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Old Posts are Great Reading


Hosta Scholars,

We are not finished with our discussion on Chimeras and their causes (
and probably never will be finished because there is always something
new to learn). I want to share with you an old post from Dr.
Marcotrigiano of about two years ago. I am sure he would not mind you
reading his words.

I had written to him on the U of Minn tc listserv which had more than a
thousand member participants at the time to ask his opinion on Hosta
Chimeras, especially mosaic streakies we all are interested in as
breeding pod parents. He wrote the following about two years ago...it is
still current today: I suggest you read this post several times. If you
don't understand it, then go back later and try again. It contains the
conventional wisdom we have been talking about during the last five or
six weeks. Discover it for yourself and it will stick!

Jim Hawes

//////////////////////////////////////////////////////////////////////

Subject:    Re: Chimeras?
   Date:
        Thu, 18 Mar 1999 13:37:51 -0500 (EST)
   From:
        Michael Marcotrigiano <marcotrigiano@pssci.umass.edu>
     To:
        hawesj@gcnet.net

Jim: I am currently off the tc list (too much email these days) so this,
I
think, will go to you only. If you want you can edit it and send it to
the
list since they probably got your original query.

At 12:36 PM 3/17/99 -0500, you wrote:
>TCers:
>
>After a study type read (four times) of Dr. Marcotrigiano's Article in
>Hort Science Vol. 32(5), August 1997, entitled "Chimeras and
>Variegation: Patterns of Deceit", I am convinced that Dr Marcotrigiano
>is one of the leading authorities on Chimeras. I also note that his
>article made no reference to chimeras in Hostas or micropropagation of
>Hostas. This Genus is now the most popular shade garden perennial in
>American gardens. Since it is notoriously slow using  conventional
>propagation methods, its recent popularity is attributed largely to the

>handful of commercial tc labs who have rapidly propagated the hundreds
>of new cultivars recently appearing on the market.
>
>Also because of the high incidence of chimeral and other type bud
sports
>in the Genus, even more new cultivars are appearing on the scene daily.

>Among them are chimeral forms that are known as "streaked", unstable,
>striated types. These appear as longitudinal, alternating green/white
or
>green/yellow patterns of L1 and L2 tissue in leaves. They are highly
>prized as "breeding pod parent plants" because of their ability to
>produce a high percentage of variegated seedlings.
>
>My inquiry to Dr. Marcotrigiano, addressed openly to the plant tc
>lineserve to benefit the entire readership is, COULD YOU DESCRIBE THE
>CAUSAL FACTORS for these unique, morphological variants found both in
>gardens and in tc labs?

It's difficult to say since many mutants with the same type of
variegation
have different genetic mechanisms controlling the phenotype. In general
streaked and striated leaves represent unsorted plastid mutants where
some
cells have white plastids, some green, and some mixed. The mixed keep
sorting giving a pattern of blotches or streaks. The mutation is in the
plastid not the nucleus. In maternally inherited species the streaked
plants
produce some eggs which have normal and defective proplastids and can
give
rise to a proportion of variegated seedlings. If your variegated
seedlings
sort out to Mendelian ratios (e.g 3:1) I would not expect my above
explanation but rather a nuclear gene causing plastid destruction as in
japonica 1 striping of maize.

 They have been called by some in the scientific
>literature , mosaic type variegation plants ,suggesting they may not be

>chimeras.

Mosaic types vs. chimeras can be a matter of semantics. To me a chimera
is a
mosaic where the mutant and non-mutant cells coexist in the shoot apical

meristem and continue to give rise to mosaic organs.

 They appear to me to be chimeras, since they are streaked when
>they are juvenile but they (new divisions from rhizomes) readily change

>to mericlinal and periclinal chimeral forms as well as monocolored
forms
>when they mature. Could you comment please to allow a tc lab operator
to
>benefit by a better understanding of morphological and histological
>changes that may be occurring in these bud sports when tc'ing hostas?

The ONLY way to assure that a stable marginal type of chimeral leaf
pattern
is maintained is through the recovery of plants from preformed buds in
the
leaf axils. Adventitious shoots can be non-chimeral, totally white or
green.
Or some new types may appear. With very rapid proliferation even buds in
the
leaf axil can divide very rapidly, become smaller and smaller and
therefore
be less stable. So, the propagation of stable periclinal chimeras in
tissue
culture is difficult at best.  The streaked kinds where cells may be
green,
white, or mixed plastid should give rise to many streaked plants from
culture. But remember, TC results in rapid proliferation so once
something
goes wrong (or right) it will result in many cultures with the same
type.

Hope this helps. Since I am off the TC listserv for awhile anyone
wishing to
discuss this further should email me privately at
marcotrigiano@pssci.umass.edu

>Thank You.

You are welcome
>
>Jim Hawes
>Potomack Tree Farm
>hawesj@gcnet.net
>
>
*************************************************************
Michael Marcotrigiano (email:  marcotrigiano@pssci.umass.edu)
Professor
Rm 211 French Hall
Dept. of Plant and Soil Sciences
Univ of Massachusetts
Amherst, MA 01003  USA
------------------------------------
voice: 413-545-5227
fax: 413-545-3075 att: Michael Marcotrigiano




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