The doctrine of plant immunity

Main article: Plant immunity

Vavilov subdivided plant immunity into structural (mechanical) and chemical. The mechanical immunity of plants is due to the morphological features of the host plant, in particular, the presence of protective devices that prevent the penetration of pathogens into the plant body. Chemical immunity depends on the chemical characteristics of plants.

Vavilov immunity plant breeding

Creation of N.I. Vavilov of the modern doctrine of selection

The systematic study of the world's plant resources of the most important cultivated plants has radically changed the idea of ​​the varietal and species composition of even such well-studied crops as wheat, rye, corn, cotton, peas, flax and potatoes. Among the species and many varieties of these cultivated plants brought from expeditions, almost half turned out to be new, not yet known to science. The discovery of new species and varieties of potatoes completely changed the previous idea of ​​the source material for its selection. Based on the material collected by the expeditions of N.I. Vavilov and his collaborators, the entire cotton breeding was based, and the development of the humid subtropics in the USSR was built.

Based on the results of a detailed and long-term study of varietal wealth collected by expeditions, differential maps of the geographical localization of varieties of wheat, oats, barley, rye, corn, millet, flax, peas, lentils, beans, beans, chickpeas, chinka, potatoes and other plants were compiled . On these maps it was possible to see where the main varietal diversity of the named plants is concentrated, i.e. where to get the source material for the selection of this crop. Even for such ancient plants as wheat, barley, corn, and cotton, which have long been settled throughout the globe, it was possible to establish with great accuracy the main areas of primary species potential. In addition, the coincidence of the areas of primary morphogenesis was established for many species and even genera. Geographical study led to the establishment of entire cultural independent floras specific to individual regions.

The botanical and geographical study of a large number of cultivated plants led to the intraspecific taxonomy of cultivated plants, as a result of which the works of N.I. Vavilov "Linnean species as a system" and "The doctrine of the origin of cultivated plants after Darwin".

In contrast to medicine and veterinary medicine, where acquired immunity is of decisive importance in the protection of humans and animals, acquired immunity has been used very little in practical phytopathology until recently.

In plants there is a significant circulation of juices, although not in closed vessels. When solutions of mineral salts or other substances are applied to parts of a plant, after some time these substances can be found in other places of the same plant. Based on this principle, the Russian scientists I. Ya. Shevyrev and SA Mokrzhetsky developed the method of foliar plant nutrition (1903), which is widely used in agricultural production. The presence of sap circulation in plants can explain the appearance of root cancer tumors far from the place of introduction of the causative agent of this disease - Pseudomonas tumefaciens Stevens. This fact also indicates that the formation of tumors is not only a local disease, but the whole plant as a whole responds to the disease.

Acquired immunity can be created in various ways. In particular, it can be created by vaccination and chemical immunization of plants, by treating them with antibiotics, as well as by some methods of agricultural technology.

In animals and humans, the phenomena of acquired immunity resulting from past illness and vaccination with weakened cultures of the pathogen are well known and studied in detail.

The great successes achieved in this area served as a stimulus for the search for similar phenomena in the field of phytoimmunology. However, the very possibility of the existence of acquired immunity in plants was at one time called into question on the grounds that plants do not have a circulatory system, and this excludes the possibility of immunization of the entire organism. The acquired immunity of plants was considered as an intracellular phenomenon, excluding the possibility of diffusion of the substances formed in the affected cells into neighboring tissues.

It can be considered established that in some cases the resistance of plants to infection increases both after the disease and as a result of vaccination. As a vaccine, waste products of pathogens (culture medium), weakened cultures and preparations from microorganisms killed by anesthesia or heating can be used. In addition, bacteriophage prepared in the usual way, as well as serum from animals immunized with a microorganism pathogenic for plants, can be used for immunization. Immunizing substances are administered primarily through the root system. It is also possible to spray into the stems, apply as a lotion, spray on the leaves, etc.

Methods of artificial immunization, widely used in medicine and veterinary medicine, are also of little promise in plant growing practice, since both the preparation of immunizing agents and their use are very laborious and expensive. If we take into account that immunization is not always sufficiently effective and its action is very short-lived, and also that the immunization process, as a rule, depresses the plant, it becomes clear why the results of work in the field of acquired immunity are not yet used in agricultural practice.

There are isolated cases of plant immunization as a result of a viral infection. In 1952, Canadian scientists Gilpatrick and Weintraub showed that if the leaves of Dianthus borbatus are infected with the necrosis virus, then uninfected leaves become resistant. Subsequently, similar observations were made by other researchers on many plants infected with various viruses. At present, facts of this kind are considered as phenomena of immunity acquired as a result of a disease.

In search of a protective factor arising in the tissues of virus-resistant forms of plants, researchers first of all turned to the hypersensitivity reaction, attributing a protective role to the polyphenol-polyphenol oxidase system. However, experimental data on this issue did not give definite results.

In some works, it is noted that the juice from the cells of the immune zone that forms around the necrosis, as well as from tissues that have acquired immunity, has the ability to inactivate the virus. The isolation and study of this antiviral factor showed that it has a number of properties similar to animal interferon. Interferon-like protein, like animal interferon, is found only in virus-infected resistant tissues, easily diffuses from infected cells to uninfected ones, and does not have antiviral specificity. It inhibits the infectivity of various plant-specific viruses from different families. The antiviral factor is active against viruses both in vitro, i.e. when mixed with an extract from virus-infected leaves, and in vivo, i.e. when it is introduced into the leaves of a plant. It is believed that it can act either directly on the particles of the virus, or on the process of its reproduction, suppressing metabolic processes, as a result of which new viral particles are synthesized.

