The Situation in Biological Science, 78-86 (1948)
S. I. Isayev
Head of the Department of Fruit and Vegetable Breeding, Saratov Agricultural Institute

The remarkable development of the theory and practice of selection in the U.S.S.R. is intimately associated with the name of the eminent Soviet scientist, Ivan Vladimirovich Michurin—the founder of the Soviet school of creative Darwinism.

Darwin discovered the law of development of the organic world, and gave an on the whole correct conception of the evolution of the living beings which inhabited and inhabit the earth. But Darwin did not give any concrete indication as to how evolution can be directed so as deliberately to create new plant forms useful to man. This task of creatively developing Darwinism fell to I. V. Michurin. The Michurin doctrine is a new stage in the development of materialist biology.

"We know from science," I. V. Michurin wrote, "that all the countless species and varieties of living organisms arose by a very slow process of evolution, extending over tens and millions of years, from an original unicellular organism…

"But it is possible, with man's intervention, to force any form of animal or plant to change more quickly and in a direction desirable to man. There opens before man a broad field of activity of the greatest value to him, namely, the improvement and creation of new forms of horticultural, medicinal and industrial plants."

Michurin provided a firm theoretical foundation for selection, whose tasks he thus defined so broadly and profoundly, and elaborated methods of directing the form-building process in order deliberately to create new forms of plants. Michurin showed that the individual development of plants may be directed, and that their hereditary nature may be modified and valuable varieties created for socialist agriculture.

It was in Soviet times that Michurin, inspired by the interest and solicitude of the great scientists and friends of science, Lenin and Stalin, produced the best of his new, varieties and summed up the conclusions of his sixty years of creative activity in works of capital importance.

After Michurin's death, T. D. Lysenko continued his work in biological science. He developed Michurin's theory and extended it to all plants, as a general biological theory of heredity and its variability. Lysenko defended Michurin's theory against the attacks and misrepresentations of the Mendelist-Morganists. He directed and united us, Michurinists, in elaborating and constructively applying Michurin's advanced theory. And now the triumph of the Michurin theory is becoming more and more apparent, for it has armed us with the best, the most rapid and effective methods of transforming the vegetable kingdom for the benefit of the working people.

In defiance of the false and essentially idealistic conceptions of the Mendel-Morgan genetics, Michurin established a correct, dialectical-materialistic approach to the study of the phenomena o heredity and variation. He looked upon the plant organism from the angle of its process of development and profound interaction with its environment.

I. V. Michurin laid the foundation of the theory of individual development of the plant organism. He established that the seedling of a cultivated fruit tree undergoes a series of changes in the course of its individual development. Not only does the outward appearance of the plant change; so also does its relation to the conditions of its environment. A young plant organism which is still in the stage of formation is distinguished by high plasticity, it is prone to be deeply affected by the influence of its environment. Hence, by creating appropriate conditions of training, deep changes may be induced in the young seedling which will also be reflected in its progeny.

Consequently, by skilfully directing the individual development of an organism, the breeder can direct its heredity, modify the hereditary properties of the organism in the direction he desires, and produce a variety with sought-for qualities.

In the past twenty years Michurin's fundamental precepts were developed in the works of Academician T. D. Lysenko, who evolved the theory of the phasic development of the plant organism. Lysenko showed that the developmental phases are characterized and determined primarily by a succession of demands which the growing plant makes on its environment. By studying these demands we may direct the development of plants, and this is of immense importance to agriculture and plant breeding. T. D. Lysenko illustrated this by such brilliant examples as the vernalization of seed, summer planting of potatoes, and other agricultural innovations which have added millions of tons to the food resources of the country.

Taking his stand on the Michurin theory, and armed with a profound knowledge of the laws of phasic development of plants, T. D. Lysenko gave concrete examples indicating what general conditions are necessary for the remoulding of the nature of plants by means of training.

