PLANT BREEDING AND THE THEORY OF PHASIC DEVELOPMENT OF PLANTS
T. D. Lysenko

The Choice of Parental Pairs, the Law of Dominance, and
the Nature of Heterosis as Espressed in Duration of Vegetative Periods

After first investigating the laws of the individual development of plant forms, and studying the necessary conditions and character of the individual development of each prospective choice for crossing, we, to a certain extent, learn the hidden nature of the hereditary foundation of the picked candidates. If we guide ourselves by the theory of the development of the hereditary foundation (genotype), we shall be able intelligently to choose the parental pairs.

This intelligent choice of pairs for crossing includes the possibility:

  1. of foretelling, before crossing, the pattern of dominance of the developmental phases of one or the other parent, and hence, of foreseeing the length of the vegetative period of F1 compared with that of both parents;
  2. of deliberately changing the pattern of the dominance of vegetative periods;
  3. of foreseeing, from the length of the vegetative period of F1, the duration of vegetative growth of the earliest ripeners among the potential segregates and of culling the combinations accordingly, beginning with F1;
  4. of foretelling the general pattern of the likely segregation of heterozygotes according to length of vegetative period from the data of any generation;
  5. of not confining ourselves to the chance appearance of heterosis and the accidental breeding of early-ripening varieties from the crossing of [79] late ripeners, but of deliberately creating them under given conditions by means of an intelligent choice of parental pairs.

Usually plant breeders, juggling with combinations of individual characters and ignorant of the immediate basis of character development—the law of phasic development—stumble upon the combinations needed for producing a particular variety only by chance, and hence very rarely. With the vegetative period, too, plant breeders operate simply as if it were a "character," losing sight of the fact that this "character" is the final result of an entire course of development, the immediate basis of which is the law of phasic development. After all, it is the length of time required to complete the given phases of development under the conditions of existence required by the phases, as well as delay in the passage from one phase to the next as a consequence of the absence of the conditions of existence for the new phase, that, in the main, determines the length of the vegetative period, determines whether the variety will be an early-spring, late-spring, semiwinter, winter, or some other variety. The extremely diverse influencing factors that inevitably invade a plant's life in the field, of course, alter somewhat, shorten or lengthen, the ripening period. But these deviations are insignificant and keep within the limits of the period determined by the law of phasic development.

Juggling with lengths of vegetative period as if this were a character, and ignorant of the causes that determine it, the plant breeder cannot know for certain which pair to take for crossing in order to obtain a radical change in the duration of this period. If he tries to get the shortest vegetative period from the available varieties he will inevitably drag into the heterozygote, along with the short period, any number of bad indices. This is just what the plant breeder is usually compelled to do.

He takes into account the immunity to smut, rust, etc., of one variety and the shorter ripening period of another, with the result that in his quest for a short ripening period he introduces into the heterozygote susceptibility to various diseases, susceptibility to Hessian and frit flies, low resistance to drought, bad milling and baking properties, etc. That is why the plant breeder cannot know beforehand when, if at all, he will get from his combination the variety he picked and whether its yield will be better or worse. Only subsequent tests will reveal to him the results obtained.

Knowing no other way out and wishing to protect the zygote from deterioration, wishing to deal with a smaller number of unknown quantities in the segregation of the heterozygote, plant breeders have advanced the principle of producing varieties by inbreeding. However, in doing so they deprive themselves of the opportunity to enrich the hereditary basis, of the opportunity, for example, to eliminate a bad (long) vernalization phase by creating heterozygotes from a cross with another variety possessing a good (shorter) vernalization phase. Therefore, when it is necessary to create a variety with a shorter vegetative period, inbreeding is not only of no avail but even harmful. [80]

We, however, proceed from entirely different principles in breeding a variety with a relatively guaranteed yield in a given district.

From the available varieties it is necessary to choose such specimens for crossing as have the potentiality of showing good indices in respect to all types of hardiness and productivity, provided inability to traverse the first phase (vernalization) or the second (photo) phase as well as delay in passing through either of these phases under the conditions of a given district are eliminated from the hereditary basis.

But how are these potentialities to be discovered? How can the potential yield of a variety be ascertained if it usually does not ripen, or ripens late and produces grain of bad quality?

