Essential Oils of Sage, Rosemary, and Bay Laurel Inhibit the Life Stages of Oomycete Pathogens Important in Aquaculture.

Anđela Miljanović,Ana Bielen,Igor Jerković,Dorotea Grbin,Zvonimir Marijanović,Dora Pavić,Maja Dent

doi:10.3390/plants10081676

Anđela Miljanović, Ana Bielen + Show 5 more

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https://doi.org/10.3390/plants10081676

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Abstract

Saprolegnia parasitica, the causative agent of saprolegniosis in fish, and Aphanomyces astaci, the causative agent of crayfish plague, are oomycete pathogens that cause economic losses in aquaculture. Since toxic chemicals are currently used to control them, we aimed to investigate their inhibition by essential oils of sage, rosemary, and bay laurel as environmentally acceptable alternatives. Gas Chromatography–Mass Spectrometry (GC–MS) analysis showed that the essential oils tested were rich in bioactive volatiles, mainly monoterpenes. Mycelium and zoospores of A. astaci were more sensitive compared to those of S. parasitica, where only sage essential oil completely inhibited mycelial growth. EC50 values (i.e., concentrations of samples at which the growth was inhibited by 50%) for mycelial growth determined by the radial growth inhibition assay were 0.031–0.098 µL/mL for A. astaci and 0.040 µL/mL for S. parasitica. EC50 values determined by the zoospore germination inhibition assay were 0.007–0.049 µL/mL for A. astaci and 0.012–0.063 µL/mL for S. parasitica. The observed inhibition, most pronounced for sage essential oil, could be partly due to dominant constituents of the essential oils, such as camphor, but more likely resulted from a synergistic effect of multiple compounds. Our results may serve as a basis for in vivo experiments and the development of environmentally friendly methods to control oomycete pathogens in aquaculture.

Highlights

Saprolegnia parasitica and Aphanomyces astaci (Oomycota) cause significant economic losses in freshwater aquaculture: S. parasitica affects salmonid hatcheries and farms [1], and A. astaci crayfish rearing facilities [2,3,4]
The chemical composition of essential oils was analyzed by Gas Chromatography– Mass Spectrometry (GC–MS) (Figure 1, Table S1, Supplementary material)
All essential oils were rich in volatile components, with the highest number of compounds identified in rosemary (65 compounds, 90% of total GC peak area), followed by bay laurel (53 compounds, 93% of total GC peak area), and eventually sage essential oil (35 compounds, 98% of total GC peak area)

Summary

Introduction

Saprolegnia parasitica and Aphanomyces astaci (Oomycota) cause significant economic losses in freshwater aquaculture: S. parasitica affects salmonid hatcheries and farms [1], and A. astaci crayfish rearing facilities [2,3,4]. Saprolegnia parasitica is parasitic to salmonid fishes such as Oncorhynchus mykiss and Salmo salar and infects all developmental stages [5,6,7] It can infect crayfish species, especially when the animals are injured, and its pathogenicity towards Astacus astacus, Pacifastacus leniusculus, and Procambarus clarkii has been confirmed by infection experiments [8]. Its hyphae penetrate the cuticle of crayfish and spread throughout the tissues, leading to the development of a fatal disease [10,11] It is mainly known for its destructive effect on native European crayfish species, while North American crayfish are considered carriers of the pathogen but can still succumb to the disease under certain stressful conditions, such as in a high-density farming environment [12,13]. A. astaci may pose a serious threat to the crayfish farming industry on a global scale, both to native (e.g., Astacus astacus) and invasive (e.g., Procambarus clarkii and Cherax quadricarinatus) crayfish [2,4,14]

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