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With the continuous increase of plant species, plant cultivation methods continue to diversify, and plant diseases become more and more serious. However, there are many drawbacks to the traditional methods of chemical control. For example: The large-scale use of chemical pesticides causes serious environmental pollution and pesticide residues in agricultural products. It is also becoming more and more serious, the drug resistance of the bacteria is getting faster and faster, and a series of harmful effects on people's lives. In today's low-carbon economy, eco-friendly and conservation-oriented society, seeking new technologies that can both protect human life and increase production are well adapted to the development of today's society. The most widely used plant disease detection instrument is currently used to detect plant diseases. The author mainly introduced the use of microorganisms to prevent plant diseases. This control method utilizes biological diversity to achieve sustainable control of pests and pollution-free treatment, in line with today’s society. Development and requirements have broad application prospects.
1 The concept of microbial control 1.1 Biological control Biological control is the use of a biological or its products against another biological method, divided into insecticide, bacteria treatment and bacteria treatment three categories. It takes advantage of the interrelationships between biological species to inhibit one or another type of organism or its product against another or another type of organism. There are many methods for biological control, and microbial control is one of them.
1.2 Microorganism control Microorganism prevention mainly uses beneficial microorganisms to inhibit the survival and activity of certain pathogens through competition among organisms, antibiotic effects, parasitic effects, bacteriolysis and induced resistance. That is, by using the ecological phenomena and certain biological characteristics that are interdependent and mutually restricted among various organisms in the ecosystem, one or the other type of organism or its product inhibits the other or the other type of organism. In short: Treating pests with bacteria and treating them with bacteria; Their advantages are rich resources, strong selectivity, no residue, no pollution, low cost, combined prevention and treatment, increased production and income, maintaining ecological balance and long-term effect. .
Therefore, the development of microbial pesticides has broad application prospects. The term “microbial pesticides†refers to the generic term for microorganisms and their metabolites that are used to prevent pests or regulate crop growth in crops. The production and use of microbial pesticides are an important means of microbial control.
2 Microbiological Control Mechanisms There are many mechanisms for microbial control of plant diseases. The following are the main ones:
2.1 Competition Competition Microbial competition mainly includes nutrition competition and site competition. The competition between nutrition and space sites refers to the phenomenon of competition for space, nutrition, oxygen and the like between two or more microorganisms existing in the same microbiological environment. However, in the biological control of plant diseases, the most important thing is the competition of ecological sites. Because only those sites on the plant that are likely to be infested by pathogens can be quickly occupied, the competition of pathogens in oxygen, moisture and nutrients can be effectively performed in these places, and the role of controlling plant diseases can then be achieved.
2.2 Antibiotics The antibiotic effect means that the antagonistic microorganisms can inhibit the growth and metabolism of pathogenic microorganisms by producing metabolites at low concentrations, thereby affecting the survival and activity of the pathogenic microorganisms, that is, the two microorganisms living together. One produced substance has a toxic effect on the other, that is, it becomes resistant to life. One of these microorganisms is often able to produce antibiotics. In nature, there are many phenomena of antibiotics. Any combination of four kinds of microorganisms, such as bacteria, fungi, algae and protozoa, can produce antagonistic substances that have inhibitory effects on themselves or other microorganisms. These antagonists include: antibiotics, protein antibacterial substances and volatile antibacterial substances, lysozyme or protease. Antibacterial effects such as ammonia, organic acids, catalase and other by-products in the initial metabolic pathways and other secondary metabolites.
2.3 Parasitic effects The microbial infestation takes place between antagonistic microorganisms and pathogenic bacteria. If plant pathogens provide nutrition to antagonistic microorganisms, the growth of pathogenic bacteria will be inhibited. Antagonistic microbial "organs" can be simple appressorium cells or mycelial openings. Parasitic bacteria on the mycelium can inhibit its activity, parasitic on the sclerotia can effectively reduce the number of infections. Parasitic bacteria recognize parasites by chemotaxis and agglutination of specific lectins, and then entangle them on the hyphae of pathogenic bacteria or invade hyphae to cause death of mycelium, thereby protecting plants from pathogens.
