Erwinia carotovora contamination of Finnish seed potatoes and the prevalence of bacterial subspecies and serogroups

Symptomless contamination with the rot-inducing bacterium Erwinia carotovora was detectable by the tuber incubation method in 82% of the commercial seed potato stocks surveyed. E. carotovora subsp. atroseptica (Eca) was more common than E. carotovora subsp. carotovora (Ecc ) among the tuber contaminants. In a four-year survey of ten meristem-based seed stocks, recontamination with both Eca and Ecc occurred typically during the second field generation, but three stocks remained free of detectable contamination throughout the survey period. The first blackleg symptoms occurred typically during the third field generation. The serogroup distribution of Finnish Eca isolates was different from that reported from other countries. The predominant serogroup, I, constituted only 74% of all Eca isolates, since serogroups XXXV and XLI occurred relatively frequently. Serogroup I was more common among isolates from diseased stems than among those from latently contaminated tubers. The results also suggest that serogroup I is more dominant in the southern than in the northern parts of the country