The Lactoperoxidase System: a Natural Biochemical Biocontrol Agent for Pre‐ and Postharvest Applications

Abstract

Controlling pests in pre-and postharvest crops using natural and lowimpact products is a major challenge. The lactoperoxidase system is an enzymatic system that exists in all external secretions in mammals and is part of the non-immune system. We tested its efficacy in in vitro microplates on Phytophthora infestans, Penicillium digitatum, Penicillium italicum, Penicillium expansum and Botrytis cinerea to determine the most suitable concentrations for use. Then, we verified its efficacy in planta under controlled conditions. Solutions prepared with 5.4 mM iodide and 1.2 mM thiocyanate and diluted threefold inhibited pathogen growth in vitro by 63-100%. Twofold-diluted solutions protected potato plants against P. infestans by 60-74% under controlled conditions. Undiluted solution inhibited orange's and apple's postharvest pathogens in curative application with efficacy levels ranging between 84 and 95% in orange and between 63 and 74% in apple. 1.5-fold concentrated solutions inhibited postharvest pathogens of apple in curative application with efficacy levels ranging between 84 and 92%. Our results also show that the oxidative stress response of fruit following wounding could interfere with ion efficiency. Our tests demonstrate for the first time that this biochemical method is as efficient as a conventional synthetic chemical method under controlled conditions. 2011). Then, sexual reproduction spread across northern Europe, leading to higher genetic diversity (Cooke et al. 2011;Yuen and Andersson 2013;Wiik 2014). This also increased the capacity of the pathogen to J Phytopathol 165 (2017) 22-34 Ó 2016 Blackwell Verlag GmbH 22 J Phytopathol Penicillium expansum, Penicillium digitatum, Penicillium italicum and Botrytis cinerea cultures Penicillium expansum (CBS 484.75), P. digitatum (MUCL 39704), P. italicum ( MUCL 15608) and B. cinerea strain V (isolated from decayed fruit in our laboratory) were grown on potato dextrose agar at 25°C in a culture chamber. After 10 days (for the Penicillium strains) and 3 weeks (for B. cinerea) of incubation, conidia were collected by adding 9 ml of sterile 0.05% Tween water on the plate. Conidia were scraped off with a sterile inoculating loop and filtered through a sterilized double-layer fine cloth. The

Reaction Product Variability and Biological Activity of the Lactoperoxidase System Depending on Medium Ionic Strength and pH, and on Substrate Relative Concentration

“…A lactoperoxidase‐catalyzed ion solution in tap water inhibited several pre‐ and post‐harvest fungi in vitro and in planta . We checked the efficacy of the reaction product with an optimized buffer instead of tap water.…”

“…Against Aggregatibacter actinomycetemcomitans , the peroxidase system with I − , Cl − , or a combination of I − and Cl − is effective but addition of SCN − cancelled the antibacterial effect . On the other hand, a cooperative effect of I − addition in the SCN − lactoperoxidase system has been demonstrated against Candida albicans , Escherichia coli , Staphylococcus aureus , Aspergillus niger , Pseudomonas aeruginosa, Phytophthora infestans, Penicillium expansum, P. italicum, P. digitatum , and Botrytis cinerea . During a long period it has been supposed that concomitant presence of I − and SCN − as substrates in lactoperoxidase‐H 2 O 2 system should give a mixture of I 2 /HOI and OSCN − ions without demonstration of the presence of those molecules until now .…”

“…The potential application of the lactoperoxidase system against plant pathogens was only recently investigated in our laboratory. The objective was to evaluate the efficacy of the ions produced by the lactoperoxidase system and applied separately from the enzyme in vitro and in planta on several pre‐ and postharvest plant pathogens . An aqueous solution obtained after lactoperoxidase (LPO) oxidation of iodide (I − ) and thiocyanate (SCN − ), was applied in vitro against five plant pathogens.…”

“…An aqueous solution obtained after lactoperoxidase (LPO) oxidation of iodide (I − ) and thiocyanate (SCN − ), was applied in vitro against five plant pathogens. Inhibition ranged from 70% to 100% . In planta tests showed that the active molecules were efficient against pathogens infecting growing potatoes and against several pathogens of harvested fruits, without any signs of phytotoxicity .…”

“…[31] In planta tests showed that the active molecules were efficient against pathogens infecting growing potatoes and against several pathogens of harvested fruits, without any signs of phytotoxicity. [31] Tap water was used to produce the active solution. As enzymes work better in buffers, we found it important to check the antifungal efficacy of a solution produced after LPO oxidation of I À and SCN À in a buffer and characterized the active metabolites produced.…”