Mechanisms of action of the organophosphorus fungicide pyrazophos

摘要: In plant protection organophosphorus compounds are well-known for their insecticidal and acaricidal action. Since 1960, a number of fungicides have also been introduced. an in vivo screening these some related against Sphaerotheca fuliginea on cucumber, pyrazophos (O,O-diethyl O-(5-methyl-6-ethoxycarbonylpyrazolo[1,5-a]pyrimidin-2-yl) phosphorothioate) proved to be most active. The chemical displayed both protective curative action the disease; addition, considerable toxicity Pyricularia oryzae barley was found. Pyrazophos rather selective because hardly any other fungi sensitive were found study vitro spectrum antifungal activity. Hinosan (O-ethyl S,S-diphenyl phosphorodithioate) Kitazin S-benzyl about as toxic P. oryzae, but much less than S. fuliginea. view results, investigations mechanisms fungitoxic orianophosphorus mainly focused pyrazophos. Both its phosphate analogue (PO-pyrazophos) inhibit activity carboxylesterases S.fuliginea. However, no correlation could established between inhibition enzymes by PO-pyrazophos, fungitoxicity, this effect probably does not account mechanism Neither pyrazophos, all experiments studied with attributed cell membrane permeability, shown present upon incubation mycelium fungus Kitazin. affected nucleic acid protein synthesis, only slightly inhibited oxygen uptake. short-term experiments, using time 2 hours, 100-1000 x fungal growth mycelial suspensions radial agar liquid media inoculated conidia. latter tests, assayed after I week incubation. These results can partly ascribed fact that is metabolically converted into two breakdown products, PO-pyrazophos 2-hydroxy-5-methyl-6-ethoxycarbonylpyrazolo(1,5-a)pyrimidine (PP). PP buffered at pH 4.0 even considerably higher PO-pyrazophos. might, therefore, regarded actual principle This hypothesis supported finding PP, contrast inhibitory towards synthesis uptake fungus. weak effects processes insufficient conversion under conditions. Regarding site hypotheses suggested. First, specifically hence indirectly cellular synthetic like synthesis. Secondly, might react aspecifically components hence, directly affect biosynthetic processes. Pythium debaryanum Saccharomyces cerevisiae practically insensitive Upon fungicide products detected. Therefore, sensitivity seems result and/or PO has demonstrated P.oryzae.