Thursday, March 11, 2010

Geneticist (Phalaenopsis cvv.), Part I

The main problem with trying to write a Phalaenopsis profile is that there's so much information available, it's easy to get bogged down and lose track of what's interesting and what isn't. Not that everybody's going to agree on what's interesting in the first place, of course. But you know what I mean. Much to sort through. I started this off with really good intentions, but quickly wound up on weird tangents, and then some of the tangents had tangents, and then at some point I looked up and saw that I'd written 2000 words without ever getting to how you're supposed to take care of them. So if you're here to find out how to actually grow Phalaenopsis, you'll want to skip on ahead to Part II (which will post next Wednesday). Otherwise, read on. They're kind of messed up.

As you can guess from the title, there will be some genetics involved. I'll try to make it as clear as I can, but some vocabulary is unavoidable. So brace yourself.

Phalaenopsis NOID.

Popular science writing likes to use the image of, if all the DNA in a single one of your cells were fully extended into one long strand, that strand would be . . . however long that turns out to be.1 It may be useful to present the idea of DNA in this way -- it does, at least, give the suggestion of a very long and skinny molecule, which DNA is -- but it's also a bit misleading, in that the DNA in a human cell is not present as a single very long molecule, but instead as forty-six of them, of varying lengths, plus assorted proteins on which the DNA is wound. Each of these forty-six chunks of DNA are called chromosomes.

In humans, most of the chromosomes in a cell are referred to by either a number (for example, "chromosome 5") "X," or "Y." Most human cells will contain two copies of each of the numbered chromosomes (1-22), a single X, and then either a Y or a second X.2 With me so far?

When your body produces egg cells, or sperm cells, the chromosomes which are in pairs split up. Human egg cells contain a single copy of each chromosome from 1 to 22, and an X. Human sperm cells contain a single copy of each chromosome from 1 to 22, and either an X or a Y. At least, this is how it's supposed to work. Sometimes the cells fuck up, and you get a sperm with an extra chromosome 5, or an egg has one more X than it's supposed to.

Phalaenopsis NOID. This pink-purple is a much more typical color for modern Phalaenopsis varieties.

Now. Human beings are, for reasons I don't really understand and am not quite sure anybody really knows, put together in such a way that having any extra chromosomes, beyond that 2(1 to 22) + X + (X or Y), really fucks us up, developmentally. Most of the time, having even one single extra chromosome from one parent or the other causes everything to go off-kilter, and the fetus eventually reaches the point where it can't develop any further, and it dies. An extra chromosome 2, for example, is hopeless. Winding up with three copies of every chromosome is no good either: it's not just that you have to have the same numbers of each of the numbered chromosomes, but the number also pretty much has to be two. Two copies, for everything, all the way down the line, except for the X and Y.3

The situation with plants is similar up to a point. Phalaenopsis have nineteen paired chromosomes, for a total of thirty-eight per cell. Reproductive cells are formed the same way as in humans: one chromosome of each pair goes one way, and the other goes the other way, and you wind up with a reproductive cell containing nineteen chromosomes. When two such cells from different plants come together, the new embryo develops with thirty-eight chromosomes in each cell.

Also like people, plants usually won't develop normally if they have a single extra copy of a single chromosome. However, unlike people, they don't seem to mind if they get a whole extra set of chromosomes.

How all this relates to Phalaenopsis is . . .

Phalaenopsis Sogo Manager.

Once, long ago, I was talking to a Phalaenopsis grower in Florida about the yellow-flowered varieties. I forget how the subject came up, but I remember him saying something to the effect that the yellow ones all had fucked-up chromosomes4 and were consequently hard to produce in large number.

Which I remembered, because I was hoping to understand why this was the case at some point in the future.