The phenomena of acquired immunity may include an increase in resistance to diseases caused by chemicals. Soaking seeds in solutions of various chemical compounds increases the resistance of plants to diseases. The properties of immunizers are macro- and microelements, insecticides and fungicides, growth substances and antibiotics. Pre-sowing soaking of seeds in solutions of trace elements also increases the resistance of plants to diseases. The healing effect of microelements on the plant was preserved in some cases for the next year.

Phenolic compounds are effective as chemical plant immunizers. Soaking seeds in solutions of hydroquinone, paranitrophenol, orthonitrophenol, etc., can significantly reduce the susceptibility of millet to smut, watermelons, eggplant and pepper - withering, oats - crown rust, etc.

Resistance caused by various chemical compounds, as well as natural, genetically determined, can be active and passive. For example, chemical treatment of seeds and plants can increase their mechanical resistance (increase the thickness of the cuticle or epidermis, affect the number of stomata, lead to the formation of internal mechanical barriers to the path of the pathogen, etc.). In addition, most chemical plant immunizers are substances of intraplant action, i.e., penetrating into the plant, they affect its metabolism, thereby creating unfavorable conditions for the nutrition of the parasite. Finally, some chemical immunizers can act as agents that neutralize the action of pathogen toxins. In particular, ferulic acid, being an antimetabolite of pyricularin, a toxin of Piricularia oryzae, increases rice resistance to this pathogen.

BASES OF PLANT IMMUNE TO DISEASE

With the most severe epiphytosis, plants are affected by the disease differently, which is associated with the resistance and immunity of plants. Immunity is understood as absolute invulnerability in the presence of infection under conditions favorable for infection of plants and the development of diseases. Resilience is the ability of an organism to resist severe disease damage. These two properties are often identified, meaning the weak damage of plants by diseases.

Stability and immunity are complex dynamic states that depend on the characteristics of the plant, the pathogen and environmental conditions. The study of the causes and patterns of resistance is very important, since only in this case successful work on the development of resistant varieties is possible.

Immunity can be congenital (hereditary) and acquired. Innate immunity is passed from parents to offspring. It changes only with a change in the genotype of the plant.

Acquired immunity is formed in the process of ontogenesis, which is quite common in medical practice. Plants do not have such a clearly defined acquired property, but there are methods to increase the resistance of plants to diseases. They are being actively studied.

Passive resistance is determined by the constitutional features of the plant, regardless of the action of the pathogen. For example, the thickness of the cuticle of some plant organs is a factor in passive immunity. Factors of active immunity act only when the plant and the pathogen come into contact, i.e. arise (induced) during the period of the pathological process.

Distinguish between specific and nonspecific immunity. Nonspecific - this is the inability of some pathogens to cause infection of a certain plant species. For example, beets are not affected by pathogens of smut diseases of cereal crops, potato late blight, potatoes are not affected by beet cercosporosis, cereals are not affected by potato macrosporosis, etc. Immunity that manifests itself at the level of a variety in relation to specialized pathogens is called specific.

Factors of plant resistance to diseases

It has been established that stability is determined by the total action of protective factors at all stages of the pathological process. The whole variety of protective factors is divided into 2 groups: preventing the introduction of the pathogen into the plant (axenia); preventing the spread of the pathogen in plant tissues (true resistance).

The first group includes factors or mechanisms of a morphological, anatomical and physiological nature.

Anatomical and morphological factors. The thickness of the integumentary tissues, the structure of the stomata, the pubescence of the leaves, the wax coating, and the structural features of the plant organs can serve as an obstacle to the introduction of pathogens. The thickness of the integumentary tissues is a protective factor against those pathogens that penetrate plants directly through these tissues. These are primarily powdery mildew fungi and some representatives of the Oomycetes class. The structure of the stomata is important for the penetration of bacteria, pathogens of downy mildew, rust, etc. into the tissue. Usually, it is more difficult for the pathogen to penetrate through densely covered stomata. The pubescence of the leaves protects plants from viral diseases, insects that transmit a viral infection. Due to the wax coating on leaves, fruits and stems, drops do not linger on them, which prevents the germination of fungal pathogens.

Plant habit and leaf shape are also factors preventing the initial stages of infection. So, varieties of potatoes with a loose structure of the bush are less affected by late blight, as they are better ventilated and infectious drops on the leaves dry out faster. Less spores settle on narrow leaf blades.

The role of the structure of plant organs can be illustrated by the example of rye and wheat flowers. Rye is very strongly affected by ergot, while wheat is very rarely affected. This is due to the fact that the lemmas of wheat flowers do not open and the spores of the pathogen practically do not penetrate into them. The open type of flowering in rye does not prevent spores from entering.

Physiological factors. The rapid introduction of pathogens can be hindered by high osmotic pressure in plant cells, the rate of physiological processes leading to wound healing (formation of wound periderm), through which many pathogens penetrate. The speed of passage of individual phases of ontogeny is also important. So, the causative agent of durum smut of wheat is introduced only into young seedlings, therefore, varieties that germinate together and quickly are less affected.

