Graft-chimaera

In horticulture, a graft-chimaera may arise in grafting at the point of contact between rootstock and scion and will have properties intermediate to those of its "parents". A graft-chimaera is not a true hybrid but a mixture of cells, each with the genotype of one of its "parents": it is a chimaera. Hence, the once widely used term "graft-hybrid" is not descriptive; it is now frowned upon.

Propagation is by cloning only. In practice graft-chimaeras are not noted for their stability and may easily revert back to one of the "parents".

Nomenclature

Article 21 of the "ICNCP" stipulates that a graft-chimaera can be indicated either by
* a formula: the names of both "parents", in alphabetical order, joined by the plus sign "+":: "Crataegus" + "Mespilus"
* a name:
** if the "parents" belong to different genera a name may be formed by joining part of one generic name to the whole of the other generic name. This name must not be identical to a generic name published under the "ICBN". For example +"Crataegomespilus" is the name for the graft-chimaera which may also be indicated by the formula "Crataegus" + "Mespilus". This name is clearly different from ×"Crataemespilus", the name under the "ICBN" for the true hybrid between "Crataegus" and "Mespilus", which can also be designated by the formula "Crataegus" × "Mespilus".
** if both "parents" belong to the same genus the graft-chimaera may be given a cultivar name. For example "Syringa" 'Correlata' is a graft-chimaera involving "Syringa vulgaris" (common lilac) and "Syringa" ×"chinensis" (Rouen lilac, which is itself a hybrid between "S. vulgaris" and "S. laciniata"). No plus sign is used, because both "parents" belong to the genus "Syringa".

A graft-chimaera cannot have a species name, because it is simultaneously two species. Although +"Laburnocytisus" 'Adamii', for example, is sometimes seen written as if it were a species (+"Laburnocytisus adamii"), this is incorrect.

Graft Hybrids in Darwin's works

Charles Darwin [http://www.darwin200.nl/vartn10h/chap11.html «The Variation of Animals and Plants Under Domestication»] , 1868 г.:

I will therefore give all the facts which I have been able to collect on the formation of hybrids between distinct species or varieties, without the intervention of the sexual organs. For if, as I am now convinced, this is possible, it is a most important fact, which will sooner or later change the views held by physiologists with respect to sexual reproduction. A sufficient body of facts will afterwards be adduced, showing that the segregation or separation of the characters of the two parent-forms by bud-variation, as in the case of Cytisus adami, is not an unusual though a striking phenomenon. We shall further see that a whole bud may thus revert, or only half, or some smaller segment.

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