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, pathogen and conditions. external environment. 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 grain 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 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 class Oomycetes. The structure of the stomata is important for the introduction into the tissue of bacteria, pathogens of false powdery mildew, rust, etc. Usually, it is more difficult for the pathogen to infiltrate through densely covering 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 explained by 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. Speed is also important individual phases ontogeny. 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 can suppress the development of pathogens, essential oils and a number of other compounds. 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. By 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 some chemical substances, 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 reaction 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.

BASES OF PLANT IMMUNE TO DISEASE

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.

Factors of plant resistance to diseases

The first group includes factors or mechanisms of 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 class Oomycetes. 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.

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.

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

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

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.

Genetics of resistance and pathogenicity. Types of sustainability

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

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. For 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.

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

Causes of loss of stability

plant immunity- this is their immunity to pathogens or invulnerability to 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 the established interactions of plants and their consumers (consumers). It is a system of barriers that limits the colonization of plants by consumers, negatively affects the life processes of pests, as well as a system of plant properties that ensures their resistance 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 organ-forming, anatomical, morphological, physiological, biochemical and other features of plants.

Plant immunity to pests is manifested at various taxonomic levels of plants (families, orders, tribes, genera and species). For relatively large taxonomic groupings of plants (families and above), absolute immunity is most characteristic (complete immunity of plants by this type of pest). At the level of genus, species and variety, the relative importance of immunity is predominantly manifested. However, even the relative resistance of plants to pests, especially manifested in varieties and hybrids of agricultural crops, is important for suppressing the abundance and reducing the harmfulness of phytophages.

The main distinguishing feature of plant immunity to pests (insects, mites, nematodes) is the high degree of barriers that limit the selectivity of plants for feeding and laying eggs. 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 ontogeny.

It is known that insects are unparalleled in the diversity of species and life forms represented in this class. Among invertebrates, they have reached the highest level of development, primarily due to the perfection of their sense organs and movement. This provided insects with prosperity based on the wide possibilities of using a high level of activity and reactivity while gaining 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 populate 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 fecundity and well-defined instincts of "care for offspring" require from this group of phytophages, as well as from other arthropods, extremely high energy costs. Therefore, we classify insects in general, including phytophages, as organisms with a high level of energy expenditure, and, consequently, very demanding in terms of the intake of energy resources with food, and the high fecundity of insects determines their high need for plastic substances.

The results of comparative studies of the activity of the main groups of hydrolytic enzymes in the digestive tracts of phytophagous insects can serve as one of the proofs of the increased demands of insects for the provision of energy substances. These studies, carried out on many species of insects, indicate that in all the examined species, carbohydrase-enzymes that hydrolyze carbohydrates were sharply distinguished by the comparative activity of carbohydrase. The established ratios of the activity of the main groups of digestive enzymes of insects well reflect the corresponding level of needs of insects in the substances of the main metabolism - carbohydrates, fats and proteins. The high level of autonomy of the way of life of phytophage insects from their food plants, in combination with well-developed abilities of directed movement in space and time, and the 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 diseases is a fodder plant. These distinctive features indicate the great complexity of its functioning, and hence the emergence of more complex problems in its study and analysis. On the whole, however, the problems of immunity are largely of an ecological-biocenotic nature; they are based on trophic relationships.

The conjugate evolution of phytophages with forage plants has 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 has given 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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10. Plants named after Vavilov
11. Vavilov's awards

Expeditions

180 botanical and agronomic expeditions around the world, which brought "to world science the results of paramount importance, and their author deserved fame as one of the most outstanding travelers of our time." The result of the Vavilov scientific expeditions was the creation of a unique, richest collection of cultivated plants in the world, numbering 250,000 specimens in 1940. This collection has found wide application in breeding practice and has become the world's first important gene bank.

Development of scientific theories

The doctrine of plant immunity

Vavilov subdivided plant immunity into structural 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.

