Converting Winter Wheat to Spring
VII. THE LIQUIDATION OF THE CONSERVATISM OF THE NATURE OF ORGANISMS
Alteration of the nature of plant organisms. Our conception of heredity permits us to devise methods of directed change in the nature of plant organisms by means of treating plants with conditions of the external environment. Such changes make plants better adapted to various field conditions. Thus, winter cereals can not undergo the process of vernalization when sown in spring when no period of low temperature is available. On account of their heredity they are unable to go through one of the stages of their development, and, hence, cannot bear fruit. They may be forced to bear fruit in two different ways. The first way, is to furnish to winter plants the proper temperature conditions (0°-10°C approximately) for 30-50 days depending upon the variety. After such treatment winter plants will be able to continue and to complete their development under the usual spring or summer field conditions. The second way is to change the nature of winter plants, whereupon they will cease to be winter plants in respect to their heredity. In either case the change of the development of winter crops with spring sowing must be accomplished through the influence of proper temperature conditions. The only difference is as follows. In the first case, winter plants, or seeds just beginning to grow, receive the low temperature required by their natures. Hence the vernalization takes place normally for the development of the winter varieties; the changes are the usual ontogenetic ones. The seeds of such plants possess the same heredity, and they will be winter plants like those of the preceding generations. In the second case, the plants receive at a certain stage of the process of vernalization, not the temperature normally required by them for this process (close to 0°C), but the usual spring temperatures. One of two things will take place: either the vernalization will not occur and the plants will not pass through this process on account of the lack of proper temperature conditions, or else the process of vernalization will still take place at the unsuitable temperature conditions. In these altered temperature conditions the process of vernalization will be completed in a way different from the normal conditions of low temperature. It is self evident that the change in the process will change the body which results from this process. Even if this body does not differ in appearance from normal, unchanged, plants, the entire further development of this body will take place differently, as can easily be seen in plants of following generations. These following generations will be inclined to select for the process of vernalization the conditions which were forced upon the preceding generation. Instead of winter varieties we obtain plants inclined to be spring varieties.
Many genetically spring varieties have been derived from winter varieties in the relevant experiments made by Com. A. A. Avakian and other scientific workers in the laboratories of the All-Union Institute of Selection and Genetics directed by the writer. Spring forms have been obtained from every standard winter wheat taken for experiment. Conversely, a whole series of spring varieties of wheat and barley were transformed into genetically winter varieties.
From the point of view of the experiments on the directed change of the nature of organisms the transformation of winter varieties into spring ones is more interesting than the converse transformation. The former experiments are easier and their results are easily detected. The results are manifest as soon as the seeds collected from the experimental plants are sown in spring. All plants which form an inflorescence testify to the fact that their winter heredity has been altered to spring heredity. The changes of spring varieties into winter ones are difficult to demonstrate, however, even in the material known to have been changed. If such plants are sown in spring, they scarcely differ from the usual, unchanged, spring forms because the acquired inclination toward the winter habit has not become fixed. They will form shoots. If they are sown in fall, the change in their nature is difficult to ascertain even if the experimental plants overwinter. It is known that even the usual spring varieties frequently can overwinter if no heavy frosts occur. If heavy frosts do occur, the weak change of the spring into the winter habit seldom saves these plants from the lethal effects of winter tribulations. The change must be a strong one, and this can be realized only in a series of generations.
The experiments whereby spring varieties of cereals are transformed into winter ones have a great practical interest for obtaining winter‑resistant varieties. We have already obtained several winter varieties of wheat and barley from spring varieties through education, through the influence of the external environment. These forms are no less winter resistant, and frequently even more resistant, than the most resistant varieties known.
Before agrobiological science stands the task of evolving more and more concrete methods for altering the heredity of plant organisms in the direction desired.
Changing the heredity of winter varieties into the spring habit, and vice versa. Let us outline briefly the technique of changing the heredity of the winter forms of cereals into the spring state, and vice versa. We know that the winter forms require a prolonged period of low temperatures to induce the stage of vernalization. The spring forms have no such requirements. In order to transform a form with a hereditary winter habit into a hereditary spring form, the process of vernalization must be induced not by a low temperature close to 0°C, but by the high temperature which takes place in the field conditions of spring. In accordance with our conception, the alteration of the processes, if it takes place, will correspond to the inducing cause.
