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speed and consequence of gentic "drift" in varietial strains?

Posted by windfall_rob vt4 (My Page) on
Sat, Mar 23, 13 at 12:26

I have been wondering about the rate of change (on average) of a given variety over time....and how it might reflect in our choices of scion source for a given variety

Obviously sometimes a genetic change manifests itself in an strongly apparent fashion and a new strain or sport of a variety is propagated from the altered parent

But presumably smaller less noticeable changes are also accumulating....and accumulating differently among the many trees of a given variety being progressively "copied" as well as within a given tree over time.

Furthermore, the rate and extent of change would likely run differently depending how many "generations" are involved in the chain of propagation....where an individual tree represents a single "generation"

This must have been studied...how different are our present heirlooms from the apples of same name consumed early in their history?
At what point does the divergence and accumulation of small alterations become significant enough to warrant attention?
Should the fussier among us be paying closer attention to the age and history of the source tree of our scions?

Just some questions that were rambling round my head on a long drive yesterday, and a quick search this morning didn't present any obvious leads.


Follow-Up Postings:

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RE: speed and consequence of gentic "drift" in varietial strains?

  • Posted by fruitnut z7b-8a,4500ft SW TX (My Page) on
    Sat, Mar 23, 13 at 13:52

Probably more of this happens and faster than we'd expect. From what I've read there are numerous strains of various varieties of wine grapes. Since those folks are always looking for the smallest edge, they test quite a few strains of a given variety.

It could also be part of the reason why there are so many cultivars of common fig. But I'm thinking many of those arise as seedlings that just pop up somewhere and then get named and propagated much to the delight of fig nurseries.

I'm sure there are many more examples but I haven't read anything scientific or detailed about this subject.


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RE: speed and consequence of gentic "drift" in varietial strains?

  • Posted by ericwi Dane County WI (My Page) on
    Sat, Mar 23, 13 at 14:35

I used to have a bird feeder filled with black oil sunflower seeds, but the local squirrels kept emptying the "squirrel-proof" feeder so often that I finally gave up. This would have been around 1995. Some of the sunflower seeds germinated in our yard, and I let them mature into sunflower plants, which typically had 10 or 12 inch diameter seed-heads, and had to be propped up in August. We kept on getting volunteer sunflowers, and every spring I would transplant them to a good location. By 2000, the mature sunflower plants no longer needed to be propped up, because the typical seed-head might be three inches across, and instead of having one or two seed heads, now each plant might have 6 or 8. So, it took 5 or possibly 10 generations for the sunflower plant to revert back to a more robust plant that did not require human intervention in order to survive.


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RE: speed and consequence of gentic "drift" in varietial strains?

I also have wondered about this some....
but I really do think that much of the "Drift" is really selection....

Read historical, British accounts of Pears... Inedible, likely to produce diarrhea and swollen, painful joints if eaten fresh... and most of those ended up being fermented and aged out into Ciders of one sort or another... My guess is that most of those have been chopped down and more "Friendly" eating and culinary varieties have sprung up....

There's really no sense in spending a whole lot of time propagating stuff that's not useful for something.... Look at flowering pears - being bred for Itty Bitty pea-sized fruit....

Another fine example is the Elberta peach... A peach that literally changed and took over the *Entire* peach market in the USA... but look at what we get when we buy a typical "Elberta"... A bland, nondescript yellow peach - that usually bears with or up to 2-weeks after Red Haven.... How could this possibly be a "Real" Elberta - which is supposed to be 53 days AFTER Red Haven - which would put it nearly into Mid-September.......... What happened to the "Real" Elberta? Did it drift, or did the "Real Elberta" get lost somewhere... or did Growers loose interest in Peaches that were getting in the way of Apple season?

While this is maybe not exactly what you are talking about... I think it's probably more what is going on than true Genetic Drift...

Thanks


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RE: speed and consequence of gentic "drift" in varietial strains?

I put "drift" in quotes because I know I am misusing the term....normally it represents changes in the proportions of given alleles over time within a population due to selection pressures and random events.

What I am referring to is slow changes to the genetics of a single variety of clonaly propagated plant...particularly fruits. Assuming a starting point from an initial seedling selection.

It's also why I put "generations" in quotes. As these changes are not the result of genetic shuffling via sexual reproduction. The succeeding "generations" are meant to be copies of the original but they will inevitably have some changes resulting from mutations caused by any number of internal or external factors.

It would be interesting to attempt to gather and plant side by side a large selection of the same variety from multiple scion sources. Ideally with some from the original parent(or as close to it as possible) and some from many "generations" down the line to see if under those circumstances subtle deviations would be apparent.


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RE: speed and consequence of gentic "drift" in varietial strains?

I think the trouble you would run into is pure statistics.... As soon as you have 2 trees - by definition, you have a "Better" and a "Worse"... Then - grow out 100 and you can pick the best of 100.... Are the genes different? No... Are the outcomes different - well, sure....

Of course, then, there's also the Philosophical question... What is "Best" to the fellow picking one single tree out of 100 to pull his scion wood from?

