Introduction. founder of the doctrine of plant immunity n. And. Vavilov, who initiated the study of its genetic nature, believed that plant resistance to pathogens. Plant immunity to infectious diseases Plant immunity to infectious diseases
BASICS OF PLANT IMMUNITY TO DISEASE
In the most severe epiphytotics, plants are affected by the disease unequally, which is associated with the resistance and immunity of the plants. Immunity is understood as absolute innocence in the presence of infection under conditions favorable for infection of plants and the development of diseases. Resilience is the ability of the body to withstand severe disease damage. These two properties are often identified, meaning that plants are weakly affected by diseases.
Resistance 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 stability is very important, since only in this case is it possible successful work on breeding resistant varieties.
Immunity can be congenital (hereditary) or acquired. Innate immunity is passed on from parents to offspring. It changes only with changes in the genotype of the plant.
Acquired immunity is formed during ontogenesis, which is quite common in medical practice. Plants do not have such a clearly defined acquired property, but there are techniques that can increase plant resistance to disease. They are being actively studied.
Passive resistance is determined by the constitutional characteristics of the plant, regardless of the action of the pathogen. For example, the thickness of the cuticle of some plant organs is a factor of passive immunity. Active immunity factors act only upon contact between the plant and the pathogen, i.e. arise (induced) during the pathological process.
The concept of specific and nonspecific immunity is distinguished. Nonspecific 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 grain crops, potato late blight, potatoes are not affected by beet cercospora blight, grains are not affected by potato macrosporiosis, etc. Immunity that manifests itself at the variety level in relation to specialized pathogens is called specific.
Factors of plant resistance to disease
It has been established that resistance is determined by the total effect of protective factors at all stages of the pathological process. The whole variety of protective factors is divided into 2 groups: preventing the penetration 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. Barriers to the introduction of pathogens can be the thickness of the integumentary tissue, the structure of the stomata, the pubescence of the leaves, waxy coating, and structural features of plant organs. 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 mushrooms and some representatives of the Oomycetes class. The structure of stomata is important for the introduction into tissue of bacteria, pathogens of false powdery mildew, rust, etc. Usually, it is more difficult for the pathogen to penetrate through tightly covered stomata. The pubescence of leaves protects plants from viral diseases and insects that transmit viral infection. Thanks to the waxy 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 that inhibit the initial stages of infection. Thus, potato varieties with a loose bush structure are less affected by late blight, since they are better ventilated and infectious droplets on the leaves dry out faster. Fewer 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 explained by the fact that the scales of wheat flowers do not open and the spores of the pathogen practically do not penetrate into them. Open type flowering in rye does not prevent spores from entering.
Physiological factors. Rapid penetration of pathogens may be hampered by high osmotic pressure in plant cells, the speed of physiological processes leading to healing of wounds (formation of wound periderm), through which many pathogens penetrate. The speed of passage of individual phases of ontogenesis is also important. Thus, the causative agent of durum smut of wheat penetrates only into young seedlings, therefore varieties that germinate amicably and quickly are less affected.
Inhibitors. These are compounds found in plant tissue or synthesized in response to infection that inhibit the development of pathogens. These include phytoncides - substances of various chemical natures that are factors of innate passive immunity. Phytoncides are produced in large quantities by the tissues of onions, garlic, bird cherry, eucalyptus, lemon, etc.
Alkaloids are nitrogen-containing organic bases formed in plants. Plants of the legume, poppy, nightshade, asteraceae, etc. families are especially rich in them. For example, solanine in potatoes and tomatine in tomatoes are toxic to many pathogens. Thus, the development of fungi of the genus Fusarium is inhibited by solanine at a dilution of 1:105. Phenols can suppress the development of pathogens, essential oils and a number of other compounds. All of the 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. By chemical composition all of them are 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 induction of phytoalexins. Many phytoalexins are known and identified. Thus, rishitin, lyubin, and fituberin were isolated from potato plants infected with the causative agent of late blight, pisatin from peas, and isocoumarin from carrots. The formation of phytoalexins represents typical example active immunity.