In the following generation all the developmental processes must take place again in the same way as in the preceding generation. In the preceding generation the process of vernalization, influenced by a high, instead of a low, temperature, was altered in a way corresponding to the influence. Hence in the following generation the process of vernalization, which took place in the preceding generation at a high temperature, will require the same condition, i.e., high temperature. In numerous experiments this statement has been checked by the writer and by many other scientific workers. But the desired results are not obtained with certainty in every concrete case, despite the correctness of the general principle. The concrete possibilities and methods of changing the nature of organisms in each particular case must still be worked out.
Conservatism of heredity is the cause of the non‑acceptance of the influence of conditions by the organism. The influence of high temperature on the process of the vernalization stage is necessary for changing the winter into spring varieties. The process of vernalization does not take place, or takes place very slowly, in winter varieties. Winter wheat plants or plants of some other forms can grow at high temperatures for months without passing through vernalization, and, hence, without changing this process.
In practice, many winter varieties are sown for many years and over large areas at the beginning or in the middle of August, i.e., rather long before the advent of the winter cold. The low autumn temperatures usually arrive a month, or even two, after sowing. And yet, the winter varieties are never transformed into spring ones in such sowings. In experiments, the winter plants may also be kept for months in a warm room, in a greenhouse, and they will remain as grass. They will not vernalize and will not give shoots. Hence, the process of vernalization not changed at the high temperature. The winter forms do not give shoots because the low temperatures needed for the stage of vernalization were lacking.A false‑conclusion can be made, and geneticists frequently make it, that it is impossible to direct the change of the nature of the organism through the influence of living conditions. Yet, as shown by our numerous experiments, winter varieties can be transformed into hereditary spring ones. Moreover, this transformation takes place only under the influence of high temperatures on the process of vernalization, of temperatures which usually occur in the field in the spring. The instances in which changes of heredity do not occur despite a prolonged treatment of winter plants with high temperature conditions tell us only that the plants, or rather their vernalization process, failed to accept these conditions. In this case, the plant organisms failed to accept the treatment because of the conversatism of heredity. Consequently, the experimenter has the task of finding better and better means whereby to administer the requisite treatment. A method is already available with the aid of which various percentages of hereditary spring forms can be obtained from hereditary winter forms of any variety of cereals.
Experimental data, as well as a series of general biological observations, have led the writer to the conclusion that, in order to transform the heredity of winter varieties into the spring state, the relatively high temperature conditions must be administered not at the beginning of the process of vernalization (and in general not during this process) but at the end, at the time of its completion. The success of the treatment is contingent on this.
Sown in Ganja on April 15; presowing vernalization lasts 36 days, after which the wheat ears normally
The usual duration of the process of vernalization in most winter cereals at low temperatures (0°-10°C) is 30-50 days, depending upon the variety. The plants must be permitted to go through the process of vernalization at the low temperature suitable to their heredity. The plants must be placed at the usual spring conditions, i.e., the high temperature must be created, just before the completion of the process of vernalization. The process of vernalization of winter forms usually does not take place at high temperature. But if a high temperature is created just before the completion of the process, the plants will slowly, so to speak ailingly, complete it. The following development will go on normally, since the conditions of the external environment in spring and summer are suitable for this development.
