Multilocus sequence analysis of blackleg soft rot pathogens in potato reveals increasing pathogenicity and biocontrol strategies

Pectobacterium and Dickeya species are pectolytic Gram-negative pathogenic bacteria that cause blackleg and soft rot (BSR) in potato. Analysis of 329 diseased potato samples from Western Canada between 2021 and 2024 by bioassay and multi-locus sequence analysis (MLSA) revealed an increase in the Pectobacterium species diversity and confirmed the absence of the relatively aggressive Dickeya species. Previous studies reported that blackleg and soft rot in Western Canada were caused mostly by Pectobacterium atrosepticum and Pectobacterium carotovorum. Recovery of additional relatively pathogenic Pectobacterium polaris, Pectobacterium parmentieri, and most recently Pectobacterium brasiliense, was observed more frequently in the present study. A rapidly expanding potato industry is increasing seed movement between regions and environmental conditions are contributing to blackleg incidence, diversity, and impact. Although low temperatures at sprouting usually increase the incidence of blackleg, the occurrence of highly pathogenic Pectobacterium species produced blackleg even under relatively dry and warm conditions. Isolation and characterization of blackleg pathogen endemic lytic bacteriophage from field samples identified members of the Siphoviridae. Phage bioassays reduced disease severity by >90 %, providing an environmentally friendly biocontrol treatment to enhance potato yield and quality. Application of integrated pathogen management strategies will minimize disease losses associated with increasing pathogen diversity, an expanding industry, and climate challenges.