The doctrine of the centers of origin of cultivated plants

The doctrine of the centers of origin of cultivated plants was formed on the basis of Charles Darwin's ideas about the existence of geographical centers of origin of biological species. In 1883, Alphonse Decandol published a work in which he established the geographical areas of the initial origin of the main cultivated plants. However, these areas were confined to entire continents or to other, also quite extensive, territories. After the publication of Decandole's book, knowledge in the field of the origin of cultivated plants expanded significantly; monographs were published on cultivated plants of various countries, as well as individual plants. Nikolai Vavilov developed this problem most systematically in 1926-1939. On the basis of materials on world plant resources, he singled out 7 main geographical centers of origin of cultivated plants.

Centers of origin of cultivated plants:
1. Central American, 2. South American, 3. Mediterranean, 4. Western Asian, 5. Abyssinian, 6. Central Asian, 7. Hindustanian, 7A. Southeast Asian, 8. East Asian.
Based on The Living Fields: Our Agricultural Heritage by Jack Harlan

South Asian Tropical Center
East Asian Center
Southwest Asian Center
mediterranean center
Ethiopian Center
Central American Center
Andean Center

Many researchers, including P. M. Zhukovsky, E. N. Sinskaya, A. I. Kuptsov, continuing the work of Vavilov, made their own corrections to these ideas. Thus, tropical India and Indo-China with Indonesia are considered as two independent centers, and the South-West Asian center is divided into Central Asian and Western Asian ones, the basis of the East Asian center is the Huang He basin, and not the Yangtze, where the Chinese, as a people-farmers, penetrated later. Centers of ancient agriculture have also been established in Western Sudan and New Guinea. Fruit crops, having more extensive areas of distribution, go far beyond the centers of origin, more consistent with the ideas of Decandol. The reason for this lies in their predominantly forest origin, as well as in the features of selection. New centers have been identified: Australian, North American, European-Siberian.

Some plants have been introduced into cultivation in the past outside these main centers, but the number of such plants is small. If earlier it was believed that the main centers of ancient agricultural cultures were the wide valleys of the Tigris, Euphrates, Ganges, Nile and other large rivers, then Vavilov showed that almost all cultivated plants appeared in the mountainous regions of the tropics, subtropics and the temperate zone.

Other scientific achievements

Among other achievements of Vavilov, one can name the doctrine of a species as a system, intraspecific taxonomic and ecological-geographical classifications.

The law of homologous series in hereditary variability

In the work “The law of homological series in hereditary variability”, presented in the form of a report at the III All-Russian Selection Congress in Saratov on June 4, 1920, Vavilov introduced the concept of “Homological series in hereditary variability”. The concept was introduced in the study of parallelisms in the phenomena of hereditary variability by analogy with the homologous series of organic compounds.

The essence of the phenomenon is that when studying hereditary variability in close groups of plants, similar allelic forms were found, which were repeated in different species. The presence of such repeatability made it possible to predict the presence of yet undiscovered alleles that are important from the point of view of selection work. The search for plants with such alleles was carried out during expeditions to the supposed centers of origin of cultivated plants. It should be remembered that in those years the artificial induction of mutagenesis by chemicals or exposure to ionizing radiation was not yet known, and the search for the necessary alleles had to be carried out in natural populations.

The first formulation of the law included two regularities:

The first regularity that catches the eye during a detailed study of forms in any plant linneons belonging to the same genus is the identity of the series of morphological and physiological properties that characterize varieties and races in closely related genetic linneons, the parallelism of the series of species genotypic variability ... The closer genetically the species are, the sharper and more precisely the identity of the series of morphological and physiological characters is manifested.

…the 2nd regularity in polymorphism, essentially following from the first one, consists in the fact that not only genetically close species, but also genera show identities in the series of genotypic variability.