I. V. Michurin was a bold innovator who had the courage to discard scientific traditions if he saw that they hampered the advancement of science. He trenchantly criticized the "pea laws," as he called them, of Mendel, which the Mendelians proclaimed universal laws of heredity. How absurd are the attempts of the Morgan geneticists, Professors Dubinin, Altshuller and others, to adjust the Michurin doctrine to the Mendel-Morgan genetics. T. D. Lysenko, in his address. very clearly defined the basic principle of Michurin genetics, showing that it was fundamentally antithetical to the false ideas of Mendelism-Morganism, which are so pernicious to agricultural practice.

The Mendelist-Morganists hold that the conditions of growth of plants of any given variety have no influence on the alteration of its nature, on its varietal qualities. In opposition to this idea, which is so false and injurious to practical farming, T. D. Lysenko gave prominence, as the guiding principle for seed growing, to the fundamental precept of I. V. Michurin that the maintenance, as well as the improvement or deterioration, of the breed of organisms depends on their conditions of life.

Thanks to the work of T. D. Lysenko, the Michurin doctrine has been made the foundation for the reconstruction of Soviet seed raising, and this has been of great benefit to our socialist agriculture. Here again we have manifested the fundamental method bequeathed to us by Michurin, namely, that of tackling profound theoretical problems from the standpoint of practice, and of dealing with actual problems of the day, the needs of socialist production.

It is difficult at this session to go into individual detailed questions; it is highly necessary that the Academy should in its further work draw general deductions from the creative experience of the thousands of Michurinists. However, I should like to dwell briefly on some questions arising out of my work on vegetative hybridization at the Michurin Research Institute and the Saratov Agricultural Institute, in order to show what potentialities are opened up by the application of Michurin's precepts to practical plant-breeding problems and to theoretical problems of genetics and selection. Let me say right away that our researches in vegetative hybridization were conducted in the process of handling concrete breeding assignments connected with the production of improved varieties of apple trees, with enhanced frost-resistant qualities, for the central areas of the U.S.S.R.

Vegetative hybridization, that is, the obtaining of crosses by grafting, is acquiring ever increasing importance in the theory and practice of plant breeding as Michurin's precepts are progressively mastered and elaborated.

Darwin, in his Variation of Animals and Plants Under Domestication, made a very thorough collection and analysis of cases of vegetative hybridization known in his time. But, Darwin wrote, we do not know under what conditions this rare form of reproduction is possible.

In Darwin's days vegetative hybrids were obtained by accident, and were therefore a rare and inexplicable phenomenon. The credit for having obtained vegetative hybrids deliberately and systematically belongs to I. V. Michurin, who made a profound study of the conditions of their formation and elaborated the mentor method, as a method of practical utilization of vegetative hybridization for plant-breeding purposes.

It is important to note that the vegetative hybrids obtained by I. V. Michurin are not mere curiosities, but economically valuable varieties. Such, for instance, is Reinette-Bergamote—a vegetative cross between apple and pear, which has been included in the list of standard fruit trees in 19 regions of the R.S.F.S.R.

Michurin's doctrine of vegetative hybridization has been further elaborated as a result of researches made by T. D. Lysenko and the entire Michurin school, and we now have a fairly good knowledge of the major conditions needed for deliberate and systematic production of vegetative hybrids.

As T. D. Lysenko said in his address, the incontrovertible fact that vegetative hybrids have been obtained is in complete and irreconcilable contradiction to the fundamental tenets of the Mendelist-Morganists, who hastened to declare these vegetative hybrids unauthentic, or, speaking plainly, illegitimate. But Michurin in his day said that vegetative hybridization can be denied only by ignoramuses—"imitators" and "copiers," as he called them. Study of vegetative hybrids has revealed that the characters acquired by them as a result of vegetative crossing may be transmitted in propagation through seed, and, moreover, that in a number of cases that segregation of characters is to be observed which is met with in the offspring of ordinary sexual crossings.