Since they do not investigate the laws governing individual development, ordinary plant breeding and formal genetics are incapable of penetrating the latent potentialities of the hereditary foundation. They underrate these potentialities, regard them merely as characters which usually come to the surface of their own accord when plants are sown in geographically different localities or when hybridological analyses are made. These latent potentialities can be partly revealed by inducing them to operate in a plant's individual development. This can be done artificially by creating for each of the parents the conditions necessary for their phasic development which are absent in the fields of the given district. For example, one of the parents may have to be vernalized, and suitable photo conditions created for the other. The result will be that in reproduction each parent will go through its whole cycle in its own way, and this will enable people to ascertain the whole course and period of its development, and also its yield. That is precisely what is meant by investigating the potentialities of a parent's hereditary foundation, by getting at the latent potentialities of the genotype. Discovering the parents' potential ripening period and potential yield—provided there is a continuous, undelayed development of their hereditary foundations through all phases to reproduction—and thereby ascertaining the one weak spot (different in each parent) in the hereditary bases under the given conditions, make it possible deliberately to create a heterozygote in which both these weak spots are certain to be eliminated. If one of the parents belongs to a variety which possesses all economically valuable properties but requires that its sole weak spot—poor adaptation of the vernalization phase to the conditions of the given district—be eliminated, this weak spot can be eliminated by introducing into the zygote the gametes of the other parent, which possesses a well-adapted vernalization phase and also all economically valuable indices but requires that its own weak spot—poor adaptation of the photo phase to the conditions of the given district—be eliminated. Thus, by crossing these two parents a heterozygote will be created possessing a real possibility of developing, and rapidly at that, under the conditions of the given district, both the first and second phase, and at the same time having all the parental gametes' other indices [81] that are desirable under the conditions of the given district. That is how the Laboratory of the Physiology of Plant Development of the Institute of Selection and Genetics approaches the choice of parental pairs, and it formulates this approach in the following way:

Parental pairs for crossing must be chosen not according to the maximum number of favourable characters observed in the parents, but according to the minimum number of unfavourable characters, that is, of weak spots in the potentialities of adaptation of the hereditary foundation which restrict the yield in the given district. This for the purpose of creating in the heterozygote the possibility of the mutual elimination of the parents' weak spots.

In the case of plants like cereals, soya bean, cotton and a number of others, the yields of which are restricted in a vast number of districts by the time required for maturation, parental pairs must be chosen from the entire world collection in such a way that the parents shall have not the same, but different sole "weak spots" as regards potential development of the hereditary foundation (vernalization phase in one parent, photo phase in the other).

These sole weak spots will be eliminated in the process of segregation of the heterozygote by the mutual substitution in the hereditary basis of the bad quality of one form by the analogous good quality of the other, and vice versa.

The creation of a zygote from deliberately chosen pairs, among whose offspring forms appear from which the parental "weak spots" have been eliminated as a result of segregation, makes it possible to know even before crossing what the general character of the development of the hereditary foundation's potentialities will be, makes it possible to ascertain which of these potentialities will be realized and, consequently, what the character of the development of the first generation (F1) will be as regards the flowering period of cotton, ripening period of wheat, etc. It also makes it possible to forecast with a great degree of probability what all the other economic indices will be.

If two forms are crossed, one with a short vegetative period and the other with a longer period, or if we cross a winter and a spring pair, a spring and a semiwinter pair, a spring late ripener and a semiwinter plant, etc.—which will be the dominant? This highly important question can be answered correctly only from the standpoint of development, by presenting and solving the problem of the general law of dominance.

Already Gregor Mendel noted (and this was one of the greatest achievements of genetics) that in the first hybrid generation (F1) of an alternative pair of characters, those of only one parent appear. Particular characters of one parent are, as it were, "swallowed up" for the time being by the "alleles" of the other. In conformity with this, Mendel established the rule of dominance, the correctness of which has been confirmed in many cases by subsequent observations and researches in genetics. But neither Mendel himself nor all the subsequent trends in present-day genetics have discovered [82] what is at the bottom of this; they have confined themselves to the mere statement of the fact that there is such a thing as dominance.

From the standpoint of the theory of development, however, which points to the role necessarily played in development by the external conditions of existence and emphasizes the part of adaptation in biological development, it is possible to find out the necessity of dominance, to understand its biological essence, and thus make considerable progress towards controlling the law of dominance.

In the zygote that is formed by hybridization, two ancestral bases, two hereditary foundations, unite and introduce all their features into the zygote as a basis for the potential development of phases. These, in their turn, determine the potential concrete formation of the organism's characters. But which of the pairs of potentialities (allelomorphs) inherited from the different parents will be materialized, will become realities, will develop?

This is not predetermined in any particular direction in the zygote itself. It depends upon the extent to which external conditions correspond to the biological requirements of a given feature of the zygote to be adapted to the conditions of existence of its development. Therefore, in F1 that allelomorphic feature of the heterozygote will develop which finds suitable conditions of existence for its development. Precisely for this reason, under the given conditions, only that feature of the zygote will develop, only that possibility of the hereditary foundation will become a reality, which finds the conditions that it needs, and is best adapted to the available conditions of existence. It is this that determines which of the two allelomorphic features of the zygote will develop, i.e., will be dominant.