Inhibitors. These are compounds found in plant tissues or synthesized in response to infection that inhibit the development of pathogens. These include phytoncides - substances of various chemical nature, which are factors in innate passive immunity. Phytoncides are produced in large quantities by the tissues of onion, garlic, bird cherry, eucalyptus, lemon, etc.

Alkaloids are nitrogen-containing organic bases that are formed in plants. Plants of the legume, poppy, solanaceous, aster and other families are especially rich in them. For example, potato solanine and tomato tomato are toxic to many pathogens. So, the development of fungi of the genus Fusarium is inhibited by solanine at a dilution of 1:105. Phenols, essential oils and a number of other compounds can suppress the development of pathogens. All listed groups of inhibitors are always present in intact (undamaged tissues).

Induced substances that are synthesized by the plant during the development of the pathogen are called phytoalexins. In terms of chemical composition, they are all low molecular weight substances, many of them

are phenolic in nature. It has been established that the plant's hypersensitive response to infection depends on the rate of phytoalexin induction. Many phytoalexins are known and identified. So, from potato plants infected with the causative agent of late blight, rishitin, lyubin, phytuberin were isolated, pisatin was isolated from peas, and isocoumarin was isolated from carrots. The formation of phytoalexins is a typical example of active immunity.

Active immunity also includes the activation of plant enzyme systems, in particular oxidative ones (peroxidase, polyphenol oxidase). This property allows you to inactivate the hydrolytic enzymes of the pathogen and neutralize their toxins.

Acquired or induced immunity. To increase the resistance of plants to infectious diseases, biological and chemical immunization of plants is used.

Biological immunization is achieved by treating plants with weakened cultures of pathogens or their waste products (vaccination). It is used to protect plants from certain viral diseases, as well as bacterial and fungal pathogens.

Chemical immunization is based on the action of certain chemicals, including pesticides. Assimilated in plants, they change the metabolism in a direction unfavorable for pathogens. An example of such chemical immunizers are phenolic compounds: hydroquinone, pyrogallol, orthonitrophenol, paranitrophenol, which are used to treat seeds or young plants. A number of systemic fungicides have an immunizing property. So, dichlorocyclopropane protects rice from blast due to increased synthesis of phenols and the formation of lignin.

Known immunizing role and some of the trace elements that make up the enzymes of plants. In addition, trace elements improve the intake of essential nutrients, which favorably affects the resistance of plants to diseases.

Genetics of resistance and pathogenicity. Types of sustainability

Plant resistance and pathogenicity of microorganisms, like all other properties of living organisms, are controlled by genes, one or more, qualitatively different from each other. The presence of such genes determines absolute immunity to certain races of the pathogen. The causative agents of the disease, in turn, have a virulence gene (or genes) that allows it to overcome the protective effect of resistance genes. According to the theory of X. Flor, for each plant resistance gene, a corresponding virulence gene can be developed. This phenomenon is called complementarity. When exposed to a pathogen that has a complementary virulence gene, the plant becomes susceptible. If the resistance and virulence genes are not complementary, the plant cells localize the pathogen as a result of an oversensitive response to it.

For example (Table 4), according to this theory, potato varieties with the resistance gene R are affected only by race 1 of the pathogen P. infestans or more complex, but necessarily possessing the virulence gene 1 (1.2; 1.3; 1.4; 1,2,3), etc. Varieties that do not have resistance genes (d) are affected by all races without exception, including the race without virulence genes (0).
Resistance genes are most often dominant, so they are relatively easy to pass on to offspring through selection. Hypersensitivity genes, or R-genes, determine the hypersensitive type of resistance, which is also called oligogenic, monogenic, true, vertical. It provides the plant with absolute immunity when exposed to races without complementary virulence genes. However, with the appearance of more virulent races of the pathogen in the population, resistance is lost.

Another type of resistance is polygenic, field, relative, horizontal, which depends on the combined action of many genes. Polygenic resistance to varying degrees is inherent in each plant. At its high level, the pathological process slows down, which allows the plant to grow and develop, despite being affected by the disease. Like any polygenic trait, such resistance can fluctuate under the influence of growing conditions (the level and quality of mineral nutrition, moisture availability, day length, and a number of other factors).

The polygenic type of resistance is inherited transgressively, so it is problematic to fix it by breeding varieties.

A combination of ultrasensitive and polygenic resistance in one variety is common. In this case, the variety will be immune until the appearance of races capable of overcoming monogenic resistance, after which the protective functions are determined by polygenic resistance.

Methods for creating resistant varieties

Directed hybridization and selection are most widely used in practice.

Hybridization. The transfer of resistance genes from parent plants to offspring occurs during intervarietal, interspecific, and intergeneric hybridization. To do this, plants with the desired economic and biological characteristics and plants with resistance are selected as parental forms. Donors of resistance are often wild species, so undesirable properties may appear in the offspring, which are eliminated during backcrosses, or backcrosses. Beyer wasps repeat until all signs<<дикаря», кроме устойчивости, не поглотятся сортом.

With the help of intervarietal and interspecific hybridization, many varieties of cereals, leguminous crops, potatoes, sunflowers, flax and other crops have been created that are resistant to the most harmful and dangerous diseases.

When some species do not cross with each other, they resort to the “intermediary” method, in which each type of parental forms or one of them is crossed first with a third species, and then the resulting hybrids are crossed with each other or with one of the originally planned species.

