whether a living entity is a human, dog, or even a plant. These strings of DNA are called genes and genes are located on structures called chromosomes. Humans have 23 pairs or 46 chromosomes.
Chromosomes come in pairs to make sexual reproduction easier. Through a process called meiosis, the pairs of chromosomes separate. This allows us to receive half of our chromosomes from our mothers and half from our fathers.
Plants aren’t always so fussy when it comes to meiosis. Sometimes they don’t bother dividing up their chromosomes and simply pass the entire array to their progeny. This results in multiple copies of chromosomes. This condition is termed polyploidy.
Polyploid Plant Info
Extra chromosomes in people is bad. It causes genetic disorders, such Down syndrome. In plants, however, polyploidy is very common. Many types of plants, such as strawberries, have multiple copies of chromosomes. Polyploidy does create one little glitch when it comes to plant reproduction.
If two plants which crossbreed have differing numbers of chromosomes, it’s possible that the resulting offspring will have an uneven number of chromosomes. Instead of one or more pairs of the same chromosome, the offspring can end up with three, five, or seven copies of the chromosome.
Meiosis doesn’t work very well with odd numbers of the same chromosome, so these plants are often sterile.
Seedless Polyploid Fruit
Sterility is not as serious in the plant world as it is for animals. That’s because plants have many ways of creating new plants. As gardeners, we’re familiar with propagation methods such as root division, budding, runners, and rooting plant clippings.
So how do we get seedless fruit? Simple. Fruits like bananas and pineapples are called seedless polyploid fruit. That is because banana and pineapple flowers, when pollinated, form sterile seeds. (These are the tiny black specks found in the middle of bananas.) Since humans grow both these fruits vegetatively, having sterile seeds is not an issue.
Some varieties of seedless polyploid fruit, like Golden Valley watermelon, are the result of careful breeding techniques that create polyploid fruit. If the number of chromosomes is doubled, the resulting watermelon has four copies or two sets of each chromosome.
When these polyploidy watermelons are crossed with normal watermelons, the result are triploid seeds that contain three sets of each chromosome. The watermelons grown from these seeds are sterile and don’t produce viable seeds, hence the seedless watermelon.
However, it’s necessary to pollinate the flowers of these triploid plants in order to stimulate fruit production. To do this, commercial growers plant normal watermelon plants alongside the triploid varieties.
Now that you know why we have seedless polyploid fruit, you can enjoy those bananas, pineapples, and watermelon and no longer have to ask, “how do we get seedless fruit?”
It’s quite possible that you have seen a commercial for “23 and Me”, advertising an ancestral DNA test. The “23” represents the DNA in a human being, contained in 23 chromosomes. Now this number is misleading, because humans have two sets of chromosomes, one from their mother, and one from their father. However, “46 and Me” doesn’t have the same ring to it. With few exceptions, most animals have two sets of chromosomes, and we refer to them as diploid (di = two, ploidy = sets of chromosomes in a cell). Physical size isn’t a factor: in comparison to humans (46), mice have 40, elephants have 56, and dogs have 78 chromosomes.
Strawberries have eight sets of chromosomes. Source: Morguefile
It should come as no surprise that plants are weird and different, even when it comes to their chromosomes. Plants can have multiple sets of chromosomes, which is called polyploidy. Many of your favorite fruits and vegetables are polyploids, and this makes them even more delicious. Polyploidy can occur naturally, where wild species “add together” their DNA. Two good examples of this are wheat and strawberries. Wheat is a hexaploid, which means it has six sets of chromosomes, and strawberries are octoploids – you guessed it – eight sets!
Simple graphic depiction of the number of sets of chromosomes in various foods.
Plant breeders intentionally develop polyploids with desirable traits – for example, seedless watermelons. Normally, watermelons are diploid, and have seeds. By using chemicals, such as colchicine, plant breeders can double the number of chromosomes in a plant. Then, the tetraploid (four sets of chromosomes) watermelons are crossed with a standard diploid watermelon to make triploid watermelon seeds.
These triploid watermelon seeds are sterile, because you need pairs of chromosomes to form seeds – this is why animals and plants always have multiples of two chromosomes. You need to plant at least one regular seeded watermelon in your garden with sterile seedless watermelon seeds as a pollen source. Seedless watermelon seeds are more expensive because it costs a lot of money to maintain tetraploid lines and produce triploid seeds every year.
