Genomic mutations occur as a result. Types of mutations

Hereditary changes in genetic material are now called mutations. Mutations- sudden changes in genetic material, leading to changes in certain characteristics of organisms.

Mutations according to their place of origin:

Generative- originated in germ cells . They do not affect the characteristics of a given organism, but appear only in the next generation.

Somatic - arising in somatic cells . These mutations appear in this organism and are not transmitted to offspring during sexual reproduction (a black spot against the background of brown wool in astrakhan sheep). Somatic mutations can be preserved only through asexual reproduction (primarily vegetative).

Mutations by adaptive value:

Useful- increasing the viability of individuals.

Harmful:

lethal- causing death of individuals;

semi-lethal- reducing the viability of an individual (in men, the recessive hemophilia gene is semi-lethal, and homozygous women are not viable).

Neutral - not affecting the viability of individuals.

This classification is very conditional, since the same mutation can be beneficial in some conditions and harmful in others.

Mutations by nature of manifestation:

dominant, which can make the owners of these mutations unviable and cause their death in the early stages of ontogenesis (if the mutations are harmful);

recessive- mutations that do not appear in heterozygotes, therefore remaining in the population for a long time and forming a reserve of hereditary variability (when environmental conditions change, carriers of such mutations can gain an advantage in the struggle for existence).

Mutations according to the degree of phenotypic manifestation:

large- clearly visible mutations that greatly change the phenotype (double flowers);

small- mutations that practically do not give phenotypic manifestations (slight lengthening of the awns of the ear).

Mutations that change the state of a gene:

straight- transition of a gene from wild type to a new state 1;

reverse- transition of a gene from a mutant state to a wild type.

Mutations according to the nature of their appearance:

spontaneous- mutations that arose naturally under the influence of environmental factors;

induced- mutations artificially caused by the action of mutagenic factors.

Mutations according to the nature of the genotype change:

Gene - mutations that are expressed in changes in the structure of individual sections of DNA

Chromosomal - mutations characterized by changes in the structure of individual chromosomes.

Genomic – mutations characterized by changes in the number of chromosomes

Mutations according to the place of their manifestation:

1. Chromosomal

   Point - Gennaya mutation, which is a replacement (as a result of transition or transversion), insertion or loss of one nucleotide.

   Genomic

Cytoplasmic – mutations associated with mutations non-nuclear genes located in mitochondrial DNA and plastid DNA - chloroplasts.

20. Gene mutations, mechanisms of occurrence. The concept of gene diseases.

Gene mutations arise as a result of errors in replication, recombination, and repair of gene material. They appear suddenly; they are hereditary, non-directional; Any gene locus can mutate, causing changes in both minor and vital signs; the same mutations can occur repeatedly.

Most often, gene mutations occur as a result of:

replacing one or more nucleotides with others;

nucleotide insertions;

loss of nucleotides;

nucleotide duplication;

changes in the order of alternation of nucleotides.

Types of gene mutations:

Point – loss, insertion, replacement of nucleotide;

Dynamic mutation - an increase in the number of repeated triplets in a gene (Friedreich's ataxia);

Duplication – doubling of DNA fragments;

Inversion – rotation of a DNA fragment of 2 nucleotides in size;

Insertion - movement of DNA fragments;

Lethal mutation - leads to death

Missense mutation - a codon corresponding to a different amino acid occurs (sickle cell anemia);

Nonsense mutation is a mutation with a nucleotide replacement in the coding part of a gene, leading to the formation of a stop codon;

Regulatory mutation - Changes in the 5" or 3" untranslated regions of a gene disrupt its expression;

Splicing mutations are point substitutions of nucleotides at the exon-intron boundary, and splicing is blocked.

Gene diseases are diseases that arise as a result of gene mutations. For example, sickle cell disease, p. splenomegaly,

Subsequence nuclear DNA for any two people it is almost 99.9% identical. Only a very small fraction of the DNA sequence differs between different people, providing genetic variability. Some differences in DNA sequence have no effect on phenotype, while others are direct causes of disease. Between the two extremes are changes responsible for genetically determined phenotypic variation in anatomy and physiology, food tolerance, response to treatment, or side effects medications, susceptibility to infections, susceptibility to tumors, and perhaps even variability in various personality traits, athletic abilities, and artistic talent.

One of the important concepts of human genetics and medical genetics - that genetic diseases are only the most obvious and often extreme manifestation of genetic differences, one end of a continuum of variations from rare variants, causing disease, through more frequent variations that increase susceptibility to disease, to the most common variations that are not clearly related to the disease.

Types of mutations in humans

Any change in the nucleotide sequence or arrangement of DNA. Mutations can be classified into three categories: those that affect the number of chromosomes in a cell (genomic mutations), those that change the structure of individual chromosomes (chromosomal mutations), and those that change individual genes (gene mutations). Genomic mutations are changes in the number of intact chromosomes (aneuploidy) resulting from errors in chromosome segregation in meiosis or mitosis.

Chromosomal mutations- changes affecting only part of the chromosome, such as partial duplications, deletions, inversions and translocations, which can occur spontaneously or arise due to abnormal segregation of translocated chromosomes during meiosis. Gene mutations are changes in the DNA sequence of the nuclear or mitochondrial genome, ranging from mutations in a single nucleotide to changes spanning many millions of base pairs. Many types of mutations are represented by a variety of alleles at individual loci in more than a thousand different genetic diseases, as well as among the millions of DNA variants found throughout the genome in the normal population.

Description of different mutations not only increases awareness of human genetic diversity and the fragility of the human genetic heritage, but also promotes the information needed to detect and screen for genetic diseases in specific families at risk and also, for some diseases, in the population as a whole.

Genomic mutation, resulting in the loss or duplication of an entire chromosome, changes the dosage and thus the expression level of hundreds or thousands of genes. Likewise, a chromosomal mutation that affects most of one or more chromosomes can also affect the expression of hundreds of genes. Even a small gene mutation can have large consequences, depending on which gene is affected and what the change in expression of that gene causes. A gene mutation in the form of a change in a single nucleotide in the coding sequence can lead to a complete loss of gene expression or the formation of a protein with altered properties.

Some DNA changes, however, do not have phenotypic effects. A chromosomal translocation or inversion may not affect a critical part of the genome and may have absolutely no phenotypic effects. A mutation within a gene may have no effect because it either does not change the amino acid sequence of the polypeptide or, even if it does, the change in the encoded amino acid sequence does not change the functional properties of the protein. Therefore, not all mutations have clinical consequences.

