Examples of alien pathogens in Finnish potato production - their introduction, establishment and consequences

Most pathogens on potato have been imported into Finland via contaminated seed more than hundred years ago. The history of migration and the consequences for potato production of potato wart, blackleg and soft rot, Potato mop-top virus (PMTV) and its vector powdery scab are reviewed as examples of economically important and biologically different potato pathogens. Potato wart spread alarmingly during 1920-1960. Plant quarantine acts and the use of resistant cultivars were successful in eradicating the disease. The pathogens causing blackleg and soft rot increased rapidly in 1960-1970. Development of seed certification schemes after the end of the 1970s decreased disease incidence and made the disease insignificant other than for seed potato production. Introduction of new strains of blackleg bacteria in 2003 caused the disease again to become a considerable threat to potato production. PMTV was imported into Finland in the 1970s where it spread rapidly, especially in starch potato production. Currently it is common in all potato production except that of seed potato. The disease cannot be eradicated but contamination of clean fields can be prevented. New diseases can spread to Finland in future but population changes of existing pathogens have recently caused more problems than species completely new to Finland.