At the First All-Russian Congress on Applied Botany, which was held from September 6 to 11, 1920 in Voronezh, at the request of the organizing committee of the congress, Vavilov made a repetition of the report on the law of homological series. In 1921, the law was published in the journal Agriculture and Forestry, and in 1922 an expanded version of the law was published in a large article in the Journal of Genetics. In 1923, Vavilov included a discussion of the law in the work "Recent Advances in the Theory of Breeding", in which he showed that, due to the regularity in the manifestation of varietal differences in species and genera, "it is possible to definitely foresee and find the corresponding forms in the plant under study." Indeed, on the basis of the law of homological series, Vavilov and his collaborators predicted the existence of certain forms hundreds of times, and then discovered them. Vavilov noted that "general series of variability are sometimes characteristic of very distant, genetically unrelated families." Vavilov assumed that the series of parallel variability would not necessarily be complete and would be deprived of some links as a result of natural selection, lethal combinations of genes, and extinction of species. However, "despite the enormous role of natural selection and the extinction of many connecting links, ... it is not difficult to trace the similarities in hereditary variability in closely related species."

Although the law was discovered as a result of the study of phenotypic variability, Vavilov extended its effect to genotypic variability: “Based on the striking similarity in the phenotypic variability of species within the same genus or close genera, due to the unity of the evolutionary process, we can assume that they have many common genes along with the specificity of species and genera.

Vavilov believed that the law was valid not only in relation to morphological features, foreseeing that the already established series “will not only be replenished with missing links in the corresponding cells, but will also develop, especially in relation to physiological, anatomical and biochemical features.” In particular, Vavilov noted that related plant species are characterized by "the similarity of the chemical composition, the production of close or the same specific chemical compounds." As was shown by Vavilov, intraspecific variability of chemical composition concerns mainly quantitative ratios with a constant qualitative composition, while within a genus the chemical composition of individual species differs both quantitatively and qualitatively. At the same time, within the genus, "individual species are usually characterized by isomers or derivatives theoretically envisaged by chemists and are usually interconnected by mutual transitions." Parallelism of variability characterizes close genera with such certainty that "it can be used in the search for the corresponding chemical components", as well as "to obtain synthetically within a given genus by crossing chemicals of a certain quality."

Vavilov found out that the law manifests itself not only within the limits of kindred groups; parallelism of variability has been found "in different families, genetically unrelated, even in different classes", but in distant families the parallelism is not always homologous. “Similar organs and their very similarity are in this case not homologous, but only analogous.”

The law of homological series did not remove all the difficulties, since it was clear that the same changes in phenotypic traits could be due to different genes, and the level of knowledge that existed in those years did not allow a trait to be directly associated with a particular gene. With regard to species and genera, Vavilov noted that “so far we are mainly dealing not with genes, about which we know very little, but with characters in a certain environment,” and on this basis he preferred to talk about homologous characters. “In the case of parallelism of distant families, classes, of course, there can be no question of identical genes even for outwardly similar characters.”

Despite the fact that initially the law was formulated on the basis of a study of predominantly cultivated plants, later, having considered the phenomenon of variability in fungi, algae and animals, Vavilov came to the conclusion that the law is universal and manifests itself “not only in higher, but also in lower plants as well as animals.

The progress of genetics had a significant impact on the further development of the formulation of the law. In 1936, Vavilov called the first formulation unnecessarily categorical: "Such was the state of genetics then...". It was common to think that "genes are identical in closely related species", biologists "represented the gene as more stable than at present." Later it was found that "close species can be characterized by many different genes in the presence of similar external features." Vavilov noted that in 1920 he paid "little ... attention to the role of selection", concentrating his main attention on the patterns of variability. This remark by no means meant forgetting the theory of evolution, because, as Vavilov himself emphasized, already in 1920 his law “first of all represented a formula of exact facts based entirely on evolutionary doctrine.”

Vavilov considered the law he formulated as a contribution to the then popular ideas about the regular nature of variability underlying the evolutionary process. He believed that hereditary variations regularly repeated in different groups underlie evolutionary parallelisms and the phenomenon of mimicry.

Plants described by Vavilov

Avena nudibrevis Vavilov
Hordeum pamiricum Vavilov
Linum dehiscens Vavilov & Elladi
Linum indehiscens Vavilov & Elladi
Secale afghanicum Roshev.
Secale dighoricum Roshev.
Triticum persicum Vavilov

Plan

1. Factors of plant immunity to pests.

2. Immunogenetic barriers.

Literature basic

Shapiro I.D. Immunity of field crops to insects and mites. - L .: Kolos, 1985.