All three types of mutations occur with significant frequency in many different cells. If a mutation occurs in the DNA of germ cells, it can be passed on to subsequent generations. In contrast, somatic mutations occur randomly in only a subset of cells in certain tissues, leading to somatic mosaicism, as seen, for example, in many tumors. Somatic mutations cannot be passed on to subsequent generations.

A certain DNA sequence stores hereditary information that can change (distort) throughout life. Such changes are called mutations. There are several types of mutations that affect different parts of the genetic material.

Definition

Mutations are changes in the genome that are inherited. The genome is the collection of haploid chromosomes inherent in a species. The process of occurrence and consolidation of mutations is called mutagenesis. The term "mutation" was introduced by Hugo de Vries at the beginning of the twentieth century.

Rice. 1. Hugo de Vries.

Mutations arise under the influence of environmental factors.
They can be of two types:

• useful;
• harmful.

Beneficial mutations contribute to natural selection, the development of adaptations to a changing environment and, as a result, the emergence of a new species. They are rare. More often, harmful mutations accumulate in the genotype, which are rejected during natural selection.

Due to their occurrence, there are two types of mutations:

• spontaneous - arise spontaneously throughout life, often have a neutral character - do not affect the life of the individual and his offspring;
• induced - occur under unfavorable environmental conditions - radioactive radiation, chemical exposure, the influence of viruses.

Nerve cells of the human brain accumulate about 2.4 thousand mutations over a lifetime. However, mutations rarely affect vital sections of DNA.

Kinds

Changes occur in certain areas of DNA. Depending on the extent of the mutations and their location, several types are distinguished. Their description is given in the table of types of mutations.

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Rice. 2. Sickle anemia.

The main source of accumulation of mutations in a cell is incorrect, sometimes erroneous, DNA replication. At the next doubling the error can be corrected. If the error is repeated and affects important sections of DNA, the mutation is inherited.

Rice. 3. Impaired DNA replication.

What have we learned?

From a 10th grade lesson we learned what mutations exist. DNA changes can affect a gene, chromosomes, genome, or manifest itself in somatic cells, plastids or mitochondria. Mutations accumulate throughout life and can be inherited. Most mutations are neutral - they do not affect the phenotype. Beneficial mutations that help adapt to the environment and are inherited are rare. Harmful mutations that lead to diseases and developmental disorders occur more often.

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Types of gene mutations:

Gene mutations occur more often than chromosomal and genomic mutations, but they change the structure of DNA less significantly and mainly affect only the chemical structure of a single gene. They represent the replacement, deletion or insertion of a nucleotide, sometimes several. Gene mutations also include translocations (transfers), duplications (repetitions), inversions (180° flip) of gene sections, but not chromosomes.

Gene mutations occur during DNA replication, crossing over, and are possible in other periods cell cycle. Repair mechanisms do not always eliminate mutations and DNA damage. In addition, they themselves can serve as a source of gene mutations. For example, when joining the ends of a broken chromosome, several nucleotide pairs are often lost.

If repair systems cease to function normally, then a rapid accumulation of mutations occurs. If mutations occur in genes encoding repair enzymes, the functioning of one or more of its mechanisms may be disrupted, as a result of which the number of mutations will greatly increase. However, sometimes the opposite effect occurs when mutation of genes for repair enzymes leads to a decrease in the frequency of mutations of other genes.

In addition to primary mutations, reverse mutations can also occur in cells, restoring the original gene.

Most gene changes, like mutations in the other two types, are harmful. The appearance of mutations that cause beneficial traits for certain environmental conditions occurs rarely. However, it is they who make the process of evolution possible.

Gene mutations do not affect the genotype, but individual sections of the gene, which, in turn, causes the appearance of a new variant of the trait, i.e., an allele, and not a new trait as such. Mouton is an elementary unit of the mutation process that can lead to the appearance of a new variant of a trait. Often, it is enough to change one pair of nucleotides. From this point of view, a muton corresponds to one pair of complementary nucleotides. On the other hand, not all gene mutations are mutons in terms of consequences. If a change in the nucleotide sequence does not entail a change in the trait, then from a functional point of view the mutation has not occurred.

One pair of nucleotides corresponds to and recon- the elementary unit of recombination. During crossing over, in the event of a recombination disorder, an unequal exchange of regions occurs between the conjugating chromosomes. As a result, the insertion and loss of nucleotide pairs occurs, which entails a shift in the reading frame, subsequently disrupting the synthesis of a peptide with the necessary properties. Thus, one extra or lost pair of nucleotides is enough to distort genetic information.

The frequency of spontaneous gene mutations ranges from 10 -12 to 10 -9 per DNA nucleotide per cell division. To conduct research, scientists expose cells to chemical, physical, and biological mutagens. Mutations caused in this way are called induced, their frequency is higher.

Replacing nitrogenous bases

If there is a change in only one nucleotide in DNA, then such a mutation is called point. In the case of mutations such as the replacement of nitrogenous bases, one complementary nucleotide pair of the DNA molecule is replaced by another in a series of replication cycles. The frequency of such incidents is about 20% of the total mass of all gene mutations.

An example of this is the deamination of cytosine, resulting in the formation of uracil.

Nucleotide is formed in DNA couple G-U, instead of G-C. If the error is not repaired by the enzyme DNA glycolase, then the following will happen during replication. The chains will separate, cytosine will be installed opposite guanine, and adenine will be installed opposite uracil. Thus, one of the daughter DNA molecules will contain an abnormal Y-A pair. During its subsequent replication, thymine will be installed in one of the molecules opposite adenine. That is, in the gene the G-C pair will be replaced by A-T.

Another example is the deamination of methylated cytosine to form thymine. Subsequently, a gene with a pair T-A instead of C-G may arise.

There may also be reverse substitutions: pair A-T in certain chemical reactions it can be replaced by C-G. For example, during the replication process, bromuracil can join adenine, which, during the next replication, adds guanine to itself. In the next cycle, guanine will bind to cytosine. Thus, the A-T pair in the gene will be replaced by C-G.

Replacing one pyrimidine with another pyrimidine or one purine with another purine is called transition. Pyrimidines are cytosine, thymine, uracil. Purines - adenine and guanine. Replacing purine with pyrimidine or pyrimidine with purine is called transversion.

A point mutation may not lead to any consequences due to the degeneracy of the genetic code, when several triplet codons encode the same amino acid. That is, as a result of replacing one nucleotide, another codon can be formed, but encoding the same amino acid as the old one. This nucleotide substitution is called synonymous. Their frequency is about 25% of all nucleotide substitutions. If the meaning of a codon changes, it begins to code for another amino acid, then the replacement is called misense mutation. Their frequency is about 70%.

