Plant breeding is the science of creating qualitatively new and improving existing cultivar varieties. Selection is based on its main methods - selection and hybridization. The theoretical basis of selection is the science of genetics.
Features of plant breeding are due to the successful solution of the tasks that confront it. The study of the varietal, tribal, and species diversity of cultures, the influence of the environment on the development of the main characters, patterns of inheritance of these characters for hybridization, as well as the characteristics of the selection process and artificial selection strategy is very significant.
Each plant variety is adapted to certain specific conditions, and therefore in different places there are different specialized stations and breeding farms for checking and comparing new plant varieties.
For plant breeding to be successful, the breeder must have varietal diversity of the source material. Scientist N.I. Vavilov at one time gathered a huge collection of plant varieties and their ancestors from all over the planet Earth, which today is successfully replenished and is considered the basis for work on the selection of any culture.
N.I. Vavilov identifies seven centers of origin of plant crops: South Asian tropical, East Asian, Mediterranean, South West Asian, Abyssinian, South American, Central American. The richest regions in the number of cultures are the ancient centers of civilization. In such places, the earliest crop of agriculture, respectively, and plant breeding, and artificial selection are carried out for a longer time. Let us consider in more detail what this concept is.
There are certain methods of plant breeding: selection and hybridization. Selection in turn can be individual and mass.
Mass selection refers to the form of artificial selection, which is used in the selection of so-called "cross-pollinated" plants (rye, corn, sunflower). In this case, the variety is a population that consists of heterozygous individuals, where each seed carries a unique genotype. Thanks to mass selection, varietal characteristics are maintained and improved, however, the results of such selection are very unstable due to indefinite cross-pollination.
Individual selection is used in the selection of plants that are pollinated independently (barley, wheat). The offspring preserves all the signs of the parental form without exception and is called the clean line (the offspring of one self-pollinated homozygous individual is called so). Since mutational processes occur constantly, in fact, homozygous individuals are extremely rare. Under the control of artificial and natural selection, they fall only after the transition to a homozygous state.
Plant selection by natural selection plays a very important role. Any plant throughout its life is influenced by certain external factors, therefore it must be resistant to diseases and pests, adapted to the water and temperature conditions.
Inbreeding is a closely related cross. This phenomenon occurs in cross-pollinated plants with self-pollination. For this selection method, plants are selected whose hybrids are able to give the maximum effect of heterosis. Such plants are subject to forced self-pollination for many years.
There is also a method such as remote hybridization. This is the name of the crossing of plants that belong to different species. As a rule, distant hybrids are sterile, so gametes are not formed.
Plant breeding also has such methods as the use of somatic mutations, experimental mutagenesis, as well as selection methods proposed by I.V. Michurin. You can learn more about these and other methods by reading the works of the aforementioned scientists.