What Is Heterosis And Its Use In Plant Breeding

2024 Author: Sebastian Paterson | [email protected]. Last modified: 2023-12-16 13:47

Read the previous part. ← Varieties or heterotic hybrids

Heterosis: reproductive, somatic and adaptive

It is no coincidence that I dwelt in detail on the production aspect of the significance of the variety for a particular area. Many varieties that were once valuable for this area, they were maintained for generations, but over the years they have been lost - a different climate, new diseases, other technologies, a different life.

Now there are no those Murom, Vyaznikovsky, Klinsky, Rzhevsky cucumbers, although they sell something under this brand. It is known that many old varieties have been preserved by enthusiasts who have saved seeds from year to year. Some seeds traveled around the world in the pockets or letters of immigrants, so in America it is now easier to find ancient varieties of Russia, Italy, Japan, France, Germany … True, it is difficult to check whether they had such a taste a hundred years ago, but, according to the assurances of the owners of companies selling old varieties - exactly like that.

The taste of vegetables is highly dependent on growing conditions: soil, climatic and light parameters. Everyone knows how the taste of potatoes depends on the nature of the soil, tomatoes of the same variety grown in the south are sweeter and more fragrant than those grown in the north. Interestingly, the very poisonous mushroom fly agaric in the northern latitudes loses its toxicity, and the natives use its broth as a heady drink. Probably, for each site there is the most optimal variety or hybrid.

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Let's return to the modern world, where heterotic F1 hybrids are becoming more and more in demand.

What is

heterosis? I have already mentioned this phenomenon, and now we will dwell on it in more detail. Heterosis - hybrid vigor, manifested in the superiority of hybrids over their parental forms. Heterosis is not manifested with every hybridization. Moreover, heterosis may not affect all plant traits. Distinguish: reproductive heterosis, which is expressed in the better development of reproductive organs, leads to an increase in the yield of fruits and seeds; somatic heterosis, leading to a powerful development of the vegetative mass; adaptive, or adaptive heterosis, which is expressed in a general increase in vitality, although the development of economically valuable traits usually does not coincide with biological benefits.

The manifestation of heterosis depends on the direction of crossing and can be observed only in one of the reciprocal (mutual) crosses, i.e. as a maternal and sometimes as a paternal form. When creating a heterotic hybrid, breeders have to multiple check the combination of traits for their combinational ability, that is, for the ability to form productive hybrids. To create heterotic hybrids with certain traits, a very high level of seed production equipment and large material costs are required. Leading domestic and foreign breeding centers and specialists are involved in this program.

Above in the article, I gave an example with Kolomenskaya cabbage, which grows preferably in flooded meadows, absorbs a lot of moisture. The property of drought resistance, consists of 15 components, ranging from the arthotropic nature of the roots, which should go down, and not go to the sides and take moisture deep, until the leaves are pubescent. Then energy, that is, the work of mitochondria. Then the membrane. Then the osmotic pressure in the root systems: the higher the osmotic pressure in the roots, the better they take away moisture from the drier soil. And osmotic pressure is the product of all 25,000 genes. And how can you find a specific gene here.

To develop a drought-resistant hybrid of this cabbage, you need to collect the most valuable positive deviations for each of the 15 components in one variety. In F1 hybrids, it is possible to combine a complex of genes that determine resistance to major diseases. They are also irreplaceable when obtaining forms that are resistant to cold, heat, drought, and violation of dietary regimes.

However, it should also be noted that heterotic strength in all its power is manifested with a certain technology of growing a particular hybrid, corresponding to nutrition. Agrofirms that produce hybrids usually give their recommendations, which it is advisable to follow. Let me give you an example from the Syngenta company. For her heterotic racemose tomato hybrids, she gives the following recommendation: “The formation of the brushes should be carried out to maintain the optimal balance of the plant and the formation of the same weight of fruits on the brushes; the main goal is to get 750 to 1000 grams of total fruit weight per cluster to maintain good balance of the plant and to continue the ovary on subsequent clusters.

The formation of the brushes is mainly carried out on the first 4 brushes, then fewer flowers will appear, and the brushes will be more uniform due to the correct loading of the plant with fruits and a good balance of nutrition. Removal of flowers can be carried out immediately after the ovary, the sooner the better, as this will avoid unnecessary absorption of nutrients.

Example of brush formation:

200-250 g: leave 4-5 fruits on the brush;

150-200 g: leave 5-6 fruits on the cluster;

120-150 g: leave 6-8 fruits on the cluster.

If, when transplanting seedlings into the ground, the temperature in the greenhouse is below the optimum, the brushes will not tie correctly, the number of flowers on the brush will be high, and the plant will be overloaded with fruits on the first brushes. By shaping the brushes for a certain number of fruits, this can be avoided."

Perhaps for amateur vegetable growers it is not so important - to obtain such uniformity of fruits, but for commercial purposes it is perhaps important. In general, any tomatoes grown on their own plot improve our mood, because they contain serotonin - the hormone of happiness.

Read the next part. Is it true that varieties are tastier than hybrids? →

Vladimir Stepanov, Doctor of Biological Sciences

Photo by O. Rubtsova