In the case of a misense mutation, the wrong amino acid will be included in the peptide during translation, causing its properties to change. The degree of change in the more complex characteristics of the organism depends on the degree of change in the properties of the protein. For example, with sickle cell anemia, only one amino acid is replaced in the protein - glutamine with valine. If glutamine is replaced by lysine, then the properties of the protein do not change much, i.e. both amino acids are hydrophilic.

A point mutation can be such that a stop codon (UAG, UAA, UGA) appears in place of the codon encoding an amino acid, interrupting (terminating) translation. This nonsense mutations. Sometimes there are reverse substitutions, when a semantic one appears in place of a stop codon. With any such gene mutation, a functional protein can no longer be synthesized.

Frame shift

Gene mutations include mutations caused by a reading frame shift, when the number of nucleotide pairs in the gene changes. This can be either a loss or an insertion of one or more nucleotide pairs in the DNA. There are the most gene mutations of the reading frameshift type. They most often occur in repeating nucleotide sequences.

The insertion or deletion of nucleotide pairs can occur as a result of exposure to certain chemicals that deform the DNA double helix.

X-ray irradiation can lead to loss, i.e. deletion, of a region with a large number of nucleotide pairs.

Insertions are not uncommon when so-called mobile genetic elements, which can change their position.

Unequal crossing over leads to gene mutations. Most often it occurs in those regions of chromosomes where several copies of the same gene are localized. In this case, crossing over occurs in such a way that a deletion of a region occurs in one chromosome. This region is transferred to the homologous chromosome, in which a duplication of the gene region occurs.

If a deletion or insertion of a number of nucleotides not a multiple of three occurs, the reading frame shifts, and the translation of the genetic code is often meaningless. In addition, a nonsense triplet may occur.

If the number of inserted or dropped nucleotides is a multiple of three, then we can say that the reading frame does not shift. However, when such genes are translated, extra or significant amino acids will be included in the peptide chain.

Inversion within a gene

If an inversion of a DNA section occurs within one gene, then such a mutation is classified as a gene mutation. Inversions of larger regions are referred to as chromosomal mutations.

Inversion occurs due to the rotation of a DNA section by 180°. This often occurs when a loop forms in the DNA molecule. When replicating in a loop, replication occurs in the opposite direction. Next, this piece is stitched with the rest of the DNA strand, but turns out to be upside down.

If an inversion occurs in a sense gene, then during the synthesis of a peptide, some of its amino acids will have the reverse sequence, which will affect the properties of the protein.

Mutations are changes in a cell's DNA. Occur under the influence of ultraviolet radiation, radiation (X-rays), etc. Passed on by inheritance, serve as material for natural selection. Differences from modifications

Gene mutations– change in the structure of one gene. This is a change in the nucleotide sequence: deletion, insertion, substitution, etc. For example, replacing A with T. Causes: violations during DNA doubling (replication). Examples: sickle cell anemia, phenylketonuria.

Chromosomal mutations– change in the structure of chromosomes: loss of a section, doubling of a section, rotation of a section by 180 degrees, transfer of a section to another (non-homologous) chromosome, etc. The reasons are violations during crossing over. Example: Cry Cat Syndrome.

Genomic mutations– change in the number of chromosomes. The causes are disturbances in the divergence of chromosomes.

• Polyploidy– multiple changes (several times, for example, 12 → 24). It does not occur in animals; in plants it leads to an increase in size.
• Aneuploidy– changes on one or two chromosomes. For example, one extra twenty-first chromosome leads to Down syndrome (the total number of chromosomes is 47).

Cytoplasmic mutations– changes in the DNA of mitochondria and plastids. They are transmitted only through the female line, because mitochondria and plastids from sperm do not enter the zygote. An example in plants is variegation.

Somatic– mutations in somatic cells (cells of the body; there can be four of the above types). During sexual reproduction they are not inherited. Transmitted during vegetative propagation in plants, budding and fragmentation in coelenterates (hydra).

Induced mutagenesis.

Experimental production of mutations in plants and microorganisms and their use in breeding

In effective ways obtaining the starting material are methods induced mutagenesis– artificial obtaining of mutations. Induced mutagenesis makes it possible to obtain new alleles that cannot be detected in nature. For example, highly productive strains of microorganisms (antibiotic producers), dwarf plant varieties with increased early maturity, etc. have been obtained this way. Experimentally obtained mutations in plants and microorganisms are used as material for artificial selection. In this way, highly productive strains of microorganisms (producers of antibiotics), dwarf plant varieties with increased early maturity, etc. were obtained.

To obtain induced mutations in plants, physical mutagens (gamma radiation, X-ray and ultraviolet radiation) and specially created chemical supermutagens (for example, N-methyl-N-nitrosourea) are used.

The dose of mutagens is selected in such a way that no more than 30...50% of the treated objects die. For example, when using ionizing radiation, such a critical dose ranges from 1...3 to 10...15 and even 50...100 kiloroentgen. When using chemical mutagens, their aqueous solutions with a concentration of 0.01...0.2% are used; processing time - from 6 to 24 hours or more.

Pollen, seeds, seedlings, buds, cuttings, bulbs, tubers and other parts of plants are processed. Plants grown from treated seeds (buds, cuttings, etc.) are indicated by the symbol M 1 (first mutant generation). IN M 1 selection is difficult, since most mutations are recessive and do not manifest themselves in the phenotype. In addition, along with mutations, non-inherited changes are often found: phenocopies, terates, morphoses.

Therefore, the isolation of mutations begins at M 2 (second mutant generation), when at least some of the recessive mutations appear, and the probability of persistence of non-hereditary changes decreases. Typically, selection continues for 2...3 generations, although in some cases up to 5...7 generations are required to cull non-heritable changes (such non-hereditary changes that persist over several generations are called long-term modifications).

The resulting mutant forms either directly give rise to a new variety (for example, dwarf tomatoes with yellow or orange fruits) or are used in further breeding work.

However, the use of induced mutations in breeding is still limited, since mutations lead to the destruction of historically established genetic complexes. In animals, mutations almost always lead to reduced viability and/or infertility. A few exceptions include the silkworm, with which intensive breeding work was carried out using auto- and allopolyploids (B.L. Astaurov, V.A. Strunnikov).

