Langcake, P; Kuhn, PJ; Wade, M
Current knowledge concerning the biochemical action modes of systemic/therapeutic fungicides is reviewed. Most fungicides commercialized during the 1970s have been identified as sterol biosynthesis inhibitors with buthiobate, triarimol, triforine, triadimefon and triadimenol inhibiting sterol demethylation; while tridemorph, dodemorph, and fenpropemorph inhibit delta-8-isomerase and delta-7-isomerase. cis-Crotonanilides interfere with respiration. Edifenphos, S-benzyl-O,O-di-isopropyl-phosphorothioate, S-benzyl-O,O-diethyl-phosphorothioate, and pyrazophos interfere with membrane component formation or function. Isoprothiolane is suspected of having a pronounced effect on lipid biosynthesis, while prothiocarb and propamocarb are thought to affect fungal membrane permeability. Ethirimol, dimethirimol, metalaxyl, furalaxyl, milfuram, benalaxyl, benzimidazoles, griseofulvin, chloroneb, and pyroxychlor interfere with nucleic acid metabolism and cell division. Polyoxins interfere with chitin synthesis. Cycloheximide, streptomycin, blasticidin, and kasugamycin are known to inhibit protein synthesis. Fungicides for which a mode or action have not been defined or remains equivocal include cymoxanil, etridiazole, and cyclic imides. Fungicides with an indirect mode of action include tricyclazole, tris-O-ethyl-phosphonate, and probenazole. The authors conclude that action mode studies have increased knowledge of target organisms, can reveal fungal target sites which may be attacked with other chemically unrelated and practically more effective compounds, may enable the full biological properties of a given compound to be predicted and exploited, and may facilitate a further understanding of both resistance and cross resistance. With few exceptions, systemic fungicides inhibit metabolic processes which are common to fungi, their hosts, and other non target organisms, including humans. The authors recommend that future research be aimed at the biochemical bases of systemic fungicide selectivity and the structural requirements governing the systemic movement of compounds in plants.