The theory of vegetative hybridization is one of the central principles of Michurin genetics and selection, around which a battle has raged, ay, and is still raging, between the Mendelist-Morganists and the Michurinists. It would therefore not be amiss to cite one more example taken from our work on vegetative hybridization of apple trees.

Among the Michurin varieties there is the classic vegetative apple-pear hybrid, Reinette-Bergamote, which is obtained by grafting the bud of a one-year, phasically young, apple seedling onto the crown of a pear tree. For already half a century Reinette-Bergamote, when propagated vegetatively, firmly retains the character it acquired from vegetative hybridization—the pear-shaped form of the fruit near the stalk. In 1935, we, in our turn, crossed Reinette-Bergamote with various varieties of apples. Hybrids grown from seed obtained from this cross have since 1944 been bearing fruit at the experimental station of the Michurin Research Institute. And it is interesting to note that among these hybrids there are some which have inherited the type of fruit, resembling a pear, characteristic of Reinette-Bergamote; in other words, they have inherited in sexual propagation a character acquired from vegetative hybridization.

Particularly interesting in this respect is the hybrid Pepin Shafranny X Reinette-Bergamote. And it is important to stress that in order to preclude any fortuitous inaccuracies in the experiment, Reinette-Bergamote in these crossings was taken as the paternal plant.

But Michurin's theory of the mentor and vegetative hybridization has not only provided plant breeders with a highly effective method of producing new varieties; it also helps us to get a better understanding of the phenomenon of hereditary and sexual propagation, as Darwin in his time predicted.

In this connection, permit me also to dwell on the role of the maternal plant in shaping the heredity of hybrids.

Generally, this question may be formulated as follows: is there any difference between the progeny of direct crosses and reciprocal crosses; if so, what is this difference, and how is it to be explained?

From the point of view of practical plant breeding this means: is it a matter of indifference which of the members of a pair to be crossed is taken as the maternal plant and which as the paternal plant, or must a definite choice be made, bearing in mind, in the light of Michurin's leaching, the special role played by the maternal plant in heredity?

The answers given to this concrete question may be used as an example to demonstrate the impotence of the Mendelist-Morganist interpretation of the phenomena of heredity, and the creative power of the Michurin theory. What was the answer given to this question from the standpoint of Mendelism-Morganism? In his book, Introduction to the Breeding of Agricultural Plants, Professor Zhegalov plainly says: "From the point of view of the results obtained, it is a matter of indifference which plant is taken as the maternal, and which as the paternal."

And, indeed, so it should be from the standpoint of the Mendelist-Morganist shuffling of gene factors. But this assertion does not accord with the real facts of life, with the real facts of nature, of which Michurin spoke.

Cayeux (1929) found the same thing in crosses with Rosa gigantea: "The second cross, that is to say, the Tea rose x R. gigantea, produced several very excellent and beautiful hybrids, chiefly characterized by their soft coloring, their great profusion of blooms, and their greater resistance to cold."

We, for example, in our experiments on apple hybrids ascertained the following: if in a cross between a northern and a southern variety, a northern frost-resistant variety was taken as the maternal plant, the offspring were more frost-resistant than in the case of the reciprocal cross, when a southern variety non-resistant to frost was taken as the maternal plant. A similar phenomenon was to be observed in apple hybrids also in respect to the size of the fruits. With one and the same pair of initial forms, the progeny as a rule bore bigger fruit when a variety with large-sized, and not small-sized, fruit was taken as the maternal plant in the pair. Other plant breeders, in the literature on the subject, have also noted that dissimilar results are obtained from direct and reciprocal crossing.

The dominating influence of the maternal plant is thus a widespread phenomenon in nature, and the practical plant breeder should give serious heed to it. This does not mean that the progeny must necessarily take after the mother, that the characteristics of the mother will necessarily dominate in the offspring. But the features and properties of a given plant will display themselves more strongly in the offspring, if this plant is taken as the maternal, and not the paternal, member in the pair to be crossed. That is why Michurin wrote that "choice of the maternal variety is in practice of exceedingly great importance."