Well. Welcome to the future! Sorta. There are no flying cars,5 but I understand what's up with the yellow phals now.6

Phalaenopsis ordinarily have nineteen pairs of chromosomes in each cell, so thirty-eight chromosomes total. The botanical word for having pairs of each chromosome is diploid. However, occasionally a tetraploid plant appears, which has four of each chromosome (so a total of 76 individual chromosomes all packed into the cell). This can be done on purpose, by breeders and researchers (tetraploids are often "better" than the parent plants in certain important ways),7 or it may happen naturally. Either way.

Phalaenopsis without bloom.

As you can imagine, tetraploid plants must be very useful to people who are trying to develop new varieties of Phalaenopsis, then, because there's kind of an obvious market for a plant with bigger, more abundant flowers. Tetraploids can breed with one another more or less normally, too: instead of dividing nineteen pairs of chromosomes into nineteen individual chromosomes, like a diploid plant does, a tetraploid instead divides its thirty-eight pairs of chromosomes into thirty-eight individual chromosomes. So when you cross a tetraploid plant with another tetraploid, you wind up with: a tetraploid.

However -- and this is the part where the explanation about yellow phals starts to happen, so pay attention -- you can also cross a diploid with a tetraploid. Everything works the same way: the diploid parent supplies half of its chromosomes, or one set of nineteen, and the tetraploid parent supplies one half of its chromosomes, or one set of thirty-eight, and you get an offspring with three sets of chromosomes. This situation is called triploidy, and plants constructed this way are called triploids. Triploids are also usually a little bigger, a little faster/larger/prettier/whatever, than your regular diploids, and they're not uncommon in the world of Phalaenopsis breeding. In fact, a lot of the best yellow Phalaenopsis varieties happen to be triploids.

But, there is a huge catch. Suppose you have a beautiful yellow Phalaenopsis that happens to be a triploid, and you want to breed it with another triploid.

You are completely boned. The problem is that, with three copies of each individual chromosome, there's no way to divide up the number of copies evenly. For some chromosomes, the gametes might wind up with two copies; other chromosomes will have to make do with only one copy, and the uneven numbers of everything will basically lead to a trainwreck. If the gamete being formed is even able to develop far enough to encounter another gamete (usually they can't), they'll wind up in a situation where there are two, three, or four copies of various chromosomes, the new baby plant will fall to pieces, and all the effort will have been for nothing. And obviously it doesn't help to try pairing a triploid with a diploid, or triploid with a tetraploid, because the triploid's chromosomes are not going to divide evenly, no matter what you pair them with as the other parent. So triploids are dead ends, genetically, for all intents and purposes.8 - It's long, so you might want to go to the bathroom first.

Phalaenopsis NOID.

Which means you can't use them for breeding new varieties. So you can come up with a pretty nice yellow, and tissue culture as much of them as you need,9 but you can't cross it with much to make an even better yellow, so it doesn't do you much good.

Now, not all yellow Phalaenopsis are triploids, and not all triploids are yellow. Breeders do have some usable yellows to work with. But the situation could be better. Some of the non-triploids are even more messed up, and are what are called aneuploids, which have extra individual chromosomes, or missing chromosomes, or chromosomes where part of the DNA is gone, or whatever. Aneuploids, obviously, have an even tougher time reproducing than triploids, and it's kind of amazing that they can get it together to grow and bloom at all.

The relative absence of a good yellow stud Phalaenopsis also affects the attempts to produce good true-red flowers: without any yellow pigment, Phalaenopsis flowers tend to be pinkish-purple. With a little yellow underneath, the color gets closer to a true red.10 So we can expect to see the appearance of some nice true-red flowers at about the time we see some nice blinding-yellow ones.

One last semi-related bit before we move on to Part II:

Phalaenopsis, like other orchid genera, can cross-breed with a number of other orchids. The most common crosses are Doritaenopsis, which involve Phalaenopsis crossed with Doritis. I've never seen a straight Doritis, but I'm told they looks so much like phals, and cross so easily with phals, that most11 taxonomists think they are phals, and don't count Doritis as a separate genus. I have seen a Doritaenopsis (Dtps.) before --

Doritaenopsis Taida Salu 'M-P0247.' Clearly named by a gentle, poetic soul.

