Principles and Methods (1929)
Ivan V Michurin



Fig. 49. Dwarf nine-year-old blackthorn

In the early period of my activity (back in the eighties of the past century) devoted to the improvement of fruit plants of superior-flavour qualities with a view to making them more hardy in our locality, I could not of course even dream of introducing in our orchard culture fruit plants so exacting in regard to warmth as apricots and peaches. All the more so since among our wild forest types there was not a single representative of these plant species, and, consequently, I could not in this case even think of hybridization, i. e., of crossing delicate cultivated strains with our wild species with the aim of obtaining more frost-resistant seedlings, just as I do with pears, apples, cherries and plums. The almond I obtained by crossing the dwarf almond (Amygdalus nana L.) with Prunus Davidiana Franch. (David's peach), which I named Posrednik, even though it does cross with cultivated peach varieties, produces for the most part seedlings entirely identical either with the maternal plant or with the paternal plant, and with hardiness insufficiently enhanced. Besides, all the attempts of horticulturists to introduce peach culture in localities north of the Crimea, even in places much more to the south than our parts, for example, in Kiev or Chernigov, usually ended in complete failure.

But in spite of this I never gave up the idea of finding some means of overcoming all these obstacles. In the end, after further searches I obtained the stones of several hardy varieties of the Manchurian apricot and a semi-cultivated type of peach from middle Manchuria and, later, of another semi-cultivated type of peach from North Korea, which thrive in places even severer than our locality (as regards climatic conditions in the winter period, the absence of a snow cover throughout the first half of the winter and the temperature dropping to 33 below zero Centigrade). The only material difference is the longer summer period in their native regions, owing to the fact that their latitude is much lower south than that of our locality. Though, on the other hand, they are partly subject to fog and cloudiness (the number of sunny days there is greatly reduced), which almost equalizes the longer summer period in the home of the Korean peach with our relatively short summer. Nevertheless, in our locality the majority of first-generation seedlings (owing to the late germination of the stones) have shoots of summer growth insufficiently ripened and, naturally, their tips and sometimes the entire shoots suffer from the winter frosts and freeze down to the snow line. Such individuals, which suffered in the first winter, should be replanted without fail in the spring of the second year, their roots being shortened by one-third. Otherwise they will develop during the summer of the second year very luxuriant shoots replacing the destroyed parts and then they will again freeze in the second winter. The individuals which terminate their growth earlier have to be singled out. The specimens obtained cannot of course as yet represent quite suitable varieties for extensive peach culture on commercial lines in our parts, because the fruits will not have a good enough flavour and will ripen very late. Besides, the saplings of these varieties selected for hardiness will have the defect of early blossoming and, consequently, their flowers will often be destroyed by morning frosts in late spring. But all these defects can be eliminated by one of three methods or by a combination of these methods simultaneously applied.

1This approach towards acclimatization of exotic plants is,
firstly, quite new and, secondly, fully serves the purpose.

The first and simplest method consists in planting large numbers of stones from several generations of seedlings selected for relative hardiness and early maturation of fruits in our locality. The second method, which lakes less time, consists in altering the constitution of the peach seedlings at the earliest stage of their development through the influence of the stock (vegetatively), for which purpose the seedling in the first half-year after its germination from the seed should be budded upon a stock of our local feebly-growing blackthorn. The third method is that of hybridization, of crossing the peach with the hardy dwarf almond or its hybrid, Posrednik. Lastly, a more reliable way is to combine the action of the second and the third methods. In this case, by shield budding with still not fully ripened buds from half-year-old peach seedlings upon blackthorn, we introduce considerable alterations into the constitution of the young and still unstable organism through the influence of the stock in the direction of reducing the vegetation period. This is observable even in the fact alone that the buds grafted upon blackthorn stocks complete their formation a full week earlier than the buds of seedlings grown on their own roots. From the very first year all such grafts develop a more squatty growth and complete it much earlier, as a result of which the woody tissue matures much more fully and, naturally, becomes more hardy to the winter frosts. Then, in the spring, the sap from the roots of the stock begins to move much later, with the result that the beginning of blossoming is retarded, and the fruits are thereby safeguarded from being injured by morning frosts in the spring. All such alterations provide in their sum the opportunity of obtaining quite sturdy and hardy forms close to cultivated peach varieties.1

At present the production in our parts of hardy hybrid varieties of peaches by means of hybridization with old varieties which yield large-sized fruits of superior flavour no longer offers any difficulties.

