The extensive system of agriculture and unreasonable chemicalization greatly complicate the phytosanitary situation. Imperfect agricultural technology, monoculture, uncultivated weedy fields create exceptionally favorable conditions for the spread of infection and pests.
At all stages of ontogeny, plants interact with many other organisms, most of which are harmful. The cause of various diseases of plants and seeds can be mushrooms , bacteria and viruses .
Diseases are manifested as a result of the interaction of two organisms - a plant and a pathogen that destroys plant cells, releasing toxins in them, and digests them through depolymerase enzymes. The reverse reaction of plants consists in neutralizing toxins, inactivating depolymerases, and inhibiting the growth of pathogens through endogenous antibiotics.
The resistance of plants to pathogens is called immunity , or phytoimmunity . N. I. Vavilov singled out natural , or congenital , and acquired immunity. Depending on the mechanism of protective functions, immunity can be active and passive . Active, or physiological, immunity is determined by the active reaction of plant cells to the penetration of a pathogen into them. Passive immunity is a category of resistance, which is associated with the features of both the morphological and anatomical structure of plants.
The effectiveness of physiological immunity is mainly due to the weak development of the pathogen with a sharp manifestation of immunity - its early or late death, which is often accompanied by local death of the cells of the plant itself.
Immunity is completely dependent on the physiological reactions of the cytoplasm of the fungus and host cells. The specialization of phytopathogenic organisms is determined by the ability of their metabolites to suppress the activity of defense reactions induced in the plant by infection. If plant cells perceive an invading pathogen as a foreign organism, a series of biochemical changes occur to eliminate it, so infection does not occur. Otherwise, infection occurs.
The nature of the development of the disease depends on the characteristics of both components and environmental conditions. The presence of infection does not mean the manifestation of the disease. Scientist J. Deverall in this regard distinguishes two types of infection: 1) high if the pathogen is virulent and the plant is susceptible to the disease; 2) low, characterized by the virulent state of the pathogen and increased plant resistance to it. With low virulence and weak resistance, an intermediate type of infection is noted.
Depending on the degree of virulence of the pathogen and the resistance of the plant, the nature of the disease is not the same. Based on this, Van der Plank singles out vertical and horizontal plant resistance to diseases. Vertical stability observed in the case when the variety is more resistant to one races of the pathogen than to others. Horizontal resistance is manifested to all races of the pathogen in the same way.
The immunity of a plant to diseases is determined by its genotype and environmental conditions. NI Vavilov gives information that soft wheat varieties are very affected by brown rust, while durum wheat forms are resistant to this disease. The founder of the doctrine of phytoimmunity came to the conclusion that hereditary differences in plant varieties in terms of immunity are constant and undergo little variability under the influence of environmental factors. Regarding physiological immunity, N. I. Vavilov believes that in this case heredity is stronger than the environment. However, giving preference to genotypic features, he does not deny the influence of exogenous factors on disease resistance. In this regard, the author points to three categories of immunity factors, or vice versa, susceptibility: 1) hereditary properties of the variety; 2) selective ability of the pathogen; 3) environmental conditions. As an example, data are given on the negative impact of increased soil acidity on plant resistance to certain fungal diseases.
A stronger infection of wheat with hard smut occurs at low temperatures (at 5 °C the infection was 70%, at 15 °C - 54%, at 30 °C - 1.7%). Moisture in the soil and air is often a factor initiating the development of rust, powdery mildew and other diseases. Susceptibility to fungal infection is also affected by light. If you keep oat plants in the dark and thereby reduce the intensity of photosynthesis and the formation of carbohydrates, then they become immune to rust infection. Plant resistance to disease is affected by fertilizers and other conditions..
The complexity of disease prevention and control is due to objective factors. It is very difficult to develop varieties that would remain resistant to the pathogen for a long time. Often, resistance is lost as a result of the emergence of new races and biotypes of pathogens against which the variety is not protected.
The fight against diseases is further complicated by the fact that pathogens are adapting to chemical defenses.
The above factors are the main reason why the cost of plant protection in the conditions of modern agriculture is growing, outpacing the growth rate of agricultural production by 4-5 times. In the main grain-growing regions, the disease is often a limiting factor in obtaining high grain yields. In this regard, for the further intensification of agricultural production, new, advanced methods of plant protection are needed.
When developing new plant protection systems, it is necessary to focus on the regulation of the number of harmful organisms in the agroecosystem. In the methodological plan, it is necessary to determine the complexes of harmful organisms that infect plants in different phases of development. It is necessary to create models that reflect the influence of certain types of pathogens and their complexes on crop formation and allow optimizing these processes through agrotechnological, organizational, economic and protective measures.
One of the most important prerequisites for obtaining seeds with high biological properties is the absence of pathogenic microflora. Diseases cause great harm to seeds at all stages of their life - during formation, storage and germination.
Through seeds, pathogens can be transmitted in three ways: 1) as mechanical impurities (sclerotia in rye seeds); 2) in the form of spores on the surface of seeds (hard smut of cereals); 3) in the form of mycelium in the middle of the seeds, for example, loose smut.
The microflora of seeds is divided into several groups. epiphytic microflora are microorganisms that inhabit the surface of seeds and feed on the waste products of plant cells. Under normal conditions, such pathogens do not invade the internal tissue and do not cause significant harm ( Alternaria, Mucor, Dematium, Cladosporium and etc.). Endophytic (phytopathogenic) microflora consists of microorganisms that can penetrate into the internal parts of plants, develop there, cause disease in seeds and plants growing from them ( Fusarium, Helminthosporium, Septoria and etc.). Microorganisms that accidentally enter the seeds upon contact with contaminated surfaces of warehouse equipment, containers, soil particles, plant residues with dust and raindrops ( Рenісіllium, Aspergillus, Mucor and etc.). Storage mold, which develops as a result of the vital activity of fungi ( Рenісіllium, Aspergillus, Mucor and etc.).