Close-up of Doritaenopsis Taida Salu 'M-P0247' flower.

-- and now so have you. I don't really see a difference, personally. I'd be happy to call them all Phalaenopsis.

Phalaenopsis will also cross with several other genera to form intergeneric hybrids with tongue-twister names like Stamiariaara, Nakagawaara, and Meechaiara. I've never seen any of the intergenerics, nor heard of any of their names before I went looking, so I would be surprised if they were commercially important.

If you like, you may now move on to Part II, in which I tackle the question of how to actually care for one of these genetic freaks.

References:
www.hort.purdue.edu (highly recommended, very readable history of phal production)
www.bedfordorchids.com (1) (Somewhat less readable, about breeding yellow phals)
www.bedfordorchids.com (2) (ditto)
www.bigleaforchids.com (chromosome problems with red and yellow phals, red in particular)
http://www.robert-bedard.com/orchids/phal_venosa.html (using the species P. venosa in breeding; includes a reference to a successful cross with a triploid)
http://commons.wikimedia.org/wiki/Phalaenopsis (includes photos of the flowers of some species of Phalaenopsis)


-

Photo credits: All my own.

1 Googling suggests that the answer is about 6 feet (2 meters), give or take.
2 If an X, then you're a female. If a Y, then you're a male.
It's not actually as simple as this, of course. Brains are wired up during fetal development, in a way which usually corresponds to the X/Y system but doesn't always, so there are a minority of people whose genes say they're male but whose brains tell them they're female, or vice-versa.
This is not at all relevant to Phalaenopsis, and in fact we started out on something of a tangent, so this is a tangent of a tangent of a tangent, minimum, but I didn't want to breeze along as though there were only males and females, and genetics determine which you are, end of story, because that's not universally true.
3 The exceptions to this general rule: fetuses can develop more or less like normal if they have a third chromosome 21 (Down syndrome), if they wind up with sex chromosomes that are XXX, XXY, or XYY (XXX and XYY are usually not even distinguishable from the general population, though they may be learning disabled to some degree), and occasionally babies may be born who have extra copies of 13 or 18, though being born with an extra 13 or 18 generally means you're not going to survive very long.
Wikiposedly, 95% of fetuses with extra or missing chromosomes will miscarry, usually in the first trimester of pregnancy.
4 He did not actually say "fucked-up."
5 Why are flying cars the standard by which futureness is measured? Who would even want cars flying overhead? Imagine what happens if two of them were to collide. Over your house. And you know they'd have to collide occasionally. I mean, I don't see people being more careful drivers in flying cars than they are in the earthbound ones.
6 Phalaenopsis is frequently shortened to "phal." I don't do this a lot, ordinarily, because there's another genus of orchids called Paphiopedilum, which is shortened to "paph," and for some reason I get the two short forms mixed up in my head (they're both four-letter words, starting with "p," and have three out of four letters in common, so I think this is forgivable), so I always have to stop and think about the short form, which having to stop and think kind of defeats the purpose of even having a short form. I'll probably be using "phal" here from time to time, because I'll need the variety, it's shorter to type, and there's no danger that I might actually mean Paphiopedilum in this post. But ordinarily, I find it too confusing to use.
7 Why would you want four sets of chromosomes, when the plant can get by just fine with two? Well, among other things, plants that have more sets of chromosomes are often larger and more robust. The flowers may be more abundant, or larger, or both. The fruit may be bigger than normal, more abundant, or contain more seeds. Tetraploid plants may grow faster or be more disease-resistant. Stuff like that. (This, by the way, should make you glad that tetraploid human embryos don't survive: the last thing we need is a bunch of huge, super-healthy, super-fertile men and women with huge genitals running around making fun of the rest of us.)
Tetraploidy in plants is usually induced by soaking seeds in a solution of a chemical called colchicine, which if you're getting ready to disapprove of it because it's a chemical and chemicals are bad, catch that knee before it jerks: colchicine is perfectly natural, and is found in the bulbs of the autumn crocus, Colchicum autumnale. In fact, colchicine is the reason why the autumn crocus is dangerously poisonous.
You can either get purified colchicine and soak seeds in it for whatever length of time, or you can throw a couple Colchicum bulbs in a blender, puree for a couple seconds, and then soak your seeds in that. But then you have to remember not to re-use the blender during Lab Margarita Party Night, because, you know: poison.