Somatic mutations. As a result of induced mutagenesis, partially mutant plants (chimeric organisms) are often obtained. In this case they talk about somatic (kidney) mutations. Many varieties of fruit plants, grapes, and potatoes are somatic mutants. These varieties retain their properties if they are reproduced vegetatively, for example, by grafting buds (cuttings) treated with mutagens into the crown of non-mutant plants; In this way, for example, seedless oranges are propagated.

The tasks of agricultural production include a worldwide increase in the production of grain, industrial, vegetable and fruit crops.
The solution of these problems is possible in the presence of new promising, intensive varieties of various crops. Obtaining new varieties of intensive type is possible, in particular, with the help of chemical mutagens.
The impact of mutagenic factors on the original forms increases the frequency of mutations and makes it possible to create the richest breeding material with a complex of valuable economic traits and properties.
Thus, in many scientific institutions in our country and abroad, new varieties were obtained as a result of the use of physical and chemical mutagens. These are varieties of spring and winter wheat, characterized by increased yield, resistance to many diseases and other useful properties. Tomato varieties have also been obtained, which are distinguished by high productivity, high taste and technological qualities, suitable for mechanized harvesting.
Recently, intensive studies are also being conducted on induced mutagenesis in industrial fish farming - carp, silver carp, rainbow trout. The purpose of such studies is to determine the effectiveness and features of the action of various chemical mutagens, followed by the selection of mutants for further selection.
Research is also being conducted to study mutagens in microbiology. Mutant strains of microorganisms were obtained that have the ability to destroy harmful substances contained in rubber production wastewater.
It is likely that the power of the new methods was manifested with particular force in the selection of those organisms in which many individuals can be used to obtain mutations and selection, giving a rapid change of generations. Such conditions are best met in microorganisms. Many bacteria, fungi, antinomycetes and other forms are of great practical interest for agriculture and medicine. The microbiological industry, which provides amino acids, vitamins, antibiotics, fats and other substances, has enormous opportunities.
Mutation selection has proved to be an indispensable link in the new field of intensive use of the most important microorganisms in the service of man. The influence of radiation or chemical mutagens on molecular structures causes new forms of biochemical processes in the cell.
So, it is possible to obtain radiation and chemical mutants of microorganisms with the properties of "oversynthesis" according to the right substance. It is in this way that the radiation and chemical selection of penicilli, actinomycetes, yeasts and other lower fungi and bacteria has shown the possibility of creating forms that were previously practically impossible to obtain. Methods for cultivating plant cells and regenerating plants from them, developed for many agricultural crops, already now make it possible to experimentally realize the possibilities of cell selection, that is, to use it to create new plant varieties. List of mutants with important agricultural traits, the selection of which is feasible on cellular level, quite big. These include mutants of resistance to stress factors, herbicides, various diseases, superproducers of essential amino acids.
Directions of research, which are solved with the help of cell selection, are not limited to the creation of valuable source material. Cell selection methods underlie a number of technologies for the industrial cultivation of cell cultures, producers of economically significant substances. These areas of research are also important for the development of fundamental issues of mutagenesis, genetics, molecular biology, physiology and biochemistry of plants. Thanks to new technology Through selection, numerous cell lines and plants have been obtained, which are widely used as starting material for theoretical research. Using them, mutants previously unknown in plants were isolated, as well as the first antibiotic-resistant mutants.
The application of genetic engineering achievements in agriculture is very widespread. This is the production of food and feed protein, the disposal of substances harmful to environment, the creation of waste-free production technologies, the production of biogas, the breeding of highly productive animal breeds, new plant varieties that are resistant to diseases, herbicides, insects, and stress.

Mutations are the primary changes upon which evolution and selection are built. The natural manifestation of mutations is a process that is constantly going on in all organisms. It is based on changes in the chemistry of genes, various structural transformations in chromosomes, changes in the number of chromosomes.
Mutational variability underlies any source material for selection, because the original, primary hereditary diversity arises only on the basis of mutations. The ability to control the process of mutations leads to the most serious changes in the whole problem of starting material for selection.
The mutation process can be controlled in different ways. On the one hand, a sharp increase in the general processes of variability leads to a large amount of the maximum diversity of genes and chromosomes. On the other hand, the use of such factors that have the ability to cause a specific mutation is of paramount importance. In this case, it becomes possible to differentially control the process of mutations, causing a limited circle of necessary mutations, and in the end to obtain only the necessary mutations.
The natural mutation process depends on external factors. Environmental factors form the basis for the appearance of natural mutations. The frequency of mutations in the natural environment can increase under the influence of temperature, ultraviolet light, ionizing measurements, chemical mutagens.
Now it is possible, using environmental factors, to interfere with the chemical structure of genes, causing mutations of genes and chromosomes in any desired amount. This solves the problem of source material for breeding in a new way. Methods of induced mutagenesis fundamentally complement all other sections of the doctrine of the source material. Only after passing through strict selection, and in some cases even crossing, mutations can give rise to new varieties. The selection itself is carried out by classical genetic methods, since mutations are only raw material for creating a variety.
The natural mutation process is the basis of evolutionary transformations of species, and throughout all past selection it was the basis of selection in the creation of plant varieties. As a result of the action of natural and artificial selection, hereditary changes - mutations, depending on their adaptive or economic value, are fixed during sexual or vegetative reproduction or are not subject to mutations or genetic changes under the influence of environmental changes.
The role of natural and induced mutations in the selection of plants and animals, microbiology, and biotechnology is great, which is the basis for the successful development of agricultural production.

6. Polyploids: types of polyploids and their use in breeding.

Polyploidy. As is known, the term “polyploidy” is used to refer to a wide variety of phenomena associated with changes in the number of chromosomes in cells.

Autopolyploidy is the repeated repetition of the same chromosome set (genome) in a cell. Autopolyploidy is often accompanied by an increase in cell size, pollen grains, and overall size of organisms. For example, triploid aspen reaches gigantic sizes, is durable, and its wood is resistant to rotting. Among cultivated plants, both triploids (bananas, tea, sugar beets) and tetraploids (rye, clover, buckwheat, corn, grapes, as well as strawberries, apple trees, watermelons) are widespread. Some polyploid varieties (strawberries, apples, watermelons) are represented by both triploids and tetraploids. Autopolyploids are characterized by increased sugar content and increased vitamin content. The positive effects of polyploidy are associated with an increase in the number of copies of the same gene in cells, and, accordingly, an increase in the dose (concentration) of enzymes. As a rule, autopolyploids are less fertile compared to diploids, but the decrease in fertility is usually more than compensated by an increase in the size of the fruit (apple tree, pear, grape) or an increased content of certain substances (sugars, vitamins). At the same time, in a number of cases, polyploidy leads to inhibition of physiological processes, especially when very high levels ploidy. For example, wheat with 84 chromosomes is less productive than wheat with 42 chromosomes.

