Principles and Methods (1934)
SELECTION OF HYBRID SEEDLINGS
In essence, I divide plant breeding into two sharply different kinds. The first is selection from the mass planting of a certain species or variety of plants of chance deviations expressed in the form of mutations, or such as result from natural crossing with other varieties. I regard this kind of plant breeding as the meanest kind of work an originator can undertake, for only an utter ignoramus can plant haphazardly tens of thousands of plants belonging to one variety and then pick two or three of the best specimens and destroy all the rest. What does man give the seeds of the plants to help them to acclimatize themselves? In all such operations he relies solely on chance, he hopes that among the seedlings there will accidentally appear one out of several thousand specimens that will be relatively more hardy.
This haphazard method of acclimatization is not only totally unscientific, but involves the state in heavy and scarcely productive expenditure of forces and funds for conducting the work on these lines.
Nature alters the structure of living organisms, adapting them to the conditions of their environment only very slowly, barely perceptibly, in the course of whole milleniums.
By means of artificial cross-pollination (hybridization), however, it is possible to produce in relatively short periods of time considerable changes in the hybrid plants which gradually acquire complete stability if this crossing is repeated for several years.
Consequently, man should proceed only along this more reliable road and resort to selection from simple mass planting only in extreme cases when the possibility of employing hybridization is completely absent. Nevertheless, the majority of our experimental stations base themselves in their work exclusively upon selection from simple mass planting and put this method in the forefront.
Such miserable treasure hunters base themselves solely on the material possibility of mass planting and later are satisfied with isolated, chance finds among these plantings. It is permissible to resort to these methods of selection only as subsidiary work, when there is an extreme lack of experience in raising new varieties.
The originator must strive with the aid of hybridization and individual selection to prepare beforehand not a hundred thousand, but only some lens of seedlings with approximately the desired structure of organisms and then, by proper training, to improve the largest possible number of them and make them worthy of and useful to man. In all my work I pursue only this aim, and very rarely, in extreme cases, only in between other work, do I permit the seeking for luck, In magazines and various pamphlets certain highly imaginative writers put my work in an extremely false light by placing it on a par with the work of the late Burbank, an advocate of planting many thousands.
Except for error at the beginning of my work, I have not based myself on mass planting and have never been carried away by silly treasure hunting, for I regard such work in horticulture as being, to say the least, of very little value and inevitable only on the introduction in our gardens of entirely new species of plants hitherto unseen in our localities, hybrids of which it is, as yet, impossible to have as, for example, the wild fig tree (Ficus carica L.), persimmon (Diospyrus lotus L.), wild lemon (Citrus trifoliata), etc.
But for such plantings I was unable in the past to procure seeds in any considerable quantity owing to lack of means; now, however, I receive, through government institutions, some of the seeds of this kind in sufficient quantities for planting for selection purposes when thousands and not tens of seeds are required.
Here it is necessary to explain how the process of selection itself should be carried out; what to select, and by what characters one must be guided in selecting, will be shown later.
The first selection should be made when the plant is still in the cotyledon state: relatively large cotyledons, their considerable thickness and short and thick stalk under them (hypocotyl), and tricotyledonous sprouts are the best signs of cultivation.
The colouring in various shades of the lower and particularly of the upper part of the cotyledon always infallibly indicates the future colouring of the fruit, and in flower plants, roses, for example, the colour of the flowers.
During the second selection, in the last month of the vegetative period of the first year before the seedlings drop their leaves, it is necessary to inspect them several times a day with the sun shining on them on different sides. This is necessary because only by means of such an all-round inspection is it possible more fully to note all the peculiarities of the habit of every seedling. Even a change in the direction of the wind sometimes sharply reveals one or another previously unnoticed character of the seedlings. At the first general glance at the seedlings the best are noted as regards stouter build, size of leaf blades, thickness and shortness of petioles and thicker shoot tips.