Active immunity also includes activation of plant enzyme systems, in particular oxidative ones (peroxidase, polyphenoloxidase). This property allows you to inactivate the hydrolytic enzymes of the pathogen and neutralize toxins.
Acquired, or induced, immunity. To increase plant resistance 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 metabolic 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. Assimilating in plants, they change 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 immunizing properties. Thus, dichlorocyclopropane protects rice from blast disease by enhancing the synthesis of phenols and the formation of lignin.
The immunizing role of some microelements that are part of plant enzymes is also known. In addition, microelements improve the supply of essential nutrients, which has a beneficial effect on plant resistance to disease.
Genetics of resistance and pathogenicity. Types of Resilience
The resistance of plants and the 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 pathogens, in turn, have a virulence gene (or genes) that allows it to overcome the protective effect of resistance genes. According to X. Flor's theory, 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, plant cells localize the pathogen as a result of a hypersensitive reaction to it.
For example (Table 4), according to this theory, potato varieties that have the resistance gene R are affected only by race 1 of the pathogen P. infestans or a more complex, but necessarily possessing 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 during 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 invincibility 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 is inherent to varying degrees in each plant. At a 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 (level and quality of mineral nutrition, moisture supply, 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 common combination of hypersensitive 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 protective functions determines polygenic resistance.
Methods for creating resistant varieties
In practice, directed hybridization and selection are most widely used.
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 parent forms. Donors of resistance are often wild species, so undesirable properties may appear in the offspring, which are eliminated by backcrossing or backcrossing. Beyer wasps are repeated until all signs<<дикаря», кроме устойчивости, не поглотятся сортом.
With the help of intervarietal and interspecific hybridization, many varieties of grains, leguminous crops, potatoes, sunflowers, flax and other crops that are resistant to the most harmful and dangerous diseases have been created.
If some species do not cross with each other, they resort to the “intermediary” method, in which each type of parental form or one of them is first crossed 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 stability of hybrids is checked against a strict infectious background (natural or artificial), i.e., with a large number of pathogen infections, under conditions favorable for the development of the disease. For further propagation, plants that combine high resistance and economically valuable traits are selected.
Selection. This technique is a mandatory 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 desired characteristics (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 changes in the pathogenic properties of pathogens of infectious diseases, or a violation of the immunological properties of plants during their reproduction. In varieties with a hypersensitive type of resistance, it is lost with the appearance 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 breeding varieties only with a hypersensitive type of resistance is futile.
There are several reasons contributing to 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, mutations are 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 of fungi. The third way is heterokaryosis, or heteronuclearity, of haploid cells. In fungi, heteronucleation can occur due to mutations of individual nuclei, the transition of nuclei from hyphae of different quality through anastomoses (fused sections of hyphae) and recombination of genes during the fusion of nuclei and their subsequent division (parasexual process). Heteronuclearity and the asexual process are of particular importance for representatives of the class of imperfect fungi, which lack the sexual process.
In bacteria, in addition to mutations, there is a transformation in which DNA isolated by one strain of bacteria is absorbed by the cells of another strain and is included in their genome. During transduction, individual chromosome segments from one bacterium are transferred to another using a bacteriophage (bacterial virus).
In microorganisms, the formation of races occurs constantly. Many of them die immediately, being uncompetitive due to a lower level of aggressiveness or lack of other important traits. As a rule, more virulent races become established in the population in the presence of plant varieties and species with genes for resistance to existing races. In such cases, a new race, even with weak aggressiveness, without encountering competition, gradually accumulates and spreads.
For example, when cultivating potatoes with resistance genotypes R, R4 and R1R4, races 1 will predominate in the population of the late blight pathogen; 4 and 1.4. When varieties with genotype R2 are introduced into production 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 due to changes in their growing conditions. Therefore, before zoning varieties with polygenic resistance in other ecological-geographical zones, they must be immunologically tested in the zone of future zoning.