In any case, the resistance of hybrids is checked against a severe infectious background (natural or artificial), i.e., with a large number of infection of the pathogen, under conditions favorable for the development of the disease. For further reproduction, plants are selected that combine high resistance and economically valuable traits.

Selection. This technique is an obligatory step in any hybridization, but it can also be an independent method for obtaining resistant varieties. By the method of gradual selection in each generation of plants with the necessary traits (including resistance), many varieties of agricultural plants have been obtained. It is especially effective for cross-pollinating plants, since their offspring are represented by a heterozygous population.

In order to create disease-resistant varieties, artificial mutagenesis, genetic engineering, etc. are increasingly being used.

Causes of loss of stability

Over time, varieties, as a rule, lose resistance either as a result of a change in the pathogenic properties of pathogens of infectious diseases, or a violation of the immunological properties of plants in the process of their reproduction. In varieties with a supersensitive type of resistance, it is lost with the advent of more virulent races or complementary genes. Varieties with monogenic resistance are affected due to the gradual accumulation of new races of the pathogen. That is why the selection of varieties with only a supersensitive type of resistance is unpromising.

There are several reasons for the formation of new races. The first and most common are mutations. They usually pass spontaneously under the influence of various mutagenic factors and are inherent in phytopathogenic fungi, bacteria and viruses, and for the latter, mutation is the only way of variability. The second reason is the hybridization of genetically different individuals of microorganisms during the sexual process. This path is characteristic mainly for fungi. The third way is heterocariosis, or multinucleation, of haploid cells. In fungi, multinucleation can occur due to mutations of individual nuclei, the transition of nuclei from different-quality hyphae along anastomoses (fused sections of hyphae) and recombination of genes during nuclear fusion and their subsequent division (parasexual process). Diversity and pair asexual process are of particular importance for representatives of the class of imperfect fungi, which do not have a sexual process.

In bacteria, in addition to mutations, there is a transformation in which DNA isolated from one strain of bacteria is absorbed by cells of another strain and included in their genome. During transduction, individual segments of a chromosome from one bacterium are transferred to another with the help of a bacteriophage (a virus of a bacterium).

In microorganisms, the formation of races is ongoing. Many of them die immediately, being uncompetitive due to a lower level of aggressiveness or the absence of other important traits. As a rule, more virulent races are fixed in the population in the presence of plant varieties and species with resistance genes to existing races. In such cases, a new race, even with weak aggressiveness, without encountering competition, gradually accumulates and spreads.

For example, when potatoes with resistance genotypes R, R4 and R1R4 are cultivated, races 1 will predominate in the late blight pathogen population; 4 and 1.4. With the introduction of varieties with the R2 genotype instead of R4, race 4 will gradually disappear from the pathogen population, and race 2 will spread; 1.2; 1,2,4.

Immunological changes in varieties can also occur in connection with changes in their growing conditions. Therefore, before releasing varieties with polygenic resistance in other ecological and geographical zones, their immunological testing is mandatory in the zone of future regionalization.

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In the presence of a viable pathogen and all the necessary conditions for infection. In practice, more often they talk about disease resistance, which can be characterized as a genetic feature of some plants to be affected by the disease to a weak degree. Immunity is absolute, resistance is always relative. Like immunity, resistance is determined by the characteristics of the genome, and there are genes for resistance not only to pathogens, but also to adverse environmental factors.

The direct opposite of immunity is susceptibility, the inability of a plant to resist infection and the spread of a pathogen. In some cases, a plant susceptible to some pathogens may be tolerant, or hardy, to others, i.e. it does not reduce or slightly reduces its productivity (the quantity and quality of the crop) when infected.

Distinguish between specific and nonspecific immunity. The first manifests itself at the level of the variety in relation to certain pathogens and is also called varietal immunity. The second, or non-specific (species) immunity can be defined as the fundamental impossibility of a given plant species from being infected by specific types of pathogens or saprotrophs. For example, tomato is not affected by pathogens of smut diseases of cereals, cucumber is not affected by cabbage clubroot, pepper is not affected by apple scab, etc.

Immunity can be congenital or acquired. Innate, or natural, immunity is genetically controlled and inherited. It can be passive or active. Passive immunity is determined by the constitutional features of the plant only and does not depend on the features. Passive immunity factors are divided into two groups:

Acquired, or artificial, immunity manifests itself in the process of ontogenesis, is not fixed in the offspring, and acts during one, less often, several growing seasons. To form acquired immunity to an infectious disease, plants are treated with biological and chemical immunizers. In biological immunization, treatment is carried out with weakened cultures of pathogens (vaccination) or their metabolites. For example, tomato plants infected with a weakly pathogenic TMV strain are not subsequently affected by more aggressive strains of this virus.

Chemical immunization, as one of the methods of disease prevention, is based on the use of substances called resistance inducers, or immunomodulators.

They are able to activate the course of protective reactions. Some systemic, phenol derivatives, chitoses, etc. have this effect. The drugs Narcissus, Immunocytophyte, etc. are also listed as registered immunomodulators.

N. I. Vavilov, the founder of the doctrine of plant immunity, who laid the foundation for the study of its genetic nature, believed that plant resistance to pathogens developed in the course of millennia of evolution in the centers of origin. If plants acquired resistance genes, pathogens could infect plants due to the emergence of new physiological races resulting from hybridization, mutation, heterokaryosis, and other processes. Within the population of a microorganism, shifts in the number of races are possible due to changes in the varietal composition of plants in a given area. The emergence of new races of the pathogen may be associated with the loss of resistance of a variety that was once resistant to this pathogen.

