pbs Digest, Vol 46, Issue 26: "clonal breakdown" viruses and weasel words, also called "spin" or euphemism, etc.

Adam Fikso adam14113@ameritech.net
Tue, 21 Nov 2006 14:59:38 PST
----- Original Message ----- 
From: <pbs-request@lists.ibiblio.org>
To: <pbs@lists.ibiblio.org>
Sent: Tuesday, November 21, 2006 4:29 PM
Subject: pbs Digest, Vol 46, Issue 26


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> Today's Topics:
>
>   1. Re: Virus (totototo@telus.net)
>   2. Lilies & virus (John Bryan)
>   3. Re: Lilies & virus (John T Lonsdale)
>   4. Re: Lilies & virus (Alani Davis)
>   5. Re: Lilies & virus (Jim McKenney)
>   6. Re: Lilies & virus (John T Lonsdale)
>   7. Clonal breakdown (John Bryan)
>   8. Re: Clonal breakdown (Diane Whitehead)
>   9. Re: Clonal breakdown (Boyce Tankersley)
>  10. Re: Lilies & virus (eob@vqme.com)
>  11. Re: Neomarica - more (piaba)
>  12. Re: Clonal breakdown (Jim McKenney)
>  13. FW:  Clonal breakdown (John T Lonsdale)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 21 Nov 2006 10:29:34 -0800
> From: totototo@telus.net
> Subject: Re: [pbs] Virus
> To: pbs@lists.ibiblio.org
> Message-ID: <20061121182902.73KSKR1U83@priv-edmwaa05.telusplanet.net>
> Content-Type: text/plain; charset=US-ASCII
>
> On 1 Jan 90, at 0:21, John Bryan wrote:
>
>> ...Growers in the Netherlands are very conscious of the need to
>> sell only the best possible stock.
>
> I nearly choked on my morning bagel when I read that. Maybe they're
> *conscious* of this need, but Dutch growers don't seem to act on that
> consciousness. The Dutch bulb trade is notorious for mislabelling
> what they send out, and it's well known that some types of bulbs from
> Dutch sources are virtually always virused, lilies being the classic
> example. I could mention the horrible virused form of Crocus
> kotschyanus, but I won't.
>
> The mislabelling is insidious because they are generally careful to
> substitute something with approximately the same look. Out of some
> bluish Crocus biflorus cultivar? Just grab a bunch of C.
> tommasinianus; no one will ever notice the difference. It is no
> accident and esp. now when the bulbs are all prepackaged, it isn't
> due to customers mixing the contents of the bins. That's the excuse I
> used to get when I complained about misnamed bulbs!
>
> And some of the other "bulbs" one buys are diseased in other ways:
> one friend with access to the necessary equipment determined that a
> dahlia from Dutch sources was loaded with nematodes.
>
> It may be that you are distinguishing "growers" from "wholesalers"
> and "distributors", but a man is known by the company he keeps. The
> entire Dutch bulb trade is, I am sorry to say, unreliable and has
> known for its failings since at least 1950 when E. B. Anderson
> inveighed against mislabelled Dutch bulbs.
>
> Simply put, it appears that the Dutch bulb industry is long on profit
> motive at the expense of ordinary everyday ethics and honesty. Their
> long history of selling wild-collected bulbs, with the end result of
> near extinction of many species, is just another example.
>
>
> -- 
> Rodger Whitlock
> Victoria, British Columbia, Canada
> Maritime Zone 8, a cool Mediterranean climate
>
> on beautiful Vancouver Island
>
>
> ------------------------------
>
> Message: 2
> Date: Mon, 01 Jan 1990 00:38:06 -0800
> From: John Bryan <johnbryan@worldnet.att.net>
> Subject: [pbs] Lilies & virus
> To: pbs@lists.ibiblio.org
> Message-ID: <259F16EE.728A69A6@worldnet.att.net>
> Content-Type: text/plain; charset=us-ascii
>
> Way back in the 60's, the lily hybrid Enchantment, introduced by Jan de
> Graaff's Oregon Bulb Farms, began to loose the size of flowers and the
> bud count. Many acres of this hybrid had been grown for a great number
> of years. It was decided to propagate, by tissue culture, a new stock.
> Enchantment was, the first lily to receive a Patent, being grow widely
> for cut flower production as well as a garden plant and we exported many
> thousands to the Netherlands. It is to be noted that the plants did not
> show signs of virus, just the flower size and count diminished. This was
> thought to be a clonal breakdown, not an unusual occurrence and I think
> this was a correct diagnosis.
