Heredity and its Variability
T. D. Lysenko

translated from the Russian by Theodosius Dobzhansky (1946)

Vegetative Hybrids

Beginning with I. V. Michurin himself, Michurinists have found methods of mass production of vegetative hybrids. But the Mendelian-Morganian geneticists denied for a long time certain instances of vegetative hybrids which had long been known. Examples of vegetative hybrids, such as Cytisus Adami, hybrids of Crataegus with Mespilus and certain others had been quoted by Darwin. But the geneticists regarded all these examples not as hybrids but as so-called chimaeras, in which the tissues of the different breeds have grown together vegetatively but have not fused biologically. When the Michurinists in recent years found a method of mass production of vegetative hybrids which behave like the usual sexual hybrids when propagated by seeds, the geneticists were unable to raise objections They simply ignored these facts, from time to time calling them experimental errors. But they do not undertake to repeat these investigations because they are afraid to obtain vegetative hybrids.

Variability in grafting trees of both old, well established, and of young varieties. Reference is frequently made to the well known phenomenon that grafting different varieties of fruit trees, which in practice reproduce only by this method, onto most diverse stocks does not change the hereditary properties of the grafted varieties. One must, however, not forget that these varieties are already established, having passed the developmental stages. They can not, therefore, be altered in those properties and qualities which have accomplished their development long before grafting. The result is different when young, incompletely established, varieties of fruit trees are grafted. As a rule they change the entire process of their further formation owing to the grafting.

One must know that the entire process of the development of plant organisms, for example the annual cereal crops, consists of processes, steps, or phases which are separate, successively connected, and which successively pass into each other. It is rather easy to prove experimentally that the winter cereals for example can not pass through the stages succeeding the stage of vernalization without first passing through that stage. Moreover, after passing through the stage of vernalization, or through the light stage which follows, the plants will not go through these stages again, regardless of how much they may multiply vegetatively, that is, through tissues which have already passed the vernalization or the light stages.

It becomes understandable on this basis that, in practice, the old, established, varieties of fruit trees can and must be reproduced through grafting, without danger of losing their good hereditary properties. By contrast, organisms which have not passed the stages of establishment will always alter their development compared with the plants which retain their own roots, i.e., the not‑grafted ones.

Any living particle possesses the property of heredity. Vegetative hybridization is important not only in practice but also has a considerable theoretical interest for a correct understanding of the most important phenomenon of living nature, namely heredity. The union of the grafted plants gives rise to an organism of a different breed, namely a combination of the breeds of the scion and the stock. Among the progeny obtained from the seeds of the scion and of the stock there will be some plants which will possess the properties not only of the breed producing the seeds but also of that with which the former was united through grafting.

It is well known that an exchange of plastic substances takes place between the scion and the stock. The scion and the stock can not exchange either the chromosomes of the cell nuclei or the cytoplasm. And yet the hereditary properties can be transmitted from the stock to the scion and vice versa. Hence, the plastic substances elaborated in the scion and in the stock possess the properties of the breed, i.e., the heredity. They possess the properties of the breed in which they are elaborated.

The numerous facts of vegetative hybrids obtained in recent years clearly show that the very basis of the theory of the Mendelians and Morganians is wrong. According to this theory, heredity is confined only to some special substance, differing from the usual body and concentrated in the chromosomes of the cell nucleus. But any claim that the property of heredity is connected with some special substance is wrong, regardless of what part of the body or the cell in which this substance may be located. Any living body part, and even a droplet (if the body is liquid) possesses the property of heredity, i.e., the property of demanding relatively determined conditions for its life, growth, and development.