Allopolyploidy is the combination of different sets of chromosomes (genomes) in a cell. Allopolyploids are often obtained by distant hybridization, that is, by crossing organisms belonging to different species. Such hybrids are usually sterile (they are figuratively called “plant mules”), however, by doubling the number of chromosomes in the cells, their fertility (fertility) can be restored. In this way, hybrids of wheat and rye (triticale), cherry plum and sloe, mulberry and tangerine silkworm were obtained.

Polyploidy in breeding is used to achieve the following goals:

Obtaining highly productive forms that can be directly introduced into production or used as material for further selection;

Restoring fertility in interspecific hybrids;

Transfer of haploid forms to the diploid level.

Under experimental conditions, the formation of polyploid cells can be caused by exposure to extreme temperatures: low (0...+8 °C) or high (+38...+45 °C), as well as by treating organisms or their parts (flowers, seeds or plant seedlings, eggs or animal embryos) with mitotic poisons. Mitotic poisons include: colchicine (an alkaloid of the autumn crocus - a famous ornamental plant), chloroform, chloral hydrate, vinblastine, acenaphthene, etc.

7. Classification of source material.

Selection work begins with the selection of source material, on which, as N.I. Vavilov believed, the success of selection work primarily depends.
The source material in breeding is the cultivated and wild forms of plants used to breed new varieties.
The following materials are used as starting material: 1) forms and varieties of plants that are found in great diversity in nature; 2) plant forms created in the selection process itself through hybridization and under the artificial influence of various external conditions,
In modern breeding, the following main types and methods of obtaining source material are used.
I. Natural populations. These include wild forms, local varieties of cultivated plants and samples of the world collection of agricultural plants.
II. Hybrid populations. There are two types of hybrid populations: 1) intraspecific, obtained as a result of crossing varieties and forms within one species; 2) created by crossing different types and plant genera (interspecific and intergeneric).
III. Self-pollinated lines (incubated lines). They serve as an important source of starting material in the selection of cross-pollinating plants. They are obtained by repeated forced self-pollination of these plants. The best lines are crossed with each other or with varieties to create heterotic hybrids, resulting in hybrid seeds that are used within one year. Hybrids obtained from self-pollinated lines, unlike conventional hybrid varieties, must be reproduced annually.
IV. Artificial mutations and polyploid forms. This type of source material is created by exposing plants to various types of radiation, chemicals, temperature and other mutagenic agents.
Meaning various types source material in the history of the development of selection and at the present time is not the same. For many centuries, its only species were natural populations. Then genetics theoretically substantiated the use of hybridization. The use of this method in practical selection began in our country in the 20s. Since the 30s. hybridization as a method of creating source material is becoming increasingly important, and currently intraspecific hybridization is the main method when working with almost all crops. Despite the enormous difficulties of distant hybridization, it is also widely used to create source material in the breeding of a number of important agricultural crops.
Mutations and polyploid forms are new sources of initial material, the use of which is expanding every year and in working with some crops gives practically valuable results. The most important method of selection was and remains artificial selection. However, the selection process includes two groups of activities: evaluation of the starting material and selective propagation (reproduction) of the selected organisms or their parts. Let's consider methods for evaluating source material using plants as an example.

During the selection process, the material is evaluated according to its economic and biological properties, which are the object of selection. But regardless of the characteristics of the object and the objectives of selection, the material is assessed according to the following criteria:

A certain rhythm of development corresponding to the soil and climatic conditions in which further exploitation of the variety is planned;

High potential productivity with high quality products;

Resistance to the adverse effects of physical and chemical environmental factors (frost resistance, winter resistance, heat resistance, drought resistance, resistance to various types of chemical pollution);

Resistance to diseases and pests (assessed by immunity);

Responsiveness to agricultural technology.

Ideally, a variety should meet not individual requirements, but a complex of them. However, in practice this often turns out to be impossible, and that is why the creation of compositions consisting of lines (clones) with different hereditary properties is considered the fastest and most reliable way to increase the overall sustainability of agroecosystems. It has been proven that in genetically heterogeneous systems, compensatory interactions arise between individuals with different characteristics of growth and development, sensitivity to the dynamics of environmental factors, diseases, and pests.

The material is assessed at all stages of ontogenesis, since different signs appear at different age states. In this case, the material is assessed as direct, and by indirect signs. For example, when assessing the winter hardiness of winter cereals and perennial plants, the most important direct indicator is the overall degree of freezing in points. At the same time, winter hardiness can be assessed by determining the sugar content in the cell sap. This indicator is indirect. Estimation based on indirect evidence is considered less accurate, but in some cases it becomes convenient and even inevitable, for example:

If there is a high and stable correlation between direct and indirect signs;

If direct signs appear only in certain years (abnormally dry, rainy...);

If direct signs appear in the later stages of ontogenesis;

If direct signs are characterized by high modification variability.

To evaluate breeding material, field, laboratory and laboratory-field methods are used.

Field methods give the most reliable results, since the material is assessed in natural conditions using direct characteristics. However, the use of field methods is not always possible. For example, to assess the frost resistance of annual seedlings, a frosty, snowless winter is required; if there was no such winter in a given year, then the material remains without evaluation. Similarly, assessment of immunity against the background of natural infection can only be carried out during years of strong spread of the disease or pest.

Laboratory methods allow you to change the gradation of environmental factors at the will of the experimenter. For example, damage to shoots is simulated by pruning. However, in some cases the use experimental methods requires special equipment; for example, winter hardiness studies require freezers with intense light sources.

Laboratory-field methods combine the advantages and disadvantages of the actual field and laboratory methods.

A special group is allocated provocative methods, with the help of which it is artificially created provocative background, that is, the conditions for identifying the attitude of plants to unfavorable physicochemical and biotic factors. The intensity of provocative methods should be optimal. If the provocative background is too weak, the manifestation of an undesirable trait is not guaranteed, and if the background is too harsh, plants that are sufficiently resistant to the action of this factor may be discarded.

Provocative methods include the creation of an infectious background during selection for resistance to pests and diseases. This direction of selection is extremely important and, at the same time, very difficult, so we will consider it in a little more detail.