>
> The result of the tissue culture was the new stock, so propagated,
> regained the flower size and bud count of previous years. Thus it is not
> only virus that causes such problems, but clonal breakdown is another
> factor of a decline of a variety/culivar. I suppose Enchantment is still
> being grown but has been superseded by newer hybrids, but the bloodline
> of this great Asiatic lilly can still be seen in progeny, for example
> the black tips of the buds etc.
>
> This might be of interest, the point being decline of a plant is not
> always due to a virus, but continued propagation by vegetative means can
> also cause problems. Cheers, John E. Bryan
>
>
> ------------------------------
>
> Message: 3
> Date: Tue, 21 Nov 2006 14:26:18 -0500
> From: "John T Lonsdale" <john@johnlonsdale.net>
> Subject: Re: [pbs] Lilies & virus
> To: "'Pacific Bulb Society'" <pbs@lists.ibiblio.org>
> Message-ID: <009301c70da2$eb9fa600$6601a8c0@XPS400>
> Content-Type: text/plain; charset=us-ascii
>
> John Bryan,
>
> Can you please explain what you mean by 'clonal breakdown'?  How does TC 
> of
> a lily suffering from 'clonal breakdown' fix this?
>
> Thanks.
>
>
> John T Lonsdale PhD
> 407 Edgewood Drive,
> Exton, Pennsylvania 19341, USA
>
> Home: 610 594 9232
> Cell: 484 678 9856
> Fax: 801 327 1266
>
> Visit "Edgewood" - The Lonsdale Garden at http://www.edgewoodgardens.net/
>
> USDA Zone 6b
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Tue, 21 Nov 2006 14:41:54 -0500
> From: "Alani Davis" <adavis@ecoresource.com>
> Subject: Re: [pbs] Lilies & virus
> To: <john@johnlonsdale.net>, "'Pacific Bulb Society'"
> <pbs@lists.ibiblio.org>
> Message-ID: <006801c70da5$19ffd4f0$0305a8c0@crinum>
> Content-Type: text/plain; charset="us-ascii"
>
> I am curious about this as well. I have heard this used many times as a
> reason for decline of a variety through clones do to excessive asexual
> reproduction, but would be the mechanism for this "decline"? How can 
> genetic
> "vigor" be "lost"? How can one "know" it is clonal breakdown and not
> environmental or pathanogenic?
>
> Alani Davis
> Tallahassee, Florida
>
>
> -----Original Message-----
> From: pbs-bounces@lists.ibiblio.org [mailto:pbs-bounces@lists.ibiblio.org]
> On Behalf Of John T Lonsdale
> Sent: Tuesday, November 21, 2006 2:26 PM
> To: 'Pacific Bulb Society'
> Subject: Re: [pbs] Lilies & virus
>
> John Bryan,
>
> Can you please explain what you mean by 'clonal breakdown'?  How does TC 
> of
> a lily suffering from 'clonal breakdown' fix this?
>
> Thanks.
>
>
> John T Lonsdale PhD
> 407 Edgewood Drive,
> Exton, Pennsylvania 19341, USA
>
> Home: 610 594 9232
> Cell: 484 678 9856
> Fax: 801 327 1266
>
> Visit "Edgewood" - The Lonsdale Garden at http://www.edgewoodgardens.net/
>
> USDA Zone 6b
>
>
> _______________________________________________
> pbs mailing list
> pbs@lists.ibiblio.org
> http://www.pacificbulbsociety.org/list.php
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> ------------------------------
>
> Message: 5
> Date: Tue, 21 Nov 2006 14:45:32 -0500
> From: "Jim McKenney" <jimmckenney@jimmckenney.com>
> Subject: Re: [pbs] Lilies & virus
> To: "'Pacific Bulb Society'" <pbs@lists.ibiblio.org>
> Message-ID: <000c01c70da5$9b4b8090$2f01a8c0@Library>
> Content-Type: text/plain; charset="us-ascii"
>
> While we're waiting for John Bryan's response on this, I'll add this. What
> John Bryan called clonal breakdown might be what I think of as clonal 
> drift.
>
>
> Clonally propagated material varies over time, and the amount of variation
> is probably proportional to the number of replications involved.
>
> To keep a clonally propagated product within the expectations of 
> consumers,
> it's necessary periodically to reselect typical material on which to base
> future cloning.