8 Sometimes you want an infertile triploid plant, though. Virtually all of the bananas you buy in the store are triploids, for example. Bananas naturally produce fairly large, hard seeds, all throughout the fruit. Triploid varieties, though, abort seed development so early that the seeds are so tiny as to be un-noticeable, which is why triploidy is desirable in bananas.
Wait a minute, you may be thinking, you just said triploids were infertile. How do we get new banana plants, if the parent banana plants can't produce any seeds?
The trick is that bananas also produce asexually, by offsetting. As long as you have one plant producing fruit you like, you can cut away the offsets and plant them elsewhere until you have an entire field of identical, triploid bananas. The catch is that, because they're all identical plants, they're all susceptible to the same pests and diseases.
The reason your grandfather says bananas these days suck compared to what he had when he was a kid is not because he's a bitter, broken old man who's glorifying his own past -- though he may be that too -- but because the original cultivated banana, the Gros Michel, fell victim to a fungal disease which basically wiped the variety completely out of existence by the early 1960s. (An early outbreak of Panama Disease -- this is what the fungus is called -- in Honduras and the Caribbean in the early 1920s basically eliminated the entire crop for a while, leaving banana importers no bananas to import and periods of banana shortages. Hence the song "Yes, We Have No Bananas." Seriously. That's where that song comes from.) The variety we eat today, the Cavendish, was the first reasonably good-tasting banana to come along that could resist Panama Disease, though most people who have tasted both say that the Gros Michel was larger, sweeter, and better-tasting than the Cavendish.
You, by the way, will be telling your own grandchildren someday about how much better Cavendishes were than the crappy bananas they're eating: the Cavendish is now on its way out too, because a strain of Panama Disease that can kill Cavendish plants has arisen.
Or, possibly, you'll just be boring your grandchildren with tales of this bizarre, mushy, bland, long, yellow fruit called the "banana," which they'll never have seen, edible bananas having disappeared before they were born. And they will find this incredibly boring. Maybe they'll think you're making them up. (Who, after all, would name a fruit something as silly-sounding as "banana?" I mean, come on, grandpa. This is worse than that time you said the name of George H.W. Bush's Chief of Staff was John Sununu.)
See Popular Science for more details on the bananapocalypse.
You've also probably eaten a triploid watermelon or two in your time, and for the same reason -- triploid watermelon seeds abort early, leaving "seedless" varieties. These are generated anew every year, sexually, by crossing a diploid line of watermelon with a tetraploid variety and harvesting the triploid fruits that result. Which is kinda fucked up. Fern Richardson, of Life on the Balcony, pointed out to me via Twitter that this also leaves farmers who want to grow seedless watermelons at the mercy of the seed companies who maintain the separate diploid and tetraploid lines. In fact, customers get a product most of them (I assume) probably prefer, and seed suppliers have a semi-captive audience, so everybody, in theory, benefits from the triploid seedless watermelon except the farmers who grow them. Typical.
9 Most commercial orchids are grown from tissue culture instead of from seed. You can get a lot more plants in a shorter amount of time this way, and also, so long as the stock plant is healthy and disease-free, the tissue-cultured clones will be also. The disadvantage of tissue culture is that you need highly-skilled workers and a really, really clean environment, which means it's expensive to get started. Perhaps I'll explain tissue culture in some future post, sometime.
The existence of tissue culture, by the way, makes the original comment from the grower kind of inexplicable. Yes, the yellows often have fucked-up chromosomes, but they should still be easy enough to produce in large numbers so long as they can be tissue-cultured. It's possible that he didn't have the money for tissue-culture production, and therefore was having to raise his plants from seed.
10 There are, apparently, no true red phals in nature, which raises the question of why, exactly, anybody thinks the world needs a true-red Phalaenopsis. I'm not sure. Plant breeding appears to be a matter of people trying to create plants that satisfy certain arbitrary goals, for the sake of novelty, except novelty by itself isn't enough. With Phalaenopsis breeding, for example, the first "red" I ever saw was 'Sogo Rose,' which has slightly pointed petals, instead of rounded ones.