Mention should be made also of a special variety of dwarf blackthorn, two metres in height, suitable for this purpose, which I bred in the course of forty years by planting four generations, by training the seedlings and by strict selection of specimens for low growth and absence of root shoots.

As a result of all this the new variety is easily reconciled to the new plant community. In general, as regards phytocenosis (plant community) it is to be presumed that in the vegetable kingdom, with the exception of epiphytes, cenosis (community) plays an important role only in the beginning of the origin of each species. Later the effect of community presents no serious obstacles either for propagation or for the spreading of a species to a different locality; otherwise we would not be witnessing the diffusion of numerous identical species in various parts of the globe.

In this case, apparently, the plant should also more easily acquire the property of changing from a constitution characteristic of short-day plants to a type characteristic of plants adapted to the longer day in our locality, and photoperiodism will not present many difficulties in this respect.

Of the numerous species and genera of stone plants, so far scarcely more than a dozen species have been introduced in our orchard culture; the rest still remain largely in a wild state in various parts of our vast Union.

Fig. 50. Korean peach

In this review I shall only mention a small part of the new types I have introduced into culture with varying degrees of success. Yet if many of them had been subjected to the powerful action of hybridization and selection we should most likely have obtained numerous new varieties of good quality as regards productivity and effectiveness for culture in our orchards. Furthermore, in this sphere (introduction to culture of wild species of stone fruits) we come across utterly unexpected phenomena such as the fact that in the case of the universally-known delicate warmth-loving apricots and peaches which in our country are grown only in the southernmost sections of the Union (Crimea, Kazakhstan, the Caucasus), closely-related species are found in the Far Eastern Territory and in the northern part of Korea. Such plants (see Fig. 50) sometimes prove resistant to even intenser frosts than occur in our parts. In their native haunts they endure frosts of 35° below zero Centigrade in snowless winters and produce fruits of a good flavour, only the layer of flesh is much thinner than in the European varieties.

Here is a list of them.

1. A special type of hairy peach grows in middle Manchuria, where it is known by the name of Mao-Tkha-Or. Its fruits have a juicy flesh of a good flavour, but the skin is so thickly covered with down that it must be pared off before the fruit can be used. Its stone has an obtuse end (see Fig. 51) and is not always easily detachable from the flesh. Its hardiness to frost is even greater than that of the Korean peach varieties. The fruits ripen by October 15. In its native haunts in middle Manchuria this species withstands frosts of 35° below zero Centigrade in extremely dry. snowless winters with withering north winds. The Americans usually classified it as belonging to the northwest Chinese species, closely related to the peach and known as Amygdalus Kansuensis; however, there is an essential difference between these species as regards the structure of stones, and also as regards the structure of branch growth and of the skin of the fruit.

It is already three years since I introduced this species in large numbers of seedlings into the experiment nursery.

Fig. 51. Stones of peach species:
A—The prickly cherry Prunus plagiosperma Oliv.; BPrunus Davidiana; CAmygdalus Kansuensis; DAmygdalus Mao-Tkha-Or; E—Korean Amygdalus; F—Peach Amygdalus

2. There are several varieties closely related to cultivated strains of apricots, from whose seedlings I have produced here in Michurinsk as many as ten kinds which freely withstand our winter and yield tasty fruits of different shapes. Only late spring frosts sometimes interfere with their early blossoming.

