International Genetics Symposia at Tokyo & Kyoto (1957)
The Phenomenon of Polyfertilization in Plants
I. E. Glushchenko

Institute of Genetics, Academy of Sciences, USSR

Our experiments on crossing a tomato mother plant with two father plants began in 1954. Among a series of tests the cross of Zholty Michurina which had two recessive characters (stalked bush, yellow fruit) with Shtambovy Alpatyeva (stalked bush, red fruit) and Zholty Grushevidny (non-stalked bush, yellow fruit) is especially interesting. The control tests have shown that stalked plants with red fruit were obtained in F1 from the cross of Zholty Michurina x Shtambovy Alpatyeva whereas non-stalked plants with round yellow fruit were produced in F1 in the cross of Zholty Michurina x Zholty Grushevidny. The usual segregation of the characters is observed in F2.

The combined hybrids from artificial pollination with a pollen mixture of two father plants look quite differently. Indeed, among 68 F1 plants obtained from 2 fruits 29 possessed the characters of the both paternal forms being non-stalked and bearing round or oblong red fruit. The characters of the two paternal plants were found to be well combined in F1 plants obtained in such a combined cross. The remaining 39 plants of this cross had all stalked bushes and red fruit, i.e., we may suppose that their eggcells were fertilized exclusively by "Shtambovy Alpatyeva" gametes.

In 1956 the F2 plants were obtained of the combination Zholty Michurina x (Shtambovy Alpatyeva + Zholty Grushevidny). 1) The progeny produced by the non-stalked forms is segregating into stalked and non-stalked plants; 2) The progeny obtained from stalked forms remains generally stalked with the exception of only one family that produced 9 stalked and 31 non-stalked plants. Thus, this recessive stalked form produced most of the plants with a dominant non-stalked character. We have never observed anything similar in ordinary pair-crosses of tomatoes.

G. M. Zakharova has obtained white maize grains by crossing Rumanian White with Rice White and yellow grains by crossing Rumanian White with Rumanian Yellow and Bezenchuk Yellow. These pair-crosses have served as controls in the experiments on pollination with pollen mixture. In the year of crossing the combination No. 1 {Rumanian White x (Rice White + Rumanian Yellow)} and combination No. 2 {Rumanian White x (Rice White + Bezenchuk Yellow)} both gave round white and yellow grains. Before being planted the grains of all cobs obtained in combination No. 1 and No. 2 were first divided into two colour fractions (white and yellow). The maternal inflorescences of F1 plants were pollinated with the pollen of the initial maternal plant.

In combination No. 1, 6 out of 235 plants inherited properties of two pollinators: the yellow colour and the beak-like grain. The remaining plants had either white or yellow round grains, i.e., they inherited the visible characters only of one of the two paternal plants. In combination No. 2, 2 plants out of 166 had cobs with yellow beaked grains. The yellow colour was due to the pollen of Bezenchuk Yellow and the beak-like grains to Rice White. All other plants had either white or yellow round grains, i.e., they showed no obvious characters of the second father.

The grains which gave F2 plants with the attributes of the two pollinators were taken from F1 plants, that also showed the influence of bi-paternity. To sum up, we may say that the pollination of maize plants with pollen mixture gives rise to hybrids bearing the characters of two paternal forms, and that the attributes of two pollinators may also be preserved in the following generations.

A series of experiments has been carried out by G. B. Medvedeva, on the pollination of soft winter and hard spring wheats with a pollen mixture of different wheat varieties. The aim of these experiments was to produce wheat combining the morphological characters of two father forms. Winter wheat varieties were combined in the following ways

  1. Albidum (white grain and spike) x {Ukrainka (white spike, red grain) + Alborubrum (red spike, white grain)}
  2. Albidum (not downy, white spike) x {Velutinum (thick-downy, white spike) + Milturum (not downy, red spike)}
  3. Erythrospermum (not downy, white spike) x {Velutinum + Milturum}

An analysis of the data obtained showed that 154 plants out of 266 of the first combination had white spikes with embryonal awns and red grains, i.e., they had the characters of the paternal variety Ukrainka, 30 plants had white grains and intermediate coloured spikes without awns, i.e., they had the characters of Alborubrum, 47 plants belonging to the third group had red grains, embryonal awns and intermediate colour spikes, i.e., they had the characters of both father varieties (35 plants were of the maternal type). Two types of hybrid plants were produced in F1 in the second combination, and there were no plants bearing the characters of both pollinators among them. There were three types of hybrid plants in F1 of the third combination: 61 plants out of 267 had white downy spikes, i.e., they had the characters of Velutinum; 152 had smooth spikes of an intermediate colour, i.e., they had the characters of Milturum. There were, moreover, 27 plants with coloured and downy spikes in the third group, i.e., they had the characters of both father plants. 27 plants were of the maternal type.

Similar results were obtained in tests with hard wheats where as maternal forms the varieties Affine, Leucurum and Hordeiforme were used.

The following characteristic feature of the F1 hybrid plants produced from the pollination with the mixture of pollen is especially interesting. The groups of plants on which the influence of both parents was not manifest were marked by the high degree of the variability of the characters inherited from the father. This was especially clearly seen in such characters as the colour of the spikes and grains. As F1 plants from usual pair-crosses of the above named varieties were uniform, we may conclude that the variability noted is obviously due to the influence of the second pollinator which affects to a different degree depressingly the characters of the first father form.

V. J. Bazavluk made experiments on polyfatherhood in Mirabilis jalapa. Let us examine the results of the experiment with pollination by two father forms: white x (crimson + yellow), and with three father pollinators : white x (crimson + yellow + white). It is interesting that besides the white, yellow and crimson parent forms, plants with orange-crimson corolla, i.e., bearing the characters of their two father forms have been produced in F1. Such results have not been observed in control pair-crosses.

The progeny of the plants bearing the characters of the two father forms, i.e., with the crimson-orange colour of the flowers, are especially interesting. A great range of variations has been obtained among them in F2 not the three types which are usual in pair-crosses but in fact ten types. The analysis of the F3 plants has demonstrated that parental types obtained in F2 are constant. The progeny of intermediate forms of F2 behaved as those in pair-crosses.

Today J. E. Ellenhorn and V. V. Sviatozarova's cytological studies have shown that the fertilization process is not restricted to an egg-cell and polar-cell fertilization but that a fusion of the spermatozoids with the nuclei of the somatic cells of the nucellus and of the ovary walls is also possible. Favourable conditions for the development of the embryo are thus produced. The latter is developing in the environment of the tissues fertilized, in a way, by the spermatozoids of the father plant. The penetration of the spermatozoids into vegetative cells provokes not only changes in the latter but also in the neighbouring cells. The authors hold that the change in the metabolism of surrounding somatic cell creates more favourable conditions for the development of the embryo.

In this, it seem to me lies one of the most important phenomena of the process of fertilization.

These new genetical and cytological investigations confirm I. V. Michurin's opinion of the existence of "another fertilization process" influencing directly the vegetative tissue and the genetical characters and properties of the hybrid plant.

Mirabilis bibliography