We must at once parry the objection that may be raised that in a number of cases very definite characters dominate, regardless of the fact that the organisms develop in different environments. This possible objection is based on the failure to distinguish between "environment" and "conditions of existence" in the course of development. We must ascertain from the plant and not simply guess at random whether transferring it to a different habitat is the same as transferring it to different "conditions of existence." Big differences in a plant's environment may turn out to be of no importance to the plant. At the same time seemingly unimportant changes in environment which happen to be the conditions of existence at any stage of a plant's life may cause most important changes in it.

Figure 27 illustrates the difference between some barley plants and others. Some of the plants are earing; others are creeping on the ground, not having even stalks. Yet they are all of the same variety, grown in the same field from ordinary, unvernalized seeds. The only difference is that some of them were sown in the field on March 12, 1928, whereas the others were sown next to them two days later (March 14). The difference of two days radically affected the entire behaviour of the plants. The reason for the difference between them is now perfectly well understood: some of the plants (those sown on March 12) secured the conditions of existence that [83] their vernalization phase required, because, during those two days the temperature was 2°-3° lower than throughout the rest of the vegetative period. The subsequent much bigger changes in temperature were only passive environmental elements in the development of the vernalization phase.


Fig. 27. Barley Pallidum 419
Sown at intervals of two days from March 1 to autumn 1928 in Ganja. The plants in all the sowings, including that of March 12, proved to be of spring habit. All the plants sown from March 14 onward (the March 14 planting is not shown in the illustration) proved to be of winter habit and did not ear. The difference of two days in the date of sowing (March 12 and 14) played a decisive role in the development of the plants' organs and characters

We maintain that in all cases when a hybrid plant is given really different conditions of existence for its development, this causes corresponding changes in dominance: the dominant character will be the one that has more favourable conditions for adapting itself to its development. We repeat that dominance is not predetermined in one particular direction in the zygote. Combining both parental hereditary foundations, the zygote contains the potentiality of developing both allelomorphs. The question of dominance is decided by the adaptedness of either allelomorph to develop under the given conditions of existence. Consequently, what will be dominant under one set of conditions will be recessive under another.

The conception of dominance from the standpoint of development was expressed long ago by Ivan Viadimirovich Michurin and was applied in his work. He wrote:

"The qualities of every hybrid grown from the seed of fruit obtained from the crossing of two progenitors are a combination of only those hereditarily transmitted characters of the parent plants, namely, father, mother, and their kin, the development of which at the earliest stage of the hybrid's growth was favoured by the environmental conditions (i.e., temperature [84] of the surrounding air and soil, degree of activity of atmospheric electricity, direction and velocity of the prevailing winds, intensity of light, composition of the soil, moisture content, etc.)"1

It was this conception of the zygote as of something that develops, and of dominance as the development of only those features of the zygote which are favoured by the given conditions, that guided Ivan Vladimirovich in all his immense and extremely fruitful work. It was these theoretical premises that enabled him to raise a vast number of new varieties and unprecedented plant forms. Proceeding from these theoretical premises, he propounded distant hybridization as one of the principles of his work. But Michurin's principle differs fundamentally from that of the present-day distant hybridizers. Michurin advanced the principle of distant hybridization not merely for the purpose of increasing the diversity of plant forms, irrespective of whether these forms will be interesting playthings or something that some day may perhaps, "by chance," turn out to be useful. He did not propose the crossing of just any plants as long as the pairs were remote species and geographically distant from each other.

I. V. Michurin deliberately picked parental pairs, including such as were quite remote from each other as well as from the locality for which the future variety was intended, very carefully taking into account the difference in their conditions of existence. And he did this quite concretely in order to inhibit, when necessary, the development of definite properties that was dominant owing to adaptedness to the local conditions of development, and to create the conditions required for the dominance in development of the properties he had planned to impart to the variety he was producing. In choosing hereditary foundations for crossing, Michurin always kept in mind their historically formed biological adaptational requirements. He calculated beforehand how the hereditary foundation would develop under definite conditions of existence and under definite influencing factors, choosing these conditions beforehand in order to obtain the desirable pattern of dominance. In other words, he made a blueprint in advance of his work with respect to the entire path of development with its numerous contradictions, from the hereditary foundation to the characters. To explain his principles, he cited the following example of his work, one of a vast number of similar cases:

"By crossing foreign varieties of winter pears with our Tonkovetka, Limonka and other hardy varieties, we obtained hybrids, which, while superior in flavour, were all summer ripeners and had small-sized fruit. This was the result of the dominating development of the characters of our local varieties, due to the climatic and other conditions in our locality which were suitable for them, and to which they were habituated. On the other hand, when I crossed foreign winter pears with a wild Ussurian pear which I had grown from seeds obtained from North Manchuria, I obtained hybrids [85] half the number of which produced large-sized fruit of excellent flavour, with the qualities of winter ripening in storage and ability of all the aboveground parts of the trees fully to resist our frosts..."

