The harm of plant viruses to the host is known as "plant cancer," and it is very difficult to control. After the virus infects the host, it not only competes with the host for the nutrients necessary for growth, but also destroys the nutrient transport of the plant, changes some metabolic balance of the host plant, inhibits the photosynthesis of the plant, and causes the plant to grow in a difficult and malformed state. Symptoms such as yellowing, severely caused the death of host plants. In order to effectively control plant viral diseases, various measures have been adopted, including rotation, seed detoxification, cross-protection of attenuated strains between viruses, selection of disease-resistant varieties, control of virus-mediated mediators, and use of chemical pesticides. In recent years, there have been new advances in the research of disease resistance of transgenic plants. However, these measures still cannot effectively overcome the harm of viruses, and the use of chemical pesticides has caused great harm to the environment. Under the premise of vigorously promoting green food and environmental protection, the comprehensive prevention and control of plant diseases and the use of chemical pesticides have been reduced. Become one of the key contents of plant protection workers' work. In order to develop effective antiviral agents that control the virus without causing environmental pollution, researchers continue to search for and screen natural biologically-derived antiviral substances. At present, there are many kinds of natural antiviral active substances reported at home and abroad, and some have formed products that play an important role in agricultural production. First, change the farming system, strengthen cultivation and management, and prevent the occurrence and epidemic of plant virus disease. Rotation and interplanting use different crops and varieties of crop rotation and interplanting, which can reduce the accumulation of pathogens and prevent the occurrence of serious diseases. The host of plant viruses is more abundant and wild and cultivated. For example, Cucumber Mosaic Virus can be used for wintering in a variety of weeds in the field. Later it is transmitted to tomatoes, green peppers, and other vegetables by aphids. The host of Chinese cabbage solitary virus (Fuqing mosaic virus) has many cruciferous weeds and vegetables. Such as cabbage, radish, etc., so eradication of weeds in the field has become one of the important measures to reduce the source of poison. At the same time, we must pay attention to the cultivation system of the cabbage field. The former can not be cabbage or radish, otherwise the disease will be heavy. We must also pay attention to cabbage not to be adjacent to cabbage and radish. 2. The choice of a suitable sowing date for the sowing period also has a great influence on the occurrence of viral diseases. If the Chinese cabbage seedling stage (six leaf stage) is susceptible to solitary disease, the disease will occur severely in the event of a migration peak of the winged plague. Therefore, it is necessary to select suitable sowing time for Chinese cabbage to avoid the peak of migration of winged dragonfly at the seedling stage without affecting the growth of Chinese cabbage. 3. Strengthening the management of nursery and seedlings at the seedling stage is very important for the prevention and control of the occurrence of viral diseases, because diseased plants on seed beds may become an important source of poisoning in the field. Therefore, every effort should be made to ensure that the seedlings do not become ill or have fewer illnesses, and measures such as spraying biological protection preparations in advance may be adopted. Aphids have a deterrent effect on silver-gray, silver-grey plastic film can also be used to drive off the aphids on the seedbed, such as the prevention and control of Chinese cabbage solitary disease can be set up on the seedbed bed silver-grey plastic membrane mesh nursery to drive away aphids. Strengthen the cultivation and management of the field, improve the ability of plants to resist viral diseases, eradicate the weeds in the field, remove the diseased plants to remove the source of the poison, and timely control pests and disease prevention, and also reduce the disease. Second, planting resistant, disease-resistant varieties using disease-resistant and resistant varieties can be cost-effectively prevent and reduce the occurrence of viral diseases. Most disease-resistant varieties can resist the virus replication and proliferation, and some vegetables can resist the transmission of mediators, such as melon, tomato, potato, sugar beet and other vegetables. Since the mites do not like these varieties, the transmission probability is greatly reduced. Third, control of virus-mediated mediators Most plant viral diseases are transmitted through mediators. Therefore, the prevention and control of drug-mediated mediators is an important measure for the prevention and control of plant viral diseases. However, viruses transmitted by mediators often have other transmission routes. For example, locusts are not persistently transmitted viruses. Aphids can be used to poison plants when they are eaten for a short period of time. Therefore, it is difficult to control mediators to transmit viruses. Methods for the prevention and control of virus-mediated mediators include the use of natural enemies, the use of biological pesticides, physical trapping and repellent measures. IV. Elimination of Virus Infection Sources The sources of infection of viruses are mainly seeds, propagation materials, wild plants that are poisoned, and cultivated plants. Virus-infected seeds are an important source of virus disease, especially the seeds of legumes, cucurbits, and asteraceae. There are several ways to avoid seed poisoning: You can use a disease-free strain to retain seed, or you can soak the seed with a 10% trisodium phosphate solution for 20 minutes, and then wash. In addition, seeds can be disinfected with heat. Poisonous propagation materials are mainly vegetatively propagated plant materials, including tuberous roots, tubers, bulbs, cuttings, scions, rootstocks, and seedlings. There are several ways to prevent the proliferation of reproductive materials: 1. The virus-free propagation material is obtained from the disease-free propagation material base. 2. Thermally detoxified, poisoned propagation material is treated with hot steam at high temperature to remove some or all of the virus. 