I thought that the pointed petals were kind of cool when I first saw it, just because it was at least something different from all the other Phalaenopsis I'd seen, but I've come to find out that points are considered bad, and all the breeders are trying very hard to make sure that things like that get bred out of the genus, so the public will have only the huge, flat, rounded flowers that (for the most part) bore me.
This will be seen by true breeders of Phalaenopsis as evidence that I have hopelessly vulgar taste in flowers, and they will adjust the tilt of their top hats, look through their monocles, straighten their moustaches (Because in my vision of Phalaenopsis breeders, they all wear top hats, monocles, and moustaches. Even the women.) at one another and agree to pray to their respective gods that people who believe as I do are never able to influence Phalaenopsis fashion. But I'm sorry. I get so tired of seeing the same flowers over and over again.
11 (Wikiposedly.)


16 comments:

Ginny Burton said...

Ah, Mr_Subjunctive, you have started my day off perfectly, once again! Great post!

Greensparrow said...

Just want to add re colchicine: It is REALLY toxic. Like seriously scary stuff. As in, wear two layers of gloves and work in a fume hood. So any blendering going on should NOT take place in any thing you are going to use for food ever again in the history of the blender.
Also: Other chemicals can make tetraploids too -- I've had good success making tetraploids using the pre-emergent herbicide trifluran, which is MUCH less dangerous.

Diane said...

Didn't know the whole back story on the bananas, so thanks for that. I look forward to inflicting it on my students. I used to have one of those half-yellowish, half-pinkish phals, and boy was it ugly! A pure yellow would be a lovely thing to have, though.

Sixwing said...

That footnote on bananas has totally made my morning. Thanks!

Andrew said...

The move towards rounder bigger flowers seems to be a plague in the world of orchids. It's happening with Cymbidiums and Paphs as well and I'm really not a fan.

Personally I'd prefer Phals more heavily influenced by Phalaenopsis equestris instead. There's also P. equestris 'aurea' which is white with a bright yellow lip I'd love to get my hands on.

James said...

Orchids to sex determination in human fetuses and that didn't even take the majority of the post. AFAIK, it's not just a matter of what gender than brain thinks it is, you can occasionally get people who are anatomically one gender, but whose chromosomes say otherwise. Which creates even more complexity when people tried to verify the genders of olympic athletes. And I'm now on a tangent of a tangent of a tangent of a tangent aren't I?

Anyway, this is the reason I'm glad I'm and plant geneticist, and AWESOME post!

Ivynettle said...

I absolutely love your footnotes. Both for the giggling fits they cause and for the info contained in them.
I'm with you, the pointy-petaled flowers are so much more interesting than the omnipresent rounded ones. So the breeders can frown on me, too.

Also:
"So we can expect to see the appearance of some nice true-red flowers at about the time we see some nice blinding-yellow ones"
Oh, yay - neon colours! And then next we need some sparkly flowers, and then plants that go ka-boom! ("Neon colours, sparkle and ka-boom" being my joking formula for what's considered interesting these days.)

Anonymous said...