Ivan Vladimirovich formulated this theoretical principle of his in the following way:

1Ibid., p. 28

"The farther apart the crossed parental pairs are in respect to place of origin and environmental conditions, the more easily the hybrid seedlings adapt themselves to the environmental conditions of the new locality. I attribute this to the fact that, in this case, when the properties of the father or mother and their immediate kin hereditarily transmitted to the hybrids fail to find the environmental conditions habitual in their native locality, they will be unable to dominate too strongly in the transmission of certain of their properties in the development of the hybrid organisms, which is of enormous importance for this work."1

Dominance as development determined by greater adaptability to conditions—such was the conception entertained by Ivan Vladimirovich, such the view by which he was guided and which was one of his theoretical principles that placed in his hands a powerful weapon and tool in aid of his struggle and work.

Michurin advanced this principle very long ago in opposition to the formal conception of dominance as something determined in the same way in the zygote itself independently of the conditions of adaptation. He had already come forth as an opponent of such formalism in his earlier works, where he wrote:

1I. V. Michurin, Selected Works, Eng. ed., Moscow 1950, pp. 101-103.

pood = approximately 16.38 kilograms (36.11 pounds)

"It seems to me that all of our Mendelists are disinclined to take into account the powerful influence of these factors on the development of the hybrid plant, beginning with the formation of the seed from the cross of two individuals and continuing during the first few years of growth of the young seedling right up to the stage of maturity . .. ." (Earlier in this article I. V M. enumerated the chief of the above-mentioned factors: "atmospheric pressure, the temperature conditions, the amount of moisture, the intensity of the sunlight and the activity of the atmospheric electricity; the separate effects of each of these factors as well as the combined effects rendered by their various combinations...") "The following fact may serve as an example: I pollinated the flowers of Pyrus elaegnifolia with the pollen of a well-known pear named Bessemyanka [Seedless]. When rearing these seedlings I observed that whenever they were given better nourishment externally in all their parts the hybrid seedlings invariably deviated towards the Bessemyanka type. The leaf blades became broader and had a glossy surface, the shoots became thicker and their bark acquired a colour resembling that of the shoots of Bessemyanka. On the other hand, if the seedlings were subjected to some hardship, such as replanting or the insufficient water supply in the beginning of the vegetation period due [86] to summer drought, the leaves of the hybrid plants grew narrow and elongated in shape. Similar phenomena have been recorded in hybrids from other crosses as well, whenever a cultivated variety was crossed to a wild species… I have also carried out numerous other experiments to determine the effect of the composition of the soil on the constitution of growing hybrid plants and each time I became convinced of the considerable influence exerted by this factor. This influence was particularly pronounced in those cases when I succeeded in providing for the hybrid seedlings such a soil that was closely similar in composition to that on which one of the two parental plant varieties involved in the cross had successfully developed for a long period of time, or, so to say, had been formed, whereas the type of the other parent had been developed on a soil of an entirely different composition. In almost all such cases the hybrid seedlings were observed to resemble in type the first parent. Thus, I used to order several poods of soil to be brought from the environs of Vladimir to grow the hybrids obtained in crosses between one of our cherry varieties raised in the Samara steppe region (Prunus Chamaecerasus) and the Roditeleva cherry from Vladimir. The soil ordered was the very one on which the Roditeleva cherry—a well-known Vladimir variety of cherry—was grown in its native locality. Although by means of this substitution of soil I succeeded only in partly approximating the environmental conditions in which these hybrids were reared to those of the Roditeleva cherry's native habitat, nevertheless the few specimens of hybrid seedlings that were given a mixed soil containing a high proportion of Vladimir soil, showed a pronounced trend towards the Roditeleva cherry and markedly differed from the rest of the seedlings brought up on the ordinary soil of our locality. And just to think that this result has been obtained in experiments, in which so many necessary conditions were missing! These hybrid seedlings ought really to have been planted in Vladimir, not in Kozlov, and grown in the native locality of the Roditeleva cherry, because (besides soil composition) other factors such as the composition of the subsoil, and of the subsoil water, the depth of the subsoil water table level, the lay of the site, the difference in the climatic conditions, etc., play an important role. And if even in the absence of the influence of these important factors the supplying of the native soil alone was enough to produce so marked a deviation towards the maternal plant, then how is it possible to make correct estimates. of the proportion of plants in a hybrid progeny that would deviate towards one or the other parental type and of the degree of this deviation merely on the basis of the hereditary transmission of the latter's properties?"1

We see that Ivan Vladimirovich directed the development of dominance both by choosing pairs with definite requirements of adaptation to the conditions of development and by creating the conditions of existence required for development in the desired direction. It was precisely the practical realization [87] of theoretical principles founded on the development of the hereditary basis under the conditions of existence that led Ivan Vladimirovich to such grand achievements in the breeding of varieties.