>
> This clonal drift is not necessarily a disadvantage. Many of the tulips of
> the double early division are said to be somatic mutations of the tulip
> Murillo, which itself is a somatic mutation of a single early tulip. So
> where there was originally one product, there are now many, all pieces of
> one original seedling.
>
>
> Jim McKenney
> jimmckenney@jimmckenney.com
> Montgomery County, Maryland, USA, USDA zone 7
> My Virtual Maryland Garden http://www.jimmckenney.com/
>
> Webmaster Potomac Valley Chapter, NARGS
> Editor PVC Bulletin http://www.pvcnargs.org/
>
> Webmaster Potomac Lily Society http://www.potomaclilysociety.org/
>
>
>
>
>
>
>
>
>
> ------------------------------
>
> Message: 6
> Date: Tue, 21 Nov 2006 14:46:59 -0500
> From: "John T Lonsdale" <john@johnlonsdale.net>
> Subject: Re: [pbs] Lilies & virus
> To: "'Pacific Bulb Society'" <pbs@lists.ibiblio.org>
> Message-ID: <009801c70da5$cf72ca40$6601a8c0@XPS400>
> Content-Type: text/plain; charset=us-ascii
>
> John Bryan wrote - "It is to be noted that the plants did not show signs 
> of
> virus, just the flower size and count diminished."
>
> This is rather like saying the patient didn't show signs of HIV infection,
> his CD4 cell count just plummeted; his viral load went through the roof, 
> he
> got a bunch of opportunistic infections and suffered from Kaposi's 
> sarcoma.
>
> If reduced flower size and count aren't classic signs of viral infection 
> in
> plants then I don't know what is.
>
> Perhaps you mean that the lily didn't have a bunch of yellow streaks in 
> the
> leaves?
>
> Thanks,
>
> John T Lonsdale PhD
> 407 Edgewood Drive,
> Exton, Pennsylvania 19341, USA
>
> Home: 610 594 9232
> Cell: 484 678 9856
> Fax: 801 327 1266
>
> Visit "Edgewood" - The Lonsdale Garden at http://www.edgewoodgardens.net/
>
> USDA Zone 6b
>
>
>
>
> ------------------------------
>
> Message: 7
> Date: Mon, 01 Jan 1990 03:08:44 -0800
> From: John Bryan <johnbryan@worldnet.att.net>
> Subject: [pbs] Clonal breakdown
> To: pbs@lists.ibiblio.org
> Message-ID: <259F3A3C.2871B91C@worldnet.att.net>
> Content-Type: text/plain; charset=us-ascii
>
> Dear All:
>
> Hybrid vigor, while evident in plants raised from seed, does not last
> for ever if continued asexual reproduction of a plant is continued over
> many years. The classic example perhaps is to be found in the strawberry
> Royal Sovereign, which  just failed after many years. At one time it was
> far ahead of other cultivars, but then lost many of the qualities for
> which it was renowned. To my knowledge such loss of desired qualities
> were simply lost due to the continued asexual propagation. Just what
> happens when such does take place I do not know, but such has been
> refereed to as Clonal Breakdown. Possibly the desired arrangement and
> composition of the cells in the plant(s)  was changed.
>
> John Lonsdale asked how TC fix this. Again a definitive answer, to my
> knowledge, as not been determined, but it does work. Perhaps this method
> of propagation is taking advantage of cells that are, for want of a
> better explanation, stronger and closer to the original cells of the
> first crosses and better replicas of cells carrying the desired
> qualities.
>
> I should have mentioned the plants of Enchantment did not show any
> visible signs of virus, to all intents and purposes the plants appeared
> to be the same, except for size of flowers and bud count.
>
> Here it must be stated, those plants used for asexual propagation, were
> selected in the field, the strongest, those with good flower size and
> bud count were those selected and these plants showed no color variation
> in the foliage at all. Selecting those plants that are the most vigorous
> is an ongoing practice of good growers. When growing many hundreds of
> Dahlias, I used to tag those tubers for propagation in the field and
> they were lifted first prior to the lifting of others.
>
> John Londsale asks if reduced flower size and count are not classic
> signs of viral infection, perhaps they are, but are not such accompanied
> by other signs as well, such as changes in the foliage? Does this mean
> such changes as clonal breakdown do not exist? When examined in the 60's
> for virus, using the techniques available at that time, no virus was
> found.