Then, in particular, the best signs of cultivation are: thicker leaf blades, rounded and shallow dentation of their edges, fine and close venation of the undersides of the leaves, dark, flat-coloured and wrinkled top sides, thick down (in apple trees), thick short petioles and well-developed stipules.
Selection after leaf dropping. Large, round buds at the tips of the shoots of the min stem, downy tips and faceted shape of their shoots, close steepspiral arrangement of side buds, their large size and very prominent bud cushions are all general favourable signs and, in particular, a sign of a compact structure of the pulp of the future fruit; a sparse arrangement of buds in a wide spiral, however, presages a looser structure of pulp. Broad-tipped buds, closely pressed to a straighter shoot is a good sign, whereas slender buds, deviating from a wavy shoot are signs of the wilding.
In stone-fruit plants, large round buds, arranged in groups of three and more, and large and numerous glandules on the petioles are good signs. In the majority of cases, a darker colouring of the bark of new shoots is a sign of late winter ripening of the future fruit, whereas a lighter colouring promises a summer ripening variety.
The absence of small prickles and general low growth are also good signs.
When selecting, it is useful to compare the shape of the shoots and leaves with those of their parents, and to take this or that similarity into consideration when appraising the merits of the seedling. Moreover, it must be borne in mind that all these signs in one-year hybrid seedlings are in most cases only in a rudimentary, sometimes in a barely perceptible state and gradually develop to their full dimensions only in subsequent years of the seedlings' growth.
Then again, the good merits of a seedling do not depend upon the absence of some of the signs enumerated above at any given time. Sometimes one of the signs develops earlier, while others are noted only later, at the next selection at a higher age.
In some cases even the presence of one of the bad signs does not in the least prevent the seedling from being an excellent variety. For example: in the well-known old and valuable variety of pear, the Beurré d'Hardenpont, the leaf blades and their dentation are of such a coarse structure that they positively give the tree the appearance of a wilding, and yet the fruit of this variety, for its size and flavour, is first grade.
|Fig. 41. Leaves of hybrid seedlings of Bellefleur Yuzhny (upper centre—the best of them)|
The same may be said about the Olivier de Serres pear which, with all its good qualities, has very small leaves and exceedingly feeble shoots.
The third selection is made according to the same signs in the autumn of the third year of growth, and in the following spring the selected seedlings are transplanted to their permanent locations (each seedling is given an area of two to four square metres) until the fourth and last selection for bearing, which is made according to the quality of the fruit of the third-fifth year of bearing, and the best of them, those which have fully passed the test for the stability of their characters, hardiness and yield, are propagated by the ordinary method of budding on young, two-year-old stock.
In some years, in the latter part of August, there is a long period of constant high atmospheric pressure (between 760 and 770 mm.). This, according to my observations, greatly affects the organisms of perennial plants and forces some of them to bloom again in the autumn.
In such cases, certain varieties of apple, cherry, mountain ash, bird cherry, and others have a second budding.
In such years a second flow of sap is also observed in hybrid seedlings, and this causes the plants to suffer considerable damage from autumn frost, against which we cannot take any measures; but in selecting we must not reject such damaged hybrids as lacking hardiness.
In conclusion it is necessary to point out once again that the first three selections of hybrid seedlings can be performed only by one who has acquired practical skill in carefully noting the characters of plants. It is quite impossible to give a sufficiently full description of the characters and their various combinations.
The fourth selection, according to quality of fruit, can, of course, be performed by anybody who, is in the least acquainted with varieties of fruiters.
Further, in all selections, it is necessary to watch particularly for the manifestation by the hybrid seedlings of any degree of immunity to various diseases in general, and to damage by fungi parasites and insects in particular. Such a quality in certain hybrids must be carefully noted and cherished in general. This is not only of enormous importance in cultivating the given varieties; in the future it will be possible to single out from their progeny a whole series of new varieties that will be staunch in the struggle against plant pests.