According to D. T. Strakhov, tissues resistant to plant diseases undergo regressive changes in pathogenic microorganisms associated with the action of plant enzymes and their metabolic reactions.

B. A. Rubin and his coworkers associated the reaction of plants aimed at inactivating the pathogen and its toxins with the activity of oxidative systems and energy metabolism of the cell. A variety of plant enzymes are characterized by different resistance to the waste products of pathogenic microorganisms. In immune forms of plants, the proportion of enzymes resistant to pathogen metabolites is higher than in non-immune forms. Oxidative systems (ceroxidases and polyphenol oxidases), as well as a number of flavone enzymes, are most resistant to metabolites.

In plants, as in invertebrates, the ability to produce antibodies in response to the appearance of antigens in the body has not been proven. Only vertebrates have special organs whose cells produce antibodies. In infected tissues of immune plants, functionally complete organelles are formed, which determine the ability of plant immune forms to increase the energy efficiency of respiration during infection. Respiratory failure caused by pathogens is accompanied by the formation of various compounds that act as a kind of chemical barriers that prevent the spread of infection.

The nature of plant responses to pest damage (the formation of chemical, mechanical, and growth barriers, the ability to regenerate damaged tissues, and replace lost organs) plays an important role in plant immunity to pests. Thus, a number of metabolites (alkaloids, glycosides, terpenes, saponins, etc.) have a toxic effect on the digestive apparatus, endocrine and other systems of insects and other plant pests.

In plant breeding for resistance to diseases and pests, hybridization (intraspecific, interspecific, and even intergeneric) is of great importance. On the basis of autopolyploids, hybrids between different chromosome species are obtained. Such polyploids were created, for example, by M.F. Ternovsky when breeding tobacco varieties resistant to powdery mildew. Artificial mutagenesis can be used to create resistant varieties, and in cross-pollinated plants, selection among heterozygous populations can be used. So L. A. Zhdanov and V. S. Pustovoit obtained sunflower varieties resistant to broomrape.

For long-term preservation of the resistance of varieties, the following methods are proposed:

Creation of multiline varieties by crossing economically valuable forms with varieties carrying different resistance genes, due to which new races of pathogens cannot accumulate in the resulting hybrids;

Combination of R-genes with field resistance genes in one variety;

Periodic change of varietal composition on the farm, which leads to increased sustainability.

In recent years, the development of crop production in our country has been associated with a number of negative processes associated with pollution of the environment and crop production by xenobiotics, high economic and energy costs. The maximum use of the biological potential of agricultural crops can become one of the alternative ways of developing the agronomic sector of agricultural production. Certain hopes in this regard are associated with genetic engineering - a set of methodological approaches that make it possible to change the design of the plant genome by transferring foreign genes into it, which makes it possible to obtain new forms of plants, significantly expand the process of manipulating the plant genome and reduce the time spent on obtaining new agricultural varieties. cultures. Recently, methods for creating transgenic plants are being used to obtain plants resistant to viral, fungal and bacterial diseases, as well as to some pests (Colorado potato beetle, corn stem borer, cotton moth and cutworm, tobacco leaf roller, etc.). In terms of its methods and objects, this direction differs sharply from traditional breeding for plant immunity, but pursues the same goal - the creation of forms that are highly resistant to harmful organisms.

A brilliant substantiation of the role of resistant varieties in plant protection was given by N. I. Vavilov, who wrote that among the measures to protect plants from various diseases caused by parasitic fungi, bacteria, viruses, and various insects, the most radical means of control is the introduction of immune varieties into the culture or the creation of such by crossing. For cereals, which occupy three-quarters of the entire sown area, the replacement of susceptible varieties with resistant forms is, in fact, the most affordable way to combat infections such as rust, powdery mildew, loose smut of wheat, various Fusarium, spotting.

Domestic and world experience in agriculture shows that plant protection should be based on complex (integrated) systems of measures, the basis of which is the presence of crop varieties resistant to diseases and pests.

In subsequent chapters, we will consider the main regularities that determine the presence of resistance traits in plants, ways to use them effectively in the selection process, and ways to give plants induced immunity.

1. HISTORY OF THE ORIGIN AND DEVELOPMENT OF THE STUDY ON PLANT IMMUNITY.

Ideas about immunity began to take shape already in ancient times. According to the historical chronicles of ancient India, China and Egypt, many centuries before our era, the population of the Earth suffered from epidemics. Observing their emergence and development, people came to the conclusion that not every person is susceptible to the effects of the disease and that one who has been ill with any of these terrible diseases does not fall ill with it again.

By the middle of the II century. BC e. the idea of ​​the uniqueness of human disease with such diseases as plague and others is becoming generally accepted. At the same time, those who had recovered from it began to be widely used to care for patients with plague. It is logical to assume that it was at this stage in the development of human society that, on the basis of data obtained from monitoring the spread of epidemiological diseases, immunology arose. From the very beginning of its development, it sought to use the collected observations for the practical protection of the population from infectious diseases. For many centuries, in order to protect people from smallpox, one way or another, deliberate infection with this disease was carried out, after which the body became immune to it. Thus, methods were developed to obtain immunity to this disease. However, with the widespread use of such methods, its main shortcomings were revealed, which consisted in the fact that many of the vaccinated smallpox proceeded in a severe form, often fatal. In addition, the vaccinated often became a source of infection and contributed to the maintenance of the smallpox epidemic. However, despite the obvious disadvantages, the method of deliberate infection clearly proved the possibility of artificially acquiring immunity by transferring the disease in a mild form.

