Bacteriophage cocktails displayed protective effects against soft rot-causing Pectobacterium sp. (5 tweets)

Soft rot caused by Pectobacterium spp. is responsible for significant losses in vegetable production worldwide. Methods for the effective control of this disease are limited and are primarily based on good agricultural practices. The use of phages as biocontrol agents appears to be a promising alternative to combat phytopathogens. In this study, we investigated the efficacy of lytic phages against soft rot caused by Pectobacterium carotovorum subsp. carotovorum. Designated as PPc_A3, PPc_D1, and PPc_J3, three bacteriophage isolates, which were recovered from symptomatic tissues and environmental samples, were observed to effectively lyse P. carotovorum subsp. carotovorum. PPc_A3 belongs to the Podoviridae family, while phages PPc_D1 and PPc_J3 belong to the Myoviridae family based on the morphological features of the virions as observed using transmission electron microscopy. The optimal multiplicity of infection (MOI) differed greatly among the three phages. All survived incubations at 30°C, 40°C and 50°C and at pH ranging from 3.0 to 9.0, but were all inactivated at 60°C and at pH 12. Both monophage and cocktail preparations were effective in inhibiting the growth of P. carotovorum subsp. carotovorum in in vitro challenge tests. In the semi-in planta assays, monophage treatments resulted in significant reduction of tissue maceration in potato slices, while treatment with cocktail preparations completely inhibited the development of soft rot disease. Overall, these results demonstrate the efficacy of cocktail formulations of phages PPc_A3, PPc_D1, and PPc_J3 for the biocontrol of soft rot disease caused by P. carotovorum subsp. carotovorum.

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