In-Vitro Inhibition of Pythium ultimum, Fusarium graminearum, and Rhizoctonia solani by a Stabilized Lactoperoxidase System alone and in Combination with Synthetic Fungicides

Zachariah R Hansen,Stéphane Corgié,Marie K Donnelly

doi:10.3390/agronomy7040078

Zachariah R Hansen, Stéphane Corgié + Show 1 more

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https://doi.org/10.3390/agronomy7040078

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Abstract

Advances in enzyme stabilization and immobilization make the use of enzymes for industrial applications increasingly feasible. The lactoperoxidase (LPO) system is a naturally occurring enzyme system with known antimicrobial activity. Stabilized LPO and glucose oxidase (GOx) enzymes were combined with glucose, potassium iodide, and ammonium thiocyanate to create an anti-fungal formulation, which inhibited in-vitro growth of the plant pathogenic oomycete Pythium ultimum, and the plant pathogenic fungi Fusarium graminearum and Rhizoctonia solani. Pythium ultimum was more sensitive than F. graminearum and R. solani, and was killed at LPO and GOx concentrations of 20 nM and 26 nM, respectively. Rhizoctonia solani and F. graminearum were 70% to 80% inhibited by LPO and GOx concentrations of 242 nM and 315 nM, respectively. The enzyme system was tested for compatibility with five commercial fungicides as co-treatments. The majority of enzyme + fungicide co-treatments resulted in additive activity. Synergism ranging from 7% to 36% above the expected additive activity was observed when P. ultimum was exposed to the enzyme system combined with Daconil® (active ingredient (AI): chlorothalonil 29.6%, GardenTech, Lexington, KY, USA), tea tree oil, and mancozeb at select fungicide concentrations. Antagonism was observed when the enzyme system was combined with Tilt® (AI: propiconazole 41.8%, Syngenta, Basel, Switzerland) at one fungicide concentration, resulting in activity 24% below the expected additive activity at that concentration.

Highlights

Fungicides are critical for the control of many economically important plant diseases and have been an integral component of crop production for decades [1,2,3]
Synergism ranging from 7% to 36% above the expected additive activity was observed when P. ultimum was exposed to the enzyme system combined with Daconil® (active ingredient (AI): chlorothalonil 29.6%, GardenTech, Lexington, KY, USA), tea tree oil, and mancozeb at select fungicide concentrations
The objectives of this study were to (i) test the ability of a stabilized LPO and glucose oxidase (GOx) system to inhibit the growth of P. ultimum, F. graminearum, and R. solani in vitro; and, (ii) determine if the combined effect of stabilized LPO and GOx with five commercial fungicides resulted in synergistic, additive, or antagonistic activity when compared to each active ingredient alone

Summary

Introduction

Fungicides are critical for the control of many economically important plant diseases and have been an integral component of crop production for decades [1,2,3]. All fungicides impose a selection pressure on their target pathogen populations, and some fungicides are prone to the development of resistance. This is especially true for fungicides with a single target site, as mutations in the target gene can lead to the selection of a resistant sub-population in the pathogen population with fungicide applications [4,5,6,7]. Fungicides with multi-site modes of action are less likely to select for resistance [8]. Managing fungicide resistance has been a priority since it began to appear in the 1960s and 1970s [8]

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