Evaluation of breeding material for resistance to diseases and pests

It is known that people give at least 25% of agricultural products as a tribute to diseases and pests. To reduce these losses, ever-increasing doses of pesticides are used: fungicides, insecticides, acaricides, etc. It is clear that products obtained with the use of pesticides cannot be considered harmless to humans, and the very use of pesticides not only reduces the stability of agroecosystems, but also disrupts the structure of adjacent ecosystems. Therefore, selection for immunity, i.e. for resistance to diseases and pests is perhaps the most important component of the breeding process. The foundations of the doctrine of immunity were laid by N.I. Vavilov.

The development of the disease is influenced by environmental factors that create conditions for infection and spread of the pathogen. Knowledge of these conditions allows you to create the best provocative backgrounds for identifying and rejecting affected plants. For example, the manifestation of many diseases is facilitated by monoculture, as well as the use of crop rotation with short rotation.

To identify the resistance or instability of plants to a given race of pathogen, an infectious background is created by artificially infecting plants with this race. The resistance or susceptibility of plants to a pathogen is a consequence of coevolution (coupled evolution) of two gene pools - the plant and the pathogen. The higher the diversity of these gene pools, the higher the rate of formation of new races of the pathogen. As a result, the formation of new races in pathogenic organisms occurs most intensively in breeding institutions, where there is the greatest diversity of plant genotypes and pathogen genotypes. As a result, a newly created variety that is immune to this pathogen loses its resistance after a few years. To prevent this undesirable effect, the following conditions can be recommended.

1. Create new collection plantings at a sufficient distance from natural plantings of a given species, and in cultural rotation there should not be close species among the predecessors.

2. Create dispersed collections, that is, grow groups of plants that are potentially resistant to a given pathogen in spatial isolation in relation to other similar groups.

8. Remote hybridization. Difficulties in obtaining hybrids Features of the selection of grain crops: diagram of the selection process.

Modern breeding uses a whole range of methods based on the latest achievements of many sciences: genetics, cytology, botany, zoology, microbiology, agroecology, biotechnology, information technology, etc. (some of them will be discussed in the lecture “Genetics as the scientific foundation of biotechnology”). However, the main specific selection methods remain hybridization And artificial selection.

Hybridization

Crossing organisms with different genotypes is the main method for obtaining new combinations of traits. Sometimes hybridization is necessary, for example to prevent inbreeding depression. Inbreeding depression manifests itself in closely related crossing and is expressed in a decrease in productivity and vitality (vitality). Inbreeding depression is the opposite of heterosis (see below).

The following types of crossings are distinguished:

intraspecific crosses– different forms are crossed within a species (not necessarily varieties and breeds). Intraspecific crossings also include crossings of organisms of the same species living in different ecological conditions and / or in different geographical areas ( ecological-geographical crossings). Intraspecific crosses form the basis of most other crosses.

Inbreeding– inbreeding in plants and inbreeding in animals. Used to obtain clean lines.

Interline crossings– representatives of pure lines are crossed (and in some cases, different varieties and breeds). Interline crosses are used to suppress inbreeding depression, as well as to obtain the effect of heterosis (see below). Interline crossing can act as an independent stage of the selection process, however, in recent decades, interline hybrids ( crosses, or first generation hybrids F 1) are increasingly used to obtain marketable products.

Backcrosses (back crosses) are crossings of hybrids (heterozygotes) with parental forms (homozygotes). For example, crossing heterozygotes with dominant homozygous forms is used to prevent the phenotypic manifestation of recessive alleles.

Analyzing crosses(are a type of back-crosses) – these are crossings of dominant forms with an unknown genotype and recessive-homozygous tester lines. Such crosses are used to analyze sires by offspring: if as a result of the analyzing cross there is no segregation, then the dominant form is homozygous; if a 1:1 split is observed (1 part of individuals with dominant traits: 1 part of individuals with recessive traits), then the dominant form is heterozygous.

Saturating (substitution) crosses They are also a type of backcross. With multiple backcrosses, selective (differential) substitution of alleles (chromosomes) is possible, for example, the probability of retaining an undesirable allele can be gradually reduced.

Distant crosses- interspecific and intergeneric. Usually, distant hybrids are sterile and are propagated vegetatively; to overcome the infertility of hybrids, doubling the number of chromosomes is used, in this way amphidiploid organisms are obtained: rye-wheat hybrids (triticale), wheat-couch grass hybrids.

Somatic hybridization- this is hybridization based on the fusion of somatic cells of completely dissimilar organisms. Somatic hybridization will be discussed in more detail in the lecture "Genetics as the scientific foundation of biotechnology".

Heterosis. During hybridization, it often manifests itself heterosis– hybrid vigor, especially in the first generation of hybrids. The mechanisms of heterosis are still not well understood. The two most popular theories of heterosis are the theory of dominance and the theory of overdominance. The theory of dominance is based on the idea that when crossing homozygotes in first-generation hybrids, unfavorable recessive alleles are transferred to a heterozygous state: AAbb × aaBB → AaBb; Then AaBb>AAbb, AaBb>aaBB. The theory of overdominance assumes increased constitutive (general) fitness of heterozygotes compared to any of the homozygotes: Aa>A.A. And Aa>aa. There are also more complex ideas about heterosis, for example, the theory of heterosis by V.A. Strunnikova; the essence of this theory is that in pure lines there is an accumulation of modifier genes that suppress the undesirable effects of certain alleles; when crossing different pure lines, each of them brings its own compensatory complex of modifier genes, which enhances the suppression of harmful alleles.

In some cases, it is possible to preserve the obtained genotypes and thereby consolidate heterosis, for example, when propagating plants by vegetative means. The effect of heterosis also persists when transferring diploid heterotic hybrids to the polyploid level.

The crossing of organisms belonging to different species and genera is called distant hybridization.

Distant hybridization is divided into interspecific And intergeneric. Examples of interspecific hybridization are crossings of soft wheat with durum wheat, sunflower with Jerusalem artichoke, common oats with Byzantine oats, etc. Crossings of wheat with rye, wheat with wheatgrass, barley with elymus, and others refer to intergeneric hybridization. The purpose of distant hybridization is the creation of plant forms and varieties that combine the characteristics and properties of different species and genera. In practical and theoretical terms, it is of exceptional interest, since distant hybrids are very often distinguished by increased growth and development power, the size of fruits and seeds, winter hardiness and drought resistance.

Distant hybridization is of great importance in creating varieties that are resistant to diseases and pests.