Experimental production of vegetative hybrids. In order to obtain experimental vegetative hybrids and thus to prove that vegetative hybridization is an alteration of the breed, a mixing of two breeds, it is most convenient to use annual herbs as experimental materials. Good materials are, for example, tomato varieties. Two varieties which differ strikingly in appearance must be selected, such as varieties having red or yellow or white ripe fruits, for example. Or else the varieties may be strikingly different in having round versus clearly elongated fruits, or non-dissected leaves resembling those of the potato plant versus the dissected, usual, tomato leaves. One may use varieties differing in the number of chambers in the fruit—two-chambered and many-chambered ones. One must select the character the alteration of which is to be followed. Thus, one may set himself the following task: to alter the white color of the ripe fruits of the tomato variety "Albino" into a red color, and to accomplish this not through a sexual crossing with a red-fruited variety, but through grafting a scion of a young "Albino" organism onto the stock of a more mature plant of the red-fruited variety. The younger the plant the characters of which we wish to change, the more successful will be the experiment. By contrast, the plants from which it is desired to obtain a certain property or character must be older; it is best if they are middle aged. It is desirable to make at least 10-20 grafts. They are made rather easily. The work is not time consuming. After the graft has been accomplished it is desirable to remove the leaves as frequently as possible from the branches of the variety which is to be changed. In the variety from which a certain character is to be transmitted, as many as possible of the leaves and branches should be preserved. For greater precision in the experiment the flower buds on the scion may be isolated in a cheesecloth bag during the flowering period, in order to protect them from the transfer of foreign pollen by insects (even though tomatoes are self-fertilized). In some cases the fruits on the scion, which according to their nature are white when mature, will be colored in various degrees. When the fruits are mature, their seeds, especially the seeds of the red ones if such are produced, must be taken and sown the next year. As a rule, some plants in such a planting will already have red fruits when ripe. This coloration is transmitted through the plastic substances of the grafted component of the preceding generation. Similar results can be observed with any character. Thus, the seed progenies of the two-chambered variety of tomato grafted onto the many-chambered variety were many-chambered even without repeated graftings. The prostrate variety grafted onto an erect one transmits the erect habit through a considerable number of seeds. The leaf shape, the length of the period of vegetative growth (early and late maturity), fruit size, and a series of other characters and properties have been transmitted through seed progenies in the experiments of Michurinists, scientific workers, and practical breeders.

Instances of failure to obtain graft hybrids. The selectivity of living conditions by organic processes. The problem arises: why are hybrid properties not shown by all the seeds formed on a grafted branch? Why sometimes, although rarely, can no hybrid plants at all be found? A possible answer is as follows. Hybrids are not obtained in all instances because, as stated above, the various processes taking place in each variety preferentially select their own living conditions, their own food. The plastic substances formed by one variety are to a certain extent obviously unsuitable for feeding the scion of a different variety. The scion may not assimilate them at all, or it will assimilate only the substances which happen to fit its requirements, while it will endeavor to get all other substances from the leaves or other parts of its own variety. This explains why as few leaves as possible should be left in the component the breed of which is to be changed.

The frequency of obtaining vegetative hybrids will depend upon the ability of the experimenter to force the scion to assimilate as many as possible of the nutrient materials prepared by the variety the properties of which are to be transmitted to the scion. The experlmenter must overcome the "lack of desire" (the selectivity) the part of the scion to include these materials in the building of its body.

As a rule, the experiments suggested by us will give a certain percentage of success. After making such experiments any geneticist still believing in the correctness of the foundations of Mendelism will see not only the incorrectness of this theory but its harmfulness in practical application of breeding and of seed management.

It must be emphasized that even abroad [i.e., outside the Soviet Union] genetic theory is not being used at all in the agricultural practice of seed management and selection. By means of observations and experiments which have lasted decades and centuries, good seed management practice and stock breeding practice has evolved methods and techniques for improvement of old plant varieties and animal breeds, as well as for obtaining new ones. Abroad, the science of genetics is torn from agricultural practice, which explains why it was able to develop in the wrong direction for many years.

The analogies between vegetative and sexual hybridization. Vegetative hybrids do not differ in principle from those obtained sexually. Any character can be transmitted from one breed to another through grafting as well as sexually. This conclusion is based on a large body of facts on the vegetative transmission of characters of potato, tomato, and a series of other plants with which the scientific collective directed by the writer has been operating. The behavior of vegetative hybrids in succeeding generations is likewise analogous to that of sexual hybrids. The hybrid properties are retained in the succeeding generations of seeds of vegetative hybrids—tomatoes, for example. The so-called phenomenon of segregation which often occurs in the offspring of sexual crosses takes place also in the vegetative hybrids propagated by seeds. In the latter, the so-called vegetative segregation, when the body of the organism is a mosaic of certain characters, is, however, much more frequent and more pronounced.

For purposes of demonstration, the example of grafting scions of tomatoes with white fruits onto the red-fruited ones is interesting. Seeds taken from the fruits on a branch of the white-fruited tomato gave plants in the first seed generation most of which developed red fruits. In a minority of plants the fruits were white or slightly reddish. In the second seed generation the progeny of the plants with white fruits were mostly white fruited. Only a few plants gave more or less reddish fruits; The progeny of the red-fruited plants consisted of a majority of red-fruited plants, but approximately 20-30% of the plants had white fruits. In general, the variation is as great as that observed in the experiments on sexual hybrids of analogous varieties of tomatoes.

