Graft Hybrids Bibliography

Some of the basic facts of stock/scion influence, and the sometimes hereditary transmission of graft-induced changes, were widely known and discussed in the 19th century. Nevertheless, the neo-Mendelists flatly rejected all the available observations and research because of their faith that all heredity was due to "special materials" locked in the nucleus of the cell. They missed much that had been learned by clinging to their narrow-minded dogma.

Modern research, particularly in the fields of epigenetics, RNA interference (RNAi), "genomic shock", etc. have shed new light on the subject. Here is one example:

Plant Physiology 143(2): 1037-1043 (Feb 2007)
Cross-Species Translocation of mRNA from Host Plants into the Parasitic Plant Dodder
Jeannine K. Roney, Piyum A. Khatibi and James H. Westwood

An intriguing new paradigm in plant biology is that systemically mobile mRNAs play a role in coordinating development. In this process, specific mRNAs are loaded into the phloem transport stream for translocation to distant tissues, where they may impact on developmental processes. However, despite its potential significance for plant growth regulation, mRNA trafficking remains poorly understood and challenging to study. Here, we show that phloem-mobile mRNAs can also traffic between widely divergent species from a host to the plant parasite lespedeza dodder (Cuscuta pentagona Engelm.). Reverse transcription-polymerase chain reaction and microarray analysis were used to detect specific tomato (Lycopersicon esculentum Mill.) transcripts in dodder grown on tomato that were not present in control dodder grown on other host species. Foreign transcripts included LeGAI, which has previously been shown to be translocated in the phloem, as well as nine other transcripts not reported to be mobile. Dodders are parasitic plants that obtain resources by drawing from the phloem of a host plant and have joint plasmodesmata with host cortical cells. Although viruses are known to move between dodder and its hosts, translocation of endogenous plant mRNA has not been reported. These results point to a potentially new level of interspecies communication, and raise questions about the ability of parasites to recognize, use, and respond to transcripts acquired from their hosts.

Since phloem-mobile mRNA is translocated between parasite and host, we cannot doubt that it is also shared between scion and stock.

Plant Physiol. 1996 May; 111(1): 27–37.
Highly Branched Phenotype of the Petunia dad1-1 Mutant Is Reversed by Grafting.
C. Napoli
Environmental Horticulture, University of California, Davis, California 95616.
The recessive dad1-1 allele conditions a highly branched growth habit resulting from a proliferation of first- and second-order branches. Unlike the wild-type parent, which has lateral branching delayed until the third or fourth leaf node distal to the cotyledons, dad1-1 initiates lateral branching from each cotyledon axil. In addition to initiating lateral branching sooner than the wild type, dad1-1 sustains branching through more nodes on the main shoot axis than the wild type. In keeping with a propensity for branching at basal nodes, dad1-1 produces second-order branches at the proximal-most nodes on first-order branches and small shoots from accessory buds at basal nodes on the main shoot axis. Additional traits associated with the mutation are late flowering, adventitious root formation, shortened internodes, and mild leaf chlorosis. Graft studies show that a dad1-1 scion, when grafted onto wild-type stock, is converted to a phenotype resembling the wild type. Furthermore, a small wild-type interstock fragment inserted between a mutant root stock and a mutant scion is sufficient to convert the dad1-1 scion from mutant to a near wild-type appearance. The recessive dad1-1 phenotype combines traits associated with cytokinin overexpression, auxin overexpression, and gibberellin limitation, which suggests a complex interaction of hormones in establishing the mutant phenotype.

Genetics Today: Proceedings of the XI International Congress of Genetics (1963) p. 218-219
13.29. Alterations of Hereditary Traits in Solanum melongena induced by Grafts with Solanum nigrum.
C. C. Mathon, M. Stroun and J. Stroun (Poitiers, France).
    The pupil plant is the "white round" eggplant, and the mentor plant a strain of black nightshade.
    The pupil is the epibiota and the mentor the hypobiota. Controls are represented by homografts of the pupil variety. The technical conditions are as follows: for the pupil plant: of a less advanced age than the mentor-plant and total removal of leaves all along evolution; for the mentor plant: maintenance of leaves and absence of flower-buds which are cut off as soon as they appear.
    The influence of the black nightshade mentor on the "white round" eggplant pupil became apparent only in the offsprings of the third generation of grafts. Out of 7 symbionts carrying fruit at the third generation of grafts, 2 offer in their descendency an alteration that so far prevailed down to F3: the colour of the stem is slightly purple. These anthocyanins are extremely thermolabile.
    Chromatographic analyses made so far show the Rf of anthocyanins to be different from those found in the black nightshade.
    In these interspecific grafts we did not observe any mentor-oriented alterations. However, the new traits that have become apparent in the descendency of both modified plants are of the same type, therefore, the influence of the mentor may be assumed to work in both pupils in the same direction.

Article to be published in: Comptes rendus des séances de la Société de Biologie de France, 1963; Archives des Sciences de Genève, 1963.

Genetics Today: Proceedings of the XI International Congress of Genetics (1963) p. 219
13.30. Alteration of Traits obtained in Solanum melongena as a Consequence of Inter-variety Grafts.
M. Stroun and J. Stroun (Poitiers, France).
     The "Early Violet" variety was used as mentor-plant and the "White Round" variety as pupil-plant. The mentor-epibiont / pupil-hypobiont grafting procedure is applied as follows: the pupil-plant is totally rid of its leaves all along its development, whereas the mentor-plant retains its foliage but is rid of its flower buds which are cut off. The graft is repeated on each new generation until alterations appear. Sexual crossbreeds were also made "White Round" ♀ x "Early Violet" ♂.
    The 19 homografted "White Round"/"White Round" controls did not show any alterations.
    The influence of the mentor-plant "Early Violet" on the pupil variety "White Round" appeared only at the third generation of grafts. Out of 24 fruit-bearing symbionts, 9 presented various alterations in fruit and stem colour, shape of fruit, or in a trait of the stamen. These alterations resemble the traits of the mentor variety. They are found again in the sexual descendants of the modified symbionts, studied so far down to F2. They often differ from the characteristics conveyed by sexual crossings between the two varieties used. There is a disjunction in F1, only part of the alterations being transmitted. Futhermore, new traits appear on certain plants. To all appearances therefore, grafts, as practised by the authors, seem to influence the hereditary traits of a given variety.

C. R. Acad. Sci. 255, 561-563, 1962; Arch. Sci. Genéve, 1963, to be published.

Also: Epigenetics, Gene Silencing, RNAi

Stock/Scion Influence