Thanks


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RE: speed and consequence of gentic "drift" in varietial strains?

John, I think you miss the point of my curiosity.

I am not interested in better or worse. I am not interested in using the test as a selection tool for improving a given variety. Although I suppose that would be a good justification for the effort involved.

I am curious as to how much deviation from the original parent is demonstrated and the factors that might effect the rate and significance of the deviation.


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RE: speed and consequence of gentic "drift" in varietial strains?

  • Posted by fruitnut z7b-8a,4500ft SW TX (My Page) on
    Sat, Mar 23, 13 at 22:07

rob:

The wine folks think subtle differences are apparent. But it may not all be genetic. There are many strains of apple rootstocks like M9 that have been around for a hundred years or more. One none genetic difference is latent virus infections. Rootstocks infected with some viruses result in less vigorous trees. That or similar could be part of what's making grape strains different.

There are lots of things going on. Probably other organisms than virus in there also.


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RE: speed and consequence of gentic "drift" in varietia

"What I am referring to is slow changes to the genetics of a single variety of clonaly propagated plant...particularly fruits. Assuming a starting point from an initial seedling selection."

I would say the changes would be insignificant, since sexual changes are so much more dramatic.
I would say maybe in 10 to 20 thousand years, you may see less than 1% change. But I highly doubt it. Not that much. The number of clones plays no role, the scion will grow the same, attached to parent tree or another, if doesn't even know it is a clone. I strongly disagree that this can be described as anything generational, it is not.
If the scion remains a branch or becomes a new tree, that is determined by environmental factors, growing does not alter genetics.
If a bamboo tree is cloned a thousand times, and scions are spread all over the world, in 100 years every clone will flower and die. It's happening to Fargesia nitida right now as a matter of fact.
"The first generation of seed was collected in North Szechwan, China, for the St. Petersburg Botanical Garden in the late 1880’s. Most of the established cultivars of F. nitida originated from this early collection: “Nymphenburg”, “Ems River”, “Eisenach”, “deBelder” to name a few. At the turn of the millennium, after a long and prosperous life of lending brilliant color and texture to landscapes across Europe and the United States, they are now in the midst of their 120 year flowering cycle. The first generation of F. nitida loved by many, will flower and abruptly perish within the next few years."

This post was edited by Drew51 on Sun, Mar 24, 13 at 3:07


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RE: speed and consequence of gentic "drift" in varietial strains?

Here's a similar thread I attempted to start, without much response:

http://forums2.gardenweb.com/forums/load/fruit/msg01120301450.html

You raise an interesting question, in measuring drift by finding lineage with fewer generations. I've always wondered about different strains. Is my Jonagold the same is yours?

I suppose as long as there are genetic mutations, we will have new sports and drift. Mutations are Nature's own product improvement plan. Lately I've been listening to lectures on quantum physics--makes me wonder about mutations at the sub-atomic level.

Marc


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RE: speed and consequence of gentic "drift" in varietia

What I find interesting is how places will describe the life of say a cherry tree as 30 years. They don't explain that environmental stress is what kills it, not old age. A cherry tree can probably live for thousands of years. I'm growing an Indian Free Peach tree. Thomas Jefferson grew this cultivar, and it is possible that I'm growing a tree that comes from clones, and my tree is actually about 240 years old already. Even though it is only about 30 inches tall right now.

I myself also believe a so called "sport" may result because after hundreds of years of replication (growing), the mechanism is changing. A biological entity can only replicate so long, almost like a photo copy of a photo copy of a photo copy, the process breaks down (ageing)
Maybe the genetic change you mention here, and claim to be real, is the result of the age of the clone, and not how many times it was cloned.

This post was edited by Drew51 on Sun, Mar 24, 13 at 3:52


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RE: speed and consequence of gentic "drift" in varietial strains?

Windfall - I think the situation you describe needs one of the best drivers for genetic change - Isolation. Look at the pygmy elephants in asia - a great example of isolation / "drift". Of course there are things like environmental pressures that can push this as well.

The real problem is that most people tell you NOT to grow fruit from seed (its inevitable for SOME to escape, look at the macintosh) due to the amount of variation. It is my understanding drift needs offspring to happen..

Although, it is also my understanding that many bamboo variations came from random mutations when the plant was dividing... i guess when fruit trees produce "sports" (like the red barlett), it might be some indication of drift?

Lastly, I have read an article about someone in colorado using Aloe Vera to show succesive hardiness in offspring (shoots not seedlings). Every year he exposed the plants to colder weather and eventually he go ale that took freezing temps without getting mushy. It took him 20 years but he apparently achived it


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RE: speed and consequence of gentic "drift" in varietial strains?

I think that it is impossible for those of us who exchange scion wood to differentiate between genetic change and viral contamination. It is viral problems that are probably the cause of the damage to a clone over time, in my opinion.

As to the comment about the Elberta peach, I've long included Elberta in my nursery and it consistently ripens well after Redhaven, usually starting on the first week of Sept while Redhaven is a July peach. I consider Elberta a high quality peach whose commercial value has been depreciated by the existence of better colored varieties. It is still a useful home orchard peach because of its relative resistance to brown rot and nice canning qualities.

