Some Problems of Method p. 44-51 (1934) 1952

Means of Shortening the Vegetative Period of New Plant Varieties
Ivan Michurin

The ten new hybrid varieties of hardy grape—which stand the winter without any artificial protection—that I have produced in late years made it possible to extend the zone of cultivation of the grape another five hundred kilometres northward.

Besides winter-hardiness, what is needed of the grape for the advancement of its cultivation northward is later flowering, because of the spring morning frosts, and earlier ripening of the fruit, because of the early autumn frosts. All this together presents a difficult problem, namely, how to shorten the vegetative period of the grape.

Already in the 1900's, while working on hybrid varieties of yellow cigarette tobacco, the Kommunarka early-ripening melon and hardy grape seedlings—the first to be produced in those days—I was agreeably surprised, when selecting seedlings that completed their vegetative development earlier than others, to find that some of the seedlings that had germinated from seed later than others, namely, at about the beginning of July, managed to complete their growth and mature even earlier than those that had germinated in the middle or beginning of May.

I made a note of this marked, and at the same time rather paradoxical, phenomenon, and in subsequent years I never failed to keep watch for similar manifestations in interspecific hybrids of other plants. It turned out that this phenomen is in most cases to be met with in hybrids from parents whose habitats were very far apart, and that, on the contrary, it is practically never encountered in simple seedlings or in hybrids from varieties of one and the same species coming from mutually close places of origin. This, of course, could only be explained by the fact that hybrids of parents of mutually remote places of origin are always far more susceptible to alteration of their properties under the influence of the environment than are simple seedlings or hybrids from parents whose birthplaces were not far apart. It is more difficult to find convincing reasons for the acceleration of the vegetative period in seedlings that germinate late from the seed. An exception, perhaps, is the hypothesis that the higher temperature in July, as compared with May, has an influence in accelerating cellulose formation in the shoots. But is this so? We know that in our parts shoots from later plantings usually result in plants which mature late, or which are still completely immature by the autumn. Moreover, everyone is familiar with the influence of equal quantities of heat on northern and southern plants: to equal amounts of heat northern plants react far more quickly than southern, a fact which was noted already in the seventies of the last century by A. de Candolle. This phenomenon is very natural and does not need experimental verification—it has nothing to do with our problem. What we are speaking of now is the faster rate of cellulose formation in late, July, shoots under the influence of a greater sum-total of heat, as compared with that of earlier, May, shoots, resulting in the latter case in a slower rate of growth. Well, this accelerated building of the organism in the very earliest stage of development of hybrids obtained from parent plants of mutually remote places of origin, sometimes becomes fixed and remains unaltered throughout the subsequent life of the plants. In this way varieties of plants are obtained with a shorter vegetative period, a feature of extreme importance for the northward advancement of the cultivation of southern species, e.g., grape, apricot, peach, etc.

Let us try to analyze the problem by successively examining the whole life cycle of a plant, beginning with the earliest stages of its development. Let us start with the seed and consider what it represents. Its most essential part is the embryo of the seedling, which harbours within it the rudiments of a multitude of properties hereditarily transmitted to their offspring from the parents and their forebears, and, secondly, the cotyledons which consist of a stock of nourishing substances needed for the initial development of the shoot and its radicle. The composition of this stock is not a dominating factor, as is shown by the experiment of removing the cotyledons and grafting those of a different seed in their place.

As to the large number of properties hereditarily transmitted to the embryo by the parents, only a few of them, as I have said before, will develop in one degree or another, those, namely, to which the environmental conditions of the given period of the year are favourable. Furthermore, some of the properties which under the influence of the environment acquire the ability to develop, more or less undergo alteration, while from the totality of the interactions of others, absolutely new properties result, properties not possessed by the parents, as can be seen in the given case. It is because of this process that mutational deviations are manifested more strongly in the early period of development of the plant organism, and more feebly in the later stages. Shortening of the vegetative period in some hybrid seedlings that germinated late from the seed must be regarded as one of these mutational deviations.

Further work in this direction will show whether this is so or not. The essentially important thing for us is that this phenomenon provides a base for the creation of many species of plants with a shortened vegetative period. The absence of such species of plants in the past made it impossible to introduce for commercial cultivation in the central regions and the north of Russia many southern plants with a long vegetative period: One of these southern plants is the grape. The new, precocious varieties of grape do not suffer from the winter frosts, it is true, but late spring morning frosts may kill their blossoms, and, moreover, the early frosts, which in the northerly regions sometimes occur at the end of August, likewise do not spare the fruit of the grape. What we need are hardy varieties which begin to vegetate late, to blossom late, and to ripen early.

For the solution of this problem we, in our nursery, have planted for the spring and summer of 1935 seeds of new varieties of hardy grape which needs no protection against winter frosts and which ripens early. These seeds were taken from the first fruits of the new varieties, which were completely isolated from the chance pollen of any late-ripening cultivated varieties. Seedlings obtained from the seeds of a new variety of plant at the time of its first bearing are most amenable to alteration. The last two conditions are of immense importance. The shoots from such seeds should be pricked out from the boxes and planted in the beds in rows in strict succession as they germinate, thus artificially helping to lengthen the period between the early ones and late ones. In the autumn, selection should be made by picking out the seedlings, wood formation along the vines of which has reached the greatest height. The results of the experiment should then be assessed. In this way we shall obtain already in this first generation a sufficient deviation towards later beginning of growth in the spring and earlier termination of growth in the autumn.

It should furthermore not be forgotten to terminate growth artificially at the end of the summer (beginning with August 25) by nipping off the ends and the spurs of the vine.

When selecting one- and two-year-old hybrid and simple seedlings according to habit, it should be borne in mind that in the case of the grape, as of all species of plants at a young age in general, the constitution of all parts of the organism in its infancy has an inherent tendency to deviate towards the form of the wild progenitors.

This deviation is one of the manifestations of the so-called biogenetic law, according to which every organism in its embryonic and infant development repeats all the alterations of form through which its race had passed.

When selecting seedlings, those with the shortest vegetative period should be considered the best. From these seedlings a selection should be made according to sturdiness of development, thickness and length of the vines, and largeness of the leaf laminae, and also, of course, according to frost-hardiness and immunity to disease and parasites. Later, at the time of the first bearing, selection should be made according to yield and the taste and external qualities of the fruits.

When selecting seedlings it should be remembered that not only in some hybrids, but also in pure species of grape, sometimes as many as sixty per cent of the seedlings develop into staminate plants. Such seedlings should be destroyed, since they cannot bear fruit.