2.4 bacteriolysis bacteriolysis refers to the antagonism of secondary metabolites produced by microorganisms to dissolve the cell walls of the mycelium or spores of pathogenic bacteria, resulting in perforation of cell walls, malformation, rupture of hyphae, loss of vitality due to dissolution of protoplasm, and loss of vigor, and at the same time spore malformation. Spore germination has inhibitory effects. If the fungal cell wall dissolves or the cell wall is degraded, it is generally believed that this antagonistic microbe has produced the corresponding cell wall degrading enzyme (even though it may also produce antibiotics). A lot of intensive research has been conducted and it has been confirmed that cell wall degrading enzymes in the rhizosphere exist and are active.
2.5 Induced resistance In 1933, Chester reported for the first time that induced plant immunity, induction of systemic resistance or systemic acquired resistance, as a new mechanism to protect plants has gradually attracted people's attention. Inducing plant-induced resistance means that antagonistic microorganisms not only inhibit plant pathogens, but also induce the plant's own disease resistance mechanism to enhance the plant's resistance to diseases. Antagonistic microorganisms induce physiological and biochemical reactions in plants that are beneficial to plant disease resistance and are important mechanisms for antagonizing microbial disease prevention.
3 Types of Biocontrol Microorganisms Microorganisms used for biological control mainly include many biological populations such as fungi, bacteria, actinomycetes and yeasts, but commonly used biocontrol microorganisms used in plant fungal diseases include yeasts, bacteria, and actinomycetes. And mold.
3.1 Fungal Biocontrol fungi have been reported as saprophytic fungi, parasitic fungi, and low pathogenic strains of plant pathogens. There are mainly the following:
3.1.1 Trichoderma Currently, Trichoderma is the most widely studied and applied biocontrol fungus. It is widely found on the surface of soil and can be isolated from the surface of plant diseases, seeds, and bulbs. It is mainly used for the control of soil Fusarium diseases. As an abundant antagonistic microorganism, Trichoderma has an extremely important role in the biological control of plant diseases. The antagonism of Trichoderma is broad-spectrum. According to the data, it has antagonistic effect on at least 12 pathogenic fungi of 12 genera. Trichoderma has parasitic or antagonistic effects on many plant pathogens such as Trichoderma harzianum, Trichoderma viridis, Hook-like Trichoderma spp., Trichoderma longibrachiatum, Trichoderma koningii, and newly classified as Gliocladium sp. Tian Liansheng and others used the culture of Trichoderma spp. 5 to control strawberry gray mold. The control effect was comparable to that of commonly used chemical pesticide carbendazim, and its control efficacy was over 80%. Zhao Guoqi and others treated watermelon seedlings with Trichoderma viride can effectively enhance the growth of melon seedlings, promote root growth, and inhibit the growth of Fusarium oxysporum f. Tang Jiabin and other studies have shown that the strains of Trichoderma viride have a high antibacterial rate against Rhizoctonia. Song Xiaoyu et al. found that Trichoderma strain SMF5 had a strong inhibitory effect on Verticillium dahliae. Li Qi and other studies have shown that Trichoderma koningii, Trichoderma harzianum, Trichoderma koningii, and viscomycetes have strong inhibitory effects on Fusarium oxysporum f. sp., Lettuce sclerotiorum and tomato bacterial wilt.
3.1.2 Chaetophyte Chaetomium is usually found in soils and organic fertilizers, such as plant residues, herbivores, and feces of omnivores and birds. It can effectively degrade cellulose and organic matter, and other microorganisms in the soil. Antagonism occurs. Therefore, Chaetomium has become a biological control agent for plant pathogenic bacteria and has been widely used.
As early as in 1954, Martin and Moore discovered that the seeds of various varieties of oats in Brazil were infected by coccidia and snail hulls, and would be resistant to the action of cryptosporidium toxigenicus. There are more than 300 species of Chaetomium that can prevent blight of grain seedlings, cane damping-off, reduce the incidence of tomato blight, apple spot disease, Rhizoctonia solani, Phomopsis, Brassica There are certain inhibitory effects on genus, botrytis, genus and genus of Alternaria.
3.1.3 Paecilomyces lilacinus and Verticillium sp. Verticillium paecilomyces and Verticillium verticilis are mainly effective in controlling phytopathogenic nematodes. Liu Xingzhong et al. used a culture medium of P. lilacinus to apply soil to the soybean cyst nematode for 2 to 3 years, resulting in a large number of empty cysts. Lin Maosong et al. controlled the egg parasitism rate of the southern root-knot nematode with verticillial spores to 90.8%.