Particularly interesting is the behavior of the third seed generation which was sown in 1942 at Frunze (Kirghiz SSR) by Com. I. E. Glushchenko, a research fellow of the Institute of Genetics of the Academy of Sciences of USSR. The seeds of the second generation were taken from the field of the Moscow Institute. In some of the plants the fruits on some branches were red (rose colored), and on others were white. There were several dozen of such plants. It is conjectured that this property may become fixed. One may have a form of tomatoes giving white, red, and rose colored ripe fruits on the same bush.

Plasticity of vegetative hybrids. Vegetative hybrids deserve particular attention in studies of so-called unstable heredity. They are a very plastic material for further building up of new varieties through the influence of growing conditions. Thus, a tomato variety "Best of All" grafted on a nightshade (a weed) gave changes in a series of characters. A vegetative hybrid has been obtained. Not one of the characteristics of the tomato variety "Best of All" was preserved intact. Com. A. A. Avakian selected plants which when propagated by seeds give fruits with much improved taste qualities. The fruit shape of the tomato variety used in grafting has also, changed. Forms derived from the vegetative hybrids acquired' first, the early maturity of the nightshade, and then, influenced by growing conditions, became even more early. The resulting cultivated tomatoes are the earliest of all known to us. When seeds were sown outdoors in the soil in early May at the experimental base of the V. I. Lenin All-Union Academy of Agricultural Sciences at Gorki-Leninskie (near Moscow), they gave in 1941 and 1942 a good maturation of fruits before the autumn frosts. In many cases vegetative hybridization has a high practical value for the improvement of different plant varieties by breeding, as well as for adding certain properties to the old, already existing varieties of annual plants.

Transmutation of dead elements into living ones through forced assimilation. The example of vegetative hybridization shows clearly, and hence helps in the understanding of, one of the most important biological phenomena, namely that the living conditions, the conditions of the external environment, become internal conditions if they are assimilated and included within the living body as integral parts of the latter. For example, if a given plant body assimilates, perforce, certain elements of the soil solution which it receives for the first time, these elements become biochemically included in the body, and now become necessary for the growth and the development of the altered body.

To explain the above statement let us discuss the fact of transformation through grafting of the white-fruited tomato variety into the red-fruited variety. In accordance with its heredity, the grafted branch of the white-fruited variety requires certain food elements in proper form which are used for various developmental processes, including the formation of fruits and seeds. If such food conditions are available, the grafted scion will develop according to its nature, its heredity. If the necessary food is deficient, the scion will build the less important organs and characters from less suitable plastic substances. The food which is most suitable for the given breed will be expended for the more important organs and characters, such as all the processes which lead to the formation of sex cells. The leaves on the grafted branches of the white-fruited variety must be removed in order to force these branches to build their bodies from the food, the plastic substances, formed by the roots, stems, and leaves of the red-fruited component. It goes without saying that if certain substances are completely foreign and unacceptable to the white-fruited variety, and no acceptable ones are available, the scion will die of starvation. But if these substances can be assimilated despite being not exactly suited to the requirements of the scion, then a body will be built with properties different from those of the body of the usual white-fruited variety. Furthermore, this new body will resemble to a certain extent the variety which formed the plastic substances assimilated. However, the new body will differ considerably from that of the red-fruited variety. The white-fruited variety has assimilated the plastic substances of the red-fruited one in a manner different from the latter. Each variety builds its body in its own way. This example shows that the living body biologically changes itself when it assimilates various foods. The changes result in acquisition of require ments of the conditions assimilated by the body.

In experiments on vegetative hybridization the scion receives food from the branches and roots of the stock. The scion lacks roots, and it lacks a majority of leaves, because the latter are removed artificially. A plant normally receives food from the surrounding non-living environment. The food elements from the surrounding environment are taken selectively. Only that which is suitable to the nature, the heredity, of the given organism is selected. But if suitable conditions are absent, the organism is frequently forced, as in the case of vegetative hybridization, to assimilate more or less unsuitable conditions: hence, a different composition of the body. The latter will now demand for its growth and development the conditions which it originally assimilated of necessity.

The seeds of vegetative hybrids obtained on the scion and sown into the soil will select from the surrounding environment the conditions which are, in the last analysis, necessary for building the body of the given organism. The latter, however, is now similar to that which arose for the first time through a forced assimilation of unsuitable conditions in the graft. Thus if the scion was forced to assimilate the plastic substances from which, as a result of a series of biochemical transformations, red tomato fruits are obtained, then the seeds from these fruits, when sown, will be inclined to select from the external environment all those conditions which, after many regular transformations, will give ripe fruits of a red color.

