Plant breeding

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Cultivars of maize produced by breeding

The aim of plant breeding is the genetic modification of plant populations in order to improve biological and economic properties. It is based on plant selection , seed treatment or crossing with subsequent selection of daughter plants for the next breeding cycle or the subsequent propagation as seeds of a new plant variety ( seed breeding ).

aims

The main goals of plant breeding in the field of useful plants are:

  • Increase in yield
    • Increase in area yield
    • "Low-input" plants for bioenergy production and economically effective use of medium-yield locations
  • Quality improvement
  • Environmental tolerances / resistances
    • Adaptation to new environmental situations (cooling tolerance, salt tolerance, drought tolerance)
    • higher pest resistance , tolerance and disease resistance

In the case of ornamental plants , the emphasis is also on improving pest and disease resistance, but above all on the selection of characteristics that are particularly appealing in terms of color or morphology. The latter are also very important for vegetables that are to be marketed directly ( white cabbage , ...).

In the case of medicinal plants , in addition to improving pest tolerance and disease resistance, the emphasis is primarily on the selection to increase the content of effective ingredients for the production of drugs and phytopharmaceuticals .

Classic breeding methods

Selection or selection breeding

Selection breeding is the oldest form of plant breeding. Already around 12,000 years ago, people began to select the most productive plants from wild grain species with repeated cultivation and to increase them in a targeted manner.

In selective breeding, a relatively large plant population is required as the starting material, which must contain the trait that is to be selected for. One begins with the cultivation of genotype mixtures (existing genetic lines, also wild plants). From the initial stock, seeds are produced by joint blooming, and individuals with advantageous properties are selected from the resulting plants (selection, mass selection). Often, these plants are re-flowering together. Finally, seeds from the best plants are propagated in isolation. After repeated repetition of the process and further selection, almost homozygous plants with the desired properties remain with regard to the trait to be selected .

In selection breeding, a distinction is made between negative and positive mass selection. In the negative mass selection, plants that do not meet the breeding goal are excluded from further reproduction. It is mainly used in maintenance breeding, in which properties once achieved are to be retained when the variety is propagated further. In the case of positive mass selection, on the other hand, those individuals who best meet the breeding goal are selected for reproduction. A combination of positive and negative selection is often used in practice.

The transition between selection and combination breeding is fluid. In self-fertilizing plants , such as. B. barley , bean or pea instead of the common free flowering also crosses by hand are required. Once suitable plants have been created, this process quickly leads to the breeding goal.

Instead of the common free flowering can also be done with cross- pollinated plants such. B. rye or corn, a manual fertilization of the inflorescences can be made. Later only seeds from plants with the best yield and / or best quality are used.

Selection breeding is a simple way of breeding newer plant varieties. However, since numerous generations are always necessary, it is very tedious.

Combination breeding

Combination breeding is a cross between different genotypes (lines). A new genotype is created (F 1 ). The parents are thus united in one genotype. The interaction of these genes leads to new phenotypes . Only the most promising are selected from the individual crossings. Desired features can be enhanced and undesired ones suppressed. Since the crosses split again in the next generation (F 2 ) at the latest, maintenance breeding is also required after further selection cycles (F 3 , F 4 , ...) for seed production . This combination breeding is based on the 3rd Mendelian rule of independence and recombination .

In Germany there are around 90 breeding programs for agricultural crops (e.g. rapeseed, wheat, maize, sugar beet etc.). In 2004, more than 2,700 different varieties were registered with the Bundessortenamt in Hanover.

Heterosis breeding

In heterosis breeding, almost homozygous inbred lines are bred from heterozygous parent plants in cross- pollinated crops (maize, rye ...) over several years . If you cross two such lines, the F1 generation often shows a noticeable increase in performance compared to the parent forms. This is called the “ heterosis effect ” ( luxurizing the bastards ). In the case of cereals, among other things, a higher grain yield can be achieved, in other plants and animals, above all, a higher resistance to diseases and in chickens a better laying performance.

In the offspring of the F1 generation (F2, ...) the less good characteristics of the inbred lines appear again, because they split genetically according to the split rule (Mendel). The advantageous properties only appear in the F1 generation.

Hybrid breeding

This orchid is a hybrid of cymbidium insigne and cymbidium tracyanum named Cymbidium "Doris" from 1912.

