4N Genetics

[Wren]

I've been thinking about getting a Phal. schilleriana var. purpurea (4N). Since it is advertised as having double the genes it should have more, longer lasting flowers and be a more vigorous grower. I want to know more about 4N orchids - how are they made, how do I know a seedling is a 4N, and if they are better growers. Thanks everyone!
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[ksriramkumar]

4N usually means that the plant has 2 times the regular chromosome count.

Some times, these are found naturally and most often they are manipulated during germination using a chemical like colchicine. This advantage most obviously manifests itself when the plant flowers: size is increased, and, in many cases, so is color intensity as well as substance. You can only only identify based on these parameters or may be there is an expensive test to test the chromosome count to ascertain.

[PaphMadMan]

4N plants (tetraploids) can be induced, usually by chemical treatments during seed germination or cloning (like colchicine already mentioned) but it is successful in only a usually small percentage of seedlings produced. They can also occur spontaneously. Either way, observation of the plant may suggest it is 4N but unless it is verified by a chromosome count it isn't certain.

A chromosome count isn't technically difficult, but it is tricky and time consuming, classically requires sacrifice of actively growing tissue like root tips, and is not always successful. Once you have one verified it will normally breed true when selfed or bred with another tetraploid, or can be propagated by cloning.

By observation alone a 3N (triploid) plant and a 4N may be impossible to distinguish from each other or from an unusual but normal 2N (diploid). If you just want a nice plant it doesn't matter, but it makes a big difference for breeding, and a seller should only be making claims that are true.

You should ask the seller for more information, if they haven't already provided it. Is this a verified 4N or assumed based on treatment or just on observation? Is it cloned or bred? Or is it an individual treated seedling that isn't verified? Is the seller making claims based on assumptions or on known qualities of these plants?

Tetraploid plants often have desirable characteristics like larger flowers or heavier flower texture that may last longer. They are normally healthy and often large and vigorous, but they are not necessarily easier to grow, and sometimes can be slow and compact.

[Azizan]

Tetraploid plants often have desirable characteristics like larger flowers or heavier flower texture that may last longer. They are normally healthy and often large and vigorous, but they are not necessarily easier to grow, and sometimes can be slow and compact.

Agreed on that. I just can't understand how tetraploid plants could comprehend with the doubling of chromosomes because genes code for the production of essential compounds for living such proteins etc. When the genetic material is doubled, wouldn't the gene expression be chaotic? For example Down syndrome but of course plant and human are two different organisms. Thus, I suspected it is the reason for tetraploids to be slow growing.

Aside of that, I have read that tetraploid Phalaenopsis is good as a pod parent but not pollen parent because the pollen of tetraploid Phalaenopsis could not produce good pollen tube for fertilization process to occur.

[sciencegal]

In Down syndrome only one chromosome is duplicated (so there are three instead of the normal two) as is the case with a few other syndromes caused by an extra copy of a single chromosome. Usually you only see physical characteristics if it is a sex chromosome (X or Y) because there will be a overdose of one or the other hormones.

If all of the chromosomes are doubled or tripled then there will still be the correct ratio of proteins, enzymes or hormones just maybe more. Polyploidy is very common naturally in plants. One of the reasons that plants can do fine with an extra set of chromosomes is because with the doubling or tripling the cell has to be larger. That won't bother a plant but could cause major deformities in an animal.