Photoperiodism is powerful factor in advancing the cultivation of subtropical species of perennial fruit trees northward.
Only in 1930, after the publication of the work of Garner and Allard on the importance of the length of sun illumination to plants, was the experimental study begun of this extremely important factor influencing the life of plants, as is vividly demonstrated in the recent work of Comrade Lysenko on the cultivation of cereal crops.
In 1932, photoperiodism proved to be extremely useful in the production of new varieties of fruiters, because of the possibility of shortening with its help the vegetation period of certain species of plants, this resulting in fuller maturation of the summer growth of the branches, which, in its turn, considerably enhances the resistance of these plants to winter cold.
Of course, the influence of photoperiodism on annual field crops differs considerably from its effect on perennial fruit plants. In the former case, its influence is limited to certain alterations in the details of growth of the plants in the year of its employment, and needs to be repeated annually. In the latter case—the case of perennial hybrid fruit plants—shortening of the vegetation period may be fixed all through the life of the hybrid variety, provided that photoperiodism was employed for several years in succession beginning with the moment of the hybrid shoot's germination. This may be quite feasible, because all hybrid seedlings, and especially hybrids, the habitat of whose parents, i.e., father and mother, were geographically far apart, at the time of their development from the seed and in the earliest period of their life possess the faculty of vigorously adapting themselves to environmental conditions, and correspondingly build up a constitution adapted to the shorter vegetative period. This latter property is fairly satisfactorily retained later if propagation is performed vegetatively, by graftage or layerage, but is not fully transmitted if propagation is performed sexually (from seed).
Example: A hybrid peach seedling fertilized with pollen from Posredinik (Amygdalus nana monqolica x Pr. Davidiana Franch.), when the day was shortened to twelve hours, shortened its vegetation period by a whole month.
In 1931 flowers of the Iron Kanzler peach were pollinated with the pollen of a Posrednik almond. The fruit that set was of an extremely original form: Half of the pericarp was, both in size and in flavour of the flesh, identical with the peach; the other half was half the size of the former and resembled in everything an almond; the flesh was of a bitterish flavour, like the almond.
When the fruit, after it had been removed from the tree, was opened, the walls of the stone inside proved to be divided into several parts, and at a slight touch it broke up into those parts, as may be distinctly seen on the coloured plate.
Inside the stone there was a healthy and well-filled kernel. It was immediately planted into a flower pot, where it germinated under the constant application of ionization and photoperiodism of a 12-hour day. In the spring of the next year, 1932, the seedling was planted together with the clod of earth into a bed in the ground.
As in 1932, photoperiodism continued to be applied to the hybrid seedling in 1933 and 1934, and as a result its vegetation period of growth was reduced by a whole month.
The seedling stood well the winters of 1932/33 and 1933/34, and is still developing quite normally. We are looking forward with great interest to the first fruiting of this hybrid seedling.