Role mutations play in generating new varieties

[Doug9345]

A discussion started in this thread about all OP being hybrids once and it when on to discuss mutations here are the relavent posts

http://tomatoville.com/showthread.php?t=30879&page=5

Originally Posted by drew51

Are not all hybrids a cross between two or more OP's? They would have to be to produce a consistent F1. All OP/Heirloom were hybrids too! Still are in the true sense of the word. Many hybrids taste great. Sun Sugar, Jasper cherries are amazing. I see that many sell stable hybrids, as they tasted so good, it was worth the effort to stabilize the genes. Also the line between commercial and heirloom is age, which to me, means it tasted good enough to keep around, again all were hybrids at one point. Every single heirloom was a hybrid.

I can see some of the super resistant types might have a taste change, but those are needed as some growing areas have so many problems. it's great that one can at least grow something in those areas.

Originally Posted by carolyn137

Only the earliest of F1 hybrids have but two stable OP parents, ones like Ramapo, Better Boy, Big Boy, etc. More modern hybrids are constucted with two breeding lines and in each line there can be up to 4 different parental inputs, then the last one in each line is crossed with the other one, giving you the final F1 hybrid.

Not all OP heirlooms were hybrids at one point. That leaves out the important mechanism of mutation, which was a major force, especially when tomatoes were first evolving, and even now when random spontaneous mutations do occur from time to time, and that means both seed DNA ones as well as somatic mutations which occur in the cell of a plant.

Carolyn

Originally Posted by WhippoorwillG

This may take us on a tangent, so it may be more appropriate to move this to a new thread or the one referenced below to prevent muddying the waters in this thread.




I wanted to address this in the last op vs hybrid vs heirloom thread, but didn't want to take explanations to the Nth degree in an attempt to keep it basic. However, since you brought it up, I am very curious about any known non-hybrids that are passed around today outside of numerous small/medium fruited wild types.

In the above referenced thread, I made the blanket statement that all heirlooms were hybrids at one point. I had originally inserted a disclaimer about it being mostly true, outside of wild types and "land races," but deleted it for the sake of brevity (not a natural attribute of mine ) I did not intend to discount mutations, since we would be hard pressed to explore the genetic diversity of the tomato(or anything with genetic coding) and its relatives if there weren't mutations.

However, I do not consider a gene mutation alone to make a new non-hybrid variety. I am specifically speaking to traits such as PL vs. RL. If a hybrid is found/created that eventually mutates from a RL to a PL, or red to green fruit, it is still a product of a hybrid. Is it genetically different? Yes. But is it still a hybrid with respect to the ancestry? Yes.

My primary curiosity is: Are there any large fruited varieties still in cultivation today that are thought to be solely evolved from small green wild types? Large fruit is heavily a product of increased locule count, along with several other contributing factors, but I have not seen any referenced as ancient or passed down from antiquity. That's not to say they don't exist...I just haven't seen mention of them in the text I've read. Of course there are the numerous wild types, and selections made from wild populations, but all I am familiar with are between tiny and small, not slicing size.


As always, thanks to those that are willing to share their knowledge.

Originally Posted by carolyn137

I agree that this thread is not the place for this discussion, so I'll be brief.

Tomatoes from Chile and Peru, the wild types, evolved not from the green fruited ones, but from the red fruited one Solanum pimpinellfolium. This is known from many studies where restriction analysis of snips have confirmed that.

Each gene can have one or more alleles.

Right now I don't remember the gene designation for leaf form, as to PL and RL, I should remember so I'm going to claim Senior Citizen amnesia, but here's an example.

Let P be domininant

Let p be recessive

So one can have"

PP, homozygous dominant and RL

Pp, heterozygous and domininant, RL

pp, homozygous recessive and PL

If with Pp the p mutates, then the result is from Pp, RL to pp, and PL.

And for some tomato genes there are many alleles, alternative forms of a single gene.

There are other ways of going from RL to PL as well, that involve DNA events such as repeats, looping out, inversions, and genes can be altered in that way also.

(However, I do not consider a gene mutation alone to make a new non-hybrid variety. I am specifically speaking to traits such as PL vs. RL. If a hybrid is found/created that eventually mutates from a RL to a PL, or red to green fruit, it is still a product of a hybrid. Is it genetically different? Yes. But is it still a hybrid with respect to the ancestry? Yes.)

If the assumption is that a stable OP is homozygous for all genes, as it should be, then a mutation could change any particular trait to another phenotype.

I guess it's best that we agree to disagree on the evolution of tomatoes, starting with the currant tomato b'c the work of several scientists has shown that it was upsized due to mutation initially and initially from few locules to several.

No one knows for sure what happened in Mexico where they first showed up, but it's clear that the first ones taken from Mexico to Spain were yellow. Subsequently red ones also showed up in Italy, all by mutation.

Yes, it happens. Green Gage is a pre 1800 variety that I've grown and one year one branch had all red fruits while all other fruits on the plant were the normal yellow. That's called a somatic mutation where the mutation is in a plant cell, as opposed to a seed DNA mutation.