Distant hybridization has a history of more than two centuries. The first distant hybrid between two types of tobacco was obtained in 1760 by I. Kelreuter. Since then, the problem of distant hybridization has consistently attracted the attention of many prominent botanists, geneticists and breeders around the world. A great contribution to the development of the theory and practice of distant hybridization was made by I. V. Michurin, who, based on this method, created a large number of new varieties and forms of fruit plants.

Distant hybridization encounters great difficulties. They are associated with poor crossability or uncrossability of different species and genera and the sterility of the resulting first generation hybrids.

A number of ways to overcome the uncrossability of plants during distant hybridization were proposed by I. V. Michurin. When producing hybrids between apple and pear, cherry and bird cherry, quince and pear, apricot and plum, he used a mixture of pollen. Apparently, the secretions of various pollen applied to the stigmas of flowers of the mother plant promote the germination of pollen of the pollinating species.

In some cases, germination of pollen from the father plant was stimulated by the addition of pollen from the mother plant. So, when crossing a rose with a rose hip, I.V. Michurin could not get seeds. When rose pollen was added to rose hip pollen, seeds were formed, and hybrid plants grew from them.

To develop winter-hardy peach varieties, I.V. Michurin decided to cross cultivated peach varieties with a winter-hardy form of wild almond-legume. But he was unable to obtain seeds from such a crossing. Then he carried out a preliminary crossing of the bean seedlings with the wild David peach. The result was a hybrid, which he called the intermediary. It had sufficient winter hardiness and easily crossed with cultivated peach varieties. This stepwise crossing method for hybridizing different plant species is called the intermediary method.

During distant hybridization, crossings are carried out on a large scale, since with a small number of pollinated flowers, a misconception may arise about the uncrossability of certain species or genera of plants. Interspecific and intergeneric hybrids of the first generation, as a rule, are sterile or have very low fertility, although their vegetative organs may be well developed.

The reasons for the infertility of hybrids of the first generation of distant crosses are as follows:

• underdevelopment of generative organs. Most often, male generative organs - anthers - are underdeveloped, sometimes they do not even open. The female reproductive organs are often sterile;
• meiotic disorder. During the formation of gametes, poor or incorrect conjugation of chromosomes of different species is possible. In this case, two cases are possible.

1. Crossed species have different numbers of chromosomes. For example, species A (2n=14) is crossed with species B (2n=28). In first-generation hybrids, the number of chromosomes will be 21. During gametogenesis, 7 pairs of bivalents and 7 univalents are formed. Univalent chromosomes are unevenly distributed between the resulting gametes. In this case, gametes with a different number of chromosomes will be formed - from 7 to 14.

2. Crossed species have the same number of chromosomes, but due to their structural differences, conjugation between them may be disrupted. During meiosis, as in the first case, non-homologous chromosomes separate incorrectly. As a result of this phenomenon, more or less pronounced sterility of the hybrids is also observed.

To overcome the infertility of distant hybrids of the first generation, the following techniques are used.

1. Pollination by pollen from one of the parents. This is one of the most commonly used methods and in most cases it gives good results. Its disadvantage lies in the return in subsequent hybrid generations of the characteristics and properties of the parent whose pollen was used for re-pollination.

2. Pollination by pollen of first generation plants. Given the large scale of work and the diversity of parental forms, among the first generation hybrids there are usually few plants with fertile pollen. They are used to pollinate sterile plants of the same generation. At the same time, the return to the characteristics of the parental forms is much weaker.

3. Treatment of germinating seeds with colchicine solution to double the number of chromosomes. This method makes it possible to obtain a large number of fertile amphidiploid forms with a balanced number of chromosomes.

9.Tasks, organization of the main links of a unified selection and seed production system in the country.

Breeding and seed production in our country is carried out on the basis of a single centralized state system, which combines breeding (selection), testing (state variety testing) and zoning of new varieties, their mass reproduction while maintaining biological and productive qualities (seed production proper), harvesting and monitoring of varietal (approbation) and sowing (seed control) qualities of seeds.

The main links of the selection and seed production system and their tasks can be presented in the following form.

1. Selection- development of new varieties in breeding centers and other research institutions.

2. Variety testing and zoning- objective comprehensive assessment of varieties and hybrids at the variety plots of the State Commission for Variety Testing of Agricultural Crops and identification of areas for their production use.

3. Seed production- mass propagation of varieties and hybrids while maintaining their varietal and yield qualities. Production of elite seeds and first reproductions in research institutions, educational farms of agricultural universities and subsequent reproductions in specialized seed farms, seed production teams and departments of collective and state farms.

4. Procurement and sale of varietal seeds- procurement, storage and sale of varietal seeds by seed farms and procurement organizations. Creation of the necessary insurance and transferable (for winter crops) seed funds for state resources.

5. Varietal and seed control- checking the varietal and seed properties of seeds, carried out in all farms and state seed inspections.

Thus, seed production work is carried out in common system selection and seed production, but the latter at the same time has its own system.

Seed system is a group of interconnected production units that, in accordance with the state plan, meet the country's need for high-quality varietal seeds of any crop or group of crops. The seed production system ensures control over the varietal and sowing qualities of seeds; its task includes the procurement and supply of high-quality varietal seeds to all collective and state farms.

The seed system should be distinguished from the seed scheme.

Seed production scheme is a group of nurseries and seed crops in which the process of reproducing a variety is carried out in a certain sequence through selection and reproduction. In the same seed production system, this work can be carried out according to different schemes. The seed production system provides for the organization of the production of varietal seeds, while the seed production scheme determines the methods and. methods on the basis of which the cultivation of seeds with high varietal and yield qualities is ensured.

The organization of production of varietal seeds of a particular crop or group of crops is built taking into account a number of factors: the biological characteristics of the crop, the area occupied by it in production, feed sowing and yield, organizational and technical conditions, etc.

In 1976, the following system of seed production of grains, oilseeds and grasses was adopted. Research institutions - originators of new varieties provide initial seed material for zoned and promising varieties to experimental production farms of research institutions and educational and experimental farms of agricultural universities and technical schools in the amounts determined by the State Agricultural Industry of the USSR.

Experimental production farms of scientific research institutions and educational and experimental farms of agricultural universities and technical schools produce seeds of the elite and I reproductions of zoned and promising varieties in quantities that ensure the satisfaction of the needs of specialized seed farms, seed production teams and departments of large collective and state farms for variety change and variety renewal.

10. Concept of variety. Types of varieties by origin and methods of creation. The variety is created by man and is a means of agricultural production.