Hybrid breeding is an example of heterosis breeding in order to achieve a high level of plant production that is suitable for the market or for the farm through hybrid growth. In hybrid breeding, for example, suitable, separately bred inbred lines are crossed with one another once (single hybrids). The offspring of the first generation (F1) of such a cross have a more abundant growth compared to the parent generation ( heterosis effect), so their crossing results in increased production. In addition, there is a combination of the desired properties of the original inbred lines.

For the farmer , however, this means that the seed has to be sourced anew every year if he wants to maintain the yield advantage compared to non-hybrids, since the heterosis effect only occurs in the F1 generation and is then lost again. While farmers in industrialized countries mostly follow this strategy, farmers in developing countries more often use offspring of hybrids ( recycle ) if these have even better properties than traditional seeds despite the loss of the heterosis effect.

In the case of rye , in some cases 10% population seed is added to hybrid seed to ensure pollination.

Mutation breeding

In mutation breeding, seeds are exposed to X-rays or neutron rays , cold and heat shocks or other mutagens in order to achieve new properties through mutation that have a positive effect. Only a very small proportion of the mutants are promising for further breeding, since most of them show defects and are unusable. The mutated plants have to be back-crossed with efficient breeding lines in order to transfer the new, positive trait into them. Although genetic information is changed in a more uncontrolled manner in mutation breeding than with genetic engineering , it is less known to the public in contrast to genetic engineering . It is not subject to any statutory regulation. This is justified by the fact that mutation breeding only represents a targeted increase in the natural mutation frequency. Although this occurs in nature anyway and is the basis of evolution , it is questionable whether it is still possible to speak of natural mutation if this is caused by radiation, as is usual in mutation breeding.

Precision breeding

Precision breeding is a further development of classic crossbreeding. When selecting the plants to be crossed with each other, the focus is no longer only on external characteristics, but the genetic material is precisely analyzed in order to then select the appropriate cross-breeding partners.

This considerably speeds up the breeding of new varieties, as lengthy cultivation attempts are not required to e.g. B. determine whether a plant is resistant to powdery mildew. Since the corresponding genes are known, a gene analysis can be used to determine whether the trait was inherited during the crossing.

Breeding with the help of genetic engineering

With the help of green genetic engineering , certain properties (e.g. disease resistance, improved vitamin content, etc.) can be transferred into plants that are difficult to transfer (e.g. only very long-term) or not transferable at all through traditional breeding.

Genetic gene transfer in plants is carried out by Agrobacterium tumefaciens or by transferring DNA with the help of so-called gene guns . The Agrobacterium tumefaciens has a TI-plasmid (TI = Tumor Inducing) into which the desired gene to be transferred into the plant, is integrated. Agrobacterium tumefaciens can infect the plant at relevant wound sites and transfer the gene into the genome of the plant cell. When transferring DNA with the “Particle Gun”, the DNA to be transferred is bound to gold or tungsten particles. These particles are hurled at plant tissue / cells at great speed so that they penetrate the cells without destroying them. The DNA bound to the particles dissolves in the cells and can integrate into the genome of the plant cell.

Royalty free breeding

The open-source seed license is committed to ensuring that users have the opportunity to propagate plants themselves and continue to use their seeds.

Important plant breeders (selection)

Germany
Other countries

literature

  • Heiko Becker: Plant breeding 2nd edition. UTB, 2008, ISBN 978-3-8252-1744-0 .
  • Wulf Diepenbrock, Jens Léon, Frank Ellmer: Agriculture, crop cultivation and plant breeding, basic knowledge Bachelor. Ulmer, 2005, ISBN 978-3-8252-2629-9 . (UTB Uni-Taschenbücher, Volume 2629)
  • Thomas Miedaner: Plant Breeding. An introduction. DLG, 2010, ISBN 978-3-7690-0752-7 .

Web links

Commons : Plant Breeding  - Collection of Images, Videos and Audio Files

Individual evidence

  1. ↑ a b c d e Holger Seipel: Expertise for gardeners. Chapter 1.4.2 .: Plant breeding. Dr. Felix Büchner, Verlag Handwerk und Technik, Hamburg, 1998, p. 85
  2. ↑ Single hybrids, double hybrids, three-way hybrids, top cross hybrids
  3. ↑ Hanswerner Dellweg: Biotechnology understandable . Springer, 1994, ISBN 3-540-56900-6 , p. 106, p. 197.
  4. ^ Hans Günter Gassen, Michael Kemme: Gentechnik. The growth industry of the future . Fischer Taschenbuch Verlag, 1996, ISBN 3-596-12291-0 .