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' * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Ask me about the worldwide Mediterannean gardening discussion group

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