>
> Rodger Whitlock almost choked on his bagel, when he read my comments
> regarding growers in the Netherlands, if you have found such poor
> practices s you describe, I hope you have reported such to all
> authorities who could challenge the practices and do something about it.
> Is this perhaps a reason why such strict regulations are now in place
> with importation of plants from overseas and which are decried by so
> many? Perhaps the USDA are correct! In any profession there are rogues,
> but firms such as Hoog and Dix, to mention but one, strive to maintain
> the highest standards in nomenclature and health of the products they
> sell. To label all growers as being, in effect, dishonest is not only
> untrue but, in my opinion a libelous statement. such as Dahlias loaded
> with nematodes. To which grower(s) are you referring?  Have you reported
> them to authorities? If not, why not? As to the selling of wild selected
> bulbs, I presume you are aware of the rule governing such and these
> rules are and have been imposed by the authorities in the Netherlands.
>
> Alani Davis asked how can one know if it is clonal breakdown and not
> environmental or pathanogenic? I do not know, but the term clonal
> breakdown was the term we used, other factors may well have played a
> part, but let us not blame virus for all such occurrences, especially
> after tests were made to see if virus was present. But as I mentioned,
> this was way back in the 60's and more recent procedures might be able
> to answer this question.
>
> The posting of Jim McKenney was interesting. I had not heard the term
> Clonal Drift before, but obviously this must be the same. jim, as
> mentioned above, steps were taken to keep the product within the
> expectations of the consumer. this is why that, during the last years I
> was with Oregon Bulb Farms, we were relying on 'strains' as such, being
> seed of crosses between established clones as were the seed parents, had
> vigor and the variation in height, color, size and number of flowers
> were between very narrow limits. Black Dragon Strain took the place of
> the clone Black Dragon, and Golden Splendor Strain took the place of the
> clone of the same name, etc.  Jim, could you explain somatic mutations?
> How do such differ from other mutations/
> Cheers and Happy Thanksgiving to all I hope your turkeys are tasty, and
> good eating and would there be clonal breakdown in such birds brought
> about by inbreeding?
>
>
> ------------------------------
>
> Message: 8
> Date: Tue, 21 Nov 2006 13:38:02 -0800
> From: Diane Whitehead <voltaire@islandnet.com>
> Subject: Re: [pbs] Clonal breakdown
> To: Pacific Bulb Society <pbs@lists.ibiblio.org>
> Message-ID: <CA623268-73B5-45D7-AE3D-16753CFFC775@islandnet.com>
> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>
>
> I have read articles on human aging that state that cells can
> duplicate themselves only a certain number of times.  I'm not sure
> what happens when this point is reached:  do they stop?  do they
> accumulate mutations?
>
> Could this limit on cell duplication also be present in plants?
>
> Diane Whitehead
>
>
> ------------------------------
>
> Message: 9
> Date: Tue, 21 Nov 2006 15:43:12 -0600
> From: "Boyce Tankersley" <btankers@chicagobotanic.org>
> Subject: Re: [pbs] Clonal breakdown
> To: "Pacific Bulb Society" <pbs@lists.ibiblio.org>
> Message-ID:
> <52857FDB394B7E45BA1F2E60D7313E2A059CC906@cbgmail.chicagobotanic.org>
> Content-Type: text/plain; charset="us-ascii"
>
> This information is from my memory so subject to error. I believe I read
> the teliospores shorten everytime a cell divides. After a number of
> years they are, in effect, down to the bare bones. It is at this stage
> that decreases in vigor and other characteristics are noticeable.
>
> Boyce Tankersley
> btankers@chicagobotanic.org
>
> -----Original Message-----
> From: pbs-bounces@lists.ibiblio.org
> [mailto:pbs-bounces@lists.ibiblio.org] On Behalf Of Diane Whitehead
> Sent: Tuesday, November 21, 2006 3:38 PM
> To: Pacific Bulb Society
> Subject: Re: [pbs] Clonal breakdown
>
>
> I have read articles on human aging that state that cells can
> duplicate themselves only a certain number of times.  I'm not sure
> what happens when this point is reached:  do they stop?  do they
> accumulate mutations?
>
> Could this limit on cell duplication also be present in plants?