3.1.4 Mycorrhizal Fungal Mycorrhiza fungi mainly promote the absorption of nitrogen, phosphorus and other nutrients by plants, especially under adverse conditions, which can improve the disease resistance of plants. The inoculation of mycorrhizal fungi showed that the photosynthetic rate of the inoculated plants increased significantly, the dry matter quality of the plants increased, or the number of microorganisms in the soil increased. The micro-ecological environment of the root zone soil was improved and accumulated for the growth of the next generation crops. Nutrients.
3.2 Bacteria Among the biocontrol bacteria, Bacillus is the most studied, and there are also non-toxic mutants of Agrobacterium, Pseudomonas fluorescens and certain pathogenic bacteria.
3.2.1 Bacillus Bacillus has a wide range of bacteriostasis, including root diseases, branch diseases, leaf disease, and disease consequences. Such as cotton fusarium wilt, verticillium wilt, blight, wheat scab, tomato bacterial wilt, apple red rot and other soil-borne and above-ground diseases. Because of its endophytic spores, strong stress resistance, simple nutrient requirements, rapid propagation and easy colonization in the plant rhizosphere, it is widely used in the biological control of plant diseases. Bacillus species currently used in biological control include Bacillus subtilis, Bacillus cereus, Bacillus megaterium, Bacillus polymyxa, and Bacillus pumilus. The use of Bacillus subtilis to control diseases caused by Rhizoctonia, Pythium, Fusarium and other diseases has achieved good results abroad.
3.2.2 Pseudomonas Pseudomonas bacteria are abundantly present in the roots of plants. Many strains have the effect of inhibiting diseases and promoting growth of plants. Among them, Pseudomonas fluorescens is the most widely reported and it is used in the prevention and control of soil-borne diseases. A class of biocontrol bacteria with good effects has varying degrees of influence on common soil-borne diseases such as potato defoliation, wilt disease, soft rot, and wheat rot in potatoes, cucumbers, beets, peas, carrots, and wheat. Control effect, and the bacteria attached to the rhizosphere of the plant, both the antagonistic effect on the pathogen and the direct or indirect effects of the main microorganisms in the rhizosphere.
3.2.3 Radiobacter sp. In the 1970s, Kerr et al. (Australia) isolated soil from the soil and obtained the radiobacilli, which can produce bacteriocin-containing bacteriocin Agrocin 84. The biocidal agent or the bacteria was used in production. The metabolite Agroein 84 can effectively control root cancer caused by Agrobacterium tumefaciens, such as peaches, cherries, grapes, and roses. In recent years, China has isolated spores of soil bacteria, HLB2, E26, and M115, which have significant effects on root cancer, and have been tested in the field for 85% to 100%.
3.3 Actinomycetes Actinomycetes used in the biological control of plant diseases are mainly Streptomyces and its related groups. At present, many molding agents are widely used in agriculture, industry and medicine. For example, Jingxiangmycin, streptomycin for agricultural use, and polyfomimycin have been widely used in China, and have achieved good economic, ecological and social benefits. However, because Jinggangmycin only has bacteriostatic effect on pathogens and no bactericidal effect, it cannot eradicate sheath blight. Therefore, we have successively developed dioscin, endotherapy drugs, 768, S-921, and Nongkang 120, which have been widely used in recent years.
Among them, agricultural streptomycin can effectively control various plant bacterial diseases such as poplar rot, crucifer soft rot, cucumber scab, pepper blight, cotton wilt, tomato early blight, gray mold and tomato canker. .
3.4 Yeast Yeast is commonly used in biological control of fruits and vegetables. Its greatest advantage lies in its ability to survive on relatively dry fruits and vegetables. It can quickly use nutrients for reproduction and is less affected by insecticides; it does not produce antibiotics and can prevent germs from growing. Antibiotics produce resistance and reduce biocontrol effects.
In recent years, a large number of yeast strains have been screened, such as Kloeckera apiculata and Candida tenuis, which control B. cinerea, and Candida famata, which controls citrus green mold. They also control apple, pear, strawberry, kiwifruit, grape botrytis, and blue. Rhodotorula glutinis and Cryptococcus laurentii for various diseases such as mildew, soft rot and melasma; Pesudomonassyingae for controlling brown rot of peach, etc.
