Chitin is one of the most abundant natural polymer compounds on the earth, and its annual biosynthesis is estimated to be as high as10 billion tons, which is equivalent to the annual output of cellulose. Chitin belongs to linear aminopolysaccharide, and its scientific name is (1, 4) -2- acetamido -2- deoxy -β-D- glucose], and its molecular formula is (c8h13no5) n. The monomers are connected by β( 1-4) glycosidic bond, and the molecular weight is average. Chitin is the only natural polymer with positive charge in nature, and its chemical structure is very similar to cellulose widely existing in plants. If the hydroxyl group (OH) on the second carbon atom of glucose molecule of cellulose is replaced by NHCOOH 3, cellulose will become chitin. In this sense, chitin can be said to be an animal fiber. In chitin molecules, due to the interaction of internal and external hydrogen bonds, an ordered macromolecular structure is formed, and its solubility is poor, which limits its application in many aspects. Chitosan, the product of deacetylation of chitin, has greatly improved solubility due to the existence of a large amount of free ammonia in its molecular structure, and has some unique physical and chemical properties and physiological functions, and has broad application prospects in agriculture, medicine, food, cosmetics and other aspects of environmental protection. Soluble chitin (chitosan), which is widely used at home and abroad at present, can be obtained by chemical method, acid-base treatment, calcium salt and protein removal, and deacetylation with strong base under heating conditions. The molecular weight of chitosan ranges from hundreds of thousands to hundreds of thousands. Due to different preparation methods, technological conditions and requirements, the degree of deacetylation can be from 60% to over 95%. Compared with chitin, the solubility of this kind of chitosan is greatly improved, and it can be dissolved in acidic solution, but not directly in water. When chitosan is degraded into low molecular weight oligosaccharides, the product can be directly dissolved in water, which expands the application scope. A large number of research results show that chitin and its derivatives are used to maintain the agricultural ecological environment and protect people's health with their unique crop mechanism. They are environmentally friendly pesticides used to produce green food, and are important resources for pollution-free agricultural products production and sustainable agriculture.
2 Chitin application in agriculture
2. 1 Pest control agent
2. 1. 1 plant pathogenic growth inhibitor
Between plant pathogens and parasitic plants, chitosan can prevent the germination and growth of plant pathogens spores and induce pathogen infection. At the age of 25. Cotton tissue cells were soaked in 0. 1% ~ 1% chitosan solution respectively. The results showed that with the increase of chitosan concentration and deacetylation degree, its inhibitory effect was enhanced, and 1% chitosan could inhibit the growth of 90% pathogens. Spraying tobacco with 0.4% chitosan solution can reduce the spread of tobacco mottle virus within 10 days; Spraying 0. 1% chitosan can prevent leguminous plants from being infected by pathogenic bacteria, and kidney beans can reduce the harm of alfalfa mosaic virus. Soaking seeds can reduce the incidence of wheat sheath blight by 30% ~ 50% and soybean root rot by 42%. Seed treatment can control rice flax leaf spot, peanut leaf spot and Egyptian bean wilt; Soaking celery seedlings with 25 ~ 50μ g/ml chitosan can control Fusarium wilt. Tomato root rot can be prevented by soaking or spraying; Adding chitosan to cucumber hydroponic solution can control the damping-off caused by pythium.
2. 1.2 disease-resistant inducer for plants or horticultural crops
In recent years, there have been many reports about chitin induced disease resistance. For example, the degradation products of chitosan can induce chitinase activity on the leaves in vitro and the whole plant of cucumber seedlings, and this induction can be carried out. Plants do not contain chitin and chitosan, but have chitinase. These enzymes can react with chitin in the skin of plant pathogens or pests to prevent them from invading plant tissues, thus enhancing the defense ability of plants against enemies. After the chitin film was attached to the tree tissue, the chitinase activity in these plant tissues was four times higher than that in the peeled tree tissue without chitin film. This chitin film was degraded and absorbed by the tree tissue within 4 ~ 24 weeks, which accelerated the wound healing of the tree tissue. Cucumber seedlings were sprayed with amino sugar, 500 times solution; After treatment with 800 times solution and 1000 times solution, the chitinase activity increased by 17.4%, 15.9% and 6. 1% respectively. When treated with 500-fold solution, the induction activity of cucumber Fusarium wilt increased by 59.6%, which indicated that chitosan oligosaccharide had a strong induction effect on plant defense enzymes.
2. 1.3 Nematodes
In recent years, nematodes have caused great harm to fruits, vegetables and food crops. A natural insecticide can be made by mixing chitosan with appropriate carrier substances, which is very effective in controlling nematodes. Insoluble in water, it will not pollute groundwater. Its insecticidal crops and chemicals have been used in the United States, and its trade name is CLANDO SAN, which is mainly used in nurseries and horticultural crops, such as strawberries. The occurrence of nematodes can be controlled within 60 days after 1% is applied to the soil.