Transformation of winter forms into spring ones. Practical experiments on the transformation of winter forms into spring ones were made as follows. Seeds of a winter variety were vernalized for various numbers of days at temperatures normal for winter plants. Before being sown in the field, a sample of seed was vernalized for 5 days, another for 10, a third for 15, etc., up to 40-50 days. all these seeds, vernalized to different degrees, were separately but simultaneously sown in field plots in spring. The plants from the completely vernalized samples developed normally, and gave straws and ears, with no delay at the stage of vernalization (since the latter had already passed). The plants from the samples with very nearly completed vernalization complete it rapidly, provided that a relatively prolonged period of low temperatures occurs after the spring sowing in the field. If this is not the case, the plants from the seeds with a slightly incomplete process of vernalization before the sowing, complete it, but after a delay. Such plants give more or less late. These plants are most interesting for experimental purposes. Hereditary spring forms are most often obtained from them. Hence, for further work aimed at obtaining spring forms from winter ones, seeds must be taken from samples incompletely vernalized before sowing, which have completed the process of vernalization after sowing in spring field conditions. Such seeds give a greater or lesser percentage of hereditary spring forms. With the aid of this method many spring forms have been obtained from all winter wheat varieties which were taken for the experiment at the Institute of Selection and Genetics of the V. I. Lenin Agricultural Academy.
It is obvious that the heredity of winter forms can be changed into that of spring forms. The change can be accomplished through the influence of the high temperatures which are suitable for the heredity of the vernalization stage of the cereal forms called "spring varieties". This confirms our view that the alteration of the heredity of any property corresponds specifically to the influence of the conditions of the external environment.
It has been stated that not all the seeds obtained on grafted plants give rise to hybrids. The frequency of the latter depends upon the ability of the experimenter to overcome, to force the grafted variety to assimilate plastic substances unsuitable to it. In the same way, spring plants are not obtained from all the seeds of a winter wheat variety harvested from parents known to have accepted, i.e., completed, the vernalization at high spring temperature.
Causes of failure to form shoots in plants altered with respect to the vernalization stage. In most such cases the situation resembles completely the behavior of plants obtained from the usual, unchanged, winter seeds. This happens because, when seeds of plants known to have been changed with respect to the vernalization stage are sown, plants are frequently obtained which fail to form shoots when sown in spring.
Thus, ordinary, unvernalized, seeds of three winter wheat varieties were sown by a sowing machine on the fields of the Odessa Institute of Selection and Genetics in 1936. The spring was early, prolonged, and cool. When winter varieties are sown in spring no shoots are usually formed, or else a few plants form shoots late in the summer. But the plants of all these three varieties ("Novokrymka 0204", "Kooperatorka", "Stepniachka") gave a uniform shoot formation and a fair yield, though after a delay. The seeds of all three varieties from this crop were again sown in the field without previous vernalization in the spring of 1937. As a parallel experiment, seeds of these varieties from the crop of the usual winter sowings were sown simultaneously. One would expect that plants of the winter varieties obtained from the crop sown in the spring of the preceding year without vernalization before sowing, should give in the new generation (when sown in spring of 1937) a more uniform shoot formation, a higher percentage of plants forming shoots, compared with the parallel experiment indicated above. But in reality the situation was the reverse. In all three varieties, the plants from the seeds planted in the spring for the first time gave, although a small percentage and with a prolonged delay, some shoot formation; while the percentage of the shoot formation was much lower in plants coming from the seeds planted in spring for the second time. To be sure, the shoot formation in plants from the seeds of the second spring planting was taking place much earlier.
The result of this experiment obviously shows that the abnormal completion of the vernalization process by plants of the winter varieties sown in the spring of 1936 altered their nature. At first sight it may seem, however, that this alteration took place not in the direction of a spring form, as it should have, but, conversely, toward a more extreme winter form. Indeed, on the plots sown to these seeds in 1937 a smaller percentage of shoot-forming plants was obtained than on plots sown to the same varieties for the first time. In reality, the alteration of the vernalization stage of the plants of the 1936 sowing took place in the direction of decreased winterness (requirement of low temperature for the occurrence of the vernalization process). But many experiments show that when an old, stabilized, hereditary property, like the property of winterness in the case under consideration, is liquidated, a new stable heredity is not yet obtained. In a great majority of such cases plants are obtained with the so-called destabilized heredity.
Destabilization of heredity. Plant organisms whose conservatism is liquidated, whose selectivity toward the conditions of the external environment is weakened, are referred to as having a destabilized heredity. Instead of a conservative heredity, such plants preserve, or acquire, only an inclination to prefer certain conditions to others.