4 Problems in the use of microorganisms in the prevention and control of plant diseases and their countermeasures 4.1 Problems in the prevention and control of plant diseases by biocontrol microorganisms 4.1.1 Poor colonization of biocontrol microorganisms under natural conditions in the field Because most biocontrol microorganisms are under test conditions Under the screening and identification, the experimental conditions differ greatly from the natural conditions in the field. Therefore, these biocontrol microorganisms often have weak colonization after application in the field, and do not form enough biological groups to reduce the control effect and affect the control effect.
4.1.2 Poor antibiotic resistance of biocontrol microorganisms Biocontrol microorganisms screened under laboratory conditions are rapidly declining in the field due to residual pesticides or pesticides, affecting their biocontrol effect.
4.1.3 Strains Stability Problems At present, biocontrol microbial preparations are mostly live bacteria preparations, which are often affected by external factors such as temperature, humidity, and soil pH during field application. Therefore, the control effect is also unstable.
4.2 Solutions to Problems in the Prevention and Control of Biocontrol Microorganisms in the Prevention and Treatment of Plant Diseases Solutions to the problems in the prevention and control of microbes in the prevention and control of plant diseases include:
1) Add to the soil substances that stimulate biocontrol organisms to produce antibiotics or induce biocontrol organisms, such as chitosan;
2) Perform strain improvement. Mutation breeding, transformation techniques and protoplast fusion were used for strain improvement.
3) Breeding resistant transgenic plants, after multiple generations of selection, to obtain stable disease-resistant plants;
4) Research and development of new biological pesticides; Application of the resistance genes of the strain to pesticide production to produce a new generation of biological pesticides.
5 Prospects for the use of micro-organisms to control plant diseases The application of bio-control microorganisms for more than 20 years has proven that bio-control microbial pesticides do not pollute the environment, and they are slow to develop resistance to humans and animals, and the resistance to bacteria is considerable. The economic benefits are considerable. With the continuous improvement of people’s awareness of the ecological environment, it is imperative to research and develop more safer microbial pesticides.
At present, although China's microbiological control is already in the advanced ranks in the world, the application of quarantine toolboxes has also been widely used, but basic research is lacking, and in-depth theoretical research is often restricted by conditions, especially in more active fields. Fewer, compared with foreign countries, there is a large gap in the diversity of technical means for research and application of biocontrol microorganisms. Biocontrol microorganisms are sensitive to the response of pesticides, their types are relatively single, their antimicrobial spectrum is relatively narrow, their colonization on plants is difficult, their biological control effects are unstable, and the cloning of beneficial genes is limited to some insect-resistant genes, antagonism and promotion. The combination of students is difficult, the microbial control measures are not perfect, and the available antagonistic microbial resources are too few, and further exploration and application are needed.
1 The concept of microbial control 1.1 Biological control Biological control is the use of a biological or its products against another biological method, divided into insecticide, bacteria treatment and bacteria treatment three categories. It takes advantage of the interrelationships between biological species to inhibit one or another type of organism or its product against another or another type of organism. There are many methods for biological control, and microbial control is one of them.
1.2 Microorganism control Microorganism prevention mainly uses beneficial microorganisms to inhibit the survival and activity of certain pathogens through competition among organisms, antibiotic effects, parasitic effects, bacteriolysis and induced resistance. That is, by using the ecological phenomena and certain biological characteristics that are interdependent and mutually restricted among various organisms in the ecosystem, one or the other type of organism or its product inhibits the other or the other type of organism. In short: Treating pests with bacteria and treating them with bacteria; Their advantages are rich resources, strong selectivity, no residue, no pollution, low cost, combined prevention and treatment, increased production and income, maintaining ecological balance and long-term effect. .
Therefore, the development of microbial pesticides has broad application prospects. The term “microbial pesticides†refers to the generic term for microorganisms and their metabolites that are used to prevent pests or regulate crop growth in crops. The production and use of microbial pesticides are an important means of microbial control.
2 Microbiological Control Mechanisms There are many mechanisms for microbial control of plant diseases. The following are the main ones:
2.1 Competition Competition Microbial competition mainly includes nutrition competition and site competition. The competition between nutrition and space sites refers to the phenomenon of competition for space, nutrition, oxygen and the like between two or more microorganisms existing in the same microbiological environment. However, in the biological control of plant diseases, the most important thing is the competition of ecological sites. Because only those sites on the plant that are likely to be infested by pathogens can be quickly occupied, the competition of pathogens in oxygen, moisture and nutrients can be effectively performed in these places, and the role of controlling plant diseases can then be achieved.
