AbstractThe putrescine analogue. (E)‐1,4‐diaminobut‐2‐ene (E‐BED), synthesized as the dihydrochloride salt, controlled five economically important crop pathogens,Erysiphe qraminisDC f.sp.hordeiMarchal.Uromyces viciae‐fabae(Pers.) Schroet,Botrytis fabaeSardina,Podosphaera leucotricha(Ell.&Ev.) Salm. andPhytophthora infestans(Mont) De Bary. The Z‐isomer. Z‐BED. was also fungicidal, although less so than E‐BED. Post‐inoculation treatment with E‐BED gave greater control of powdery mildew infection on barley and rust and chocolate spot on broad bean than did pre‐inoculation application. It was also effectivein vitroagainstBotrytis cinereaPers. ex Fr.,Pyricularia oxyzaeBr.&Cav. andPyrenophora avenaeIto&Karibay. WhenP. avenaewas grown in the presence of E‐BED dihydrochloride at 81·5 mg litre−1, growth was reduced by 58% and there were significant reductions in soluble ornithine decarboxylase (ODC) andS‐adenosylmethionine decarboxylase (AdoMetDC) activity. These changes were accompanied by a sevenfold increase in putrescine concentration, a 60% increase in spermine concentration and a 32% reduction in spermidine concentr
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