Effect of antimicrobial peptides and monoterpenes on control of fire blight

Aim of study: Antimicrobial peptides and monoterpenes are safe compounds that have been used for control of many plant diseases. Herein, the effects of two recombinant antibacterial peptides (AMPs) were compared with two monoterpenes for control of Erwinia amylovora directly or via induction of plant defense enzyme guaiacol peroxidase (GPOD). Area of study: The experiments were performed at the Ferdowsi University of Mashhad (Iran). Material and methods: The central composite design (CCD) method was used to study the effect of mixing the compounds and copper compound (Nordox) in controlling the pathogen. The resistance level was studied on shoots of tolerant (`Dargazi') and semi-susceptible ('Spadona') pear cultivars treated with the antibacterial compounds. Main results: Thanatin and 1,8-cineole showed the highest and lowest antibacterial effects. All treatments reduced E. amylovora pathogenicity on blossom. The CCD analysis revealed that the best reduction in colony number obtained by mixing Lfc, thanatin, thymol, 1,8-cineole and Nordox at concentrations of 32, 16, 24, 250 and 250 ng/mL. Thymol and 1,8-cineole at 500 ng/mL decreased disease severity significantly compared to that ofAMPs. The level of GPOD enzyme in 'Dargazi' was higher than in `Spadond . All treatments increased the GPOD levels in both cultivars. Furthermore, resistance level and GPOD ratio were negatively correlated. Research highlights: Antimicrobial peptides showed better effect on growth inhibition of E. amylovora than monoterpenes. Mixing of these peptides and monoterpens at special dosage enhanced their antimicrobial efficacy against E. amylovora; that could represent a new method in control of fire blight disease.