The plastic substances of the stock are an external element, food, with respect to the scion. Yet, these substances become, through assimilation, an integral part of the scion and alter its hereditary properties.

In a similar manner, according to our conception, the elements of the non-living nature from the environment which surrounds the plant are transformed into integral parts of the living body through a frequently forced assimilation, become living elements, and acquire the property of heredity. The developing living body will in future generations require these external conditions for the reproduction of its like.

The new food elements become necessary as a result of the processes which took place in the preceding generations because of the inclusion within the living body of a new element of the external environment. The dead elements cease to be what they were not only in appearance but also in a strict chemical sense when they are assimilated by a living body. They acquire an intense biochemical affinity, an attraction, toward those forms of the external elements which they themselves possessed before being assimilated by the living body and transformed into a given living form.

A large volume of experimental evidence has accumulated to prove the possibility of a directed alteration of the heredity of plant organisms through proper influences of the living conditions, of the external environment. To science, vegetative hybrids are a kind of an intermediate step, a transition, from changing the heredity of plant organisms through crossing, to changing it through the influence of living conditions.

The theoretical importance of controlling the process of vegetative hybridization is self evident. These hybrids clearly prove that the heredity of plant organisms may be altered by altered nutrition. Furthermore, the alterations are specific. Thus, the influence of the plastic substances of the red-fruited variety of tomatoes changes the white-fruited variety into a red-fruited one. The influence of the plastic substances of the tomato variety with leaves resembling those of the potato plant changes the variety with dissected leaves into one with potato-like ones, etc.

It is apparent that in Lysenko's view, heredity is a property of Life. To westerners, however, Life is regarded as a property or consequence of heredity. The DNA code has been called the "language of Life" as though a chromosome might summon forth a life form, when in fact a chromosome is nothing but dead matter without an existing organism to interpret it.

Most of what Lysenko claimed in the above article has been verified repeatedly by researchers around the world. Frankel (1956, 1962) demonstrated the graft-transmission of cytoplasmic male sterility in Petunia. Rick (1959) used Frankel's male sterile petunia in an attempt to induce male sterility in tomatoes, but failed—an example of the "selectivity" mentioned by Lysenko. Taller, etal. (1998, 1999) found multiple hereditary changes in grafted peppers (Capsicum annuum), precisely as Lysenko described in tomatoes.

Laburnocytisus Adami is a chimera, but some of seedlings raised from it by Herbert and Darwin were not "pure" as expected, even though the species cannot form sexual hybrids. According to Darwin (1897), "Two seedlings raised by Mr. Herbert from such seed (Journal of Hort. Soc. volume 2 1847 page 100.) exhibited a purple tinge on the stalks of their flowers; but several seedlings raised by myself resembled in every character the common laburnum, with the exception that some of them had remarkably long racemes."

Recent research has revealed that many "mutant" traits involve gene silencing rather than structural changes to the molecular gene. In some cases the silencing involves a transportable substance—presumably a strand of RNA carried by a protein. This substance can move from cell to cell, and has been shown to cross a graft-union (Matzke, et al. 1995).

More recently, Johnsen et al. (2003) have shown that ambient temperature during the development of Norway spruce embryos can influence the vegetative period and hardiness of the trees grown from them. This, of course, is a direct influence of external conditions on the expressed "heredity" of trees.

Drawing an analogy to computers, Morgan-Mendelists were concerned only with the hardware of heredity, Miehurinists (and Naudinists) with the software as well. Chromosomes ordinarily do not move from cell to cell, but strands of RNA may do so. If the differences between stock and scion are epigenetic rather than genetic, RNA may transmit the state (silenced or active) of specific genes from one tissue to another, even (in some cases) where the stock and scion are of different genera.

The technique of removing leaves from the scion makes the scion more dependent on the stock for nutrition. Presumably the RNA-protein complex is carried along with the carbohydrates.

As for the transmutation of dead elements, this appears to be literally true. According to Meagher, "evolutionary studies have shown that the mechanism for metal tolerance is uptake, not exclusion, such that metal-tolerant genotypes are also metal accumulators." Furthermore, "metal-tolerant plants do not compete well in noncontaminated sites". The plants may not require the metals to live, but certainly benefit from their presence.