We were obliged to deal here in a cursory way, as part of our exposition, with one of the theoretical principles and premises of Michurin's work. We cannot, of course, give here an exhaustive analysis of the immense wealth of his thought.

But one thing must be said: Michurin was guided by the search for the laws governing the development of plants during the whole course of their lives and he found the way to control many of these laws.

His conception of dominance as development, in contrast to the whole of official formal science, and his conscious direction of dominance, are enough in themselves to refute the arguments of some "theoreticians" about the scientific "illegitimacy" of Michurin's work.

The real science of hybridization is to be found in the works of Michurin, but not everybody is able to understand him. To be able to do so one must really take the stand of materialist development.

Of the developmental potentialities of the hereditary foundation (allelomorphs) that are of uniform type as regards their nature and demands on conditions of existence, but differ in the specific character of the demands they make on the uniform-type conditions of existence, only one can actually develop (short or long "vernalization" phase, short or long "photo" phase, etc.). We are not discussing the "dominance" of developmental potentialities that are alien to each other in nature, not the "dominance" of long over black, yellow over short, etc., but paired and allelomorphic potentialities (long-short, round-wrinkled, etc.). It is clear, therefore, that in these cases the actual development of such potentialities can only be mutually exclusive. And precisely that one of the mutually exclusive potentialities will develop which finds the surrounding conditions more favourable for the requirements of its development, which is better adapted for development under the given conditions of existence. Therefore, the adaptability or inadaptability of the heterozygote for development under the given conditions will certainly make itself felt already in F1. If the heterozygote possesses the potentiality to develop fully under the given conditions of a district, this potentiality will become a reality in the first generation. This is what determines dominance in the development of the potentialities of the hereditary foundation.

If we regard dominance as the development of one of the paired potentialities of the heterozygote because it fits the requirements better, because of the greater adaptedness of the development of this potentiality of the zygote to the given conditions of existence, it is possible beforehand, before crossing, to visualize the pattern of dominance with respect to given allelomorphic inclinations (potentialities).

For this it is necessary to study beforehand the potentialities of development of the parents' hereditary foundation; to ascertain these potentialities [88] by finding the conditions required by each of the parents for its phasic development and for the development, on this basis, of the plant's organs and characters; to ascertain which of these requirements are best satisfied by the given conditions of the place in which the plant is grown (conditions of the district).

Phasic analysis must, therefore, precede both hybridological analysis and hybridization itself. Only then will hybridological analysis not be based on blind groping for segregates, only then will it become possible to control the dominance of "characters," just as it is already possible, in the main, to control those that are the direct final result of phasic development. The length of the vegetative period is one such character. Further progress in the analysis of the conditions of existence of the process of forming organs and their characters, the development of which is a particular form of existence of the general laws governing phasic development, will create ever-increasing possibilities for dominance control.

Thus, the general law of dominance may be formulated as follows:

Dominance is the development of either of the two allelomorphic features of the hereditary foundation (heterozygote), provided the conditions of existence are suitable for its requirements and the other feature of the heterozygote cannot be developed owing to the absence of the required conditions, or to less favourable developmental conditions.

As, however, either feature of the hereditary foundation is merely the tangible vehicle of potential development, the same law of dominance may be formulated as follows:

Dominance is the transformation into reality of one of the paired (allelomorphic) and mutually exclusive developmental potentialities of the hereditary foundation owing to the existence of suitable conditions, or to lesser adaptability to these developmental conditions on the part of the other allelomorphic potentiality.

Proceeding from this law, it is possible to know in advance, even before crossing, what the dominant ripening period will be on crossing a winter and spring pair, a pair with a short and long vegetative period, a semiwinter and spring pair, etc.

For this it is necessary to make a phasic analysis, i.e., to ascertain why, thanks to which phases, the parents develop as winter, spring, early-ripening, etc., varieties.

