Production of pathogenesis‐related proteins in the cauliflower (Brassica oleracea var. botrytis)–downy mildew (Peronospora parasitica) pathosystem treated with acibenzolar‐S‐methyl

Abstract

Acibenzolar‐S‐methyl (ASM), a member of the benzothiadiazoles (BTH), was tested on cauliflower (Brassica oleracea var. botrytis) seedlings for its ability to induce resistance against downy mildew (Peronospora parasitica). Seven‐day‐old seedlings of the susceptible cultivar Billabong, sprayed with solutions containing 0·015 or 0·075 mg a.i. mL−1 ASM and inoculated 1–8 days later with P. parasitica, were assessed for disease 7 days after inoculation. Sporulation was reduced by 50% at the highest dose of ASM in plants inoculated 1 day later, with complete protection exhibited by plants inoculated 2 days after ASM treatment. Seedlings treated with 0·05 mg a.i. mL−1 ASM solution, inoculated 4 days later and harvested 0–7 days later, were analysed for pathogenesis‐related (PR) proteins, chitinase and β‐1,3 glucanase. ASM significantly induced β‐1,3 glucanase activity which increased with time in inoculated seedlings, as confirmed by the presence of PR‐2. Chitinase activity was not significantly induced by ASM, and the treated seedlings also did not accumulate the basic PR‐3C and the acidic PR‐3Q which both exhibit chitinase activity. Analysis of three other acidic (PR‐1C, PR‐5S, PR‐8) and one basic (PR‐6) PR proteins in the ASM‐treated seedlings showed that only PR‐1 and PR‐5 were slightly and slowly induced (4–5 days after treatment), but this induction was more pronounced after inoculation with P. parasitica.