Epochal significance in the development of immunity was the work of the English physician Edward Jenner (1798), in which he summarized the results of 25 years of observation and showed the possibility of cowpox vaccination in people and their acquisition of immunity to a similar human disease. These vaccinations are called vaccination (from Latin vaccinus - cow). Jenner's work was an outstanding achievement in practice, but without explaining the cause (etiology) of infectious diseases, it could not contribute to the further development of immunology. And only the classic works of Louis Pasteur (1879), which revealed the causes of infectious diseases, made it possible to take a fresh look at Jenner's results and appreciate them, which influenced both the subsequent development of immunology and the work of Pasteur himself, who proposed the use of weakened pathogens. for vaccination. Pasteur's discoveries laid the foundation for experimental immunology.

An outstanding contribution to the science of immunity was made by the Russian scientist I. I. Mechnikov (1845-1916). His work formed the basis of the theory of immunity. In 1908 II Mechnikov was awarded the Nobel Prize as the author of the phagocytic theory of protecting the organism of animals and humans from pathogens. The essence of this theory lies in the fact that all animal organisms (from amoeba to humans inclusive) have the ability, with the help of special cells - phagocytes - to actively capture and digest microorganisms intracellularly. Using the circulatory system, phagocytes actively move inside living tissues and concentrate in places where microbes penetrate. It has now been established that animal organisms protect against microbes with the help of not only phagocytes, but also specific antibodies, interferon, etc.

A significant contribution to the development of immunology was made by the works of N. F. Gamaleya (1859-1949) and D. K. Zabolotny (1866-1929).

Despite the successful development of the theory of animal immunity, ideas about plant immunity developed extremely slowly. One of the founders of plant immunity was the Australian researcher Cobb, the author of the theory of the mechanical protection of plants from pathogens. The author attributed such features of the plant as a thickened cuticle, a peculiar structure of flowers, the ability to quickly form wound periderm at the site of injury, etc. to mechanical protective devices. Subsequently, this method of protection was called passive immunity. However, the mechanical theory could not exhaustively explain such a complex and diverse phenomenon as immunity.

Another theory of immunity, proposed by the Italian scientist Comes (1900), is based on the fact that plant immunity depends on the acidity of cell sap and the content of sugars in it. The higher the content of organic acids, tannins and anthocyanins in the cell sap of plants of one variety or another, the more resistant it is to diseases affecting it. Varieties that are high in sugars and relatively low in acids and tannins are more susceptible to disease. So, in grape varieties resistant to mildew and powdery mildew, acidity (% dry matter) is 6.2 ... 10.3, and in susceptible ones - from 0.5 ... 1.9. However, Comes' theory is not universal and cannot explain all cases of immunity. Thus, the study of many varieties of wheat and rye, which have different susceptibility to rust and smut, did not reveal a clear correlation between immunity and acid content in leaf tissues. Similar results were obtained for many other cultivated plants and their pathogens.

At the beginning of the XX century. new hypotheses appeared, the authors of which tried to explain the causes of plant immunity. Thus, the English researcher Massey proposed the chemotropic theory, according to which such plants have immunity, in which there are no substances necessary to attract parasites. Investigating the pathogens of cucumber and tomato, he showed that the juice of susceptible varieties contributed to the germination of pathogen spores, while the juice of resistant varieties inhibited this process. The chemotropic theory has been seriously criticized by a number of researchers. The most detailed criticism of this theory was given by N. I. Vavilov, who considered it unlikely that the cell sap contained in the vacuoles could remotely act on the hyphae of fungi and that some substances released from the tissues to the outside cannot be identified with the cell sap obtained by squeezing out the substrates. on which the fungus was grown.

Protection of plants from diseases by creating and cultivating resistant varieties has been known since ancient times. Spontaneously carried out in places favorable for the development of pathogens of certain diseases, artificial selection for resistance to them led to the creation of varieties of agricultural plants with increased resistance to these diseases. Natural disasters caused by the spread of particularly dangerous diseases (grain rust, late blight of potatoes, oidium and mildew of grapes) stimulated the emergence of scientifically based plant breeding for immunity to diseases. In 1911, the 1st congress on selection was held, where A. A. Yachevsky (1863-1932) made a general report “On the importance of selection in the fight against fungal diseases of cultivated plants”. The data presented in the report indicated that successful work on the development of disease-resistant varieties is impossible without the development of a theory of plant immunity to infectious diseases.

In our country, the founder of the doctrine of plant immunity is N. I. Vavilov. His first works on plant immunity were published in 1913 and 1918, and the monograph "Plant Immunity to Infectious Diseases", published in 1919, was the first attempt to broadly generalize and theoretically substantiate all the material that had accumulated by that time in the field of the study of immunity. . In the same years, the works of N. I. Litvinov (1912) appeared on the assessment of the resistance of cereals to rust and E. N. Iretskaya (1912) on methods for selecting cereals for rust resistance. However, these works remained only episodes in the scientific activity of the authors.