From the standpoint of the Mendelist-Morganist shuffling of gene factors, no satisfactory explanation of this phenomenon can be given. A correct explanation of the superior role of the maternal plant in heredity can be given only from the standpoint of the Michurin doctrine, based on the theory of development, and taking account of the profound formative role of the environment, its influence on the nature of the developing organism.

The mere combination of gametes (male and female sex cells) at the moment of fertilization is in itself not sufficient fully to determine the heredity of the new organism. With regard to this fundamental question of the theory of heredity, Michurin writes the following, underscoring this passage as particularly important:

"All the distinctive characters of any variety of fruit plant is a result of hereditary transmission and a combination of the influences of external factors, both in the embryonic period of the formation of the seed and in the post-embryonic period of the development of the seedling from the seed."

What interests us in this given case is the embryonic period of development, when the embryo of the hybrid plant is forming in the fruit of the maternal plant. The embryo, organically connected with the maternal plant, and building its cells exclusively from substances elaborated by the maternal plant, must inevitably be under its profound formative influence.

The character of this influence of the adult and fully formed organism on the young organism still in the stage of formation was explained by Michurin in his celebrated theory of the mentor.

But from this viewpoint we may also regard the maternal plant as a kind of mentor, under whose influence, and at the expense of whose plastic substances, the embryo of the seed, i.e., the germ of the young hybrid organism at the most early phase of its ontogenetical development, is formed.

That in relation to the forming embryo the maternal plant must be a mentor of very great potency is a conclusion which is to be drawn from the following theoretical considerations. First, according to Michurin's theory, the younger the plant (seedling), the more plastic it is, and the easier it lends itself to the formative influence of the mentor. The developing embryo, being, as it is, in the earliest phase of its ontogenetical development, must be very easily and powerfully influenced by this formative action of the maternal plant.

Secondly, since the action of the mentor is effected through the nourishment received by the grafted plant, in the shape of the plastic substances elaborated by the leaves of the mentor plant, it follows that the action of the mentor will be stronger the less the grafted hybrid organism utilizes the products of assimilation of its own leaves. But from this it follows quite clearly that the embryo of a seed, developing exclusively at the expense of the plastic substances of the maternal plant, must be subject to very profound formative influence on the part of the maternal plant. Hence the dominating role of the maternal plant in heredity is explained by the fact that the embryo of the hybrid plant forming within the ovary finds itself, from the very first moment of its formation as a result of the fusion of the sex cells, under the constant influence of the maternal plant, which acts as a peculiar, powerful mentor.

In relation to plant breeding, this means that in all cases when the breeder wants to strengthen the influence of a given parent plant on the hybrid progeny, he must take this parent as the maternal, and not the paternal, component. This principle is now being utilized in the production of big-fruited frost-resistant varieties of apple trees for Siberia. Thus the Michurin theory of the mentor and vegetative hybridization helps us to get a deeper understanding of the phenomena of heredity and sexual propagation.

Permit me to exhibit certain specimens and documents illustrating what I have said regarding vegetative hybrids and the role of the maternal plants. (Exhibits fruits, photos and drawings.)

In concluding my speech at this notable session of the Academy, I should like to remind you of the words of Michurin, namely, that we must insistently press forward, and that every plant, even the best, must be improved and improved again. The false doctrine of Mendelism-Morganism is a stumbling block to plant breeders. But all who follow the path of Michurin may be confident that they will achieve this improvement. Thousands of Michurinists are labouring in all parts of our country, even the most remote, to produce better varieties, worthy of the fields and orchards of the great land of Socialism.

Every one of us knows that we owe all our achievements in plant breeding to the creative virtue of Michurin's teachings. And every one of us remembers the command of our teacher, those proud words of Michurin which are engraved on his monument:

"Man can and must create new breeds of plants better than Nature."