Destabilization of heredity can be obtained:
(1) Through grafting, through growing together of tissues of different varieties;
(2) Through treatment with conditions of the external environment at certain stages of certain developmental processes;
(3) Through crossing, particularly of forms sharply differing in habitat or in origin.
The best biologists, Burbank, Vilmorin, and particularly Michurin, have paid much attention to the practical significance of plant organisms with destabilized heredity. Plastic plant forms with unfixed heredity obtained by any method must be sown generation after generation in those conditions the requirements and the stability of which is desired in the organisms in question.
When the conditions necessary for the occurrence of a certain process in a plant with a stable heredity are missing, for example, when the low temperatures necessary for the vernalization stage of winter varieties are not available, the process usually does not take place. The plant, as it were, waits for the advent of the necessary conditions. If the temperature falls during the nights, the winter varieties sown in fall go through the stage of vernalization. If the temperature rises during the days, the process of vernalization is discontinued until a lower temperature comes along, even if the interval lasts for many days.
Organisms with a destabilized heredity, such for example, as the offspring of the winter varieties which completed the vernalization stage at high spring temperatures, have no fixed heredity, no requirements, but only a preference for the conditions at which the vernalization process has been completed in the plants of the preceding generation. If such a temperature is not available, the process does not wait, but begins to go on at the temperature that happens to exist. As a rule, temperatures, as well as many other conditions, vary, fluctuate, in the usual field conditions. Owing to the conservatism of their heredity, plant organisms insistently, stubbornly, select from the varying, fluctuating environment only what is necessary for the occurrence of certain processes. If, however, the heredity is destabilized or unfixed, the process fluctuates, goes in various directions, as it were. At low temperatures it goes in one direction, with the advent of high temperature in a different one. The resulting process is uncoordinated. This explains the instances of winter wheat plants with admittedly altered vernalization stage failing to form shoots when sown in spring. These plants remain in the stage of tillering not because they are winter plants, but because the process of vernalization can not be completed because of proceeding in different directions.
Growing conditions for plants with altered, destabilized, heredity must be chosen carefully. It must be kept in mind that these plants are frequently highly sensitive to environmental conditions. Hence conditions must, so far as possible, be provided leading in the direction which it is desired to fix the heredity.
The evolution of plants and animals occurs in nature through accidental alterations of the old heredity, and accidental construction and fixation of a new heredity. In experiments and in practice, it is possible to alter directionally the heredity of various processes in plant and animal organisms, and to build and to fix a new heredity according to plan.
To obtain spring varieties from the seeds of destabilized winter plants which have completed the vernalization stage at high temperatures, the sowing in the field in spring must be made at different times, from the earliest on. This will give a chance for the plants of one or another sowing to have their process of vernalization stumble accidentally toward whatever conditions of the external environment for which it has a preference. Such plants will rapidly form shoots. Seeds harvested from them will in a great majority of cases give offspring similar in behavior to spring forms. Yet, the heredity of such forms will still be in sufficiently fixed. These plants may still be deflected from their more or less established spring habit if exposed to unusual spring sowing conditions, such as an excessively long and cold, or excessively hot and brief spring. After having changed the heredity of a winter variety through the influence of spring temperature conditions on the process of vernalization at the time of its completion, the heredity of the spring habit must be stabilized gradually, in two to three generations. Only thereafter will this form be stabilized
Transformation of spring varieties into winter hardy ones. Intensification of the winter hardiness of winter varieties. Very important for many regions of the USSR is transformation of spring varieties of cereals into winter hardy winter varieties, and of winter varieties into more winter hardy ones. These experiments do not differ in principle from those in the examples discussed above. The change of varieties with a hereditary spring habit into winter ones takes place through autumn sowing. Spring forms of cereals are treated with a long period of low temperatures (autumn, winter, and early spring) while they are passing the stage of vernalization. A repeated sowing of such seeds in autumn intensifies the new property of being a winter variety. They have their requirements of low temperature conditions during the process of vernalization intensified.
Further generations of cereal plants with unfixed (destabilized) heredity, will, if sown year after year in progressively more severe winter conditions, acquire greater and greater requirements of low temperatures. They will acquire greater and greater resistance to strong frosts. Several good varieties of spring wheat which were derived by various experimenters from winter wheats are now available. These new varieties possess a degree of frost resistance not inferior to that of the winter variety "Lutescens 0329" of the Saratov Selection Station, which is considered the most frost resistant wheat.
