Although plant parasitic nematodes belong to nematode hazards, they are not plant pests, but plant diseases.
The root-knot nematode (Meloidogyne) is the most widely distributed and harmful plant parasitic nematode in the world. It is estimated that more than 2000 plant species in the world, including almost all cultivated crops, are very sensitive to root-knot nematode infection. Root-knot nematodes infect the host root tissue cells to form tumors, affecting the absorption of water and nutrients, resulting in stunted plant growth, dwarfing, yellowing, withering, leaf curl, fruit deformity, and even death of the whole plant, resulting in global crop reduction.
In recent years, nematode disease control has been the focus of global plant protection companies and research institutes. Soybean cyst nematode is an important reason for soybean production reduction in Brazil, the United States and other important soybean exporting countries. At present, although some physical methods or agricultural measures have been applied to the control of nematode disease, such as: screening resistant varieties, using resistant rootstocks, crop rotation, soil improvement, etc., the most important control methods are still chemical control or biological control.
Mechanism of root-junction action
The life history of root-knot nematode consists of egg, first instar larva, second instar larva, third instar larva, fourth instar larva and adult. The larva is small worm-like, the adult is heteromorphic, the male is linear, and the female is pear-shaped. The second instar larvae can migrate in the water of soil pores, search for the root of the host plant through the sensitive alleles of the head, invade the host plant by piercing the epidermis from the elongation area of the host root, and then travel through the intercellular space, move to the root tip, and reach the meristem of the root. After the second instar larvae reached the meristem of the root tip, the larvae moved back to the direction of the vascular bundle and reached the xylem development area. Here, the second instar larvae Pierce the host cells with an oral needle and inject esophageal gland secretions into the host root cells. Auxin and various enzymes contained in esophageal gland secretions can induce host cells to mutate into “giant cells” with multinucleated nuclei, rich in suborganelles and vigorous metabolism. The cortical cells around giant cells proliferate and overgrow and swell under the influence of giant cells, forming the typical symptoms of root nodules on the root surface. Second instar larvae use giant cells as feeding points to absorb nutrients and water and do not move. Under suitable conditions, the second instar larvae can induce the host to produce giant cells 24 h after infection, and develop into adult worms after three moults in the following 20 days. After that the males move and leave the roots, the females remain stationary and continue to develop, starting to lay eggs at about 28 days. When the temperature is above 10 ℃, the eggs hatch in the root nodule, the first instar larvae in the eggs, the second instar larvae drill out of the eggs, leave the host to the soil again infection.
Root-knot nematodes have a wide range of hosts, which can be parasitic on more than 3 000 kinds of hosts, such as vegetables, food crops, cash crops, fruit trees, ornamental plants and weeds. The roots of vegetables affected by root knot nematodes first form nodules of different sizes, which are milky white at the beginning and pale brown at the later stage. After infection with root-node nematode, the plants in the ground were short, the branches and leaves were atrophied or yellowed, the growth was stunted, the leaf color was light, and the growth of the seriously sick plants was weak, the plants were wilted in drought, and the whole plant died in severe. In addition, the regulation of defense response, inhibition effect and tissue mechanical damage caused by root-knot nematodes on crops also facilitated the invasion of soil-borne pathogens such as fusarium wilt and root rot bacteria, thus forming complex diseases and causing greater losses.
Prevention and control measures
Traditional linecides can be divided into fumigants and non-fumigants according to different methods of use.
Fumigant
It includes halogenated hydrocarbons and isothiocyanates, and non-fumigants include organophosphorus and carbamates. At present, among the insecticides registered in China, bromomethane (an ozone-depleting substance, which is being gradually banned) and chloropicrin are halogenated hydrocarbon compounds, which can inhibit the protein synthesis and biochemical reactions during respiration of root knot nematodes. The two fumigants are methyl isothiocyanate, which can degrade and release methyl isothiocyanate and other small molecular compounds in the soil. Methyl isothiocyanate can enter the body of root knot nematode and bind to the oxygen carrier globulin, thus inhibiting the respiration of root knot nematode to achieve lethal effect. In addition, sulfuryl fluoride and calcium cyanamide have also been registered as fumigants for the control of root knot nematodes in China.
There are also some halogenated hydrocarbon fumigants that are not registered in China, such as 1, 3-dichloropropylene, iodomethane, etc., which are registered in some countries in Europe and the United States as substitutes for bromomethane.