Bananas are a triploid fruit – having three sets of chromosomes. The tiny seeds in their interior are sterile. Source: Morguefile
In addition to seedless watermelons, bananas are probably the most common triploid food you eat. The next time you eat a banana, look for the small black specks in the middle of the fruit – these are the sterile seeds. Farmers do not have to buy new banana seed every year because the banana fruit grows on a plant that sends up a new shoot each season.
Polyploidy is one more tool that scientists can use to learn about the genetics of crop plants. Plant breeders use traditional plant breeding methods to change polyploidy to make improved crops faster and more efficiently. Polyploidy can be challenging because there are so many more chromosomes to work with, but it is another ‘tool’ in our plant breeding toolbox that we use to grow the most healthy, delicious plants!
Answered by Christine Bradish, Ashland Inc.
To see a video of Dr. Bradish in action or read about her work visit here.
To read a web story about the complexities of polyploidy in crop breeding, visit here.
Polyploidy: Types and Effects | Methods | Crop Improvement | Botany
In this article we will discuss about:- 1. Meaning and Types of Polyploidy 2. Induction of Polyploidy 3. Effects 4. Applications 5. Limitation.
Meaning and Types of Polyploidy:
An organism or individual having more than two basic or monoploid sets of chromosomes is called polyploid and such condition is known as polyploidy. It is estimated that about one third species of flowering plants are polyploids. In wild species of grass family polyploidy has been reported upto 70%.
Polyploidy is of two types, viz.:
Polyploids which originate by multiplication of the chromosome of a single species are known as autopolyploids or autoploids and such situation is referred to as autopolyploidy. In other words, autoploidy refers to the situation in which additional sets of chromosomes arise from the same species.
Autoploids include triploids (3x), tetraploids (4x), pentaploids (5x), hexaploids (6x), septaploids (7x), octaploids (8x), and so on. Autoploids are also known as simple polyploids or single species polyploids.
They have three sets of chromosomes of the same species. They can occur naturally or can be produced artificially by crossing between autotetraploid and diploid species. Triploids are generally highly sterile due to defective gamete formation. Triploids are useful only in those plant species which propagate asexually like banana, sugarcane, apple etc.
A few examples of practical uses of autotriploidy are given below:
Cultivated varieties of banana are triploids and seedless. Such bananas have larger fruits than diploid ones.
Some varieties of apple are triploids which are propagated asexually by budding or grafting.
Triploid sugar-beets have higher sugar contents than diploids and are generally resistant to moulds.
Triploid watermelons are seedless or have rudimentary seeds like cucumber. These seedless watermelons are produced by crossing tetraploid female with diploid male. However, the reciprocal cross is not successful.
All other autoploids with odd chromosome sets, viz. pentaploids, septaploids, etc. also behave like triploids.
They have four copies of the genome of same species. They may arise spontaneously or can be induced artificially by doubling the chromosomes of a diploid species with colchicine treatment. Tetraploids are usually very stable and fertile because pairing partners are available during meiosis.
In such individuals diploid gametes (2n) are formed. Autotetraploids are usually larger and more vigorous than the diploid species, rye, grapes, alfalfa, groundnut, potato and coffee are well known examples of autotetraploids.
A few cases of practical use are described below:
Autotetraploid rye is grown in Sweden and Germany. They have larger seeds and higher proteins than diploids.
Tetraploid grapes have been developed in California, USA, which have larger fruits and fewer seeds per fruit than diploids.
Tetraploid varieties of alfalfa are better than diploid in yield and have better recovery after grazing.
A ployploid 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. Alloploids are also known as hybrid polyploids or bispecies or multispecies polyploids.
An allopolyploid which arises by combining genomes of two diploid species is termed as allotetraploid or amphidiploid. Allopolyploidy can be developed by interspecific crosses and fertility is restored by chromosome doubling with colchicine treatment. Alloploidy has played greater role in crop evolution than autopolyploidy, because allopolyploidy is found in about 50% of crop plants.
I. Natural Alloploids:
Some important natural allopolyploid crops are wheat, cotton, tobacco, mustard, oats etc. Interspecific crossing followed by chromosome doubling in nature have resulted in the origin of allopolyploids.
The origin of some natural allopolyploid crops is briefly presented below:
The bread wheat (Triticum aestivum) is an allopolyploid. It is believed that A genome of wheat has come from Triticum monococcum (2n = 14), D genome from Triticum tauschi (2n = 14) and B genome from unknown source probably from an extinct species (2n = 14). Thus hexaploid wheat has two copies of the genomes from three species.
First allotetraploid Triticum turgidum developed from a cross between Triticum monococcum and unknown species of B genome. Then cross between T. turgidum and T. tauschi resulted in the development of hexaploid wheat T. aestivum.