>
> Diane Whitehead
> _______________________________________________
> pbs mailing list
> pbs@lists.ibiblio.org
> http://www.pacificbulbsociety.org/list.php
>
>
> ------------------------------
>
> Message: 10
> Date: Tue, 21 Nov 2006 15:58:15 -0500 (EST)
> From: eob@vqme.com
> Subject: Re: [pbs] Lilies & virus
> To: "Pacific Bulb Society" <pbs@lists.ibiblio.org>
> Message-ID: <1727.4.136.141.181.1164142695.squirrel@http://www.vqme.com/>
> Content-Type: text/plain; charset=iso-8859-1
>
> "Clonal breakdown" is an interesting term, and I do know that continued
> propagation of many plants can lead to decline in vigor, etc., but what
> does the term actually refer to? If it is actually a change in the
> genetics of the plant, then no amount of tissue culturing and "cleaning
> up" of the clone is going to change the genetics back to the original.
>
> Does anyone know what the theory is re what is actually taking place if,
> in fact, it is not removing virus. For that matter if the virus has been
> incorporated into the genes (as often happens), then how do they clean
> that up by tissue culture? Or, are the answers to these questions to
> technical for this list?
>
> Ernie O'Byrne
> Eugene, Oregon USA
>
>
>> Sender Allowed
>>
>> Way back in the 60's, the lily hybrid Enchantment, introduced by Jan de
>> Graaff's Oregon Bulb Farms, began to loose the size of flowers and the
>> bud count. <snip> This was
>> thought to be a clonal breakdown, not an unusual occurrence and I think
>> this was a correct diagnosis.
>>
> <snip>
>>
>> This might be of interest, the point being decline of a plant is not
>> always due to a virus, but continued propagation by vegetative means can
>> also cause problems. Cheers, John E. Bryan
>>
>>
>
>
>
>
> ------------------------------
>
> Message: 11
> Date: Tue, 21 Nov 2006 14:17:12 -0800 (PST)
> From: piaba <piabinha@yahoo.com>
> Subject: Re: [pbs] Neomarica - more
> To: Pacific Bulb Society <pbs@lists.ibiblio.org>
> Message-ID: <20061121221713.96187.qmail@web51902.mail.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> i was traveling with mauro in 2001 when we found and
> photographed that pic of N. glauca on the website.
> flowers are smaller than other Neo.  in that trip,
> there were also 2 other weird irids we found in MG
> state, unfort. neither one in bloom.  one had
> succulent leaves that were curvy (it could be the one
> that he has as Pseudo. recurvata on his website), and
> the other one had very thin and long but cylindrical
> leaves.  seeds of this last one germinated for me as
> very thin tufts of grass but none survived to
> adulthood.
>
> actually, when i think of it, we found so many weird
> plants in the "campos rupestres" of MG, incl. some
> weird yellow-flower bulb in the Rapateaceae family,
> Sysirinchiums, Zephyranthes, crazy Melastomataceae
> (not bulbs of course),and wonderful tuberous
> APocynaceae with gorgeous flowers.
>
> =========
> tsuh yang
>
> --- Lee Poulsen <wpoulsen@pacbell.net> wrote:
>> Mauro Peixoto has photos of the following species
>> (as well as two
>> very nice looking unnamed species):
>> Neomarica glauca
>>
> http://mpeixoto.sites.uol.com.br/iridaceae/…
>
>
>
>
> ____________________________________________________________________________________
> Sponsored Link
>
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>
> ------------------------------
>
> Message: 12
> Date: Tue, 21 Nov 2006 17:18:20 -0500
> From: "Jim McKenney" <jimmckenney@jimmckenney.com>
> Subject: Re: [pbs] Clonal breakdown
> To: "'Pacific Bulb Society'" <pbs@lists.ibiblio.org>
> Message-ID: <001501c70dba$f3ed93e0$2f01a8c0@Library>
> Content-Type: text/plain; charset="us-ascii"
>
> John Bryan asked "Jim, could you explain somatic mutations? "
>
> I'm glad you asked this, John because it gives me the chance to tie 
> together
> some disparate threads in my past postings.
>
> Somatic mutations are nothing more than what gardeners for centuries have
> called sports. In the old days, with no knowledge of genetics and cell
> division, this process must have seemed very mysterious.
>
> Somatic mutations are also the basis for my repeated assertion that the
> elements which make up a clone are not necessarily genetically uniform.
>
> There are many ways of classifying the cells in an organism. One way is to
> make the distinction between germinal cells (those which produce gametes,
> reproductive cells) and the cells which make up most of the body of the
> organism in question (somatic cells).