Additional

Popkova K.V. The doctrine of plant immunity. – M.: Kolos, 1979.

1. Plant immunity- this is their immunity to pathogens or invulnerability to pests. It can be expressed in plants in different ways - from a weak degree of resistance to its extremely high severity. Immunity is the result of the evolution of established interactions between plants and their consumers. Plant immunity to pests differs significantly from immunity to diseases:

1) Autonomous (free) way of life of insects. Most insects lead a free lifestyle and come into contact with the plant only at certain stages of ontogenesis.

2) Diversity of morphology and feeding types of insects. If the fungus damages the cells and tissues of plants, then the pest is capable of damaging or destroying the entire organ of the plant within a short time.

3) Activity in choosing a fodder plant. Well-developed legs and wings allow insects to select and populate consciously forage plants.

In accordance with the reaction that plants cause in insects, the following immunity factors are distinguished:

1. rejection (antixenosis) and selection of plants by insect phytophages;

2. antibiotic effect of the host plant on phytophages;

3. factors of endurance (tolerance) of damaged plants.

When choosing a pest of plants for nutrition, the primary role is played by:

1. feed and nutritional value of the crop;

2. absence or low level of mechanical barriers;

3. the presence of appetite stimulants;

4. level of content of physiologically active substances;

5. the molecular form of the main nutrients and the degree of their balance.

The phytophage receives this information with the help of olfactory, tactile and visual receptors. Taste buds are used for the final choice of food site. To do this, the insect makes trial bites of plants. So, thanks to the system of visual and olfactory receptors, insects at a great distance can capture the color, shape, smell and some other properties of plants. This helps them navigate the choice of plant community. The choice of the place of feeding or laying eggs is carried out with the help of taste and tactile receptors.

Vision allows insects to assess the color and shape of food plants, as well as control the direction of flight.

When studying the relationship of insects to different rays of the spectrum, it was found that cabbage whites are attracted to green and blue-green substrates, and yellow butterflies do not sit down. Many types of aphids, on the contrary, accumulate on yellow objects. And yet, not so much the color of the leaves and flowers attracts insects as the rays of the ultraviolet part of the spectrum. The ability to finely analyze the nature of radiation is manifested in insects in the ability to distinguish plane polarized light. Insects also have a wide range of possibilities for analyzing the nature of various electromagnetic radiations. Irritants of a chemical nature differ from visual stimuli by a large radius of action. Plants release a certain amount of various substances into the environment. Many of them have a high degree of volatility, which helps the insect to choose a particular plant. The odor emitted by the forage plant serves as a marker for the insect adapted to it. The smell is especially important for flying insects, which are able to explore large areas on the plant. Thus, the smell in many cases determines the attractiveness of plants.

So, a large arsenal of analyzers allows the insect to select plants, individual organs or tissues that are optimal for him in terms of age and physiological state. A long search for a host plant requires a lot of effort from the insect. This results in:

1) to increase energy costs;

2) a decrease in the fertility of females;

3) premature wear of all systems of the insect body;

4) can even lead to the death of the insect.

Antibiosis- this is an adverse effect of a plant on a phytophage, manifested when it is used by insects for food or for laying eggs.

In contrast to the factor considered earlier, antibiosis begins to act when the phytophage has chosen a plant and started feeding.

Antibiosis factors can be:

1. substances of secondary metabolism with high physiological activity for insects.

2. Structural features of the main biopolymers synthesized by the plant and the degree of their availability for assimilation by phytophages.

3. The energy value of the plant for the pest.

4. Anatomical and morphological features of plants that make it difficult for a phytophage to access zones of optimal nutrition.

5. Growth processes of plants leading to self-purification of the plant from the pest or violating the conditions for the normal development of the phytophage.

In the general degree of protective properties of plants, antibiosis factors play an important role. On varieties with antibiotic properties, a high mortality of the pest is noted, and the surviving individuals are usually characterized by reduced viability (low fecundity, increased sensitivity to extreme conditions, low survival during the wintering period).