2.2 Seed treatment agent
Chitosan is used for seed treatment (seed soaking, seed dressing and coating) of various grain and vegetable crops, which can promote seed germination in advance, promote crop growth, stimulate disease resistance and improve yield and quality. In recent years, there are many research results in this field. The mechanism of chitin applied to seed treatment to improve yield, quality and disease resistance is being deeply studied. Chitosan can form a protective film on the surface of seeds, which is beneficial to maintain the water content of seeds and help crops absorb water in the environment. If there is too much water in the soil, it can block water and prevent seeds from rotting, which is beneficial to seed germination and emergence. Different amounts of chitosan were used to treat the seeds of wheat, rice, corn, cotton, barley, oats, soybeans, sweet potatoes and vegetables. It is reported that all these have increased production. According to foreign reports, tea is more fragrant, the cold resistance of rice is improved, the color of tomatoes is beautiful and the sugar content is increased.
2.3 Fertilizers and soil improvers
Chitin/chitosan can improve soil properties, and chitosan can be combined with soluble protein (such as collagen) to synthesize liquid soil improver. The improver has proper stability and biodegradability, and it is a high-quality organic fertilizer that can be absorbed and utilized by crops after degradation. It can also inhibit the growth and reproduction of pathogenic bacteria in the soil and effectively improve the aggregate structure and microbial flora of the soil. This liquid soil improver can form a film after spraying on the soil surface, which can protect crops from moisture. When applied to clay, it can greatly increase the yield of crops. The foliar fertilizer for soilless culture can be made of chitosan as the basic component, fertilizer, trace elements and other nutrients and preservatives.
2.4 Fruit and vegetable preservatives and food preservatives
Chitosan preservative is natural, safe and non-toxic, and it is an environmental protection and health care preservative that comes from nature and returns to nature. It has excellent film forming and adhesion. Forming a protective film with selective air permeability, limiting the entry of oxygen, but not affecting the penetration of carbon dioxide, so that the fruit is in a self-regulating micro-atmosphere state, thus delaying the ripening and aging process of the fruit; Has broad-spectrum antibacterial activity. It not only affects the permeability of carbon dioxide, but also makes the fruit in a self-regulating micro-atmosphere state, thus delaying the bacteria on the surface of the fruit and resisting the invasion of external bacteria to achieve the effect of preservation; Has good moisture retention. On the one hand, it inhibits the transpiration of fruits and vegetables, on the other hand, it has good moisturizing performance, creates a good and stable humidity environment, and is conducive to preservation; Has excellent antioxidant activity. Prevent discoloration of fruits and vegetables and improve commodity value. In a word, the function of chitosan preservative is to create a good gas environment for fruits and vegetables, slow down the biochemical reaction of ripening and aging of fruits and vegetables, reduce the transpiration of water, resist and inhibit the infection of pathogenic bacteria, improve the preservation rate and extend the shelf life, so as to achieve the effect of preservation.
Some characteristics of chitin products as pesticides
Chitin products, as a kind of pesticide, show many excellent characteristics in the practical application of planting, which can be summarized as: 10.
3. 1 is completely nontoxic and harmless.
Chitin and chitosan are natural polymer compounds, which are non-toxic and tasteless and biodegradable. The subacute experiment of chitin on animals showed that the LD50 was 65438±06g/kg of rat body weight. The subacute toxicity test of chitosan to ICP zokor was carried out at daily gain 18g/kg for 19 days, and no abnormal phenomenon was found. It can be considered that chitosan, like sucrose and salt, is harmless to people and animals. At home and abroad, health foods, cosmetics and medicines made of chitin and chitosan have been sold as commodities. This is the necessary and basic feature that chitin products can become the leading products of green agriculture. In fact, the toxicity grade of chitin products should be non-toxic, but the classification of pesticide toxicity grade in China's current pesticide management system has not been established (there has never been a completely non-toxic pesticide in the past), so chitin products (such as OS- Sterling) have to be marked with the word low toxicity on the packaging.