Having ascertained what conditions each of the parents needs for the development of each of these phases in order that development from phase to phase may proceed more quickly and continuously, it is possible, after studying the conditions of the district, to forecast how the heterozygote will develop in F1 into a winter, spring, semiwinter, late, early, or other form, and to act accordingly in choosing pairs for crossing and the conditions of existence (choice of district) for obtaining the necessary pattern of dominance with respect to length of ripening period in the first generation (Figs. 28 and 29). [89]

Fig. 28. Illustration shows two late-ripening spring varieties of wheat (under Odessa conditions), Hordeiforme 2508 and Melanopus 069

Presowing vernalization of the seeds of Hordeiforme 2508 under Odessa conditions accelerates earing. Consequently, this variety, under Odessa conditions, is a late ripener owing to stow passage through the vernalization phase. The plants in the sheaf on left, grown from vernalized seeds, eared; those in the second sheaf on the left were grown from ordinary seeds. Presowing vernalization of Metanopus 069 seeds does not accelerate earing. But under long-day conditions, plants of this variety do ear more quickly. Consequently, under Odessa conditions this variety is a late ripener owing to slow passage through the photo phase. The hybridization of these two forms creates a hereditary foundation from which the two weak spots of these parents are eliminated. The phasic analysis of the two parental forms made it possible, already before crossing, to foresee that their offspring would develop as early-ripening forms. Note eared plants of first hybrid generation (F1), second sheaf from right.
Fig. 29. The phasic analysis of Hordeiforme 2506 and of Melanopus 069 showed that these two late ripeners will produce an early-ripening hybrid (see second sheaf from right); Hordeiforme has (under Odessa conditions) a long vernalization phase, Melanopus has a long photo phase

Hybridization creates a hereditary foundation containing the potentiality of rapid passage through both phases (under Odessa conditions)

When crossing two varieties, one of which develops as a winter variety and the other as a spring variety under the given conditions of existence (conditions of the district), a heterozygous hereditary foundation is obtained which contains a real potentiality for spring development. The hybrid seed when sown in the spring, will find the necessary conditions of existence for the development of the "spring" potentiality present in the hereditary basis. [90]

Thus, "spring habit" will dominate over "winter habit." It must always be borne in mind, however, that this springness of either of the parents will be preserved only under the given conditions of existence; under other conditions it will become "winter habit." Therefore, the first generation resulting from the cross of these same parents may turn out to be of winter habit if developed under other conditions.

Such a mistake can be avoided only by a prior phasic analysis of the parents to be crossed. It is also necessary to ascertain before crossing what conditions of existence are required by each parent for the vernalization phase. After that it will be possible to foretell whether the first generation will be of winter or spring habit if sown in any district and not only in the district where the parents were grown.

If, when crossing two parents, only one develops as a spring variety under the given conditions, we always know beforehand that under the same conditions the development of hybrid F1 will also be of the spring type, i.e., we know beforehand what the pattern of dominance will be.

If a semiwinter and a spring form are taken for crossing, then, for the same reason, namely, the possession by the heterozygote of a real potentiality for "spring" development under the given conditions of existence, that is to say, if sown in the warm season of the year, F1 will be of spring habit, i.e., "spring habit" will dominate over "semiwinter habit."

When two forms are taken for crossing, one of which is an early ripener and the other a late ripener under the given conditions of a district, then, since the heterozygote will possess a real potentiality for early development under the given conditions, and since these conditions are present, F1 will develop as an early ripener. Thus, in this case, early ripening 'Will dominate over late ripening.

It is possible to formulate the following law of the duration of vegetative periods, which accords with and is a concretization of the general law of dominance.

In the first generation of hybrids (F1) from two parents, one of which ripens early and the other later, early ripening will dominate, other conditions being equal. The first generation will always be as early ripening as, or even more early ripening than, the most early ripening of the parents. (Tables 1 and 2 on pp. 94-95.)

Cases of F1 being earlier ripening than either of the homozygous parents have long been known to modern genetics, and in our opinion they are of the same common nature as cases of the more vigorous growth of F1 than either of the parents, being a form of so-called "heterosis." But failing to analyze the regularities of the development of characters on the basis of phasic development, formal genetics is unable to explain heterosis. From the standpoint of phasic development, however, heterosis as regards early ripening becomes understandable, and this enables us to foretell such heterosis and deliberately to create it. We proceed from the proposition that [91] early-ripening heterosis is the resultant of dominance in the development of several more rapidly passing phases during hybridization.

Fig. 30. "Heterosis" in respect to early ripening created by choosing pairs on the basis of a phasic analysis of wheats Fig. 31. Early-ripening "heterosis" created by choosing pairs on the basis of a phasic analysis of barley.

Pallidum 883/6 from the Azerbaijan station is not adapted for passing through the vernalization phase when sown in the spring under Odessa conditions (see sheaf on left). Pallidum 046 from the Odessa station (see sheaf on right) is badly adapted for traversing the photo phase under these conditions of spring sowing. The hybridization of these forms creates an early-ripening "heterosis"

When hybridizing two hereditary bases, one with a more favourable (more rapid) phase of vernalization under the given conditions, but with a bad (prolonged) photo phase, and the other with a more favourable development of the photo phase under the same conditions, but with a bad (prolonged) vernalization phase, we, owing to the law of dominance, will necessarily obtain early-ripening heterosis in F1.