A winter form was obtained after several generations of autumn sowing from the spring variety "Erythrospermum 1160" by A. F. Kotov and N. K. Shimanski, scientific collaborators of the Institute of Selection and Genetics. This form manifested good possibilities when sown at the experimental Base of the V. I. Lenin All-Union Academy of Agricultural Sciences at "Gorki-Leninskie" in the Moscow region, as well as on experimental plots of the Krasnoufimsk, Barnaul, and Semipalatinsk selection stations, and in a series of other places.
It is interesting to note that the seeds of this wheat variety sent to all the above points in the fall of 1940 were taken from the same bag. Yet, since this wheat is not yet fixed, is still highly plastic, it has become modified toward the living and growing conditions of each place where it was planted. The conditions of each place have left their imprint on this plastic, pliable plant form. In the severe overwintering conditions of Siberian regions this wheat is becoming progressively more frost and winter resistant from year to year.
Com. A. A. Avakian has transformed the spring wheat "Lutescens 1163" of the Institute of Genetics and Selection into a winter variety by means of a fall sowing. At present, this wheat approaches the most frost resistant winter varieties in its resistance to the vicissitudes of winter. A series of wheats exceeding in this respect the most frost resistant "Lutescens 0329" was obtained by transforming the volunteer plants of Siberian spring wheats into winter ones. Thus, a wheat collected by the kolkhoz member Sekisov (the Michurin kolkhoz, Barnaul district, Altai region) is known to exceed in frost resistance the "Lutescens 0329" from Saratov. A series of other winter forms obtained from spring volunteers at selection stations in Siberia are rich in potentialities for breeding highly winter resistant wheats.
The scientific worker Com. Solovey has, by means of autumn sowing, obtained a winter form from the spring barley "Pallidum 032" of the Odessa station. Owing to the plasticity of this form, it proved to be easily adaptable to rather severe winter conditions. In the opinion of the writer, this is one of the most winter resistant winter barleys known. It has withstood fairly well two winters in the field at the experiment Base and the Academy of Agricultural Sciences at "Gorki-Leninskie" near Moscow, as well as at the State Selection Station at Kazan. The usual winter barleys do not overwinter in these regions.
Creation of conservative heredity of desirable properties in the progeny of a destabilized organism. The most interesting practical feature of these experiments is that the resistance to frosts and other unfavorable overwintering conditions in these forms of wheat and barley can be rather easily increased from year to year. The unfixed forms with destabilized heredity can easily be changed in the direction of increased resistance by means of the influence of progressively more severe winter conditions. The acquired characters will be more and more fixed from generation to generation. But with a wrong management of the first generations of such an unfixed material the acquired characters may easily be lost. For example, the winter barley obtained by Com. Solovey from the spring variety "Pallidum 032" proves to be, as already pointed out, the most winter resistant known variety of winter barleys when planted on experimental plots in the Central Region of our Union. A specimen of this barley was sown in spring of 1940 on the plots of the All-Union Agricultural Exposition. It behaved for some time as a winter variety. The plants were prostrate, the straw (shoots) did not develop. These barley plants, being a winter variety, supposedly could not pass the vernalization stage at the spring temperature conditions. Yet, all the plants on this 100-meter plot rapidly produced shoots and gave a fair yield of grain. This shows that the heredity peculiar to a winter variety has not yet become fixed in this form of barley. Having been sown in spring, the plants, after waiting for some time for the advent of cool temperatures, which, naturally, did not arrive, became vernalized according to a new type, i.e., the spring one. The seed crop of these plants was sown by Com. Avakian in the fall of the same year 1940 on the plots of the experimental Base of the V. I. Lenin All-Union Academy of Agricultural Sciences near Moscow.