There are other peaches, such as July Elberta, that some nurseries probably just shorten the name for marketing. I don't even think July Elberta is a sport of the original and is a selected seedling instead.


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RE: speed and consequence of gentic "drift" in varietial strains?

Rob, I have asked the same question myself. One experiment I always wanted to do if I could find the space is to get every version of some old apple variety, say Roxbury Russet to be concrete, plant in one stand, and compare what comes out. My expectation is the drift would not be all that great, but subtle differences would be noticeable. All of the sport varieties were picked because they were on a limb that grew something different than the rest, they are the "freak show" and not the norm. So, if someone is randomly grabbing a scion it will not likely be from a freak limb.

In 50 years someone will have probably genetically sequenced Roxbury Russet and folks will be arguing over what the "true" sequence is :-)

Scott


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RE: speed and consequence of gentic "drift" in varietia

"Lastly, I have read an article about someone in colorado using Aloe Vera to show succesive hardiness in offspring (shoots not seedlings). Every year he exposed the plants to colder weather and eventually he go ale that took freezing temps without getting mushy. It took him 20 years but he apparently achived it"

You can't train for genetic mutations, they are random, he trained the plant's metabolism or kept trying different sports till he found one that could tolerate the cold. He was searching for a random mutation in hardiness, and it appears it took 20 years to find one. It would have been easier using seedlings. Currently they are searching for a fungal resistant banana seedling to overcome the pending extinction of bananas. (all commercial banana trees are gone in Australia and China due to a mutated fungus).

You can imagine how hard that must be because how many seeds have you found in bananas? The Nature Of Things TV show did a show on the problems with monoculture. A facinating show!

Here is a link that might be useful: The Nature Of Things

This post was edited by Drew51 on Sun, Mar 24, 13 at 12:13


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RE: speed and consequence of gentic "drift" in varietial strains?

To Windfall Rob's last observation on my post....

The largest single cause of the "Drift" over time....

Look into the mirror...

By and large... The cause of that drift is us... Scions aren't picked in a vacuum....

As hobby/backyard growers - we can grow out one example and decide if we like it or not and move on...

If you own a peach orchard in South Carolina or Georgia - you better darned well sell Red Havens and Elbertas... and so you pick scions that do the best on your farm, crop the best, etc.... so you do just that.... plant grafted stock from your trees that excel above all the others...

Thanks


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RE: speed and consequence of gentic "drift" in varietial strains?

Glad to see others are interested

Fruitnut
I couldn't agree more, the are so many factors at play that actualy teasing out which are causing what may well be impossible. Virus is a great example.

Drew
I have to disagree with you on several points.

The changes may or may not be significant depending on how many changes have occurred and where in the coding the alterations are. A single change on one gene can give us a new "sport" if it occurs in the right location. 1% would be HUGE deviation. I think the change is fatser than thousands of years...the rapid development of multiple sports on some modern varieties would seem to support that.

Growing does cause genetic change. Growth is by definition cell division; and unlike animals, plants don't replace tissue they divide and expand outward. Replication errors during division are well documented in all organisms. And so since trees are growing out, those errors will inevitable accumulate so long as the cell is viable with the error.
We also have external cause of mutation like EM radiation, high energy particles, and chemical substances. These I assume would be more random in their rate of occurrence, but possibly larger in the degree of change per incidence.

As I said before "generations" is just the best phrase I can come up with. I don't think the cloning process itself causes mutation, but with each successive removal from the parent source a new "line" is being isolated and diverging in a different manner since most mutations and replication errors are random.
I don't mean that each clone from the parent will be different, but that a clone is sold, grown out and the cloned again by somebody else, who grow it out and then passes a clone to another grower, who grows it out...

MArc,
I think our thinking is largely in parallel

Canada plant,
I don't know how to make it any clearer I am not talking about drift in a sexually reproducing population, isolation is irrelevant to clonal propagation.

Harvestman,
I think you are right, this is l;argly just an intellectual excercise for me. But surely tthere must be some research outthere on this...can a virus create a new sport?

Scott,
That is the experiment I was imagining. It would be a quite an endeavor to do well and eliminate as many of the variables as possible.. You would need all you rootstocks to be concurrent clones from the same parent source and you would need to attempt to get virus free stock or remove virus from those you get....and you would need enough examples of each individual scion grown out to remove differences due to "chance" growing conditions. As john pointed out early in the discussion even 2 identical trees may not grow the same.

John,
I don't know how many commercial operations select and choose their own scion to propagate. Nor do I know how many trees of a given cultivar commercial nurseries maintain for scion source. So I really don't know how much selection comes into play. Certainly it could be a factor. But for many of us we have one tree or one branch to cut and share scion from so there isn't much opportunity for selection there.


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RE: speed and consequence of gentic "drift" in varietial strains?

John.....the mirror....well said. Apparently today's Red Delicious is quite different than the original. This is due to selection of sports for their red color alone--resulting in today's bland apple. I've read that this is the fate of most good varieties. Someday Honeycrisp may be just another bland red apple.

Marc


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