Mass Selection in Animal Breeding
Selection as an independent method of plant breeding is based on the use of natural intraspecific variability of plants.
In breeding, selection methods are used depending on the tasks of specific breeding programs and the characteristics of the breeding culture (self-pollinator, cross-breeding, vegetatively propagating plant) and the genetic structure of the future variety (self-pollinated line, clone, variety-population, simple or complex hybrid, variety consisting of separate lines or families). E. E. Geshele emphasizes that in the practice of selection for immunity it is necessary to clearly distinguish between such concepts as genotype, phenotype, environment, and the rate of reaction of the genotype.
Genotype – the totality of all the hereditary factors of the body – genes localized in the chromosomes, and all extrachromosomal cytoplasmic hereditary elements (plasmon). The genotype determines the rate of response of the body in changing environmental conditions and forms an individual phenotype based on interaction with the environment.
Phenotype – a combination of all external and internal structures and functions of the body, including the protective mechanisms of the host plant, which are active and passive in nature.
The relationship between genotype and phenotype can be expressed by a simple formula: genotype + environment = phenotype.
The same genotype under the same conditions gives the same phenotypes, and in different environmental conditions – different phenotypes. The latter phenomenon is called modification.
Speaking about the inheritance of plant resistance, it must be borne in mind that it is not signs of resistance that are inherited, but the rate of reaction, which, in interaction with the environment, exhibits what we call the degree of resistance.
With the improvement of self-pollinating crops, selection is most important when working with mixed material, such as local varieties. Improvement of such varieties begins with mass (population) selection, which is replaced at the subsequent stages of selection with individual selection. During mass selection, all individuals from the seeded population (varieties), which are distinguished by increased resistance to a harmful organism, are selected and used for subsequent sowing. Such selection is carried out from generation to generation until the variety is reached on the basis of stability.
The greatest effect is obtained by selection carried out on an infectious background in ordinary years or on a natural background during the years of mass reproduction of pests or epizootics.