There are two cultivated species of tobacco, viz. Nicotiana tabacum and N. rustica. N. tabacum is an amphidiploid between N. sylvestris (2n = 24) and N. tomentosa (2n = 24). N. rustica is believed to be amphidiploid between N. paniculata and N. undulata. Each of these two species has 2n = 24.
The tetraploid American cotton (Gossypium hirsutum) is believed to be an amphidiploid between G. africanum, and G. raimondii. Both these species are diploid with 2n = 26. The chromosomes of G. africanum are larger than G. rainondii.
The cultivated oat (Avena sativa, n = 21) is an allohexaploid which is considered to have originated from a cross between A. barbata (tetraploid, n = 14) and A. strigosa (a diploid, n = 7).
In brassica, there are there basic species, viz. Brassica nigra (BB, n = 8), B. oleracea (CC, n = 9) and B. campestris (AA, n = 10). The cross between B. nigra and B. oleracea gave rise to B. carinata. Cross between B. campestris and B. oleracea led to the development of B. napus, and cross between B. campestris and B. nigra resulted in the development of B. juncea. All the resulting species are amphidiploids.
II. Artificial Alloploids:
Artificial alloploids have been synthesized in some crops with two main objectives, viz.:
(a) Either to study the origin of naturally available alloploids or
(b) To explore the possibilities of creating new species.
Some examples of artificial alloploids are given below:
This is a classic example of artificially synthesized alloploid. This was developed between radish (Raphanus sativus, n = 9) and cabbage (Brassica oleracea, n = 9) by Russian geneticist Karpechenko in 1928. He wanted to develop a fertile hybrid between these two species with roots of radish and leaves of cabbage. But he got a fertile amphidiploid (4n = 36) by spontaneous chromosome doubling which unfortunately had roots of cabbage and leaves of radish. Thus it was of no use.
Clausen and Goodspeed synthesized a new hexaploid species of tobacco (Nicotiana) from a cross between Nicotiana tabacum (2n = 48) and N. glutinosa (2n = 24). The F1 was sterile with 2n = 36, which was made fertile by doubling of chromosome through colchicine treatment. The new species is known as N. digluta.
Triticale is a new crop species which has been synthesized from a cross between wheat (Triticum aesitvum) and rye (Secale cereale, n = 7). Some triticales are developed from cross between tetraploid wheat (Triticum turgidum) and rye and some from cross between hexaploid wheat (T. aestivum) and rye.
The F1 was sterile, which was made fertile by colchicine treatment. Triticales produced using tetraploid and hexaploid wheat are hexaploid and octaploid, respectively. Titicale is now commonly grown in Canada, Mexico, Hungary and some other countries.
In wheat, Mc Fadden and Sears developed hexaploid between Triticum turgidum (formerly T. dicoccum) and T. tauschi (formerly Aegilops squarrosa). This resembled T. aestivum (formerly T. spelta) and produced fertile F1 when crossed with natural T. aestivum. This suggested involvement of these two species in the evolution of T. aestivum in the long past.
The American upland cotton (Gossypium hirsutum) was synthesized from a cross between G. herbaceum and G. raimondii . Both these species are diploid with 2n – 26. The former is Old world cultivated diploid and the latter, New world wild diploid. This suggested involvement of these two species in the evolution of upland cotton.
Induction of Polyploidy:
Polyploidy is mainly induced by treatment with a chemical known as colchicine. This is an alkaloid which is obtained from the seeds of a plant known as Colchicum autumnale, which belongs to the family Liliaceae. Colchicine does not affect Colchicum from which it is extracted, because this plant has an anti-colchicine substance.
Colchicine is applied in a very low concentration, because high concentration is highly toxic to the cells. For effective induction of polyploidy, usually concentrations of 0.01% to 0.5% are used in different plant species. The colchicine induced polyploidy is known as colchiploidy.
In plants colchicine is applied to growing tips, meristematic cells, seeds and axillary buds in aqueous solution or mixed with lanolin. The duration of treatment varies from 24 hours to 96 hours depending upon the species of plants.
Colchicine induces polyploidy by inhibiting formation of spindle fibres. The chromosomes do not line up on the equatorial plate and divide without moving to the poles due to lack of spindle fibres. The nuclear membrane is formed around them and the cell enters interphase. Thus nucleus has double the chromosome number.
Effects of Polyploidy:
Polyploidy has marked effects on the morphology of plants. The distinct features of autoploids are increase in general vigour and size of various plant parts. Such features are generally referred to as gigantism.