3.2 Effectively induce crops to enhance resistance.
This is the most competitive and promising feature of chitin products. Traditional plant protection technology relies too much on chemical pesticides, and almost all pesticides follow the principle of direct killing. Under the guidance of this concept and technology, the drug resistance of pests and diseases is increasing, but the disease resistance and stress resistance mechanism of plants is gradually weakened, passivated, dormant or even lost. This is the fundamental reason why pest control is becoming more and more difficult now. It can be seen that in order to make plant protection out of the misunderstanding and thoroughly remould itself, we must first focus on mobilizing the immune mechanism of crops through various means, and chitin products just create conditions and provide material basis for this. Chitin crops in plants can induce them to produce a large number of various resistant substances in a short time, so that crops in plants can induce them to produce a large number of various resistant substances in a short time, which greatly improves the crops' immunity. Once the pathogen invades, these drug-resistant substances can be removed from multiple targets. This effect lasts for a long time, and it is difficult for bacteria to develop drug resistance. Practice shows that it is no longer difficult to control many diseases by grasping the main line of mobilizing crop autoimmunity, emphasizing prevention first, supplemented by scientific management and appropriate control of exogenous pesticides. It even brings bright prospects for the prevention and treatment of diseases that have been plagued for a long time and are considered almost hopeless.
3.3 Preventable and treatable
The application of chitin emphasizes prevention, and chitin products are best used before crops get sick to achieve the best results. However, because the crop mechanism of chitin is to induce crops to produce resistant substances, which can quickly annihilate invasive bacteria, it is often better to use chitin products in time after crop diseases. Practice shows that the application of chitin products can directly control anthracnose, epidemic disease, virus disease, Fusarium wilt and root rot. For most other diseases, or when the disease is serious, it can be combined with pesticides (reduction) for external inhibition, internal resistance for external inhibition, and crops, and satisfactory results can be achieved in most cases. This is especially important for the early market development of chitin products.
3.4 The range of disease prevention and control is very wide.
Chitin induces crops to produce a variety of anti-biomass, so it is effective for the prevention and control of viruses, fungi and bacteria, especially for virus diseases, which is often a difficult problem in plant protection, but the prevention and control effect with chitin products is very ideal. These have been verified by practice.
3.5 Auxiliary pest control
Practice shows that crops that often use chitin are not prone to insect pests. There is still a lack of in-depth research on the crop mechanism of this effect. It is reported that insect skin contains chitin, and chitin-induced chitinase can degrade chitin in insect skin, thus destroying insect skin and leading to its death. Some people think that chitin is absorbed by crops, then absorbed by plants to decompose chitinase on the inner wall and then enters the body, making it lose biofilm and living conditions. These conditions are the best when insects hatch into larvae. Chitin products have obvious contact with various aphids, which has been verified by practice.
3.6 Enhance the resilience of crops
Chitin-induced crop resistance is not only manifested in disease resistance, but also in stress resistance. The application of chitin is beneficial for crops to resist the imbalance of cold, high temperature, drought and flood, salinity, fertilizer, gas and nutrition. This is because chitin has many good effects on crops and soil environment. For example, some resistant substances induced by chitin can prevent, reduce or repair the damage of adversity to plant cells. For another example, chitin can promote the healthy growth of crops, and healthy plants naturally have strong stress resistance; The following describes the impact of chitin on the soil environment. In practice, when crop seedlings wither due to cold injury, plants can recover quickly by using chitin in time. When the roots of crops are aging for some reason, the use of chitin will soon promote the emergence of dynamic new roots; When the branches and leaves of crops are withered by pesticides, chitin can help detoxify and make them quickly extract new branches and leaves. These are typical examples of chitin enhancing crop stress resistance.
3.7 Increase output and improve quality.
Chitin also plays a very prominent role in increasing crop yield, because chitin can activate and enhance the physiological and biochemical mechanisms of plants, promote the development of roots and thick stems and leaves, and enhance the ability of plants to absorb and utilize water, fertilizer and photosynthesis. Practice shows that when chitin is used in grain crops, the yield can be increased by 5%-65% only by treating seeds; It can increase the yield by more than 20%-40% when it is used for sprinkler irrigation of fruits and vegetables. It also has obvious effects on improving crop quality, such as increasing the contents of protein and gluten in grains, sugar content in fruits and vegetables, and improving the flavor of products. With the improvement of people's quality of life, the quality of products will be paid more and more attention, and chitin will play an increasingly important role in this respect.
3.8 is conducive to improving the distribution of microorganisms in the soil.
This is an interesting property of chitin. Studies have shown that chitin can greatly promote the proliferation of beneficial bacteria such as nitrogen-fixing bacteria, cellulose-decomposing bacteria, lactic acid bacteria and actinomycetes, and inhibit the growth of harmful bacteria such as mold and filamentous bacteria. For example, the number of actinomycetes can be increased by nearly 30 times. This characteristic determines that chitin can effectively improve the living environment of soil and crops, and is also an important reason for preventing and controlling soil-borne diseases and promoting crop growth.