2.2 Antibiotics The antibiotic effect means that the antagonistic microorganisms can inhibit the growth and metabolism of pathogenic microorganisms by producing metabolites at low concentrations, thereby affecting the survival and activity of the pathogenic microorganisms, that is, the two microorganisms living together. One produced substance has a toxic effect on the other, that is, it becomes resistant to life. One of these microorganisms is often able to produce antibiotics. In nature, there are many phenomena of antibiotics. Any combination of four kinds of microorganisms, such as bacteria, fungi, algae and protozoa, can produce antagonistic substances that have inhibitory effects on themselves or other microorganisms. These antagonists include: antibiotics, protein antibacterial substances and volatile antibacterial substances, lysozyme or protease. Antibacterial effects such as ammonia, organic acids, catalase and other by-products in the initial metabolic pathways and other secondary metabolites.
2.3 Parasitic effects The microbial infestation takes place between antagonistic microorganisms and pathogenic bacteria. If plant pathogens provide nutrition to antagonistic microorganisms, the growth of pathogenic bacteria will be inhibited. Antagonistic microbial "organs" can be simple appressorium cells or mycelial openings. Parasitic bacteria on the mycelium can inhibit its activity, parasitic on the sclerotia can effectively reduce the number of infections. Parasitic bacteria recognize parasites by chemotaxis and agglutination of specific lectins, and then entangle them on the hyphae of pathogenic bacteria or invade hyphae to cause death of mycelium, thereby protecting plants from pathogens.
2.4 bacteriolysis bacteriolysis refers to the antagonism of secondary metabolites produced by microorganisms to dissolve the cell walls of the mycelium or spores of pathogenic bacteria, resulting in perforation of cell walls, malformation, rupture of hyphae, loss of vitality due to dissolution of protoplasm, and loss of vigor, and at the same time spore malformation. Spore germination has inhibitory effects. If the fungal cell wall dissolves or the cell wall is degraded, it is generally believed that this antagonistic microbe has produced the corresponding cell wall degrading enzyme (even though it may also produce antibiotics). A lot of intensive research has been conducted and it has been confirmed that cell wall degrading enzymes in the rhizosphere exist and are active.
2.5 Induced resistance In 1933, Chester reported for the first time that induced plant immunity, induction of systemic resistance or systemic acquired resistance, as a new mechanism to protect plants has gradually attracted people's attention. Inducing plant-induced resistance means that antagonistic microorganisms not only inhibit plant pathogens, but also induce the plant's own disease resistance mechanism to enhance the plant's resistance to diseases. Antagonistic microorganisms induce physiological and biochemical reactions in plants that are beneficial to plant disease resistance and are important mechanisms for antagonizing microbial disease prevention.
3 Types of Biocontrol Microorganisms Microorganisms used for biological control mainly include many biological populations such as fungi, bacteria, actinomycetes and yeasts, but commonly used biocontrol microorganisms used in plant fungal diseases include yeasts, bacteria, and actinomycetes. And mold.
3.1 Fungal Biocontrol fungi have been reported as saprophytic fungi, parasitic fungi, and low pathogenic strains of plant pathogens. There are mainly the following:
3.1.1 Trichoderma Currently, Trichoderma is the most widely studied and applied biocontrol fungus. It is widely found on the surface of soil and can be isolated from the surface of plant diseases, seeds, and bulbs. It is mainly used for the control of soil Fusarium diseases. As an abundant antagonistic microorganism, Trichoderma has an extremely important role in the biological control of plant diseases. The antagonism of Trichoderma is broad-spectrum. According to the data, it has antagonistic effect on at least 12 pathogenic fungi of 12 genera. Trichoderma has parasitic or antagonistic effects on many plant pathogens such as Trichoderma harzianum, Trichoderma viridis, Hook-like Trichoderma spp., Trichoderma longibrachiatum, Trichoderma koningii, and newly classified as Gliocladium sp. Tian Liansheng and others used the culture of Trichoderma spp. 5 to control strawberry gray mold. The control effect was comparable to that of commonly used chemical pesticide carbendazim, and its control efficacy was over 80%. Zhao Guoqi and others treated watermelon seedlings with Trichoderma viride can effectively enhance the growth of melon seedlings, promote root growth, and inhibit the growth of Fusarium oxysporum f. Tang Jiabin and other studies have shown that the strains of Trichoderma viride have a high antibacterial rate against Rhizoctonia. Song Xiaoyu et al. found that Trichoderma strain SMF5 had a strong inhibitory effect on Verticillium dahliae. Li Qi and other studies have shown that Trichoderma koningii, Trichoderma harzianum, Trichoderma koningii, and viscomycetes have strong inhibitory effects on Fusarium oxysporum f. sp., Lettuce sclerotiorum and tomato bacterial wilt.