N. I. Vavilov’s works “The Teaching on Plant Immunity to Infectious Diseases” (1935), reports at the I All-Union Conference on Combating Rust of Cereals in 1937 and at the Biological Department of the USSR Academy of Sciences in 1940, a number of his articles and speeches at different times played a huge role in the development of theoretical ideas about the genetic characteristics of plants as decisive factors determining varietal and species resistance. N. I. Vavilov substantiated the proposition that the immunity of plants is inextricably linked with their genetic characteristics. Therefore, N. I. Vavilov considered the main task of breeding for resistance to be the search for species differences in plants on the basis of immunity. The world collection of cultivated plant varieties collected by him and the staff of VIR is still a source of obtaining immune forms. Of great importance in the search for immune forms of plants is his concept of the parallel biological evolution of plants and their pathogens, which was subsequently developed in the theory of the coupled evolution of parasites and their hosts, developed by P.M. Zhukovsky (1888-1975). The regularities of the manifestation of immunity, determined by the result of the interaction of the plant and the pathogen, N. I. Vavilov attributed to the field of physiological immunity.

The development of theoretical questions of the doctrine of plant immunity, begun by N. I. Vavilov, was continued in our country in subsequent years. Research was carried out in various directions, which was reflected in various explanations of the nature of plant immunity. Thus, the hypothesis of B. A. Rubin, based on the teachings of A. N. Bach, links plant resistance to infectious diseases with the activity of plant oxidative systems, mainly peroxidases, as well as a number of flavone enzymes. The activation of plant oxidative systems leads, on the one hand, to an increase in the energy efficiency of respiration, and, on the other hand, to disruption of its normal course, which is accompanied by the formation of various compounds that play the role of chemical barriers. E. A. Artsikhovskaya, V. A. Aksenova and others also participated in the development of this hypothesis.

Phytoncide theory, developed in 1928 by B.P. Tokin on the basis of the discovery of bactericidal substances in plants - phytoncides, was developed by D.D. Verderevsky (1904-1974), as well as employees of the Moldavian Plant Protection Station and the Chisinau Agricultural Institute (1944-1976 ).

In the 80s of the last century, L. V. Metlitsky, O. L. Ozeretskovskaya, and others developed a theory of immunity associated with the formation in plants of special substances - phytoalexins, which arise in response to infection by incompatible species or races of pathogens. They discovered a new potato phytoalexin - lyubin.

A number of interesting provisions of the theory of immunity were developed by K. T. Sukhorukoy, who worked in the Main Botanical Garden of the USSR Academy of Sciences, as well as a group of employees led by L. N. Andreev, who was developing various aspects of the doctrine of plant immunity to rust diseases, peronosporosis and verticillium wilt.

In 1935 T.I. Fedotova (VIZR) discovered for the first time the affinity of host and pathogen proteins. All the previously listed hypotheses about the nature of plant immunity associated it with only one or a group of similar protective properties of plants. However, N. I. Vavilov emphasized that the nature of immunity is complex and cannot be associated with any one group of factors, because the nature of the relationship of plants with different categories of pathogens is too diverse.

In the first half of the XX century. in our country, only an assessment was made of the resistance of plant varieties and species to diseases and parasites (cereal crops to rust and smut, sunflower to broomrape, etc.). Later, they began to conduct selection for immunity. This is how sunflower varieties bred by E. M. Pluchek (Saratovsky 169 and others), resistant to broomrape (Orobanche sitapa) of race A and sunflower moth, appeared. The problem of combating broomrape of race B "Evil" was removed for many years thanks to the work of V. S. Pustovoit, who created a series of varieties resistant to broomrape and moths. V. S. Pustovoit developed a seed production system that allows maintaining sunflower resistance at the proper level for a long time. In the same period, varieties of oats resistant to crown rust were created (Verkhnyachsky 339, Lgovsky, etc.), which have retained resistance to this disease to this day. From the mid-1930s, P.P. Lukyanenko and others began breeding for wheat resistance to leaf rust, M.F. Ternovsky began work on creating tobacco varieties resistant to a complex of diseases. Using interspecific hybridization, he developed tobacco varieties resistant to tobacco mosaic, powdery mildew and downy mildew. Successfully conducted selection for the immunity of sugar beets to a number of diseases.

Varieties resistant to powdery mildew (Hybrid 18, Kirghizskaya odnosemyanka, etc.), cercosporosis (Pervomaisky polyhybrid, Kuban polyhybrid 9), downy mildew (MO 80, MO 70), root beetle and clamp rot (Verkhneyachskaya 031, Belotserkovskaya TsG 19) were obtained.

A. R. Rogash and others successfully worked on the selection of flax for immunity. Varieties P 39, Orshansky 2, Tvertsa with increased resistance to Fusarium and rust were created.

In the mid-1930s, K. N. Yatsynina obtained tomato varieties resistant to bacterial canker.

A number of interesting and important works on the development of varieties of vegetable crops resistant to clubroot and vascular bacteriosis were carried out under the direction of BV Kvasnikov and NI Karganova.

With varying success, cotton was selected for immunity to verticillium wilt. The variety 108 f, bred in the mid-30s of the last century, retained stability for about 30 years, but then lost it. The varieties of the Tashkent series that replaced it also began to lose resistance to wilt due to the emergence of new races of Verticillium dahliae (0, 1, 2, etc.).

In 1973, a decision was made to establish laboratories and departments for plant immunity to diseases and pests at breeding centers and institutes for plant protection. An important role in the search for sources of sustainability was played by the Institute of Plant Industry. N. I. Vavilov. The worldwide collections of cultivated plant specimens collected at this institute still serve as a fund of resistance donors of various crops needed for immunity breeding.

