Shifting populations of blackleg causing organisms: Significance and possible control strategies

Summary

An increasing number of (sub)species within the group of soft rot Pectobacteriaceae (SRP) are found to cause potato blackleg. Consecutively Pectobacterium atrosepticum, Dickeya dianthicola, P. brasiliense, D. solani and P. parmentieri were identified as causative agents. The prevalence of the SRP-variants varies in time and place. Recently, in North-America and Australia, severe blackleg outbreaks with aggressive strains of D. dianthicola were found. In Australia, the pathogen likely originated from infected Dahlia’s. In Europe, initial infections with D. solani were probably also derived from infected ornamentals, indicating the risks for the introduction of new SRP variants in potato from other hosts. The population structure of blackleg causing organisms can change rapidly as was experienced in the Netherlands. In 2000, D. solani was found for the first time in potato and from 2006 till 2012 it was the major causative agent of blackleg. Since 2012, P. brasiliense became the dominant blackleg causing pathogen. The introduction of a new SRP variant may initially result in an increasing blackleg prevalence and damage, but there are indication that in time, the new variants become less aggressive. Control of blackleg is still based on the use of pathogen-free seed, less susceptible varieties, on hygiene and proper cultivation practices that include avoiding plant damage, oxygen depletion in soil, and cross-contaminations. The use of biocontrol agents for field applications is still in an explorative phase. It was found that seed lots can be highly suppressive against blackleg pathogens. There is a search ongoing for treatments that can enhance suppressiveness.