Take, for example, two late-ripening forms and make a phasic analysis of each of them. If you find that they are late ripening owing to a difference in phases, you will, by crossing them, create a hereditary foundation which [92] will contain a real potentiality for a more rapid development in both phases. Under the given conditions of existence the hybrid obtained from two late ripeners will develop like an early ripener.

Fig. 32. Sesame

Both parents have long vegetative periods. Phasic analysis showed that their late ripening was conditioned by different phases. Choice of pairs on the basis of a phasic analysis showed that it was possible to create an early-ripening form out of these late-ripening forms.

Thus, if we take into account the different conditions of existence available for the development of the phases of the parents that we choose for crossing, we can deliberately create early-ripening heterosis (Figs. 30-33).

As we have already indicated, the developmental phases constitute the general biological law of the individual development of plants from seed to seed, a law that reflects the historical action of the natural selection of adaptations in the demands which the developmental phases make upon the conditions of existence.

These phases, in which the difference in the nature of the demands made by different organic forms upon their conditions of existence are based on the initial difference in the hereditary foundations of these forms, are themselves the base on which the organs and their specific characters develop. The latter, however, as well as their base (the phases), while in general developing in their turn under their own conditions of existence, concretely develop under the inevitable influence of extremely diverse and sometimes not immediately calculable external influencing factors, which are by no means inactive in the formation of the characters of each separate organism as the individual representative of the variety, for they condition specific differences in the form-building process.

Although the rapidity and duration of passage through the phases determine the rapidity and duration of shooting, budding, flowering, fruiting, etc., they do not by any means do so entirely. Therefore, changes in the [93] duration of passage through the phases, and changes in the date of budding, flowering, fruiting, etc., will necessarily diverge somewhat, and this divergence will be different in different plants, being determined by the specific nature of each plant form and by the specific development of its organs, and also by the different influences exerted by the external factors. All this notwithstanding, the general law that budding, flowering and fruiting dates depend upon the duration of passage through the phases of development remains valid.

Fig. 33. Deliberately-created "heterosis," the result of choosing phasically analyzed pairs for crossing (from world collection)

With all that has been said above as its theoretical premises, the Laboratory of the Physiology of Plant Development of the Institute of Selection and Genetics has been carrying out experiments under both field and laboratory conditions. The results obtained fully confirm the correctness of these theoretical premises, fully confirm the correctness of the law of dominance in vegetative periods that we have formulated. (Tables 1 and 2.)

By taking the above-formulated law of dominance in periods of vegetation as a basis, it became possible to cull combinations in the very first hybrid generation, which plant breeders usually ignore. From this law of dominance it follows that the best pattern of development (as regards early [94] ripening) will be presented by F1, which has a more favourable basis for richer development potentialities than all succeeding generations.

Table 11
SOWN IN FIELD MARCH 26, 1934

No. Combination Earing
F1 Maternal plants from seeds Paternal plants
Ordinary Vernalized Ordinary seeds
1 Leucur. (1241) x Melanop. 069 27/5 29/5 25/5 6/6
2     "        (1301) x        "       069 2/6 6/6 3/6 6/6
3     "        (138 ) x        "       069 1/6 1/6 26/5 6/6
4     "         (1406) x        "       069 2/6 6/6 1/6 616
5     "        (1413) x        "       069 2/6 2/6 1/6 10/6
6  Hordeif. (1522) x      "      069 27/5 27/5 25/5 6/6
7  Ersp. (2038)  x        "     069 2/6 6/6 2/6 6/6
8  Apulic. (2236) x        "       069 2/6 2/6 1/6 7/6
9  Hordeif.(2506) x        "       069 2/6 7/6 2/6 7/6
10     "        (2508) x        "       069 2/6 7/6 2/6 6/6
11     "        (2753) x        "       069 2/6 6/6 1/6 6/6
12     "        (2577) x        "       069 2/6 11/6 2/6 6/6
13     "        (2813) x        "       069 3/6 8/6 5/6 6/6
14 Apulic. (3418) x        "      069 25J5 26/5 24/5 6/6

1The numbers in parentheses are taken from the catalogue of the All-Union Institute of Plant industry.