After the discovery by E. Stekman of physiological races in the causative agent of stem rust of cereals, similar work was launched in our country. Since 1930, the VIZR (V. F. Rashevskaya et al.), the Moscow Agricultural Experimental Station (A. N. Bukhgeim et al.), and the All-Union Breeding and Genetic Institute (E. E. Geshele) began to study physiological races brown and stem rust, smut. In the postwar years, the All-Russian Research Institute of Phytopathology began to deal with this problem. Back in the 1930s, A.S. Burmenkov, using a standard set of differentiating varieties, showed the heterogeneity of races of rust fungi. In subsequent years, especially in the 60s, these works began to develop intensively (A. A. Voronkova, M. P. Lesovoi, etc.), which made it possible to reveal the reasons for the loss of resistance by some varieties with a seemingly unchanged racial composition of the fungus. Thus, it was found that race 77 of the causative agent of wheat leaf rust, which prevailed in the 70s of the XX century. in the North Caucasus and southern Ukraine, consists of a series of biotypes differing in virulence, formed not on wheat, but on susceptible cereals. The studies of smut fungus races, begun at VIZR by S.P. Zybina and L.S. Gutner, as well as by K.E. Murashkinsky in Omsk, were continued at VIR by V.I. Tymchenko at the Institute of Agriculture of the Non-Chernozem Zone.

N. A. Dorozhkin, Z. I. Remneva, Yu. V. Vorob’eva, and K. V. Popkova were very productive in studying the races of Phytophthora infestans. In 1973 Yu.T.Dyakov together with T.A. Kuzovnikova et al. discovered the phenomenon of heterokaryosis and parasexual process in Ph. infestans, allowing to some extent to explain the mechanism of variability of this fungus.

In 1962 P.A.Khizhnyak and V.I. Yakovlev discovered aggressive races of the causative agent of potato cancer Synchythrium endobioticum. It was found that at least three races of S. endobioticum are distributed on the territory of our country, affecting potato varieties resistant to the common race.

In the late 70s - early 80s of the last century, A. G. Kasyanenko studied the physiological races of the fungus Verticillium dahliae, L. M. Levkina studied Cladosporium fulvum, M. N. Rodigin and others, the causative agent of powdery mildew of wheat, peronosporosis tobacco - A. A. Babayan.

Thus, the study of plant immunity to infectious diseases was carried out in our country in three main areas:

The study of race formation of pathogens and analysis of the structure of populations. This led to the need to study the population composition within species, the mobility of the population, the patterns of appearance, disappearance or regrouping of individual members of the population. The doctrine of races arose: accounting for races, forecasting and regularities in the appearance of some races and (or) the disappearance of others;

assessment of disease resistance of existing varieties, search for resistance donors and, finally, the development of resistant varieties.

Innate, or natural, immunity is the property of plants not to be affected (not damaged) by a particular disease (pest). Innate immunity is inherited from generation to generation.

Innate immunity is divided into passive and active immunity. However, the results of numerous studies lead to the conclusion that the division of plant immunity into active and passive is very conditional. At one time, this was emphasized by N.I. Vavilov (1935).

The increase in plant resistance under the influence of external factors, which occurs without changing the genome, is called acquired or induced resistance. Factors whose effect on seeds or plants leads to an increase in plant resistance are called inducers.

Acquired immunity is the property of plants not to be affected by one or another pathogen that arose in plants after the transfer of a disease or under the influence of external influences, especially plant cultivation conditions.

Plant resistance can be increased by various methods: the introduction of microfertilizers, changing the timing of planting (sowing), seeding depth, etc. Methods for gaining resistance depend on the type of inductors, which can be biotic or abiotic in nature. Techniques that promote the manifestation of acquired resistance are widely used in agricultural practice. So, the resistance of cereal crops to root rot can be increased by sowing spring crops at the optimal early, and winter crops at the optimal late time; resistance of wheat to hard smut, which affects plants during seed germination, can be increased by observing the optimal sowing dates.

Plant immunity may be due to the inability of the pathogen to infect plants of this species. So, grain crops are not affected by late blight and potato scab, cabbage - by smut diseases, potatoes - by rust diseases of cereal crops, etc. In this case, immunity is manifested by the plant species as a whole. Immunity based on the inability of pathogens to cause infection of plants of a certain species is called non-specific.

In some cases, immunity may not be manifested by the plant species as a whole, but only by a particular variety within this species. In this case, some varieties are immune and are not affected by the disease, while others are susceptible and are affected to a great extent by it. So, the causative agent of potato cancer Synchytrium endobioticum infects the Solanum species, but inside it there are varieties (Kameraz, Stoilovy 19, etc.) that are not affected by this disease. Such immunity is called varietal specific. It is of great importance in breeding resistant varieties of agricultural plants.

In some cases, plants may be immune to pathogens of various diseases. For example, a winter wheat variety may be immune to both powdery mildew and leaf rust. The resistance of a plant variety or species to several pathogens is called complex or group immunity. The creation of varieties with complex immunity is the most promising way to reduce crop losses from diseases. For example, wheat Triticum timophevi is immune to smut, rust, and powdery mildew. Tobacco varieties are known that are resistant to the tobacco mosaic virus and the downy mildew pathogen. By zoning such varieties in production, it is possible to solve the problem of protecting a particular crop from major diseases.