3.1.2 Chaetophyte Chaetomium is usually found in soils and organic fertilizers, such as plant residues, herbivores, and feces of omnivores and birds. It can effectively degrade cellulose and organic matter, and other microorganisms in the soil. Antagonism occurs. Therefore, Chaetomium has become a biological control agent for plant pathogenic bacteria and has been widely used.
As early as in 1954, Martin and Moore discovered that the seeds of various varieties of oats in Brazil were infected by coccidia and snail hulls, and would be resistant to the action of cryptosporidium toxigenicus. There are more than 300 species of Chaetomium that can prevent blight of grain seedlings, cane damping-off, reduce the incidence of tomato blight, apple spot disease, Rhizoctonia solani, Phomopsis, Brassica There are certain inhibitory effects on genus, botrytis, genus and genus of Alternaria.
3.1.3 Paecilomyces lilacinus and Verticillium sp. Verticillium paecilomyces and Verticillium verticilis are mainly effective in controlling phytopathogenic nematodes. Liu Xingzhong et al. used a culture medium of P. lilacinus to apply soil to the soybean cyst nematode for 2 to 3 years, resulting in a large number of empty cysts. Lin Maosong et al. controlled the egg parasitism rate of the southern root-knot nematode with verticillial spores to 90.8%.
3.1.4 Mycorrhizal Fungal Mycorrhiza fungi mainly promote the absorption of nitrogen, phosphorus and other nutrients by plants, especially under adverse conditions, which can improve the disease resistance of plants. The inoculation of mycorrhizal fungi showed that the photosynthetic rate of the inoculated plants increased significantly, the dry matter quality of the plants increased, or the number of microorganisms in the soil increased. The micro-ecological environment of the root zone soil was improved and accumulated for the growth of the next generation crops. Nutrients.
3.2 Bacteria Among the biocontrol bacteria, Bacillus is the most studied, and there are also non-toxic mutants of Agrobacterium, Pseudomonas fluorescens and certain pathogenic bacteria.
3.2.1 Bacillus Bacillus has a wide range of bacteriostasis, including root diseases, branch diseases, leaf disease, and disease consequences. Such as cotton fusarium wilt, verticillium wilt, blight, wheat scab, tomato bacterial wilt, apple red rot and other soil-borne and above-ground diseases. Because of its endophytic spores, strong stress resistance, simple nutrient requirements, rapid propagation and easy colonization in the plant rhizosphere, it is widely used in the biological control of plant diseases. Bacillus species currently used in biological control include Bacillus subtilis, Bacillus cereus, Bacillus megaterium, Bacillus polymyxa, and Bacillus pumilus. The use of Bacillus subtilis to control diseases caused by Rhizoctonia, Pythium, Fusarium and other diseases has achieved good results abroad.
3.2.2 Pseudomonas Pseudomonas bacteria are abundantly present in the roots of plants. Many strains have the effect of inhibiting diseases and promoting growth of plants. Among them, Pseudomonas fluorescens is the most widely reported and it is used in the prevention and control of soil-borne diseases. A class of biocontrol bacteria with good effects has varying degrees of influence on common soil-borne diseases such as potato defoliation, wilt disease, soft rot, and wheat rot in potatoes, cucumbers, beets, peas, carrots, and wheat. Control effect, and the bacteria attached to the rhizosphere of the plant, both the antagonistic effect on the pathogen and the direct or indirect effects of the main microorganisms in the rhizosphere.
3.2.3 Radiobacter sp. In the 1970s, Kerr et al. (Australia) isolated soil from the soil and obtained the radiobacilli, which can produce bacteriocin-containing bacteriocin Agrocin 84. The biocidal agent or the bacteria was used in production. The metabolite Agroein 84 can effectively control root cancer caused by Agrobacterium tumefaciens, such as peaches, cherries, grapes, and roses. In recent years, China has isolated spores of soil bacteria, HLB2, E26, and M115, which have significant effects on root cancer, and have been tested in the field for 85% to 100%.