A variety is a group of cultivated plants with similar economic and biological properties and morphological characteristics, selected and propagated for cultivation in appropriate natural and production conditions in order to increase productivity and product quality. It is important to emphasize the following main points.

1. The group of plants that make up the variety has a common origin. It is the multiplied offspring of one or a few plants.

2. By propagating the original parent plants, their offspring, through selection, achieve similarity in economic and biological properties and morphological characteristics. The degree of this similarity may vary depending on the source material and selection methods.

3. The variety is created for cultivation in certain natural and production conditions. Given appropriate natural and production conditions, the variety should ensure consistently high yields and high-quality products.

Varieties of agricultural plants differ in origin and breeding methods. Based on their origin, they are divided into local and selective. Local varieties are those created as a result of a long-term action of natural and simple methods of artificial selection in the cultivation of a particular crop in a particular area. A lot of good local varieties of various crops have been created as a result of folk selection. Many of them, having a wide variety of economic and biological characteristics, serve as a valuable source material for breeding breeding varieties.

Breeding called varieties created in research institutions on the basis of scientific breeding methods. They are distinguished by significantly greater uniformity in morphological characteristics and economic and biological properties: linear varieties, clone varieties, mutant varieties and varieties of hybrid origin.

Population varieties are obtained by mass selection of cross-pollinating or self-pollinating plants. They are hereditarily heterogeneous. Varieties-populations of self-pollinators are in most cases heterogeneous morphologically and in terms of economic and biological properties. Varieties-populations of cross-pollinators, due to constant cross-pollination, are characterized by high uniformity. All local varieties and varieties of cross-pollinated crops are population varieties.

Linear are varieties bred through individual selection from self-pollinating crops. A linear variety is the propagated offspring of one plant, so it is characterized by high uniformity in all characteristics and properties. Under the influence of natural cross-pollination, mechanical contamination and mutation, linear varieties gradually lose their uniformity. Linear varieties include winter wheat Ulyanovka and Gorkovchanka, spring wheat Lutescens 62 and Erythrospermum 841, oats Pobeda and Sovetsky, barley Wiener and Nutans 187, millet Saratovskoe 853, Veselopodolyanskoe 38 and a number of others.

Mutant varieties created by selection from populations obtained under the influence of mutagenic factors. Mutant varieties of winter wheat Kiyanka, spring wheat Novosibirskaya 67, barley Temp and Minsky, soybean Universal, lupine Kyiv early ripening, bean Sanaris 75, etc. have been zoned.

Varieties obtained by crossing and selecting from hybrid populations are called hybrid. In self-pollinators they are less aligned than in the line variety. From them it is sometimes possible to develop new varieties through repeated selection. For almost all crops, the majority of released varieties are hybrid. Among them are winter wheat Bezostaya 1, Priboy and Odesskaya 51, spring wheat Saratovskaya 46, Moskovskaya 35 and Leningradka, oats Drug and Slavutich, barley Odessa 100, Nosovsky 9, millet Early ripening 66 and Saratovskaya 6, rice Start and Spalchik. Sometimes, not one, but several morphologically, homogeneous, but biologically different hybrid lines are selected from a hybrid population. Combining the progeny of such lines produces a hybrid multiline variety. These varieties include winter wheat Odessa 51, spring wheat Moskovskaya 35, spring barley Donetsk 4, etc. Such varieties are characterized by ecological plasticity and occupy large areas.

Clone varieties are obtained by individual selection from vegetatively propagated plants (potato, Jerusalem artichoke, onion, etc.). They are the offspring of a single vegetatively propagated plant, so they have a very high degree of evenness. Their change occurs under the influence of natural mutagenesis. Potato clone varieties include Zazersky, Skorospelka 1, Maikopsky, etc.

In taxonomy, the concepts of “form” and “variety” coincide. But this concerns only the botanical and ecological similarities between them. The essential difference is in the origin - the variety is created by man and is a means of agricultural production.

A variety is a group of cultivated plants of the same species that are similar in economic and biological properties and morphological characteristics, selected and propagated for cultivation in appropriate natural and production conditions in order to increase productivity and product quality.

Copra crops vary in origin and methods of breeding. Based on their origin, they are divided into local, selective and introduced.

Local varieties are those created as a result of long-term natural and elementary methods of artificial selection during the cultivation of a particular crop in a certain area. They are usually created by folk selection.

Breeding varieties are those created in research institutions based on scientific selection methods. As a rule, they are more uniform in their characteristics and properties and have now replaced almost all local varieties.

Varieties that did not previously grow in a given area, but were transferred here from another country or region, are called introduced.

According to the methods of elimination, they are distinguished:

Variety populations obtained by mass selection from endogamous and exogamous plants. They are heterogeneous in characters and properties in endogamous forms, but in exogamous plants they are highly uniform;

Linear varieties developed by individual selection from endogamous plants. Essentially, these are the multiplied offspring of one plant. This variety is very uniform in characteristics and properties, but this property can be lost as a result of spontaneous mutagenesis, rare cross-pollination and accidental contamination;

Mutant varieties created by selection from populations that have been exposed to mutagenic factors;

Hybrid varieties obtained by crossing and selection from hybrid populations. Such varieties are less aligned than linear ones and new varieties can be developed from them through repeated selection;

Varieties bred by individual selection from vegetatively propagated plants, for example potatoes, onions, etc.

Typically, such varieties are very uniform in characteristics and properties, but this uniformity can be lost due to natural mutagenesis and contamination.

The specific set of characteristics and properties that a variety should have is determined by three main indicators:

1) soil and climatic conditions for which the variety is created:

2) the level of agricultural technology and mechanization (use of fertilizers, use of irrigation):

3) the direction in which the crop is used (silage or grain for corn, brewing or fodder for barley, early table or industrial potatoes, etc.).

Based on the above, the following requirements are formed that the variety must meet:

High and stable yields over the years and an adequate response to the use of agricultural technology and the use of fertilizers;

Resistance to adverse environmental factors (drought, high or low temperature, etc.);

Complex resistance to diseases and pests;

Adaptability to mechanized cultivation;

High quality products for which the variety is cultivated.

Thus, varieties are created for cultivation in a specific

Soil-climatic zone, and therefore there is not, and cannot be, varieties that are equally suitable for cultivation in different areas. However, some good varieties have a wide genotype reaction rate and are highly plastic, those biologically adapted to a sharp change in the external environment, while maintaining a stable yield. Such varieties can be cultivated over large areas and in various soil and climatic zones.

Related information.