Milsana-induced resistance in powdery mildew-infected cucumber plants correlates with the induction of chalcone synthase and chalcone isomerase

Cucumber plants (Cucumis sativus cv Corona) infected with powdery mildew (Sphaerotheca fuliginea) were used to study molecular and biochemical changes occurring in leaves following treatments with Milsana(R), a reported inducer of defence reactions in cucumber. Plants treated with Milsana(R) were significantly less infected than controls and this protective effect against powdery mildew was maintained over time. Based on analyses of foliar tissues, this induced resistance correlated with an increased extractable enzymatic activity and mRNA accumulation of two flavonoid biosynthetic genes, chalcone synthase (CHS) and chalcone isomerase (CHI) and the accumulation of flavonoid compounds in treated plants. These results are the first to link CHS and CHI increased activities with induced resistance in cucumber and highlight the implication of flavonoids in the complex defence system of this plant species. (C) 2002 Elsevier Science Ltd. All rights reserved.