3.3 Actinomycetes Actinomycetes used in the biological control of plant diseases are mainly Streptomyces and its related groups. At present, many molding agents are widely used in agriculture, industry and medicine. For example, Jingxiangmycin, streptomycin for agricultural use, and polyfomimycin have been widely used in China, and have achieved good economic, ecological and social benefits. However, because Jinggangmycin only has bacteriostatic effect on pathogens and no bactericidal effect, it cannot eradicate sheath blight. Therefore, we have successively developed dioscin, endotherapy drugs, 768, S-921, and Nongkang 120, which have been widely used in recent years.
Among them, agricultural streptomycin can effectively control various plant bacterial diseases such as poplar rot, crucifer soft rot, cucumber scab, pepper blight, cotton wilt, tomato early blight, gray mold and tomato canker. .
3.4 Yeast Yeast is commonly used in biological control of fruits and vegetables. Its greatest advantage lies in its ability to survive on relatively dry fruits and vegetables. It can quickly use nutrients for reproduction and is less affected by insecticides; it does not produce antibiotics and can prevent germs from growing. Antibiotics produce resistance and reduce biocontrol effects.
In recent years, a large number of yeast strains have been screened, such as Kloeckera apiculata and Candida tenuis, which control B. cinerea, and Candida famata, which controls citrus green mold. They also control apple, pear, strawberry, kiwifruit, grape botrytis, and blue. Rhodotorula glutinis and Cryptococcus laurentii for various diseases such as mildew, soft rot and melasma; Pesudomonassyingae for controlling brown rot of peach, etc.
4 Problems in the use of microorganisms in the prevention and control of plant diseases and their countermeasures 4.1 Problems in the prevention and control of plant diseases by biocontrol microorganisms 4.1.1 Poor colonization of biocontrol microorganisms under natural conditions in the field Because most biocontrol microorganisms are under test conditions Under the screening and identification, the experimental conditions differ greatly from the natural conditions in the field. Therefore, these biocontrol microorganisms often have weak colonization after application in the field, and do not form enough biological groups to reduce the control effect and affect the control effect.
4.1.2 Poor antibiotic resistance of biocontrol microorganisms Biocontrol microorganisms screened under laboratory conditions are rapidly declining in the field due to residual pesticides or pesticides, affecting their biocontrol effect.
4.1.3 Strains Stability Problems At present, biocontrol microbial preparations are mostly live bacteria preparations, which are often affected by external factors such as temperature, humidity, and soil pH during field application. Therefore, the control effect is also unstable.
4.2 Solutions to Problems in the Prevention and Control of Biocontrol Microorganisms in the Prevention and Treatment of Plant Diseases Solutions to the problems in the prevention and control of microbes in the prevention and control of plant diseases include:
1) Add to the soil substances that stimulate biocontrol organisms to produce antibiotics or induce biocontrol organisms, such as chitosan;
2) Perform strain improvement. Mutation breeding, transformation techniques and protoplast fusion were used for strain improvement.
3) Breeding resistant transgenic plants, after multiple generations of selection, to obtain stable disease-resistant plants;
4) Research and development of new biological pesticides; Application of the resistance genes of the strain to pesticide production to produce a new generation of biological pesticides.
5 Prospects for the use of micro-organisms to control plant diseases The application of bio-control microorganisms for more than 20 years has proven that bio-control microbial pesticides do not pollute the environment, and they are slow to develop resistance to humans and animals, and the resistance to bacteria is considerable. The economic benefits are considerable. With the continuous improvement of people’s awareness of the ecological environment, it is imperative to research and develop more safer microbial pesticides.
At present, although China's microbiological control is already in the advanced ranks in the world, the application of quarantine toolboxes has also been widely used, but basic research is lacking, and in-depth theoretical research is often restricted by conditions, especially in more active fields. Fewer, compared with foreign countries, there is a large gap in the diversity of technical means for research and application of biocontrol microorganisms. Biocontrol microorganisms are sensitive to the response of pesticides, their types are relatively single, their antimicrobial spectrum is relatively narrow, their colonization on plants is difficult, their biological control effects are unstable, and the cloning of beneficial genes is limited to some insect-resistant genes, antagonism and promotion. The combination of students is difficult, the microbial control measures are not perfect, and the available antagonistic microbial resources are too few, and further exploration and application are needed.
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