3.9 Broad-spectrum antibacterial, good film-forming, moisture retention and selective air permeability.
Chitin has broad-spectrum antibacterial activity. Studies have shown that chitin has a good killing effect on most bacteria of gram-negative bacteria and gram-positive bacteria. Chitin forms a film on the surface of plants and products to prevent the invasion of germs. This film has good moisturizing effect and selective ventilation effect. These characteristics determine that chitin can be the best raw material for fruit and vegetable preservative. Now chitin preservative has come out, and the preservation effect is very good. The antibacterial effect of chitin is also manifested in some auxiliary uses of chitin products, such as treating trauma, diminishing inflammation, stopping bleeding, relieving pain, promoting wound healing and treating beriberi.
3. 10 is easy to use and not expensive.
Chitin products are mostly aqua, which can be used for water. The price is not expensive, which is more acceptable to farmers.
To sum up, chitin products have many unique advantages, especially its induced resistance characteristics are of great significance in plant protection, which is rare in existing pesticides. The wide application of chitin products will lead to fundamental changes in plant protection from concept to technology, and bring bright prospects for reducing crop diseases and insect pests and developing high-yield, high-efficiency and high-quality green agriculture. This is becoming more and more obvious in practice.
4 Prevention of typical diseases of typical crops
4. 1 Prevent the continuous cropping of melons, vegetables, strawberries and other crops from reducing production.
Continuous cropping of melons, vegetables (mainly solanaceous fruits), strawberries and other crops has always been considered a difficult problem, and no ideal solution has been found so far. There are many reasons for continuous cropping to reduce yield, such as soil nutrient imbalance, high soil salt content, waste acidosis caused by the same crop in the previous crop, and the harm of soil-borne bacteria mainly Fusarium. Comprehensive control measures must be taken to completely solve the problem of continuous cropping. Traditional control methods, such as crop rotation, selection of disease-resistant varieties, grafting, flooding sterilization, chemical control, etc. , there are various limitations and difficulties, it is difficult to achieve the ideal effect. Using biological pesticides Jiangenbao (microbial pesticide developed by Shenyang Agricultural University) and chitin biological pesticide (Sterling), supplemented by reasonable fertilization and scientific management, is expected to open up a new and effective way to solve the problem of continuous cropping yield reduction. Jiangenbao and chitin products mainly solve the most critical and intractable problem of soil-borne diseases control in continuous cropping. Only using Jiangenbao and chitin products can solve the main problem of continuous cropping yield reduction and realize disease prevention and yield increase, which has been verified by practice.
4.2 Control of Rice Sheath Blight
Dry rice seedling raising has become the main technology of rice cultivation in China. The area is constantly expanding, but rice seedling blight is also rampant, which has become the main obstacle to the development of dry-raised seedlings. The reason of damping-off disease comes from the cold wave and chilling injury after the seedling is unearthed, which hinders the normal metabolism of the seedling, the protoplasm is destroyed, the physiological function is weakened, the resistance in the body is weakened or even lost, and bacterial infection is on camera. Therefore, it is the key to prevent seedling blight and enhance the stress resistance of seedlings, and chitin products can just undertake this important task. Soak the seeds with chitin products, and spray chitin products twice when the seedlings have one leaf and one needle to three leaves and one needle after emergence. When spraying for the first time (one leaf and one needle), it is best to add 50% of the conventional foliar fertilizer, and the effect is better.
4.3 Prevention and yield increase of underground tuber crops (including bulbs and rhizomes)
Chitin biopesticide is particularly effective for tuber crops to resist diseases and increase production, and should be actively advocated. The function of chitin is mainly manifested in the early development of crops. Taking potato as an example, chitosan, the main effective component of chitin product, is absorbed by the starch granules of potato tuber, which can replace other plant hormones as efficient cell activating factors, promote early rooting, improve the emergence rate and promote a large number of starch synthesis. This is the basic factor to obtain high yield. Chitin products can be sprayed on potato late blight at the peak of seedlings, especially when soil is inserted and potatoes are shaped, and the concentration control of chitin products can be improved if the disease occurs. According to the above measures, the emergence rate has been calculated at the stage of leaf spreading, which is 43.5% higher than that of the control, with an average of 3 days earlier; The fibrous root increased by 5%, the taproot diameter increased by 65438±0.8mm, the taproot length increased by 65438±0.8cm, and the yield increased by 16. 17% without spraying any chemicals in the middle growth stage. It can be considered that all underground tubers, bulbs and rhizomes are treated with chitin products to tap the potential of increasing production.
5 conclusion
Facing the arrival of the new century, protecting the earth, protecting the living environment, developing green agriculture and producing pollution-free, pollution-free and residue-free agricultural products have become the fashion pursuit of mankind. It can be predicted that the wide application of chitin biopesticide will certainly open up a brand-new world for the development of green agriculture and bring farmers a bright prospect of increasing production and income.