The doctrine of plant immunity
Main article: Plant immunity
Vavilov divided plant immunity into structural (mechanical) and chemical. Mechanical immunity of plants is determined by the morphological characteristics 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 selection
Creation of N.I. Vavilov modern doctrine of selection
The systematic study of the world's plant resources of the most important cultivated plants has radically changed the understanding 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 has completely changed the previous understanding of the source material for its selection. Based on material collected by expeditions of N.I. Vavilov and his collaborators, the entire selection of cotton was founded, and the development of humid subtropics in the USSR was built.
Based on the results of a detailed and long-term study of the varietal riches collected by the expeditions, differential maps of the geographical localization of varieties of wheat, oats, barley, rye, corn, millet, flax, peas, lentils, beans, beans, chickpeas, chickpeas, potatoes and other plants were compiled . On these maps one could see where the main varietal diversity of the named plants is concentrated, i.e. where the source material for breeding a given crop should be obtained. Even for such ancient plants as wheat, barley, corn, and cotton, which had long spread throughout the globe, it was possible to establish with great accuracy the main areas of primary species potential. In addition, it was established that the areas of primary formation coincided for many species and even genera. Geographical study has 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, resulting in the works of N.I. Vavilov “Linnaean species as a system” and “The doctrine of the origin of cultivated plants after Darwin.”
Unlike medicine and veterinary medicine, where acquired immunity is crucial in the protection of humans and animals, acquired immunity has been used very little in practical phytopathology until recently.
There is a significant circulation of juices in plants, 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, Russian scientists I. Ya. Shevyrev and S. A. Mokrzhetsky developed a 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 canker tumors far from the site 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 that the entire plant as a whole reacts to the disease.
Acquired immunity can be created in various ways. In particular, it can be created by vaccination and chemical immunization of plants, treating them with antibiotics, as well as certain agricultural techniques.
In animals and humans, the phenomena of acquired immunity, which occurs as a result of illness and vaccination with weakened cultures of the pathogen, are well known and studied in detail.
The great successes achieved in this area have stimulated 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 questioned on the grounds that plants do not have a circulatory system, and this excludes the possibility of immunization of the entire organism. Acquired immunity of plants was considered as an intracellular phenomenon, which excluded the possibility of diffusion of 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. The waste products of pathogens (culture medium), weakened cultures, and preparations from microorganisms killed by anesthesia or heating can be used as a vaccine. In addition, bacteriophage prepared in the usual way, as well as serum from animals immunized with a microorganism pathogenic for the plant, can be used for immunization. Immunizing substances are administered primarily through the root system. It is also possible to inject into stems, use as lotions, spray on leaves, etc.
Artificial immunization techniques, widely used in medicine and veterinary medicine, are of little promise in plant growing practice, since both the preparation of immunizing agents and their use are very labor-intensive and expensive. If we take into account that immunization is not always quite effective and its effect is very short-lived, and also that the immunization process, as a rule, inhibits the plant, then 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 consequence of a viral infection. In 1952, Canadian scientists Gilpatrick and Weintraub showed that if the leaves of Dianthus borbatus are infected with necrosis virus, then uninfected leaves become resistant. Subsequently, similar observations were made by other researchers on many plants infected with various viruses. Currently, facts of this kind are considered as phenomena of immunity acquired as a result of an illness.
In the search for a protective factor that arises in the tissues of virus-resistant plant forms, researchers first turned to the hypersensitivity reaction, attributing a protective role to the polyphenol-polyphenol oxidase system. However, experimental data on this issue have not given definite results.
Some studies note that juice from cells of the immune zone formed around necrosis, as well as from tissues that have acquired immunity, has the ability to inactivate the virus. 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 resistant tissues infected with the virus, easily diffuses from infected cells to uninfected ones and does not have antiviral specificity. It suppresses the infectivity of various viruses specific to plants 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 introduced into the leaves of a plant. It is suggested that it can act either directly on the virus particles or on the process of its reproduction, suppressing the metabolic processes that result in the synthesis of new virus particles.