Non-fumigant
Including organophosphorus and carbamates. Among the non-fumigated lineicides registered in our country, phosphine thiazolium, Methanophos, phoxiphos and chlorpyrifos belong to organophosphorus, while carboxanil, aldicarb and carboxanil butathiocarb belong to carbamate. Non-fumigated nematocides disrupt the nervous system function of root knot nematodes by binding to acetylcholinesterase in the synapses of root knot nematodes. They usually do not kill the root knot nematodes, but only make the root knot nematodes lose their ability to locate the host and infect, so they are often referred to as “nematodes paralyzers”. Traditional non-fumigated nematocides are highly toxic nerve agents, which have the same mechanism of action on vertebrates and arthropods as nematodes. Therefore, under the constraints of environmental and social factors, the world’s major developed countries have reduced or stopped the development of organophosphorus and carbamate insecticides, and turned to the development of some new high-efficiency and low-toxicity insecticides. In recent years, among the new non-carbamate/organophosphorus insecticides that have obtained EPA registration are spiralate ethyl (registered in 2010), difluorosulfone (registered in 2014) and fluopyramide (registered in 2015).
But in fact, due to the high toxicity, the prohibition of organophosphorus pesticides, there are not many nematocides available now. 371 nematocides were registered in China, of which 161 were abamectin active ingredient and 158 were thiazophos active ingredient. These two active ingredients were the most important components for nematode control in China.
At present, there are not many new nematocides, among which fluorene sulfoxide, spiroxide, difluorosulfone and fluopyramide are the leaders. In addition, in terms of biopesticides, Penicillium paraclavidum and Bacillus thuringiensis HAN055 registered by Kono also have strong market potential.
Global patent for soybean root knot nematode control
Soybean root knot nematode is one of the main reasons for soybean yield reduction in major soybean exporting countries, especially the United States and Brazil.
A total of 4287 plant protection patents related to soybean root-knot nematodes have been filed worldwide in the past decade. The world’s soybean root-knot nematode mainly applied for patents in regions and countries, the first is the European Bureau, the second is China, and the United States, while the most serious area of soybean root-knot nematode, Brazil, has only 145 patent applications. And most of them come from multinational companies.
At present, abamectin and phosphine thiazole are the main control agents for root nematodes in China. And the patented product fluopyramide has also begun to lay out.
Avermectin
In 1981, abamectin was introduced to the market as a control against intestinal parasites in mammals, and in 1985 as a pesticide. Avermectin is one of the most widely used insecticides today.
Phosphine thiazate
Phosphine thiazole is a novel, efficient and broad-spectrum non-fumigated organophosphorus insecticide developed by Ishihara Company in Japan, and has been put on the market in many countries such as Japan. Preliminary studies have shown that phosphine thiazolium has endosorption and transport in plants and has broad-spectrum activity against parasitic nematodes and pests. Plant parasitic nematodes harm many important crops, and the biological and physical and chemical properties of phosphine thiazole are very suitable for soil application, so it is an ideal agent to control plant parasitic nematodes. At present, phosphine thiazolium is one of the only nematocides registered on vegetables in China, and it has excellent internal absorption, so it can not only be used to control nematodes and soil surface pests, but also can be used to control leaf mites and leaf surface pests. The main mode of action of phosphine thiazolides is to inhibit the acetylcholinesterase of the target organism, which affects the ecology of nematode 2nd larval stage. Phosphine thiazole can inhibit the activity, damage and hatching of nematodes, so it can inhibit the growth and reproduction of nematodes.
Fluopyramide
Fluopyramide is a pyridyl ethyl benzamide fungicide, developed and commercialized by Bayer Cropscience, which is still in the patent period. Fluopyramide has certain nematicidal activity, and has been registered for the control of root knot nematode in crops, and is currently a more popular nematicide. The mechanism of its action is to inhibit mitochondrial respiration by blocking the electron transfer of succinic dehydrogenase in the respiratory chain, and inhibit several stages of the growth cycle of pathogenic bacteria to achieve the purpose of controlling pathogenic bacteria.
The active ingredient of fluropyramide in China is still in the patent period. Of its application patent applications in nematodes, 3 are from Bayer, and 4 are from China, which are combined with biostimulants or different active ingredients to control nematodes. In fact, some active ingredients within the patent period can be used to carry out some patent layout in advance to seize the market. Such as excellent lepidoptera pests and thrips agent ethyl polycidin, more than 70% of the domestic application patents are applied for by domestic enterprises.