Yellow Riesentraube? A person found ONE yellow fruit on a plant with all other fruits being the normal red. Another somatic mutation.

Carolyn

[NarnianGarden]

Thanks. I always wondered about how the mutation/evolving in the case of tomatoes actually happened.
Would be great to know what happened to cause the plants to grow larger tomatoes.
A yellow-fruited variety doesn't suddenly turn red just because of a geographical change. So what triggered the first variations? An one-time event, or a chain of events that consequently created the modern looking prototypes?
One day, I'll watch the history of mankind AND plant kingdom on a wide screen

[Doug9345]

I've been trying to figure how to word this question.

I can see how you can go from a red tomato to a yellow tomato by a mutation as I'd think there be many ways to mess up lycopene production. I can also see where a mutation could cause a plant to start producing a new chemical. I can understand a yellow tomato experiences a mutation that cause some pathway to produce lycopene and that trait is passed onto offspring.

What I don't understand is how that trait can come and go. I can see red tomatoes producing yellow ones on a somewhat regular basis because there are a lot of ways to break something. What I'm having trouble with how can a mutation to a yellow tomato let's say in Spain and another mutation in Mexico produce the SAME EXACT result. Even if mutations both produced lycopene I'd think there would be enough differences to be able to tell the two events apart.

A little reading shows that lycopene exists in other fruit such as watermelon. This leads me to the question of is the difference between red and yellow tomatoes not that yellow tomatoes can't produce lycopene, but that they don't because it gets turned off? If it's only a question of flipping a switch back and forth I can see why there could be a relatively high chance that a tomato would change color or leaf type or what ever.

Why do I have the feeling that just about the time that biochemists and geneticists have thought they knew what was going on they have, or are about to, open the door in front of them and find out it's not a closet full of detail, but the door to a big room and they are infact in the closet.

[Hermitian]

Originally Posted by NarnianGarden

...
One day, I'll watch the history of mankind AND plant kingdom on a wide screen

Suppose the two are shown together, contracting time scales linearly into a 10-hour epic. If we use accepted scientific dates of evolution and appearances of species, then the plants would dominate the entire movie and humans would get the last 2 minutes. The human portion would go something like this:

[carolyn137]

https://www.google.com/#q=vander+knapp+tomatoes

The above link illustrates the work of Dr. Esther van der Knaap who has been in the forefront of tomato evolution. Read what you want and I think you'll better appreciate what happened as to mutational events.

A few years ago her work was featured in an issue of Scientific American, with pictures of some of the tomatoes on the front cover.

To date, 15 species of tomatoes have been Ided in South America and the larger question one might ask, is where did they come from and anyone can ask that of any flora or fauna on earth.

I have no intention of discussing the origins of anything on earth in terms of spirituality, alien spores, etc.,and I hope no one else does either.

It was Dr. Charles Rick of the TGRC who first brought back seeds of many of those species and when grown out they appeared as they did in the wild, and continued to do so, thus they were not hybrids.

As I mentioned in the other thread, no one knows for sure when they first arrived in Mexico, the first being what we know as S. pimpinellifolium, the currant tomato, and from there they evolved even more with retraction of the stigma for some, but not all. Increase in the numberof locules, etc. and genes for someof these events have been Ided By Dr. van der Knaap/

Carolyn

[Hermitian]

Originally Posted by carolyn137

...
To date, 15 species of tomatoes have been Ided in South America and the larger question one might ask, is where did they come from ...

We call them hybrid species.

[carolyn137]

Originally Posted by Hermitian

We call them hybrid species.

Regardless of the fact that there was no genetic segregation with saved seeds? And that upon repeated growing from saved seeds one year to the next?

Dr. Rick was known world wide for his genetic expertise, the TGRC at UC Davis in CA is still the premier repository of the species and as far as I know none of the ones he grew, which weren't all of the species since some were discovered after he died, never did show genetic segregation which a hybrid variety should do.

Which gets back to the, if there is one, definition of what a hybrid tomato is, and it looks like you see the words hybrid tomato differently than I do.

Let's see what others think of mutational evolution of tomatoes is all about, which is what Doug titled this thread as opposed to revisiting definitions of hybrids, landraces and the like which was the topic of a different thread.

Carolyn

[ScottinAtlanta]

Alien spores. Tomatoes. I heard it from Carolyn first.

[NarnianGarden]

Hermitian: lol, the posture of the last fellow in the pic resembles something I am too familiar with...

Since my ignorant genes become most apparent when I make comments on genetics, I prefer to ask questions rather than comment on the subject.

What is the definition of the term "land race" when used in a genetics discussion? I am fairly well educated in American history so I am pretty sure it has no relationship with the Oklahoma land rush.

Ted

[carolyn137]

Originally Posted by tedln

Since my ignorant genes become most apparent when I make comments on genetics, I prefer to ask questions rather than comment on the subject.

What is the definition of the term "land race" when used in a genetics discussion? I am fairly well educated in American history so I am pretty sure it has no relationship with the Oklahoma land rush.