3. Stem tip tissue culture is detoxified. Since the virus does not generally enter the growing part of the plant, the growth point is free of viruses or viruses. The 0.1--0.2mm section of the growth point can be cut off for tissue culture, and a large number of non-toxic seedlings can be supplied. V. Application of Viral Vaccines Artificial mutagenesis is used to obtain virus strains with weak pathogenicity, called attenuated vaccines. Due to the interfering effect of virus strains, the weak strains infect the plants and can interfere with the infection of virulent strains, so that they do not show signs or symptoms to reduce, so as to control the damage of the strong virus strains to plants. Such as the use of weak strain N14, etc. to control TMV caused tomato, pepper virus disease, have a better control effect. 6. Biological Pesticides Prevention and control Chemical drug control is also one of the prevention and control measures for viral diseases. However, due to the fact that chemical agents often cause harm to the plants and cause environmental pollution, their use is limited. At present, some natural antiviral biopesticides have been manufactured and should be strongly promoted for use. However, the characteristics of bio-sourced anti-virus pesticides are quite different from those of chemical pesticides. Only by understanding the characteristics of the anti-virus pesticides and mastering the correct methods of use, can we better play its role in the prevention and control of viral diseases. Biological source pesticides include plant pesticides, agricultural antibiotics and other biological control agents. According to their characteristics, they can be divided into the following types. 1. The protective film type uses skimmed milk in the United States and other places and can be used as a representative of this mechanism of action. They form a thin film on the surface of plant leaves, covering the surface of the plant, reducing the virus-feeling point, and have a certain inhibitory effect on plant viruses infected by mechanical friction and aphids. This type of pesticide must be sprayed before the plant's sensation in order to play a preventive role. Therefore, it should be started at the seedling stage and used at regular intervals. If you wait until the virus has invaded the plant, it will not work. 2. The inactivated virus acts on the virus particles, temporarily or permanently deactivating them, losing their ability to infect. For example, protein PAP extracted from pokeweed sap can be combined with TMV to reduce its invasive activity. Certain pentahydroxyflavone analogs can form stable complexes with virions, attenuate binding between viral coat protein subunits, expose RNA, and disrupt virus particle integrity, thereby reducing virus infection. This type of preparation, both protective and a certain therapeutic effect, it is best to spray before plant flu, in order to exert its maximal effect. The biological pesticide formulations belonging to this type include anti-toxic and NS83 antagonists. 3. Inhibition of virus replication and spread in host plants The replication and spread of plant viruses within the host are divided into several processes, including shelling, viral nucleic acid replication, viral protein synthesis, virus assembly, and long-distance transport within the host. The inhibition of the link can prevent the proliferation of the virus and achieve the purpose of preventing and treating viral diseases. Such antiviral preparations have a good therapeutic effect on viral diseases and can be used in the early stages of the onset of plants. However, such pesticides are currently few, and most of them are chemical synthetic pesticides. 4. Induced Resistance Some plants can produce some antiviral substances in plants after being challenged by viruses and challenged by antiviral agents. The production of a phosphorus-containing glycoprotein with antiviral activity in TMV-infected heart smoke is known as an antiviral agent that inhibits viral replication. Some inducers can induce the production of antiviral factors, such as yeast RNA injected into the heart smoke, can induce antiviral factors, play a role in inhibiting the virus. In addition, salicylic acid, oxalic acid, etc. can induce the increase of the activity of some enzymes such as peroxides in plants, thereby enhancing the ability of plants to resist viruses. 5. Plant growth regulators, regulate growth, inhibit the expression of symptoms Some antiviral agents can regulate plant growth, such as gibberellin, alizarin and other hormones have obvious curative effect on tomato, pepper, watermelon and other vegetable viruses, after the spray performance flowers Leaves and leafy plants can be restored and new leaves are fully developed. Other plant-based antiviral agents have some influence on the content of some endogenous hormones that promote plant growth after spraying. Although the virus content in the host plants does not decrease, they can suppress the symptoms of the virus by maintaining the chloroplast content in the plants. produce. In short, the large-scale use of biological pesticides can reduce the amount of chemical pesticides, thereby reducing environmental pollution, but also to maintain a good control of the disease, to achieve sustainable control of the disease. Antiviral biopesticides are derived from animals, plants or microorganisms. They have little harm to plants, have little side effects, low residues, and have no pollution to the environment. Therefore, the development and utilization of various bio-sourced pesticides should be promoted. China Agricultural Network Editor
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