It is important to emphasize that the population of phytophages feeding on plants of resistant varieties with well-pronounced antibiotic properties is not able to maintain a high abundance. The action of antibiotics on pests is as follows:

a) death of adults and larvae;

b) lag in growth and development;

c) decrease in fertility and viability of offspring;

d) decrease in resistance to adverse environmental factors.

Endurance or tolerance, - it is the ability to preserve life and restore impaired functions that ensure the formation of the crop without noticeable losses.

On hardy plants, conditions favorable for the development of the pest are preserved. Environmental factors and growing conditions play a significant role in increasing plant endurance. This stability factor is the most variable. Before we begin to study this factor, we need to understand the concept of "harm" and "benefit" from the phytophage. After all, not every damage leads to a decrease in yield. In many cases, damaged plants stimulate metabolism, which increases their productivity. This feature is often used by a person in order to increase productivity. To do this, legume grasses are cut, the tops of the stems are removed, pinching, cuttings and other methods of alienating plant biomass. Therefore, when determining the value of damage to plants, a flexible approach to assessing the degree of damage is necessary.

Therefore, endurance occurs only when the phytophage harms the plant. The forms of manifestation of plant endurance are as follows:

1) hypersensitivity reaction in response to damage by sucking pests;

2) intensification of metabolism;

3) structural regeneration (increase in the number of chloroplasts);

4) the emergence of new organs to replace the lost ones;

5) unusual growth of individual tissues, plant organs;

6) premature ripening of seeds.

The endurance of plants in ontogeny changes significantly. This is due to differences in metabolism and organ formation.

The most critical period of plant ontogenesis is the initial stage of growth, when the root system is weak and photosynthetic organs are also insignificant. During this period, plants are the least resistant to damage to its ground and underground parts. The endurance of crop seedlings to damage to the leaf surface varies significantly and depends on the biology of the culture. Those plants that have a large supply of nutrients in the soil (these are monocotyledonous bulbous, root, tuber, dicotyledonous with an underground type of cotyledons), i.e. all those in which large seeds and nutrient reserves are inaccessible to terrestrial pests show a high degree of tolerance to them.

Seedlings of dicotyledonous plants with a terrestrial type of cotyledons, when they are destroyed, are deprived of an assimilation surface, a reserve of nutrients and a source of growth substances. Therefore, such plants at the first stage of development are very sensitive to damage. Such crops that need protection in the early stages of ontogenesis include flax and beets.

The degree of endurance at subsequent stages of plant ontogenesis is due to their ability to restore the metabolism disturbed by damage due to increased photosynthesis of undamaged parts. In this case, the growth of lateral shoots, the growth of new leaves can occur.

Plant hardiness will determine the organ that the phytophages have damaged:

When the leaf surface is damaged, the following violations of the vital activity of plants occur:

1.reduction of the assimilation surface;

2. violation of transport links in the movement of assimilated nutrients between organs;

3. lack of carbohydrates due to a decrease in their synthesis and increased expenditure on increased breathing;

4. nitrogen starvation;

5. disruption of the root system.

In plants with a well-developed assimilation apparatus, recovery processes proceed faster. This is due to an increase in the productivity of photosynthesis of intact leaves and other green plant organs. They rejuvenate the structure of chloroplasts, which acquire a fine-grained structure, which increases their surface and photosynthesis.

Damage to the roots worsens the general condition of the plants. The following features of the variety are of the greatest importance for plant endurance:

1. growth rate and the nature of the formation of the root system;

2. rate of new root formation in response to damage;

3. rates of wound healing and resistance of plants to decay.

2. In the process of evolution, plants have developed a whole complex of adaptations of various nature, which provides protection for various organs from damage by pests.

All immunogenetic barriers are divided into:

- constitutional are present in the plant regardless of the presence of the factor;

- induced appear as a result of the interaction of plants with pests.

