what do they mean by "clone"

[PaphMadMan]

Cultivars are not created equal in all types of plants, and short general definitions of the word cultivar may miss this. Orchid cultivars are asexually propagated, and no matter how that propagation took place this makes then clones as well. The same is true for apples, roses, etc.

But seed grown crops like wheat and soybeans also have cultivars, and they are defined differently. You can plant field after field of a wheat cultivar, and nearly every plant is true to type, but they are not genetically identical. Seed harvested from that field is considered the same open pollinated cultivar as long the field is reasonably isolated from other pollen sources and seed stays true to type.

Other seed grown cultivars may be inbred lines. Then they are all virtually genetically identical. The same holds true, that as long as there were no significant outside pollen sources and they stay true to type, all the seed from a single plant or a whole field is still the same cultivar. Most heirloom vegetables fall into this category.

Other seed grown cultivars can be controlled F1 or F2 hybrids between inbred lines. This is true for most non-heirloom maize, and some high end vegetable or ornamental plant seeds. In this case the seed saved from such a plant or field is not considered the same cultivar.

In theory, you can have both asexually propagated and seed grown cultivars in the same type of cultivated plant. You could use an orchid hybrid to produce an inbred line, and after a few generations if you had a uniform true to type population it could be considered a cultivar, but it would not be the same cultivar you started with, though it would be the same grex if you just kept self-pollinating. And you would create a lot of confusion and cause havoc with the judging systems.

Back to clones. The definition in Orchid Whisperer's post is correct. All genetically identical individuals derived by any method of asexual reproduction are "clones" in the vernacular sense. But clone was a well defined word in biology before it was applied to orchid cultivars or ever heard in everyday speech. It was only a noun, and almost never used in the plural. Clone referred to the genetic identity, not an individual or an aggregate group. It can be a replicated DNA sequence as well as an organism. A single unique original individual plant from seed is a clone (a genetic identity); a single asexually propagated independent plant produced from it by any process is the same clone; and any number of individuals plants produced by those means were still just "the clone" in aggregate.

Eventually it became accepted to use the plural and refer to a group of individual clones, at least in everyday speech. And it also became a verb, and laboratory means of producing clones became "cloning" and cloned individuals became clones rather than representatives of a genetic identity.

[Ray]

Originally Posted by PaphMadMan

Orchid cultivars are asexually propagated, and no matter how that propagation took place this makes then clones as well.

I'm going to nit-pick this statement, only for the purpose of clarity, as that sounds to me like you might be implying that cultivars are only created asexually.

If you have a population of sexually-propagated plants, individuals may be singled out as individual cultivars. Replication of that cultivar, indeed, must be done asexually.

[PaphMadMan]

Originally Posted by Ray

I'm going to nit-pick this statement, only for the purpose of clarity, as that sounds to me like you might be implying that cultivars are only created asexually.

If you have a population of sexually-propagated plants, individuals may be singled out as individual cultivars. Replication of that cultivar, indeed, must be done asexually.

We are in agreement. Sorry if there was any ambiguity. A cultivar is created when one plant is singled out and named. Usually that is a sexually propagated single plant, but the one awarded and named could in fact be a division, or a sport of an existing cultivar, for instance. If that plant ever is, or has been, asexually propagated then all copies are the same cultivar.

[SouthPark]

'clone' for orchids generally refers to 'mericlone'..... from meristem propagation. This involves attempts at replicating the original plant (DNA-wise) from suitable cut-out plant tissue (that will interestingly grow replicated plants - or that's the main idea of the mericlone process) .... typically done with special sterilising procedures. It is reported that mutation can occur ... not sure how ... maybe due to chemicals used. But they say that mericlones taken from the original plants are generally perfect replicas. And usually no differences between first generation mericlone and original plant, otherwise if there turns out to be slight DNA difference in a minority, then usually no superficial difference in plant visible features.

But it is said that the chance of mutation increases by some NON-negligible amount when cloning a mericlone. Maybe somebody knows the mechanisms behind the mutations. And.... any mutation.... even if not visible to the eye ... will mean a variation of the original. Any mutation at all will mean not really lead to a 'clone' as such. So expressions such 'imperfect clone' is probably a conflict of words.

[PaphMadMan]

At least one reason that mericlones tend to show mutations, especially over multiple cloning cycles:

In any organism there are mutations happening all the time, we just usually don't see them. Many are invisible anyway but aside from those, if they happen in reproductive tissue leading to seed we may see them, but most of those tend to be indistinguishable for normal seedling variation. If they happen in the center of the meristem and that particular cell goes on to become a major visible part of the plant, or the whole plant from that point on, we can see it. If it happens off to the side of the meristem and doesn't happen to contribute to visible tissue we won't.

In mericloning, almost every cell in the culture has the potential to become a whole plant. No hiding in tissues we don't see, and no chance to view it as normal seedling variation since we know exactly how the plant should appear. It is not so much that mutations happen more often in tissue culture, it is just that every mutation that does occur has a much larger chance of becoming visible.

[SouthPark]

Really nice information. Thanks for that nice contribution PMM!

[IngieBee]

I agree with @SouthPark , super info! Thank you everyone!

[SouthPark]

Does anyone know if there's a formal naming convention for mericlones (or even mericlones of mericlones) of hybrids that developed a mutation? For example, if a particular cattleya hybrid is mutated, then is there some naming convention that distinguishes it from the non-mutated plant? Will using a var. (variation) extension be used?

Eg. rlc. GREX "cultivar name" var. variation_name

[Roberta]

Var. refers to distinct populations of a species. While it also gets used for color forms, the correct designation is f. or fma. or forma. For a mericlone, if it is different enough to get judged as a distinct individual, it would just get a new cultivar name. But for mericlones that have been around for awhile (which would imply that either the original was cloned multiple times or clones of clones were made) it's a case of "buyer beware".

In fact, when people obsess about getting a particular cultivar, and are unhappy when it is unavailable. they forget that these are living things, not manufactured items. Once it's sold out, either someone decides to clone a new batch of the original (or a clone of it it) or remake the grex (which will no doubt be different since the parents are different plants, and so a new "line" begins)

[SouthPark]

Thanks so much for sharing that excellent information Roberta. I was quite interested in finding out what the naming convention is (or could be) for mutated hybrids.