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  Chimeric variegation and its pitfalls
From: "Sean O'Hara" <SAOUC at UCCMVSA.UCOP.EDU> on 1997.11.22 at 18:07:36(1647)
Fellow Varoidophiles -

All this talk of variegated plants and their instability is not a
new topic on internet forums - it comes up routinely where
variegated plants are discussed. Among plantspersons I know, there
are often strong views about what causes variegation in plants,
usually tending towards the virus factor. I know little about viral
variegation myself, but I have read a bit on the chimeric type,
which I find quite interesting. My own observations indicate to me
that most variegation in plants, especially those that tend to
revert or 'come and go', is of this type.

Chimeric variegation is due to a partial mutation IN SOME LAYERS of
the plants meristem (growing tip) tissue. Even within one layer,
the mutation may only be towards one side or only effecting a
percentage of the total tissue layer. This phenomenon takes its
name from the mythic beast, the Chimera, who was made up of
different parts of various animals, alluding to the coexistence of
different tissue in the same plant. Sometimes these mutations are
visible, as with variegation, or more subtly as with contorted
plants (one side of the stem grows faster than the other, causing
the twisting of the growth). Sometimes the mutation is not visible
in any way, but may still represent a different tissue type only
detectable by chemical analysis.

As the tissue grows, only some portions of these layers are
effected. As tht tip elongates, or new stems arise, the ratio of
normal to mutated tissue can change and alter sides, etc. This
causes the random 'splashing' and is the least stable type of
variegation. Other chimeric variegation can envolve entire selected
layers of tissue, creating a more regular variegation pattern (e.g.
pale stems/petioles and central 'flame' variegation on each leaf, as
both these areas arise from the same meristem layer).

While some chimeric variegation can be more stable that others, all
might revert at some point due to various factors (such as those
discussed - stress, light change, fertilization, etc.) which can
change the grown rate of the meristem and alter the mix of regular
and mutant tissue. They can also revert without any apparent
stimulus due to the happenstance of growth taking place in an area
free of mutation, usually much more vigorous and therefore likely to
quickly take over the plant. Careful monitoring of these plants and
selection of the best variegated parts (along with removal of
reversions to non-variegated) is the means to sustain the clone.
Often, new clones can arise from these unstable situations, or more
stable forms might be selected. It is worth observing.

Sean A. O'Hara sean.ohara@ucop.edu
710 Jean Street (510) 987-0577
Oakland, California 94610-1459 h o r t u l u s a p t u s
U.S.A. 'a garden suited to its purpose'
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