>
> In plants, somatic cells containing mutations might survive and continue 
> to
> divide. Not only that, but if the plant in question is one being subjected
> to intense asexual reproduction, there is always the possibility that
> entities will result which contain only the mutated cells or a majority of
> mutated cells. If the mutation in question is one which results in a 
> grossly
> visible difference, then the gardener calls it a sport and treats it as a
> new variety.
>
> On the other hand, when mutations occur in the germinal cells which 
> produce
> gametes (eggs, sperm), the results are not likely to be visible in the
> organism; however, because these cells produce gametes, such mutations can
> be passed on to the progeny which result from sexual reproduction.
>
> That is why if you hybridize with plants whose distinctive characteristics
> are the result of somatic mutations, any progeny which result will almost
> certainly show the pre-somatic mutation characteristics. For instance, if
> you cross parrot tulips with parrot tulips, chances are the resulting
> progeny will be ordinary single tulips with not a parrot tulip among them.
>
> On the other hand, if you have a plant in which a mutation has occurred in
> the germinal cells, there is a good chance that such a mutation will be
> passed on to the progeny and, subject to the usual rules of genetic
> expression, be apparent in such progeny. A simple example: plants which
> typically produce red flowers often have yellow variants which are the
> result of a relatively simple mutation in the germinal cells. If you cross
> two such yellow flowered plants, chances are good that you will get plenty
> of yellow flowered progeny rather than the typical red (assuming the 
> yellow
> is a simple recessive to the red).
>
> That's it in a nutshell. For those who want more information, go to 
> Google.
>
> Jim McKenney
> jimmckenney@jimmckenney.com
> Montgomery County, Maryland, USA, USDA zone 7
> My Virtual Maryland Garden http://www.jimmckenney.com/
>
> Webmaster Potomac Valley Chapter, NARGS
> Editor PVC Bulletin http://www.pvcnargs.org/
>
> Webmaster Potomac Lily Society http://www.potomaclilysociety.org/
>
>
>
>
>
>
>
>
>
>
> ------------------------------
>
> Message: 13
> Date: Tue, 21 Nov 2006 17:29:09 -0500
> From: "John T Lonsdale" <john@johnlonsdale.net>
> Subject: [pbs] FW:  Clonal breakdown
> To: "'Pacific Bulb Society'" <pbs@lists.ibiblio.org>
> Message-ID: <00c201c70dbc$76e39eb0$6601a8c0@XPS400>
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>
> When an organism or cell is propagated asexually for any period of time it
> inevitably picks up somatic mutations.  These are mutations in genes in
> cells other than germline cells and they are not passed on by sexual
> reproduction.  These mutations may be silent (not obvious) or cause a
> change in the phenotype (the organism looks or behaves differently).
> Somatic mutations may cause cancer or variegation, for example.  Many
> cancers are the result of the acquisition of many somatic mutations,
> each allowing the cell to escape from normal control mechanisms.  I can
> only assume that John Bryan's 'clonal breakdown' is the actually
> accumulation of multiple somatic mutations that cause the desirable
> features of a plant to be lost, or undesirable ones gained.  'Clonal
> breakdown' cannot be fixed.  In the case cited by JB he selected a
> single individual from the population with desirable (or in reality
> fewer undesirable) characteristics, put it into TC and propagated it
> thereafter.  It will still have carried forward all the somatic
> mutations it had previously acquired, and would continue to acquire new
> ones.
>
> Clonal drift is the same process as above.  It is a problem in many
> areas.  For example human cells passaged in culture many times will
> sooner rather than later start behaving differently to the cells that
> were originally isolated.  This has a big impact if those cultured cells
> are to be used in research because they no longer are representative of
> the cells that would be found in the body.
>
> Continued asexual reproduction, per se, does not cause a 'loss of
> vigor', that is pure bunkum!
>
> It is wrong to think that all viruses cause leaf streaking - infection
> can have many different symptoms or none at all that are visible.
> Humans carry many viruses that are silent for some, most or all of the
> time.
>
> One of the aging processes in cells other than stem cells is (as Boyce
> said) a gradual shortening of the telomeres (the caps at the end of
> chromosomes).  Once they get past a certain point the cell detects this
> and can become senescent or enters a pathway of programmed cell death
> (apoptosis).  In the devastating disease Progeria, which causes
> premature aging in humans, the telomeres become prematurely shortened.
>
> Thanks,
>
> J.
>
>
>
>
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> End of pbs Digest, Vol 46, Issue 26
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