In Vitro Cell.Dev.Biol.-Plant 45, 758 (2009)
Adventitious shoot formation in decapitated dicotyledonous seedlings starts with
regeneration of abnormal leaves from cells not located in a shoot apical meristem

Sampath Amutha, Krishnan Kathiravan, Sima Singer, Liana Jashi, Ilan Shomer, Benjamin Steinitz & Victor Gaba

Regeneration of new shoots in plant tissue culture is often associated with appearance of abnormally shaped leaves. We used the adventitious shoot regeneration response induced by decapitation (removal of all preformed shoot apical meristems, leaving a single cotyledon) of greenhouse-grown cotyledon-stage seedlings to test the hypothesis that such abnormal leaf formation is a normal regeneration progression following wounding and is not conditioned by tissue culture. To understand why shoot regeneration starts with defective organogenesis, the regeneration response was characterized by morphology and scanning electron and light microscopy in decapitated cotyledon-stage Cucurbita pepo seedlings. Several leaf primordia were observed to regenerate prior to differentiation of a de novo shoot apical meristem from dividing cells on the wound surface. Early regenerating primordia have a greatly distorted structure with dramatically altered dorsoventrality. Aberrant leaf morphogenesis in C. pepo gradually disappears as leaves eventually originate from a de novo adventitious shoot apical meristem, recovering normal phyllotaxis. Similarly, following comparable decapitation of seedlings from a number of families (Chenopodiaceae, Compositae, Convolvulaceae, Cucurbitaceae, Cruciferae, Fabaceae, Malvaceae, Papaveraceae, and Solanaceae) of several dicotyledonous clades (Ranunculales, Caryophyllales, Asterids, and Rosids), stems are regenerated bearing abnormal leaves; the normal leaf shape is gradually recovered. Some of the transient leaf developmental defects observed are similar to responses to mutations in leaf shape or shoot apical meristem function. Many species temporarily express this leaf development pathway, which is manifest in exceptional circumstances such as during recovery from excision of all preformed shoot meristems of a seedling.

Vegetative Selection

This reminded me of something I read about an attempt at a vegetative of Tomato and Cyphomandra.

D. D. Brezhnev: Wide Hybridization in Vegetable Breeding (1960)
N. V. Tsitsin, F. D. Kryzhanovskii, E. V. Ivanovskaya, and M. Z. Nazarova obtained a tomato–Cyphomandra hybrid. It had been found impossible to cross these genera previously. It was decided to produce hybrids vegetatively. In this vegetative hybridization, the scion was systematically deprived of its leaves and, as a result, a series of morphological and physiological modifications appeared. All these modifications were fully transmitted to the progeny. In the third generation derived from Cyphomandra stock grafted with the tomato variety Bizon, one plant of an intermediate type was obtained. Its seed was fully sound. From 123 seedlings produced, only one plant resembled Cyphomandra. Thus the first intergeneric hybrid was obtained.

I wonder whether the already abnormal forms of the adventitious shoots might be influenced (directed) by chemical influences (RNAi ?) nuddging the regenerating promordia into forms normal to the stock stock. The fact that these shoots are not perfectly normal from the start suggests that the form of the leaf is not entirely intrinsic to the developing leaves. Altering the expressions of genes to change the form of leaves in the tomato offspring may not fit one's notion of "hybrids", but it might well provoke Genetic Transilience, allowing other variations to follow.

Then again, it might be possible to induce specific changes if the stock already activates specific genes in the scion.

Plant Mol Biol. 2003 Nov; 53(4): 493-511.
Rootstock effects on gene expression patterns in apple tree scions.
Jensen PJ, Rytter J, Detwiler EA, Travis JW, McNellis TW
For example, the M.7 EMLA rootstock is semi-dwarfing and reduces the susceptibility of the scion to Erwinia amylovora, the causal agent of fire blight disease. ... scions grafted to the M.7 EMLA rootstock showed increased stress-related gene expression.

Adventitious Shoots