Evaluation of Biopesticide Effect and Mechanism of Hen Egg White Lysozyme Against Streptomyces scabiei Causing Potato Common Scab Disease

Abstract

Common scab, caused by the major phytopathogenic actinomycete Streptomyces scabiei (ex Thaxter 1891) Lambert and Loria 1989, is a severe disease of potatoes worldwide that results in significant reductions in tuber quality and marketability. Although soil chemical fumigation with chloropicrin is effective in controlling the bacterium, it induces adverse environmental effects, necessitating eco-friendly alternatives. Hen egg white lysozyme (HEWL) is a non-toxic compound with a broad spectrum of antibacterial activity. It has been used for decades as a natural antimicrobial agent in food, feed, and specific clinical applications. This study was therefore conducted to evaluate the biopesticidal effects of two HEWL formulations, eLYS-T1 and eLYS-T2, against S. scabiei. Our findings revealed that eLYS-T2 exhibited the highest antimicrobial activity, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 250 ppm. The effects of eLYS-T2 on S. scabiei mycelia and soil populations were assessed in vitro and through soil treatments. The eLYS-T2 demonstrated its mechanism of action by disrupting cell envelopes, leading to ruptured mycelia and reduced mycelial thickness. Although the S. scabiei population in soil was significantly reduced by 96.4–99.4% at 250, 500, and 1,000 ppm within 1–3 days compared to untreated controls, the pathogen population at 250 ppm was significantly higher after five days. These results indicated that the concentrations of 500 and 1,000 ppm were most effective for sustained suppression. Based on the results of this study, eLYS-T2 could be a promising biopesticide candidate for managing S. scabiei in agricultural soils.