Fungicides and their mode of action

Fungicides prevent or control diseases by interfering one or more processes of physiology and metabolism of pathogenic fungi. Different fungi have diferent mode of actions, through which they kill the fungus or inhibit the germination of their reproductive spores. On basis of their specificity in mode of action, fungicides are categorized into three major groups. These are:
  1. Ergosterol synthesis inhibitors
  2. Respiratory chain (mitochondrial electron transport chain) inhibitors
  3. Proteins, nucleic acids and multi-site enzyme inhibitors

Ergosterol synthesis inhibitors

Ergosterol is responsible for structural integrity and function in fungi. It is otherwise absent in plants and animals. Hence, ergosterol synthesis is a soft target for killing the fungi associated with its host. Various fungicides inhibiting ergosterol synthesis and their mode of action is listed in the table no 1.
Table no 1: Ergosterol inhibiting fungicides and their mode of action
Class Fungicides Mode of action Target fungi
Demethylation inhibitors Imidazoles, Pyrimidines and Triazoles Inhibition of C14-demethylation during ergosterol biosynthesis, thus, targeting cell membrane integrity Rust pathogens, powdery mildews and Septoria
Morpholines Amorolfine, fenpropimorph and tridemorph Inhibiting sterol reductase and sterol isomerase enzymes of the ergosterol biosynthetic pathway Ascomycetes fungi

Respiratory chain inhibitors

This group of fungicides target the mitochondrial electron transport chain, thus inhibit the vital process of fungi and kill them. Table no 2 lists the various fungicides along with their target cites and mode of action.
Table no 2: Respiratory inhibitors fungicides and their mode of action
Class Fungicides Mode of action Target fungi
Quinone-outside inhibitors Strobilurins Inhibition of electron transport at cytochrome b part of the cytochrome bc1 complex (Complex III) Rust pathogens, powdery mildews and Septoria
Quinone-inside inhibitors Cyazofamid Inhibition of complex III of respiratory chain Oomycetes fungi (Phytophtora, Cystopus)
Succinate dehydrogenase inhibitors Carboxamides Inhibition of succinate dehydrogenase (complex II) of respiratory chain Wilt fungi, Botrytis gray mold, early blight and powdery mildew;
Proton gradient uncouplers Pyrithione Inhibition of ATP synthesis by upcoupling proton gradient across the inner membrane of mitochondria Mildews
Thiol reactants Folpet and phthalimide Inhibition of activity of thiol-containing enzymes in respiration Oomycetes fungi

Proteins, nucleic acids and multi-site enzyme inhibitors

This group of fungicides target more than one process of physiology and metabolism fungal pathogens. These fungicides are more effective over other two groups because fungi can not resists the hindrance in many process at a single time. Table no 3 lists the various fungicides with their multiple target cites and mode of action.
Table no 3: Multi-site enzyme inhibitors and their mode of action
Class Fungicides Mode of action Target fungi
Multi-site enzyme inhibitors Thiram and chlorothalonil Inhibition of several thiol-containing enzymes involved in mitochondrial respiration Broad-spectrum
Nucleic acid metabolism and protein synthesis inhibitors Benzimidazoles (Benomyl, Carbendazim), dicarboximides and phenylamides Inhibition of DNA as well as RNA synthesis Ascomycetes and basidiomycetes (but not oomycetes)


Content first created on 02-06-2021
last updated on 02-06-2021