Nematicides and Metabolite Standards

Background

Nematodes belong to the class Nematoda of the linear phylum of invertebrates. Plant parasitic nematodes in plants and soils are characterized by small size, short life cycle, many species, extremely fast reproduction, wide distribution and difficult identification of damage symptoms. They are one of the main pathogens of plant invasive diseases. Compared with pathogens such as fungi, bacteria, and viruses, nematodes have the characteristics of actively tending and using needles to penetrate into the host, and transfer damage by themselves. The losses caused to crops are more difficult to estimate than other diseases. Nematodes are transmitted through soil or seeds, can infect and feed on parasitic plants, secrete biochemical toxins, transmit diseases caused by other microorganisms, affect the growth and development of crops, and cause plant yield reduction, quality decline, and even death.

Introduction of Nematicides

Historically, compounds such as carbon disulfide and formaldehyde have been used to control phytopathogenic nematodes, but the control effect is minimal. The use of agents to control nematodes is an effective method commonly used in modern agriculture, which can quickly or even completely control nematode communities in a short period of time. Therefore, when the nematicides are used, the crop yield is significantly increased.

Nematicides are a class of agents used to control plant pathogenic nematodes. The most important measures to control nematodes are chemical control, biological control, tillage and cultivation measures. Among them, the use of chemical nematicides and biological nematicides to control plant nematodes is the most simple and effective method.

Classification of Nematicides

1. Use

According to different uses, nematicides are divided into two categories. One type is obligate nematicides, that is, agents that are only active against nematodes at the concentration used, and are used to specifically control nematodes. Another group is facultative nematicides, ie agents that are active against most organisms at the concentrations used. These nematicides have a variety of uses.

2. Source

According to the source of raw materials, nematicides can be divided into chemical nematicides and biological nematicides. As an important class of nematicides, chemical nematicides have received extensive attention, and their research, development and application have played an important role in ensuring agricultural production. The variety of biological nematicides is still very limited, and the effect is not satisfactory.

(1) Biological Nematicides

Biological nematicides are a class of agents that use biologically derived preparations to control nematodes. Depending on the source, biological nematicides include bacterial-derived biological nematicides (such as Pasteurella), fungal-derived biological nematicides (such as Verticillium pachyphyllum, Paecilomyces lilacinus), plant-derived biological nematicides (eg matrine).

(2) Chemical Nematicides

According to different modes of action, nematicides can be divided into fumigant nematicides and non-fumigant nematicides. The former is volatile and plays a role in fumigation. The latter is non-volatile and acts as a contact killer.

• Fumigant Nematicides
  Fumigant nematicides are volatile liquid or gaseous nematicides that act as fumigants by spreading in the soil. This is the first class of nematicides developed and applied. Fumigant nematicides mainly include halogenated hydrocarbons and organosulfur compounds.
  
  • Halogenated Hydrocarbon
    Halogenated hydrocarbon nematicides have strong lipid solubility and destroy the respiration of nematodes through alkylation or oxidation, eventually leading to nematode poisoning and death.
  • Organosulfur
    The isothiocyanates produced by the decomposition of organosulfur nematicides have strong biological toxicity, which can inactivate the enzymes containing sulfhydryl and amino groups in the somatic cells of nematodes, thereby causing the nematodes to die.
• Non-fumigant Nematicides
  Non-fumigant nematicides do not kill nematodes directly, but act as anesthesia, affecting their feeding, development and reproduction. Non-fumigant nematicides mainly include organophosphorus, carbamate, quaternary acid and tram acid derivatives, aryl formamides, trifluorobutene compounds, oxadiazole sulfides, fused ring kind. Mainly organophosphorus and carbamate nematicides.
  
  • Organophosphorus and Carbamates
    The mechanism of organophosphorus and carbamate nematicidal action is similar to their insecticidal mechanism. The mechanism is to inhibit the activity of acetylcholinesterase, thereby hindering the normal nerve conduction of nematodes, resulting in nematode poisoning and paralysis.
  • Quaternary Acid and Tram Acid Derivatives
    Spirotetramat was the first quaternary keto acid and tranexamic acid derivative to be developed commercially as a nematicide. Spirotetramat can inhibit the activity of acetyl-CoA carboxylase in nematodes and affect the growth and development of nematodes.
  • Arylformamides
    Arylformamide nematicides inhibit the nematode's respiration by blocking the electron transfer of the mitochondrial respiratory chain complex II of nematode cells, thereby destroying the energy supply, so that the nematodes eventually die due to insufficient energy supply.
  • Trifluorobutenes
    Nematodes are irreversibly paralyzed after exposure to trifluorobutene nematicides, affecting crop positioning and infestation, egg laying, egg hatching and development, along with reduced activity, cessation of feeding, and eventual death. Its mechanism of action is to inhibit the β-oxidation of fatty acid metabolism in the mitochondria of nematode cells, and then the nematodes are inhibited or die due to insufficient energy supply.
  • Oxadiazole Sulfides
    Oxadiazole sulfide nematicides affect the metabolism and lifespan of the nematode by interfering with the normal function of the ribosome in the nematode, and finally make the nematode irreversibly paralyzed and even die.
  • Condensed Rings
    Trifluoroimididine amides containing pyridoimidazole sulfonamides are obligate nematicides of condensed rings. High concentrations of trifluoroimididine amide have no effect on conventional target sites such as acetylcholinesterase and succinate dehydrogenase, so this nematicide may have a new mechanism of action.
  • Others
    In addition to the above classes of nematicides, there are some facultative nematicides developed as nematicides, including GABA-gated chloride channel antagonists (e.g. fipronil, ethiprole), nicotine acetylcholine receptor channel blockers (eg, tetracycline), allosteric modulators of fish nicotine receptors (eg, cyhalonic acid), uncouplers that affect oxidative phosphorylation by interfering with proton gradients (eg, chlorfenapyr) and many more.

Nematicides and Metabolite Standards