Agrobiology, 290-292 (1954)
T. D. Lysenko

Overcoming Cross-incompatibility in Wheat hybrids

I. V. Michurin contributed much to a correct understanding of the sexual process in plants. He showed that by suitably training the organism, by suitable feeding, it is possible to induce forms otherwise biologically incompatible to cross. Michurin devised a method of overcoming the inability to cross by the mutual feeding of the components of the cross with each other's nutritive products. This method is called preliminary vegetative approximation. Michurin also showed that choice of the conditions of life, choice of diet, makes it possible to alter, direct the sexual process by creating the prerequisites for the absorption of the heredity of one of the components by that of the other. Michurin showed also that the hereditary properties of hybrid trees continue to form throughout the course of their individual lives right up to the first fruiting years. And the way the hybrid is fed will determine whether given properties will incline towards the one or the other component of the cross.

From all this follow the interconnection and intergrading that, exist between vegetative and sexual hybridization on the one hand, and between vegetative hybridization and the influence of environmental conditions on the other.

In this connection, mention must be made of the result of experiments conducted by A. A. Avakian at the Institute of Selection and Genetics (Odessa) and later in the greenhouse at Gorki Leninskiye, the Experiment Base of the Lenin Academy of Agricultural Sciences of the U.S.S.R. This result is of theoretical interest to the student of general biology.

Several years ago, at the Institute of Selection and Genetics, Avakian observed the following phenomenon repeating itself over and over again in experiments. When crossing the winter wheat Hostianum 0237 with the spring wheats 1160 or 1163 (the two latter are sisters) the resulting seeds are normal. From these seeds there at first develop shoots that outwardly appear normal. But as soon as the third leaf appears on the shoots, the first leaf withers; as soon as the fourth leaf appears, the second leaf withers, i.e., all the time only the two latest leaves remain alive. In the end, the plants perish. In short, we have here a phenomenon which the Morganists call the action of lethal genes. Although they have proposed a new term for this phenomenon, the Morganists have not been able to suggest any means of combating it. They have declared it to be fatal, insurmountable, and argue that there is only one way out in such cases, namely, not to interbreed plant or animal organisms that carry lethal genes.

In the experiments repeated by Avakian, there were at different times thousands of plants of this kind, but not one of them lived even to earing; they all perished. At the present time there are in the greenhouse at Gorki Leninskiye hundreds of hybrid wheat plants of the combination indicated and they are all on the verge of utter extinction.

Meanwhile, a crossing of the same combination of Hostianum 0237 and 1160 resulted in hybrids which are vegetating excellently in the same greenhouse, and developing into viable plants. The whole point here is that one of the components (the paternal form—1160) was grown for two generations before crossing not from a spring, but from an autumn sowing (1160 is a spring variety). This proved to be sufficient to produce a viable progeny after crossing this 1160 with Hostianum 0237. The changed conditions of cultivation changed the sex cells of the 1160 wheat plants; hence the difference in the hybridization results.

Here is another interesting phenomenon belonging to the same category of cases.

In experiments conducted by Avakian at Gorki Leninskiye, castrated plants of Hostianum 0237 wheat were pollinated with the pollen of 1160 (as we have already said, this combination usually results in nonviable progeny) mixed with the pollen of the maternal form Hostianum 0237. Some of the plants grown from the resulting seeds were obviously hybrids.¹ These plants proved to be viable, they did not perish. Thus, the presence of the pollen from Hostianum 0237 influenced the process and result of fertilization with the pollen from 1160, as a consequence of which a viable instead of a lethal, nonviable, progeny was obtained.

This shows that exchange of substances can take place between different varieties of pollen if a mixture is placed on the stigma, or between the pollen of different varieties and the egg cells of the mother plant. The physiology of these processes has not been investigated, but at all events it is an indisputable fact that the result of pollination with mixed pollen is different from that of pollination with the pollen of 1160 only. Michurin pointed to the advisability of mixing pollens. In this way he succeeded in crossing species and genera that could not interbreed otherwise.

I think this fact too shows that the sexual process, fertilization, is a peculiar process of assimilation, a metabolic process, just as it is in cases of vegetative hybridization.