Ted

http://tomatoville.com/showthread.php?t=30798

Ted, please see the above link of just two weeks ago about what a landrace is or is not.

Summary? No one definition.

Carolyn

Thanks Carolyn,

Yep! I don't read every thread. I'm not sure a forum search would have helped since I was looking for land race instead landrace. The most apparent reality on the subject is the fact that while no one seems to agree on a single specific definition; no one is more ignorant on the subject than me. I am now enlightened.

Ted

[Fusion_power]

There is a ton I could say on this subject and some of it would help and more would just confuse. Here is a toned down version that might help.

The first concept is that it is 1000 times easier to break something genetic than it is to implement something totally new. Using black tomatoes with the green flesh mutant as an example, tomatoes like Cherokee Purple, Black Cherry, and Black From Tula all show a common phenotype, tomatoes that retain chlorophyll in the fruit during ripening. This is caused by a mutation in a single gene that is supposed to convert chlorophyll into other compounds. It turns out that just about anything you do that messes up this single gene winds up as a black tomato. So when researchers sequenced the gene, they found that there are actually 5 separate mutations all affecting the same gene and all giving the same basic phenotype. If you dig around online, you can find a list of which varieties map to the different genes.

Then there are mutations that involve re-arranging genes sometimes by reversing a segment of a chromosome, other times by relocating part of one chromosome onto another, by deletion of part of a chromosome, or by duplicate additions of genes that are already in the nucleus. These types of mutations can result in totally new characteristics. For example, an inversion and partial deletion on chromosome 7 in chickens results in rose comb. This inversion messed up a gene for fertility in roosters such that rose comb chickens have reduced sperm survival. This is a good example of a mutation that conveys a useful trait because rose comb chickens have an advantage in cold climates, but at the same time causes a problem by reducing fertility. The immune system of tomatoes and potatoes is largely made up of duplicate additions to the genome where at some point a cell started to divide with duplication of chromosomes, then something went wrong and one chromosome wound up with too many genes. Some of those changes were highly advantageous for survival of the plant.

There are mutations that involve insertion of new genetic material into the genome. Sound like GMO? Well it is, but in this case, it is part of nature. Retroviruses in particular are really good at injecting DNA into cell nuclei. Sometimes this novel material turns out to convey a useful trait that winds up as part of the genome. It is possible for some viruses to pick up bits of DNA from one plant and move them into a completely different plant. This type change is relatively rare, but it does occur.

There are mutations that involve complete genome duplication. Tomato is thought to have gone through at least 3 of these over the ages. A plant simply goes from diploid to tetraploid having 4 sets of chromosomes instead of 2. Over time, these chromosomes go through changes that turn them into unique new traits. Eventually, the changes are significant enough that the chromosomes are no longer duplicates and voila, the plant now has twice as many unique chromosomes as it had originally.

Finally, there are mutations where related but highly diverged species manage to cross. The rutabaga is an excellent example. It is a cross between a turnip and a type of cabbage. The really interesting thing is that the rutabaga kept all of the chromsomes of a turnip and all of the chromosomes of a cabbage. It is referred to as an amphidiploid. So the next time you eat steamed rutabaga, you will remember that you are eating a cabbage turnip. Now here is the kicker, almost all of the cultivated plants that we use for food are amphidiploids! Okra and wheat are two more really good examples.

There are about a dozen more classes of mutations, most or all of which have been found in tomato.

Re tomato species, the 13 known species are divided roughly into three groups defined by how easily they cross among each other. S. Peruvianum for example is so highly diverged from domestic tomato that they can only be crossed using embryo rescue. The genes available in the wild species totally dwarf what is available in domestic tomato. I wrote some information in the wiki article about wild species and you can find more info by a google search. https://en.wikipedia.org/wiki/Tomato

[carolyn137]

Darrel, in the other thread that spawned this one, I think that was the source, I talked about pretty much what you just posted in terms of mutation mechanisms such as repeats, inversions, looping out, deletions, etc, of the DNA leading to mutational events.

I also discussed the diffeence between seed DNA mutations and somatic mutations which occur in the DNA of a plant cell.

So I'm glad to have some confirmation from you.

Keith M used to have a large section on the species and which species are used in construction of tomatoes, but I didn't see it there when I last looked.

Also, I gave a link in this thread to Dr. Esther van der Knaap who has been in the forefront of mutations and the evolution of tomatoes.

Carolyn

[Labradors2]

Fascinating stuff, Fusion_power!

Are there any Tetraploid tomato varieties? I know about them from my daylily days, and still grow a few of them in my garden. Tetraploid daylilies are bigger, stronger and more robust than their diploid counterparts. They are like giants! Sounds like something to strive for in tomatoes!

Linda

Originally Posted by Fusion_power

There are mutations that involve complete genome duplication. Tomato is thought to have gone through at least 3 of these over the ages. A plant simply goes from diploid to tetraploid having 4 sets of chromosomes instead of 2. Over time, these chromosomes go through changes that turn them into unique new traits. Eventually, the changes are significant enough that the chromosomes are no longer duplicates and voila, the plant now has twice as many unique chromosomes as it had originally.