Candidatus Erwinia dacicola is the main symbiotic bacterium of the olive fly, Bactrocera oleae (Diptera: Tephritidae), and it is essential for its suitability. The interruption of this symbiosis is a promising strategy to promote the sustainable control of the olive pest, which causes important economic losses in the Mediterranean basin countries. Since Ca. E. dacicola is uncultivated and cannot be used for in vitro inhibition tests, we evaluated the Minimum Inhibitory Concentration (MIC) of 8 active ingredients against two strains of E. persicina (1LMG 11254T and 2LMG 25707), the phylogenetically closest species to Ca. E. dacicola. The tested compounds were chosen among substances currently allowed in olive cultivation such as fungicides (copper oxychloride-Neoram WG®, dodine-Syllit 544 SC®, mancozeb-Aspor WDG, pyraclostrobin-Cabrio Olivo®, difeconazole-Score 250 EC®-), elicitors (propolis-Serbios®) and fertilizer (copper and citric acid biocomplex -Dentamet® and olive mill wastewater). For each substance, different concentrations (including the field one) were assessed in 96-well microplates, with three replicates for each strain. Subsequently, the concentration that inhibited the growth of the bacteria, were tested on agar plates to confirm the effectiveness. Overall, both strains of E. persicina showed similar MIC values for all compounds, except for propolis. Copper oxychloride (1,50 mg/mL), dodine (0,10 mg/mL), mancozeb (1,60 mg/mL), copper and citric acid biocomplex (3,42 mg/mL) showed their efficacy against E. persicina strains at lower MICs than the field rate; conversely, MICs were higher than the field rate for propolis (146,56 mg/mL and 293,12 mg/mL), pyraclostrobin (8,00 mg/mL) and difeconazole (4,32 mg/mL). Oil mill wastewater had antimicrobial activity at 2,64 mg/mL probably due to the high polyphenols content. These results suggest that these substances could be used in laboratory and field trials, with Ca. E. dacicola as a target, to confirm that E. persicina is suitable as a model for the uncultivated symbiont of B. oleae.
Antimicrobial activity of active substance against free-living Erwinia species phylogenetically closer to Candidatus Erwinia dacicola, obligate endosymbiont of Bactrocera oleae
Checchia I.
;Salvetti E.;Veneri G.;Felis G. E.;Mori N.;
2021-01-01
Abstract
Candidatus Erwinia dacicola is the main symbiotic bacterium of the olive fly, Bactrocera oleae (Diptera: Tephritidae), and it is essential for its suitability. The interruption of this symbiosis is a promising strategy to promote the sustainable control of the olive pest, which causes important economic losses in the Mediterranean basin countries. Since Ca. E. dacicola is uncultivated and cannot be used for in vitro inhibition tests, we evaluated the Minimum Inhibitory Concentration (MIC) of 8 active ingredients against two strains of E. persicina (1LMG 11254T and 2LMG 25707), the phylogenetically closest species to Ca. E. dacicola. The tested compounds were chosen among substances currently allowed in olive cultivation such as fungicides (copper oxychloride-Neoram WG®, dodine-Syllit 544 SC®, mancozeb-Aspor WDG, pyraclostrobin-Cabrio Olivo®, difeconazole-Score 250 EC®-), elicitors (propolis-Serbios®) and fertilizer (copper and citric acid biocomplex -Dentamet® and olive mill wastewater). For each substance, different concentrations (including the field one) were assessed in 96-well microplates, with three replicates for each strain. Subsequently, the concentration that inhibited the growth of the bacteria, were tested on agar plates to confirm the effectiveness. Overall, both strains of E. persicina showed similar MIC values for all compounds, except for propolis. Copper oxychloride (1,50 mg/mL), dodine (0,10 mg/mL), mancozeb (1,60 mg/mL), copper and citric acid biocomplex (3,42 mg/mL) showed their efficacy against E. persicina strains at lower MICs than the field rate; conversely, MICs were higher than the field rate for propolis (146,56 mg/mL and 293,12 mg/mL), pyraclostrobin (8,00 mg/mL) and difeconazole (4,32 mg/mL). Oil mill wastewater had antimicrobial activity at 2,64 mg/mL probably due to the high polyphenols content. These results suggest that these substances could be used in laboratory and field trials, with Ca. E. dacicola as a target, to confirm that E. persicina is suitable as a model for the uncultivated symbiont of B. oleae.
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