Autoploids have the following important features:
1. Stems are thicker and stouter.
2. Leaves are fleshy, thicker, larger and deeper green in colour.
3. Roots are stronger and longer.
4. Flowers, pollens and seeds are larger than diploids.
5. Maturity duration is longer and growth rate is slower than diploids.
6. Water contents are higher than diploids etc.
Applications of Polyploidy in Crop Improvement:
Polyploidy plays an important role in crop improvement. Both autopolyploidy and allopolyploidy are useful in several ways. However, allopolyploidy has wider applications than autopolyploidy.
Applications of autopolyploidy and allopolyploidy in crop improvement are briefly presented below:
Both triploids and tetraploids have been used in crop improvement. However, their applications have been limited to few species only. Autotriploids have been developed in sugar-beets and watermelon. Triploid sugar-beets have larger roots and higher sugar contents than diploids.
Triploid watermelons are seedless or have rudimentary and soft seeds like cucumber. The triploid seed is produced by using tetraploid as female and diploid as male. The reciprocal cross is not successful. Moreover, triploid watermelons have irregular shape and fresh seeds have to be made every year.
Autotetraploids have been developed in forage crops like berseem, alfalfa and rye vegetables like radish, turnip and cabbage and fruits like grapes. Tetraploid varieties of rye are grown in Sweden and Germany. They have larger seeds and higher proteins than diploids.
Tetraploid grapes have been developed in California USA, which have larger fruits and fewer seeds per fruit than diploids. Tetraploid varieties of alfalfa are better than diploid in yield and recovery after grazing. However, tetraploid cabbage and turnips have higher water contents than diploids.
Alloploidy is useful in four principal ways, viz.:
(1) In tracing the origin of natural allopolyploids,
(2) In creating new species,
(3) In interspecific gene transfer, and
These are briefly described below:
1. Tracing the Origin of Crop Species:
Alloploidy plays an important role in tracing the origin of natural allopolyploids. Study of chromosome pairing in a cross between allopolyploid and a diploid species helps in tracing the origin of polyploid species. The affinity in pairing indicates the involvement of diploid species in the evolution of such polyploid. Lack of pairing between the chromosomes of two species, rules out the involvement of diploid species, in the origin of polyploid under study.
2. Creation of New Species:
Alloploidy sometimes leads to the creation of new crop species. Triticale is the best example, which is allopolyploid between wheat and rye. It combines desirable characters of both the species, i.e., grain quality of wheat and hardiness of rye. Triticales are of two types, viz. primary triticales and secondary triticales.
Primary triticales are derivatives of cross involving either tetraploid wheat or hexaploid wheat with rye. Secondary triticales are derivatives of the cross either between two primary triticales or between primary triticale and wheat. These are superior to primary triticales in several aspects.
Presently cultivated strawberry originated from a cross between North and South American species in the middle of seventeenth century in Europe. Loganberry was developed from a cross between raspberry and blackberry in 1880 in California, USA.
3. Interspecific Gene Transfer:
When the desirable character is not found within the species, it is transferred from the related species. Interspecific gene transfer is done in two ways, viz. by alien addition and alien substitution. In case of alien addition one chromosome of wild species is added to the normal complement of a cultivated species.
In case of alien substitution, one pair of chromosome is substituted in cultivated species with those of wild donor species. Such type of gene transfer is generally made for disease resistance. This type of gene transfer has been achieved in crops like wheat, tobacco, cotton and oats. In cotton, lint strength has been transferred from G. thurberi to G. hirsutum.
However, in such gene transfer several undesirable characters (genes) are transferred along with desirable ones. In tobacco, mosaic resistance has been transferred from N. glutinosa to N. tabacum through alien addition.
Sometimes direct cross between two species is not possible due to sterility in F1. In such case, first an amphidiploid is made between such species and then amphidiploid is crossed with the recipient species. Such bridging crosses have been made for transfer of genes from wild species particularly in crops like tobacco and cotton.
Besides these, alloploids have some other applications. For example, heterotic effects can be conserved more easily in allotetraploids than in diploids. Moreover, interspecific hybrids can be made fertile by artificial doubling of chromosomes.
Limitations of Polyploidy:
Polyploidy has several limitations.
Some important limitations of polyploidy in crop improvement are briefly presented below:
The single species polyploidy has limited applications. It is generally useful in those crop species which propagate asexually like banana, potato, sugarcane, grapes etc.
2. Difficulty in Maintenance:
The maintenance of monoploids and triploids is not possible in case of sexually propagating crop species.