Let's take a closer look at these barriers. Group of constitutional barriers:

1) anatomical and morphological barrier represents the features of the structure of organs and tissues of plants. It is the most studied and most accessible for use in practice. That is, knowing the characteristics of the biology of the phytophage, based on the visual assessment of the variety, we can conclude how its cultivation will affect the damage by this pest. For example, heavily hairy wheat leaves will prevent hessian damage but promote hessian damage.

The pubescence of cucumber leaves prevents damage by spider mites. The pubescence of spikelets of wheat in the ear of wheat creates a barrier to the penetration of caterpillars of the grain scoop. So, let's name the main morphological features of plants that provide resistance to phytophages.

1. The pubescence of leaves, stems;

2. The presence of siliceous deposits in the epidermis of the leaves (this makes it difficult for insects to feed);

3. The presence of a wax coating does not always increase the immunity of plants to pests. For example, the presence of a wax coating attracts cabbage aphids. This is due to the fact that this pest needs wax to build its body. In this case, the absence of wax on cabbage leaves can serve as a resistance factor:

4. C tripping of the mesophyll of the leaf. For some insects, an important factor in normal nutrition is a certain ratio of spongy parenchyma. So, to obtain nutrients, the spider mite needs a thin layer of spongy parenchyma. If this tissue exceeds the length of the stylet of the tick, it cannot feed, the plant can be considered resistant.

Cabbage varieties with a compact arrangement of cells are more resistant to the penetration of caterpillars of the cabbage moth, and vice versa, a loose arrangement of cells in the mesophyll, a large number of intercellular spaces reduces the resistance of cabbage to pests.

5. Onatomical structure of the stem.

For example, a factor in the resistance of clover to stem weevils is the special arrangement of vascular-fibrous bundles. In order for the female to create an egg-laying chamber, the distance between the vascular bundles must exceed the diameter of the weevil's rostrum. On resistant varieties of clover, vascular-fibrous bundles are located very tightly, which creates an annular mechanical barrier for the pest.

For females of the stem sawfly, the rate of egg laying, and hence the harmfulness, depends on the structure of the culm. In plants in which the stem in the upper internode is characterized by high mechanical strength and parenchyma filling, the pest spends much more time and energy on oviposition.

6. The structure of the generative organs of plants. The structure of the seed chambers of apples can represent an insurmountable barrier for caterpillars of the codling moth. The pest penetrates the fruit through the calyx, and in resistant varieties, the fruits have a very small subcalyx tube, they lack a central cavity, the seed chambers are dense, closed. This prevents the caterpillars from penetrating the fruit and the seed chamber. On such fruits, caterpillars do not receive optimal nutrition and their physiological state is suppressed.

7. Parchment layer. It is present in the wings of the bean in peas. If it forms quickly, then the pea weevil larvae cannot penetrate the bean.

2). growth barrier. It is associated with the nature of the growth of various plant organs and their individual parts. In many cases, plant growth acts as a barrier when insects choose a plant as a whole or its individual organs. For laying eggs (i.e. antixenosis factor) either causes self-purification from pests, or has an antibiotic effect on the pest. For example, the speed of penetration of frit fly larvae to the growth cone of cereals depends on the nature and rate of growth, as well as the internal structure of the shoots, their strength, and the number of leaves surrounding the growth cone. On a resistant variety, the number of layers is greater, as they grow and unfold, they force out the larva, do not let it through to the growth cone, and the larva dies.

3. Physiological barrier- due to the content in the plant of physiologically active substances that adversely affect the life of the insect. Most often, these are substances of the secondary metabolism of plants.

4. Organogenetic barrier associated with the degree of differentiation of plant tissues. For example, the resistance of peas to damage by nodule weevils is due to the presence of axillary buds, from which lateral shoots develop when the growing point is damaged.

5. Atreptic the barrier is due to the specific features of the molecular structure of plant biopolymers used by phytophages for nutrition. In the process of evolution, phytophages have adapted to the use of certain forms of biopolymers. To do this, the insect has enzymes that can decompose, i.e. hydrolyze certain biochemical structures. Naturally, the phytophage must obtain the most easily digestible biopolymers in order for their hydrolysis reactions to occur as soon as possible. Therefore, varieties with easily digestible forms of biopolymers will be more strongly damaged by phytophages and increase their viability, while varieties with more complex biopolymers or those for which phytophages do not have enzymes for propagation will greatly weaken pests, i.e. induce antibiotics.