When planting the stones of these peaches and apricots in our parts we may definitely hope (by selection of seedlings and artificial shortening of their usually protracted vegetation period) to obtain new varieties suitable for our section of the country. At present the work with these plants consists only in selection of later-maturing specimens to avoid injury from late spring morning frosts in our locality. And only when we are through with this work shall we begin to apply to choice individuals various methods of increasing the layer of flesh in the mesocarp by selecting the proper seedlings in the plantings of succeeding generations and also by bringing to bear the influence of stocks of the interspecific hybrid which I call Cerapadus—stocks more nourishing and with a shorter vegetation period of development—and making sure to provide soil to which this species of peach is accustomed in its native country.

As a last resort we may, provided we are very cautious in the choice of male parent (in the sense of avoiding the danger of loss of hardiness under the influence of European varieties), try hybridization, crossing it with southern European and American cultivated large-fruited varieties.

3. A species of peach most closely related to European peach varieties has, as we now learn, been cultivated in North Korea for a long time. Its fruits are much less covered with down than the fruits of the Manchurian hairy peach, Mao-Tkha-Or.

1Found during an expedition in 1929 by N. N. Tikhonov, an explorer of the
Far East, who lives in the city of Nikolsk-Ussuriisk [now Voroshilov.—Ed.].

The place where three forty-year-old trees of this North Korean peach have been found1 is at a distance of fifteen kilometres from the sea, owing to which it is mostly foggy and there is much less sunshine than in places more distant from the sea. The intensity of the heat of the sun is also smaller. Owing to the cold current from the Sea of Okhotsk and the prevailing north winds, the climate in its place of origin is much severer—the winter is long and snowless during its first half, the soil freezes to a great depth, the summer is cool, the temperature in winter drops to -33°C.

Fig. 52. Leaf of Mao-Tkha-Or Fig. 53. Black apricot (reduced)

A specific feature of the structure of the Korean peach is the bright-brown velvety coating sharply distinguished on the trunk and on the lower part of the main branches—a feature which, as we know, is not met with in any other species and varieties of the peach and its kindred. Further, this species possesses a fairly squatty growth (provided the one-year-old seedlings are properly trained by drying and by pruning of roots) and is more hardy than all other species and varieties both of its wild kin and of cultivated peaches.

Only the Mao-Tkha-Or described above can rival the Korean peach in frost resistance.

Fig. 54. Ando cherry in bloom

The fruits of the Korean peach are of an oval shape, 30-40 mm. long, 25-35 mm. in diameter, and weighing 10 gr. The skin of the fruit is of a light-green colouring with a scarlet tint on the side, and it is all covered with down, though considerably thinner than in the Mao-Tkha-Or. The flesh, its layer 8 mm. thick, is juicy, of a good flavour, and freely detachable from the stone. The latter—with little knobs and grooves characteristic of all peaches in general—terminates in a sharp thorn.

4. Further, one more eastern species of black apricot is being experimented with—the Prunus dasycarpa Ehrh. (See Fig. 53.)

5. Considerable interest attaches to other natives of the Far Eastern Territory—the numerous varieties of the Prunus triflora Roxbg., which I have lately begun to cultivate for the purpose of hybridization with European plums.

6. Another drupe from North China, known there under the name of Ando, may play a big part in the planting of shelter belts. It is the cherry Prunus tomentosa Thbg., a low shrub, not more than 1.5 m. in height, with leaves of a peculiar shape and medium-sized sweet fruits. (See Fig. 54.)

7. Next, the eastern species of what is known as the prickly cherry Prunus plagiosperma Oliv., a rare and singular type with leaves like those of the peach, with flowers of a yellow colouring and long sharp prickles on the twigs, and the stone in the fruit entirely flat, like a button, and marked al over with tiny knobs. Some of its seedlings are fairly hardy. (See Fig. 55.)

Fig. 55. Fruits of the prickly cherry

8. Seedlings of the dwarf cherry (Prunus prostrata Labill.) from the slopes of the Tian-Shan Mountains grow splendidly in my garden. I regard them as very valuable material for breeding cherries of low height as more convenient to take care of and for the introduction of mechanization in the harvesting of the crop.