The phenomena of acquired immunity may include increased resistance to diseases caused by chemicals. Soaking seeds in solutions of various chemical compounds increases plant resistance to diseases. Macro- and microelements, insecticides and fungicides, growth substances and antibiotics have the properties of immunizers. Pre-sowing soaking of seeds in solutions of microelements also increases plant resistance to diseases. The healing effect of microelements on the plant persisted in some cases into 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, watermelon, eggplant and pepper to wilt, oats to crown rust, etc.
Resistance caused by various chemical compounds, as well as natural, genetically determined, can be active and passive. For example, treating seeds and plants with chemicals 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 parasite's nutrition. Finally, some chemical immunizers can act as substances that neutralize the effects of pathogen toxins. In particular, ferulic acid, being an antimetabolite of piricularin, a toxin of Piricularia oryzae, increases the resistance of rice to this pathogen.
Plant immunity- this is their immunity to pathogens or inability to be damaged by pests.
It can be expressed in plants in different ways - from a weak degree of resistance to its extremely high severity.
Immunity- the result of the evolution of established interactions between plants and their consumers (consumers). It represents a system of barriers that limits the colonization of plants by consumers, which negatively affects the life processes of pests, as well as a system of plant properties that ensures their tolerance to violations of the integrity of the body and manifests itself at different levels of plant organization.
Barrier functions that ensure the resistance of both vegetative and reproductive organs of plants to the effects of harmful organisms can be performed by growth and organogenesis, anatomical-morphological, physiological-biochemical and other characteristics of plants.
Plant immunity to pests manifests itself at various taxonomic levels of plants (families, orders, tribes, genera and species). For relatively large taxonomic groupings of plants (families and higher), absolute immunity (complete innocence of plants by this type of pest) is most characteristic. At the level of genus, species and variety, the relative importance of immunity is manifested predominantly. However, even the relative resistance of plants to pests, especially manifested in varieties and hybrids of agricultural crops, is important for suppressing the number and reducing the harmfulness of phytophages.
The main distinguishing feature of plant immunity to pests (insects, mites, nematodes) is the high degree of expression of barriers that limit the choice of plants for feeding and oviposition. This is due to the fact that most insects and other phytophages lead a free (autonomous) lifestyle and come into contact with the plant only at certain stages of their ontogenesis.
It is known that insects have no equal in the diversity of species and life forms represented in this class. They have reached the highest level of development among invertebrate animals, primarily due to the perfection of their senses and movement. This provided insects with prosperity based on the wide possibilities of using high levels of activity and reactivity while conquering one of the leading places in the cycle of substances in the biosphere and in ecological food chains.
Well-developed legs and wings, combined with a highly sensitive sensory system, allow phytophagous insects to actively select and colonize food plants of interest to them for feeding and laying eggs.
The relatively small size of insects, their high reactivity to environmental conditions and the associated intense work of their physiological and, in particular, locomotor and sensory systems, high fertility and well-expressed instincts of “caring for offspring” require this group of phytophages, as well as other arthropods, extremely high energy costs. Therefore, we classify insects in general, including phytophages, as organisms with a high level of energy expenditure, and therefore very demanding in terms of the supply of energy resources from food, and the high fertility of insects determines their high needs for plastic substances.
One of the proofs of the increased demands of insects to provide energy substances can be the results of comparative studies of the activity of the main groups of hydrolytic enzymes in the digestive tracts of phytophagous insects. These studies, carried out on many species of insects, indicate that in all species examined, carbohydrases, enzymes that hydrolyze carbohydrates, were sharply distinguished in their comparative activity. The established ratios of the activity of the main groups of insect digestive enzymes well reflect the corresponding level of insect needs for basic metabolic substances - carbohydrates, fats and proteins. The high level of autonomy of the lifestyle of phytophagous insects from their food plants, combined with well-developed abilities of directed movement in space and time and a high level of general organization of phytophages, manifested themselves in the specific features of the biological system phytophage - food plant, which significantly distinguish it from the system the causative agent of the disease is the food plant. These distinctive features indicate the greater complexity of its functioning, and hence the emergence of more complex problems in its study and analysis. In general, the problems of immunity are largely ecological and biocenotic in nature; they are based on trophic connections.