3. Undesirable Characters:
In bispecies or multispecies polyploids characters are contributed by each of the parental species. These characters may be sometimes undesirable as in case of Raphanobrassica.
Induced polyploids have several defects such as low fertility, genetic instability, slow growth rate, late maturity, etc.
5. Chances of developing new species through allopolyploidy are extremely low.
Polyploidy – or how do we get seedless fruit?
PUBLISHED ON May 7, 2019
MADISON, Wis. — Spitting out watermelon seeds can be a summertime rite of passage for some folks. Others like their watermelons seedless. How did those seedless watermelons (and other plants) come about? The May 7th Sustainable, Secure Food blog explains the topic of polyploidy.
“Plants can have multiple sets of chromosomes, which is called polyploidy. Many of your favorite fruits and vegetables are polyploids,” says blogger and plant scientist, Christine Bradish, Ashland, Inc. “Polyploidy can occur naturally, where wild species ‘add together’ their DNA. Two good examples of this are wheat and strawberries.”
But, plant breeders can also develop work to develop crops without seeds – like seedless watermelons. Even bananas are seedless.
“Polyploidy is one more tool that scientists can use to learn about the genetics of crop plants,” says Bradish. To read the complete blog, visit Sustainable, Secure Food at https://sustainable-secure-food-blog.com/2019/05/07/polyploidy-or-how-do-we-get-seedless-fruit
This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America . Our members are researchers and trained, certified professionals in the areas of growing our world’s food supply, while protecting our environment. They work at universities, government research facilities, and private businesses across the United States and the world.
— American Society of Agronomy and Crop Science Society of America
Creating Polyploid plants using Colchicine derived from Autumn Crocus seeds/plants
First off thanks for featuring my question on the last episode about the 12/12 from seed. To touch base on the tissue culture questions. I have a clean room area where cultures will be made and maintained, and yes I can store and create thousands of plants with a few callus masses from the tissue cultures. I’m looking to bank the tissue cultures to have hundreds of strains available without any seed(or make artificial seed with tissue cultures in the fake seed), at a moments notice. The good part is you test the plant once and it should always be the same CBD/THC levels, each time just as a clone, but without the cells being mature and the plants life cycle starts over every time you culture it.
I will be making some polyploid plants, by subjecting seeds to Colchicine derived from Autumn Crocus (a common flower which is poisonous) by crushing their seeds or extracting from the plants. This will be a big project but I think the time is worth the reward.
This has been used in the industry to create large flowers and used in breeding forever. Colchicine is used for gout treatment and over ingesting it can actually kill you, so you don’t want to be smoking the 1st generation of plants, just the ones you grow from the seed you create. It mutates the plants to double up the chromosomes and then it becomes a polyploid, not a diploid. I have read that tetraploids 4n grow slowly. So my idea is create a tetraploid, and then pollinate with a standard diploid 2n, which will make it a 3n (pretty much the equivalent of a mule, cannot create offspring sort of ) (for reference: A horse has 64 chromosomes, and a donkey has 62. The mule ends up with 63. Mules can be either male or female, but, because of the odd number of chromosomes, they can’t reproduce)
Polyploid is a natural mutation in nature in which a cells get extra sets of chromosomes(think of giant redwood trees 66 chromosomes total, I wondering if any of those extra chromosomes make them huge?). Cannabis plants are usually diploid 2 chromosome, which means that they have two complete sets of chromosomes. Those being Polyploids have a higher number of chromosomes sets, so there can be triploid (3n), tetraploid (4n ) on and on. You can keep going higher. But here comes the interesting part.
If you have a triploid (three sets 3x), for example seedless watermelons you can have an outdoor grow that cannot be pollinated ever by regular 2n diploid pollen. or pollen from hemp naturally growing. So you could breed in a grow room and not accidentally pollinate the plants, sitting next to them. not my photos, but the general idea, this i believe is the slower growing polyploid.
A common flower that now has doubled up chromosomes. They look like aliens I know.
I believe if you were to look at some strains that are higher THC they possibly could be triploid 3n plants now. which would explain if you are having issues breeding other strains to it, and the ever increasing THC levels.
I will publish videos on this also. I have some research on this subject along with the tissue cultures for a number of years just just started growing this year. So I will be posting lots of info online.
Love to hear you take on this. I know I have some ambitious projects, but there are hundreds of haters that will say 12/12 from seed is crap, and I bet with some strains sure. But when I find that strain I can produce a lot and have constant flower coming out I’ll be happy.
Also I will share my creations with giveaways, with the community.
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