Seeds of the same variety from the Exposition plot of the autumn, 1939, sowing were simultaneously sown. The seeds from the spring planting of the preceding year withstood the winter 1940-1941 incomparably worse than the variant obtained from the seeds of the fall sowing of 1939. The growing of this barley variety after a spring sowing in only a single generation has considerably weakened the winter hardiness of the offspring of these plants. This example shows that plastic, unfixed, plant forms obtained by any method should be sown generation after generation only in those conditions which are to become required and stabilized in these plants.
Plant organisms unfixed in their heredity present in many cases, most valuable material for the creation of desired forms and varieties by means of a proper education while they are still destabilized. Work is being carried on at present and results deserving attention have been already obtained, toward the creation of winter-resistant varieties of winter wheat that would stand the severe overwintering conditions of Siberia. Spring wheats, quite non-resistant to start with, are being transformed by means of destabilization and alteration of the vernalization stage into frost-hardy ones. By the same method, winter wheats are being transformed at selection stations in Siberia into still more winter-resistant winter wheats.
It is important to note that Lysenko described two distinct methods for vernalizing wheat to grow in the spring. The first, moistening and chilling the seeds for 30-50 days, satisfies the vernalization requirement and allows the grain to germinate and grow without further chilling. The heredity of the wheat is not altered in this case. The second method can be understood as an exercise in selective breeding. Various lots of seeds were chilled for different periods in order to isolate a relatively small number of plants with reduced chilling requirements. Some of the next generation seeds should require even shorter chilling periods. In principle, this is no different than selecting plants with the palest flowers, then raising their seeds and selecting again until some plants produce nearly white flowers. Nevertheless, many western geneticists (and others) have chosen to confuse the two methods and claim that Lysenko believed that chilling seed alone caused a permanent alteration of its heredity.
(CybeRose note May 4, 2005)
Furthermore, the Michurinists disagreed with the Morganists (neo-Darwinists) about the meaning of heredity or inheritance. The Morganists were primarily concerned with discrete units of heredity (genes) that are transmitted without modification — except in the case of mutations. And when mutations occur, they insisted, they were random relative to the needs of the organism. Michurinists, to the contrary, understood that evolutionary change cannot be entirely random. All around they saw plants and animals that were too well adapted to the prevailing conditions to have arisen by chance alone.
It is well known that many plants are sensitive to photoperiod. Some will not flower unless the light phase (day) is longer than some critical number of hours. Other plants flower during short days. Then there other species that respond to temperature, flowering only after a prolonged period of heat or cold. How does it happen that related species are stimulated to the same developmental phases by entirely different conditions?
Consider a long-day plant that flowers in summer. It may require 15 hours of illumination at 70°F to initiate flowering. If a group of seedlings of this species or strain are given only 14.5 hours of light, some may flower while others will not. But if we test the non-flowering specimens in varying environmental conditions — at 85°F, for example — some may be induced to flower by the extra warmth.
We may then isolate the specimens that respond to warmth, and cross among them. In the next generation we may find a few that are more capable of responding to warmth, with a consequently reduced dependence on photoperiod. That is, the plants will bloom sooner than the original stock so long as the ambient temperature is high enough. And where the high temperature period precedes the season of long photoperiod, the modified plants no longer delay their flowering until the long days arrive.
To a Michurinist, the heredity (phenotype) of the plants has been altered. A geneticist may insist that the hereditary units (genes) have not been altered, but cannot deny that the method allows numerous "genes" with trivial individual effects to be brought together in a new genotype with a distinctly altered phenotype. It is not necessary to isolate the genes, nor even to count them.
"Destablizing" the heredity (expression) is accomplished by almost satisfying the conventional requirement for passing from one developmental phase to another. In this state various minor responses are brought into high relief. A slight sensitivity to high temperature would not be noticed if the plants were already initiating flower buds because of the long photoperiod. By almost satisfying the photoperiod requirement, we allow the slight tendencies — inherent in the original stock — to "tip the scales" towards flowering, or other developmental phase.
And because there has been no previous selection for or against these small, inherent variations we may expect considerable randomness in the kinds of sensitivities. That is to say, the Michurinist method does not cause gene mutations. But it does allow slight inherent variations to be identified and collected into a new strain differing from the original primarily in the altered response to environmental triggers.