LAUSR

Abstract Yellow spot disease (YSD) is a destructive disease that usually occurs at the conchocelis nursery stage of commercially cultivated Pyropia species. Vibrio mediterranei 117-T6 has been identified as the pathogenic bacteria causing YSD. To develop a biological control program for YSD, we investigated the effects of bacteriophage vB_VmeM-Yong XC31 (phage XC31) on the density of the pathogenic bacteria, the physiological and biochemical parameters of the free-living conchocelis (FLC) and the shell-borne conchocelis (SBC) of Pyropia haitanensis infected by V. mediterranei 117-T6. The highest survival rate (83%) of infected FLC was obtained when the density of V. mediterranei 117-T6 was 108 CFU/mL and the multiplicity of infection (MOI) of phage XC31 was 1. Under these conditions, phage XC31 could kill the pathogens and significantly decrease the Vibrio density in the infection system (P