Fig. 56. Fruits of the American cherry Prunus Besseyi
9. Lastly, various forms (see Fig. 56) of the American sand cherry (Prunus Besseyi Waugh.) and a variation of it, Prunus pumila L. (var. typica). The latter, incidentally, seems to me much less suitable for our region—the fruits are small and tasteless.

In general, American plants are of much less interest to us than the plants of the Far Eastern Territory.

10. The work with sweet cherries presents a somewhat different picture. Here we are confronted not so much with the lack of hardiness in the wood and branches to our winter frosts, as with the sensitiveness of the fruit buds to frosts, from which even our old ordinary varieties of sour cherries, the Morellos, suffer. This weakness is a stumbling block in our work with sweet cherries. For example, seedlings selected for hardiness grew up into large thirty-year-old trees with rare and very small yields; finally, in the winter of 1928/29 some of them were killed by the frosts. I am referring here to seedlings of the pure species. As for hybrids of sweet with sour cherries, only those of them are distinguished by hardiness which have deviated in their constitution towards the type of ordinary sour cherries, such, for example, as Krasa Severa. The hybrids which in their habit strongly deviate towards the sweet-cherry type usually bear an insignificant quantity of fruit, because the winter frosts injure the fruit buds.

11. Some choice seedlings of the rose Virginia chokecherry (Prunus virginiana L.) produce very effective-looking clusters of ruby-coloured fruit which attract everyone's attention; their flavour is much better than that of our ordinary bird cherry. The shape of the clusters differs greatly among the numerous varieties, particularly among the hybrids with sour cherries, with which I have succeeded in crossing them in order to make their fruit larger in size.

Their trees are of small stature, from 2 to 3 in. high. They are quite hardy to the winter frosts in our locality. This plant may prove to be good for shelter belts. Besides, this new type of drupe (Cerapadus) is a very important component for hybridization and the breeding of new kinds of fruit trees in Voronezh Region, as well as in more northern regions, not excluding Siberia, where, I may mention in passing, even ordinary bird cherries are always in large demand.

12. There exists also a new variety of my breeding—the Kapolina, which is now being experimented on.

Among the other Korean, Manchurian and Japanese types of stone-fruit plants we find such as bear fruit of enviable quality but some of them possess no hardiness whatever in our region, as, for example, the Kelsey plum and its variety Poksua among the Koreans; others, like the Japanese bitter cherry (Prunus japonica Thbg.) or the Japanese apricot (Prunus mume Sieb.) and Prunus serotina Ehrh., are hardy in our parts; however, their fruit being of low quality, they are only fit for hybridization experiments, but not for culture in our orchards.

The same must be said of some wild-growing species of American plums and cherries, and also of the new hybrid varieties of fruit and small-fruit species, most of which prove sterile in our parts, and, although they are hardy to our frosts and blossom profusely, they form no fruit at all or in a negligible quantity.

Fig. 57. Interspecific cross between the chokecherry Prunus virginiana and Ideal cherry (Pr. virginiana L. X Prunus Chamaecerasus Jacq. X Pr. pennsylvanica L.).
Left, Ideal; right, Prunus virginiana; centre, the hybrid

Thus, a large number of seedlings of Prunus americana Marsh., Prunus hortulana Bailey and Prunus nigra Ait. in my possession have so far remained sterile. Apparently, because they lack pollinating varieties, or, perhaps, because they blossom very early in the spring, at a time when in our locality the insects which help their fertilization have not awakened to activity.

That is why the various enthusiasts who recommend American plants for us would do better to moderate their passion for the introduction of these varieties into our orchards.

In conclusion I consider it necessary to mention once more the special type of dwarf blackthorn (Prunus spinosa L.) which I have produced in forty years by planting four generations with strict selection for hardiness, dwarfishness and absence of root shoots.

In the regions of Central and Northern Russia there has long been felt the need for this new ideal stock to be used in grafting peaches, apricots and delicate plum varieties for culture in dwarfish shapes. This blackthorn is propagated by the planting of its stones, and it remains constant, without changing its properties.