Related diseases - are diseases that are aggravated by external factors, both biotic (the simultaneous presence of other pathogens or pests), and abiotic (the living conditions of the plant and parasite and others).
Joint development in plants of various pathogensBiotrophic parasites, as it was said, secrete biologically active substances - suppressors (effectors ), that suppress the immunity of living cells, making them defenseless for the parasite. This is often used necrotrophs, developing after the biotrophs. For example, a disease called rust fusariosis is well known to flax growers. Fungi of the genus Fusanum - necrotrophic parasites that are capable of develop in the vessels, causing infectious wilt or wilt, but rarely occur as parasites of the leaves of flax. Rusty mushroom Melampsora lini - biotroph, affecting the leaves of flax. Around the pustules of rust on leaves, fusariosis often develops, its causative agent is introduced into tissues, the protective properties of which rust fungus weakened by its secretions. Another example is the joint development of the causative agent of powdery mildew Blumena graminis and fusariases on wheat leaves (in humid weather up to 80% of leaf areas affected by powdery mildew have fusarium spots in the center) . This joint infection of the leaves is especially dangerous for plants. Potato tubers infected with Phytophthora inestans, under normal storage rarely degenerate directly from late blight, but, being a biotrophic parasite, the phytophthora suppresses the protective reactions of the tuber, which becomes an easy prey for necrotrophic bacteria and fungi. Mixed bacterial-fungal decay often causes the death of the entire batch of stored potatoes, but they are especially dangerous for tubers that are infected with late blight in the field.
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Mixed viral infections are very dangerous for plants. Some viruses are found only in plants infected with other, specific viruses. For example, C virus is found only in leaves containing particles of the virus. The reason for this was the inability of the virus C to be transmitted by aphids alone. Capsids of both viruses can not be adsorbed on the inner surface of the aphid stiletto, but the genome of the virus controls the synthesis of the helper protein, which has two domains (sections of the protein molecule): one domain binds to the viral capsid protein, the other protein of the inner surface of the stylet. This helper protein also uses the virus C for its distribution.
Such mechanisms of interaction of viruses in a plant often increase the harmfulness of mixed infections. For example, TMV very weakly multiplies in the leaves of barley and does not cause any symptoms of the disease. However, in the presence of the barley mosaic virus of the barley , the multiplication of TMV and the decrease in the yield from it are intensified. Cucumber mosaic virus and mosaic virus & quot; black eye & quot; reduce the yield of cowpea by 14% and 2.5%, respectively. When mixed with these viruses, a symptom of dwarfism occurs, and the yield is reduced by 85%. Significantly, the pathogenicity and rate of reproduction in the cells of the potato KVK in the presence of YBK are significantly increased. Most strains of IVC cause mosaic on leaves, and YBK - mosaic and necrosis of veins. When joint infection occurs a serious disease - a wrinkled mosaic, the symptoms of which are wrinkling, vesicular blisters and necrosis on the leaves, a lag in growth, a drop in the yield of tubers. The concentration of particles of the first virus in the presence of the second increases three to five times compared to single infection.
Diseases of Post-harvest Products
Post-harvest rot is one of the most harmful groups of diseases for the following reasons:
The stored products, as a rule, have a high water content in the cells (juicy fruits, bulbs, etc.);
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- the organs separated from the plant have a lower resistance compared to those on the plant;
- the loss of immunity in the process of fruit ripening was developed in the course of evolution as a necessary means for releasing seeds. For example, the marshmallow Glomerella cingulata , the causative agent of the bitter rot of apples, infects fruits even in trees. But its development in apple tissue is inhibited by the benzoic acid formed in the fruit, which has not fungicidal (killing mushrooms), but fungistatic (inhibitory growth) action. Therefore, the mycelium remains alive, but does not develop in the apple and does not harm it. The toxic effect of benzoic acid on the fungus manifests itself only in acidic medium, as the pH level increases, it disappears. While the apples do not ripen, they remain very acidic, but after ripening their acidity drops sharply (it is known that after the New Year apples become fresh, like potatoes). With a weakening of the toxic effect, the fungus immediately begins to develop, causing rotting of the pulp, which facilitates the release of seeds. The parasite and the host seem to have entered into a contractual agreement: I will keep you for the time being on a hungry diet, but then let me completely eat myself. It turns out that the human strategy (to keep apples healthy as long as possible) conflicts with the plant's strategy (using putrefactive microorganisms to free seeds for germination).
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