The coupled evolution of phytophages with food plants led to the restructuring of many systems: sensory organs, organs associated with food intake, limbs, wings, body shape and color, digestive system, excretion, accumulation of reserves, etc. Food specialization gave an appropriate direction to the metabolism of different species of phytophages and thus played a decisive role in the morphogenesis of many other organs and their systems, including those not directly related to the search, intake and processing of food by insects.
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The word immunity comes from the Latin immunitas, which means "freedom from something."
Immunity is understood as the body's immunity to the action of pathogens and their metabolic products. For example, coniferous trees are immune to powdery mildew, and deciduous trees are immune to powdery mildew. Spruce is absolutely immune to shoot rust, and pine is completely immune to cone rust. Spruce and pine are immune to the false fungus, etc.
I.I. Mechnikov understood immunity to infectious diseases as a general system of phenomena due to which the body can resist the attack of pathogenic microbes. The ability of a plant to resist disease can be expressed either in the form of immunity to infection, or in the form of some kind of resistance mechanism that weakens the development of the disease.
The different resistance to diseases of a number of plants, especially agricultural ones, has been known for a long time. Selection of crops for disease resistance, along with selection for quality and productivity, has been carried out since ancient times. But only at the end of the 19th century did the first works on immunity appear, as a doctrine of plant resistance to disease. Among the many theories and hypotheses of that time, one should mention phagocytic theory of I.I. Mechnikov. According to this theory, the animal's body secretes protective substances (phagocytes) that kill pathogenic organisms. This applies mainly to animals, but also occurs in plants.
Gained greater fame mechanical theory of the Australian scientist Cobb(1880-1890), who believed that the reason for plant resistance to diseases comes down to anatomical and morphological differences in the structure of resistant and susceptible forms and species. However, as it turned out later, this cannot explain all cases of plant resistance, and, therefore, cannot recognize this theory as universal. This theory was criticized by Erikson and Ward.
Later (1905) the Englishman Massey put forward chemotropic theory, according to which the disease does not affect those plants that do not contain chemicals that have an attractive effect on the infectious principle (fungal spores, bacterial cells, etc.).
However, later this theory was also criticized by Ward, Gibson, Salmon and others, since it turned out that in some cases the infection is destroyed by the plant after it has penetrated the cells and tissues of the plant.
After the acid theory, several more hypotheses were put forward. Of these, the hypothesis of M. Ward (1905) deserves attention. According to this hypothesis, susceptibility depends on the ability of fungi to overcome plant resistance using enzymes and toxins, and resistance is determined by the ability of plants to destroy these enzymes and toxins.
Of the other theoretical concepts, the one that deserves the most attention is phytoncidal theory of immunity, extended B.P.Tokin in 1928. This position was developed for a long time by D.D. Verderevsky, who established that in the cell sap of resistant plants, regardless of the attack of pathogenic organisms, there are substances - phytoncides that suppress the growth of pathogens.
And finally, of some interest theory of immunogenesis proposed by M.S. Dunin(1946), which considers immunity in dynamics, taking into account the changing state of plants and external factors. According to the theory of immunogenesis, he divides all diseases into three groups:
1. diseases affecting young plants or young plant tissues;
2. diseases affecting aging plants or tissues;
3. diseases, the development of which is not clearly associated with the development phases of the host plant.
N.I. Vavilov paid a lot of attention to immunity, mainly of agricultural plants. The works of foreign scientists I. Erikson (Sweden), E. Stackman (USA) also belong to this period.