In the last couple of years I've been seeing small phalaenopsis cvv. (minis?), in different colors, with less rounded petals. I think I like them more than the big monsters.

Some of red over yellow cvv. look a little lurid, but the one blooming for me now is nice. The yellow warms up the pink w/o making it too dark.

Thank you for a great post.

Paul said...

Thoroughly enjoyed the banana link! Very interesting!

Never been a fan of Phal equestris myself. Have a number of friends who think the world of it but the only use I really see for it is the breeding of miniphals with a, hopefully, high flower count and branching habit. That being said, I'm not a "phan" (bad joke I know) of the generic huge overly round Phals either. I prefer the more star-shaped ones and a number of the species (excepting P. equestris).

Playing devil's advocate for the hybridizers -- those big round phals are what most folks think of when orchids come to mind. That being the case, hybridizers go for where the money is. Among orchid hobbyists, the far less "plebeian" forms of the various species phals (a number of which are more star-shaped) are actually sought after.

Nature Assassin said...

Very, very interesting! And funny, of course. I think you may have become Doctor Subjunctive.

our friend Ben said...

Doctor Subjunctive. I love it! And I too love the species phals, especially the ones with speckled/freckled/etc. foliage. Great post, great footnotes, great banana digression. (I feel that way about the future of planes. "Yes, sonny, once upon a time people actually flew through the air in metal capsules with wings!" "Yeah, right, Grandpa!") I became hooked on orchids (admittedly in a minor way) when I was married to an orchid breeder and judge who even named a paph after me. As always when anything interests me, I've read pretty much everything written on the subject, and I still say your post on phals is outstanding. Kudos!!!

Plant Pages said...

I was searching on the web for details for my website, when I stumbled upon your blog.. All the posts are so in depth.. I have a lot to learn from you..

Daniel said...

Despite being a biochem major, I'd never before considered what tetraploid humans would be like. Very scary. Lol

Anonymous said...

I extremely like the word wikiposedly. You made my day!

Ryan said...

Re: Triploids.

Triploids *can* sometimes produce fertile offspring in most cases. It's just really low fertility. I wonder if orchid breeders have tried this...

The mechanism is usually such: Segregation of the chromosomes into daughter cells in cell division is wacky in triploids as you have mentioned. Most combinations will be dysploid (chromosome numbers that are usually quite maladaptive). Dividing the chromosomes with half in one cell and half in the other is usually abortive because of this. There is a situation, however, in which functional gametes are reliably produced: when all chromosomes go in one daughter cell and none in the other. Then you end up with a triploid gamete. Fertilizing this with the diploid gametes of a tetraploid gives you a pentaploid (2 sets plus 3 make five), which is hardly better. However, fertilizing this with the haploid gamete of a diploid gives a tetraploid (3 + 1 = 4), which is a more fertile condition. The studies I have seen typically give 1-2% of triploid gametes from triploid plants (i.e. this process happens about 1% of the time). Not great, but the progeny should be far more fertile. Typically a triploid X diploid cross gives no or frequently a very few offspring, all of which are found to be tetraploid.

So in the unlikely situation that anyone wants to go into Phalaenopsis breeding, NOW YOU KNOW! lol

The original yellow Schlumbergera truncata cultivar is triploid. I wonder if there is a pattern??

Lou Jost said...

I just found this old post, and enjoyed it very much. The last comment (by Ryan) was especially interesting. In fact, there are some triploid Phals that ALWAYS put all their eggs in one basket, so to speak, putting all three chromosomes in the embryo rather than making a mess with uneven assortments. When these are crossed with a diploid, as you said, a fully fertile tetraploid results.

The key plant for modern yellow breeding, Phal. Golden Sands 'Canary', is this rare kind of triploid. (As far as I know, it is the only Phal which does this.) Almost all yellow Phals have this plant in the background, because it forms a bridge between the small bright yellow diploid species (almost all wild Phal species are diploids) and the big round (but non-yellow) tetraploids.