Vernalization
Vernalization (Latin vernalis "spring") or Jarowization describes the natural induction (stimulation) of the shoot and flowering in plants through a longer cold period in winter.
Numerous annual and biennial plant species in regions with marked differences between winter and summer conditions only shoot and bloom after having lived through a prolonged period of low temperatures. This prevents the start of the generative phase in the unfavorable time for the plant before the onset of winter.
Gustav Gassner was a pioneer in vernalization research . The practical application of Yarovization in Russian agriculture goes back to suggestions of the Russian researcher Trofim Denisovich Lyssenko . During the reign of Josef Stalin , the methods of Lyssenko became the official scientific doctrine of the Soviet Union ( Lyssenkoism ).
Demarcation
Vernalization must be distinguished from stratification , which is the artificial treatment of seeds to encourage their germination . Like vernalization, this can be done by treating the seeds with cold.
The production and cultivation of frigo plants is not vernalization, but the artificial extension of winter dormancy to influence the harvest time.
Importance in crops
Widespread crops in which vernalization plays an important role are cereals . A distinction is made here between winter and summer cereals. Winter cereals are sown in autumn, hibernate as small plants, and shoot the next spring.
In order to be able to sow high-yielding winter cereals in the continental climate of Siberia in spring as well, they were "artificially jarowized" for a few years, ie in freezing weather the winter cereal seeds were brought into germination mood in special buildings by adding moisture and heat , after which doors and windows were opened for a few hours. to expose the seeds to the low temperatures. Through this "artificial Jarowisation" the lock inhibition in winter cereals was removed and the winter cereal varieties shot and bloomed even with the spring sowing. By jarowizing summer cereals, attempts were made to extend their sowing period.
After Stalin's agricultural reform , there were not enough seed drills available; by artificial Jarowisation of seeds the yield risks could not be prevented later sowing, but partially reduced. Thanks to better equipment with seed drills and the introduction of new, high-yielding summer cereal varieties, Jarowization soon disappeared from Russian agriculture.
If the optimal sowing time is used, there is no need for artificial vernalization.
An example of undesirable vernalization are the bolters in sugar beet , which arise when the seeds in the ground experience late frosts after sowing in spring .
physiology
The cold period and the flowering process can be relatively far apart in time. This means that the flowering process does not have to take place immediately at the beginning of the warmer period. Other factors such as the length of the day , temperature or the state of development of the plant play a role here. Plants are able to “remember” the cold spell they experienced. In some species, vernalization can already take place in the seed stage, but the plant does not flower until much later stages of development.
The vernalization obviously acts mainly on the apical meristem . If other parts of the plant, such as the leaves, are exposed to low temperatures, vernalization does not take place. Another observation is that the vernalized state of a plant cannot be transmitted through grafting . If, for example, a non-vernalized stem tip is grafted onto a vernalised base, this stem tip continues to show an unvernalised flowering behavior. This finding also suggests that the vernalized state is not spread over a greater distance in the plant and the vernalization has a direct effect on the crucial tissue , namely the apical meristem.
literature
- Gustav Gaßner : Contributions to the physiological characteristics of summer and winter annual plants, especially of cereal plants. In: Journal of Botany . Vol. 10, 1918, pp. 417-480 .
- Ernst Klapp : Textbook of arable and crop production. 5th, revised edition. Parey, Berlin et al. 1958.
- Jan Krekule: Historický vývoj a současný stav představ o průběhu jarovizáce (The historical development and corresponding experiences with Jarowisation). Prague 1957, (dissertation).
- Jiří Petr (Ed.): Weather and Yield. Developments in Crop Science (= Developments in Crop Science. 20). Elsevier, Amsterdam et al. 1991, ISBN 0-444-98803-3 .
- Manfred Gustav Raupp: What the grandfather already knew. Thoughts on the development of agriculture. Written in memory of Gustav Wilhelm Raupp (1905–1985). Manfred Gustav Raupp, Loerrach 2005 DNB 989985555 .