Table 2
SOWN IN GREENHOUSE AUGUST 24, 1933

No. Combination Earing
F1 (in different pots) Maternal plants Paternal plants
1 Ukrainka x Lutesc. (2167) 9/10, 10/10 Winter 8/10
2 Ferr. (818) x Girka 0274 29/9, 29/9, 29/9, 29/9 10/10 4/10, 6/10, 6/10
3 Ferr. (818) x Lutesc. 062 29/9 10/10 2/10, 2/10, 4/10
4 Erinac. (991) x Ferr. (2166) 29/9 10/10 29/9
5 Erinac. (1506) x Lutesc. 062 29/9 20/10 2/10, 2/10, 4/10
6 Ersp. (2038) x Lutesc. 062 30/9, 28/9, 29/9, 29/9 Winter 2/10, 2/10, 4/10
7 Ferr. (2146) x Lutesc. 062 29/9, 27/9, 28/9, 29/9, 28/9, 28/9 " 2/10, 2/10, 4/10
8 Ersp. (2150) x Lutesc. 062 29/9, 30/9, 30/9 " 2/10, 2/10, 4/10
9 Apulic. (2236) x Lutesc. 062 30/9, 4/10 6/10 2/10, 2/10, 4/10
10 Ersp. (2551) x Lutesc. 062 30/9 29/9 2/10, 2/10, 4/10
11 Ferr. (2705) x Lutesc. 062 29/9, 30/9, 30/9, 1/10, 1/10 Winter 2/10, 2/10, 4/10
12 Ferr. (2705) x Girka 0274 3/10, 3/10, 4/10, 4/10 " 4/10, 6/10, 6/10
13 Ferr. (2707) x Lutesc. 062 1/10, 1/10, 1/10 " 2/10, 2/10, 4/10
14 Ferr. (2707) x Girka 0274 30/9, 30/9, 1/10, 3/10, 3/10, 3/10 " 4/10, 6/10, 6/10
15 Ersp. (2752) x Lutesc. 062 29/9, 29/9 " 2/10, 2/10, 4/10
16 Ersp. (2752) x Girka 0274 30/9, 2/10 " 4/10, 6/10, 6/10
17 Ersp. (2774) x Ferr. 2166 rn 25/9, 25/9 " 28/9
18 Ersp. (2781) x Lutesc. 062 27/9, 29/9, 28/9, 29/9 " 2/10, 2/10, 4/10
19 Ersp. (2781) x Girka 0274 29/9, 20/9, 30/9 Winter 4/10, 6/10, 6/
20 Apulic (3418) x Lutesc. 062 25/9, 26/9 3/10 2/10, 2/10, 4/10
21 Ersp. 534/lxLutesc. 062 30/9, 3/10, 3/10, 3/10, 3/10, 3/10,
3/10, 3/10, 2/10, 3/10, 4/10, 3/10,
4/10 2/10, 3/10, 4/10, 4/10
Winter 2/10, 2/10, 4/10
22 Ersp. 534/1 x Girka 0274 2/10, 2/10, 3/10, 2/10, 2/10, 3/10,
3/10, 3/10, 3/10, 3/10, 3/10, 3/10,
3/10, 3/10, 3/10, 3/10, 3/10, 3/10,
3/10
Winter 4/10, 6/10, 6/10
23 1316/2 x Lutesc. 062 4/10, 4/10 " 2/10, 2/10, 4/10
24 1637/l x Lutesc. 062 3/10, 3/10, 2/10, 3/10, 3/10, 2/10 " 2/10, 2/10, 4/10
25 1637/1 x Girka 0274 3/10, 2/10, 2/10, 2/10, 2/10, 2/10,
2/10, 3/10
" 4/10, 6/10, 6/10
26 2522/l x Lutesc. 062 5/10, 8/10 " 2/10, 2/10, 4/10
27 2522/1 x Girka 0274 30/9, 2/10, 2/10, 2/10, 3/10, 2/10 " 4/10, 6/10, 6/10
28 3060/15 x Lutesc. 062 4/10, 3/10, 3/10, 6/10, 3/10, 4/10 " 2/10, 2/10, 4/10
29 3060/15 x Girka 0274 30/9, 3/10, 4/10, 1/10, 3/10, 3/10,
3/10, 2/10, 3/10, 3/10
" 4/10, 6/10, 6/10

The adaptability of a given potentiality of the hereditary foundation to the available conditions, if that potentiality is really present, must already make itself felt in F1 and if F1 is unable to develop fully under the given conditions, then it is useless to expect a better development (in this case, a shorter ripening period) in the succeeding generations, the hereditary foundations of which are poorer in potentialities owing to segregation.

Consequently, if F1 comes out in a form that does not satisfy the range of requirements of the variety for the given district as regards ripening period, further breeding work for obtaining segregates of the given combination will be superfluous.

None of the succeeding generations can develop a form that will be earlier ripening than F1.

[96]

Experimental hybridization work, now already carried on up to F7, fully confirms this without a single exception.

From this same conception of the hereditary foundation as the vehicle of developmental potentialities it follows that in all succeeding generations the potentialities of earlier development may be impoverished as a result of segregation, but they can never be enriched (without mutations). Therefore, F2 cannot be more early ripening than F1, F3 cannot be more early ripening than F2, and so forth.

All the experiments conducted in the Laboratory of the Physiology of Plant Development and all the data given in the literature on the subject and examined for this purpose fully confirm the correctness of this thesis.

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