In the process of conjugate evolution of plants with phytophages, a system of induced barriers has been developed that arise in response to colonization by harmful organisms and damage by them. Immunological reactions of plants depend on the nature and degree of damage, on the phase of ontogenesis, and environmental conditions.

Let us examine in more detail what induced barriers arise in plants in response to pest damage.

1.excretory barrier. In the process of evolution, the plant has adapted to synthesize substances that are not used by it, but are located in an isolated place, for example, in special outgrowths of the epidermis. When plants are damaged by pests or due to their contact with glandular outgrowths, these substances are released, which leads to the death of pests. In wild potato species, leaf blades contain a significant amount of such substances. In contact with them, the death of small insects (aphids, psyllids, leafhoppers) of the larvae of the Colorado potato beetle of the 1st age occurs.

Similarly, many pests of conifers die as a result of the resin-releasing reaction of plants to damage.

2). Necrotic barrier. It is similar to the hypersensitivity reaction during the penetration of pathogens. For pests, this barrier is less important, since the nature of the relationship between the phytophage and host plant is different. Indeed, in the process of feeding, the pest is not limited to damage to one cell, but immediately captures a significant part of the tissues, especially leaf-eating pests. But even thrips that pierce only 1 cell, after completing feeding on 1, damage 2, 3, etc. Yet for some sucking pests, the necrotic barrier presents an obstacle. For example, resistant varieties of grapes form a wound periderm, which separates phylloxera from healthy tissues, thereby depriving it of nutrition and leading to death.

3).Reparation barrier or restoration of lost organs. Reparation processes, depending on the nature of the damage done and the age of plants, can manifest themselves in various forms in the form of regrowth of the leaf surface or the formation of new organs to replace the lost ones. These processes are based on an increase in metabolism and an increase in the activity of photosynthesis in the surviving plant organs and an increase in the influx of assimilants into the zones of formation of new organs due to reserve meristematic tissues. The regulatory role in this belongs to phytohormones. For example, when the growth cone is damaged by the swedish fly, kinetin enters the site of damage. This retards the growth of the main stem, but awakens the lateral bud. Under the influence of gibberellin, which enhances the supply of nutrients, the growth of lateral stems occurs.

4). Gallogenetic and teratogenetic barriers we consider them together, since they both occur in those cases when the pest releases into the plant tissue, along with hydrolytic enzymes, some physiologically active substances (tryptophan, indomelacetic acid, and some others) along with hydrolytic enzymes. Plants respond with a peculiar reaction: there is an increase in the growth of damaged tissues, which leads to the formation of galls and terates. Thus, the plant isolates the pest, but at the same time creates favorable conditions for them to feed and exist.

5).Oxidative barrier. Its essence is as follows. In response to damage by phytophages, the activity of redox reactions in plants increases:

a) the intensity of breathing increases;

b) ATP is formed;

c) enzymes of sucking insects are inactivated;

d) as a result of oxidation, substances highly toxic to insects are formed.

e) phytoalexins are synthesized.

6. Inhibitory barrier due to the fact that in response to damage by a pest, the plant produces inhibitors of the digestive enzymes of phytophages. This barrier is important for protecting plants from sucking insects, which are distinguished by extraintestinal digestion and release large amounts of enzymes into the tissues of the damaged plant.

Questions for self-control

1. Main factors of immunity?

2. What is the difference between plant immunity and immunity to pests?

3. What determines the endurance of plants?

4. What two groups are immunogenetic barriers divided into?

5. What activities can affect the endurance of plants?

6. What are the antibiosis factors?

7. What are the constitutional barriers?

8. What do induced barriers include?

9. What are the forms of manifestation of endurance?

The study of plant immunity to infectious diseases. Creation of N.I. Vavilov of the modern doctrine of selection. development of insects. Postembryonic development