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Wheat breeding in practice

Biological diversity is constantly evolving and is characterized by different levels of organization: ecosystems, species, populations (varieties or races), and individuals. Within species, each individual has different genetic characteristics. These individuals are often grouped into varieties that have differentiated genetic characteristics.

Since the beginning of agriculture, man has drawn on the diversity of living organisms and created varieties adapted to his needs. Biodiversity is therefore a precious heritage for agriculture. Biodiversity conservation and management systems (e.g. the Genetic Resources Office) exist to pass on all these varieties to future generations. Concerning straw cereals, the Centre de ressources biologiques des céréales à pailles (experimental infrastructure of the INRAE Clermont-Auvergne-Rhône-Alpes Center - ), located in Clermont-Ferrand, groups together the major species of agronomic interest of the genera Triticum (wheat), Hordeum (barley), Secale (rye), Avena (oats) as well as their wild relatives.

Cultivated plants are derived from wild plants. The domestication of cereals was a founding element of the first human civilizations, at the end of prehistory, about 10 000 years ago, in the fertile crescent in the Near East. The different wild wheat species (Triticum, Aegilops) have undergone transformations in the course of time, following the action of man, and have generated modern species through successive events of polyploidization, interspecific crosses and progressive selection.

The hereditary material of plants consists of DNA, organized in chromosomes included in the nucleus of each cell of the individual. Any hereditary character depends on the activity of units distributed on the DNA molecule and called "genes". Each gene occupies a defined position on a chromosome. The number of chromosomes in the somatic cells of an individual (symbolized by the parameter 2n) is always a multiple of a base number (x), variable with the species. In many of them, the cells of the individual contain 2n=2x chromosomes, they are said to be diploid. But it is not rare in cultivated plants that a species has 3, 4 or more copies of the basic number of chromosomes (triploid, tetraploid ...). During a crossing, each parent gives a set of chromosomes (n) to the hybrid that is obtained. An individual is said to be homozygous if the two copies of the same gene are identical, which is the case for wheat varieties which are generally pure lines.

Contemporary genetic research shows that the genetics of cereal domestication is quite simple. In fact, domestication was facilitated for species that had favorable phenotypic traits and genetic or reproductive dispositions that favored the maintenance of a cultivated type. Because they had simple pre-existing genetic characteristics and these were taken advantage of by simple agronomic practices as well. For example: interesting agronomic traits with only 2 possible versions of the same gene (such as fragile rachis, dressed vs. naked grain...), or grouping of favorable genes on the same chromosome (which implies that it is easier to select).

Wheat cultivated today belongs to 4 species of the genus Triticum:

  • T. monococcum which is diploid (2n=14), it is the einkorn or the small spelt
  • T. turgidum and T. timopheevi which are tetraploid (2n=28), including durum wheat
  • T. aestivum which is hexaploid (2n=42), the soft wheat, generally with naked grains (wheat), sometimes with dressed grains (the great spelt)

Of the 4 species, T. aestivum is the most important economically with most of the soft wheat type varieties, adapted to various natural conditions. T. turgidum is also widely cultivated (hard wheat varieties) and is more adapted to dry climates. These species are said to be self-pollinating, which means that an individual will in most cases self-pollinate. This reproduction system gives rise to individuals that are generally highly homozygous, and the varieties are pure lines, easy to produce because they give a homogeneous and identical progeny to the parental line.