Biological pesticides for nematode control
In recent years, biological control methods that replace chemical control of root knot nematodes have received widespread attention at home and abroad. Isolation and screening of microorganisms with high antagonistic ability against root-knot nematodes are the primary conditions for biological control. The main strains reported on antagonistic microorganisms of root knot nematodes were Pasteurella, Streptomyces, Pseudomonas, Bacillus and Rhizobium. Myrothecium, Paecilomyces and Trichoderma, however, some microorganisms were difficult to exert their antagonizing effects on root knot nematodes due to difficulties in artificial culture or unstable biological control effect in the field.
Paecilomyces lavviolaceus is an effective parasite of the eggs of the southern root-node nematode and Cystocystis albicans. The parasite rate of the eggs of the southern root-node nematode nematode is as high as 60%~70%. The inhibition mechanism of Paecilomyces lavviolaceus against root-knot nematodes is that after Paecilomyces lavviolaceus contact with line worm oocysts, in the viscous substrate, the mycelium of biocontrol bacteria surrounds the whole egg, and the end of the mycelium becomes thick. The surface of the egg shell is broken due to the activities of exogenous metabolites and fungal chitinase, and then fungi invade and replace it. It can also secrete toxins that kill nematodes. Its main function is to kill eggs. There are eight pesticide registrations in China. At present, Paecilomyces lilaclavi does not have a compound dosage form for sale, but its patent layout in China has a patent for compounding with other insecticides to increase the activity of use
Plant extract
Natural plant products can be safely used for root knot nematode control, and the use of plant materials or nematoidal substances produced by plants to control root knot nematode diseases is more in line with the requirements of ecological safety and food safety.
Nematoidal components of plants exist in all organs of the plant and can be obtained by steam distillation, organic extraction, collection of root secretions, etc. According to their chemical properties, they are mainly divided into non-volatile substances with water solubility or organic solubility and volatile organic compounds, among which non-volatile substances account for the majority. The nematoidal components of many plants can be used for root knot nematode control after simple extraction, and the discovery of plant extracts is relatively simple compared with new active compounds. However, although it has insecticidal effect, the real active ingredient and insecticidal principle are often not clear.
At present, neem, matrine, veratrine, scopolamine, tea saponin and so on are the main commercial plant pesticides with nematode killing activity, which are relatively few, and can be used in the production of nematode inhibitory plants by interplanting or accompanying.
Although the combination of plant extracts to control root knot nematode will play a better nematode control effect, it has not been fully commercialized at the present stage, but it still provides a new idea for plant extracts to control root knot nematode.
Bio-organic fertilizer
The key of bio-organic fertilizer is whether the antagonistic microorganisms can multiply in the soil or rhizosphere soil. The results show that the application of some organic materials such as shrimp and crab shells and oil meal can directly or indirectly improve the biological control effect of root knot nematode. Using solid fermentation technology to fermentate antagonistic microorganism and organic fertilizer to produce bio-organic fertilizer is a new biological control method to control root knot nematode disease.
In the study of controlling vegetable nematodes with bio-organic fertilizer, it was found that the antagonistic microorganisms in bio-organic fertilizer had a good control effect on root-knot nematodes, especially the organic fertilizer made from the fermentation of antagonistic microorganisms and organic fertilizer through solid fermentation technology.
However, the control effect of organic fertilizer on root-knot nematodes has a great relationship with the environment and use period, and its control efficiency is far less than that of traditional pesticides, and it is difficult to commercialize.
However, as a part of drug and fertilizer control, it is feasible to control nematodes by adding chemical pesticides and integrating water and fertilizer.
With the large number of single crop varieties (such as sweet potato, soybean, etc.) planted at home and abroad, the occurrence of nematode is becoming more and more serious, and the control of nematode is also facing a great challenge. At present, most of the pesticide varieties registered in China were developed before the 1980s, and the new active compounds are seriously insufficient.
Biological agents have unique advantages in the use process, but they are not as effective as chemical agents, and their use is limited by various factors. Through the relevant patent applications, it can be seen that the current development of nematocides is still around the combination of old products, the development of biopesticides, and the integration of water and fertilizer.
Post time: May-20-2024