Distinguish embryonic infection when pathogens are found in any of the constituent parts of the embryo and extraembryonic infection when pathogens are found in the endosperm, sheath, pericarp and bracts. The placement of the pathogen in the seeds depends on the anatomy of the seeds and the site of entry specific to each microorganism.
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 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 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. 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 a hypersensitive 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. 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.
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 tested 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.
The word immunity comes from the Latin immunitas, which means "liberation from something."
Immunity is understood as the immunity of the body to the action of pathogens and their metabolic products. For example, conifers are immune to powdery mildew, while hardwoods are immune to shutte. Spruce is absolutely immune to shoot rust, and pine is completely immune to cone rust. Spruce and pine are immune to false tinder fungus, etc.
I.I. Mechnikov under the immunity to infectious diseases understood the general system of phenomena, thanks to which the body can resist the attack of pathogenic microbes. The ability of a plant to resist a disease may 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.
Different resistance to diseases of a number of plants, especially agricultural ones, has long been known. The selection of crops for resistance to diseases, along with the 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 the doctrine of plant resistance to diseases. Among the many theories and hypotheses of that time, one should mention phagocytic theory of I.I. Mechnikov. According to this theory, the animal body secretes protective substances (phagocytes) that kill pathogenic organisms. This applies mainly to animals, but also occurs in plants.
Gained great fame mechanical theory of the Australian scientist Cobb(1880-1890), who believed that the cause of 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, consequently, recognize this theory as universal. This theory met with criticism from Erickson and Ward.
Later (1905), the Englishman Massey put forward chemotropic theory, according to which the disease does not affect those plants in which there are no chemicals that have an attracting 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 into 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 with enzymes and toxins, and resistance is due to the ability of plants to destroy these enzymes and toxins.
Of the other theoretical concepts, the one that deserves the most attention is phytoncide theory of immunity, put forward B.P. Tokin in 1928. This position was developed for a long time by D.D. Verderevsky, who found that in the cell sap of resistant plants, regardless of the attack of pathogens, there are substances - phytoncides that suppress the growth of pathogens.
And finally, of some interest the theory of immunogenesis proposed by M.S. Dunin(1946), who 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 does not have a clear confinement to the phases of development of the host plant.
Much attention was paid to the immunity, mainly of agricultural plants, by N.I. Vavilov. The works of foreign scientists I.Erikson (Sweden), E.Stackman (USA) also belong to this period.
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.
Immunity is the immunity of the body to an infectious disease upon contact with its pathogen and the presence of the conditions necessary for infection.
Particular manifestations of immunity are stability (resistance) and endurance. Sustainability
It consists in the fact that plants of a variety (sometimes a species) are not affected by a disease or pests, or are affected less intensively than other varieties (or species). Endurance
called the ability of diseased or damaged plants to maintain their productivity (the quantity and quality of the crop).
Plants can have absolute immunity, which is explained by the inability of the pathogen to penetrate into the plant and develop in it even under the most favorable external conditions for this. For example, coniferous plants are not affected by powdery mildew, and deciduous plants are not affected by shute. In addition to absolute immunity, plants may have relative resistance to other diseases, which depends on the individual properties of the plant and its anatomical-morphological or physiological-biochemical characteristics.
Distinguish between innate (natural) and acquired (artificial) immunity. innate immunity
- this is a hereditary immunity to the disease, formed as a result of directed selection or long-term joint evolution (phylogenesis) of the host plant and the pathogen. acquired immunity
- this is resistance to a disease acquired by a plant in the process of its individual development (ontogenesis) under the influence of certain external factors or as a result of the transfer of this disease. Acquired immunity is not inherited.
Innate immunity can be passive or active. Under passive immunity
understand resistance to a disease, which is provided by properties that appear in plants regardless of the threat of infection, i.e. these properties are not defensive reactions of a plant to a pathogen attack. Passive immunity is associated with the features of the shape and anatomical structure of plants (the shape of the crown, the structure of the stomata, the presence of pubescence, cuticle or wax coating) or with their functional, physiological and biochemical characteristics (the content in the cell sap of compounds toxic to the pathogen, or the absence of compounds necessary for it). nutrition of substances, release of phytoncides).
active immunity
- this is resistance to a disease, which is provided by the properties of plants that appear in them only in the event of a pathogen attack, i.e. in the form of defensive reactions of the host plant. A striking example of an anti-infective defense reaction is the hypersensitivity reaction, which consists in the rapid death of resistant plant cells around the site of pathogen introduction. A kind of protective barrier is formed, the pathogen is localized, deprived of nutrition and dies. In response to infection, the plant can also release special volatile substances - phytoalexins, which have an antibiotic effect, delaying the development of pathogens or suppressing the synthesis of enzymes and toxins by them. There is also a number of antitoxic protective reactions aimed at neutralizing enzymes, toxins and other harmful waste products of pathogens (restructuring of the oxidative system, etc.).
There are such concepts as vertical and horizontal stability. The vertical one is understood as the high resistance of a plant (variety) only to certain races of a given pathogen, and the horizontal one is a certain degree of resistance to all races of a given pathogen.
The resistance of plants to diseases depends on the age of the plant itself, the physiological state of its organs. For example, seedlings can only lodging at an early age and then become resistant to lodging. Powdery mildew affects only young leaves of plants, and old ones, covered with a thicker cuticle, are not affected or are affected to a lesser extent.
Environmental factors also significantly affect the resistance and hardiness of plants. For example, dry weather during the summer reduces resistance to powdery mildew, and mineral fertilizers make plants more resistant to many diseases.
