Epidemiology of Clavibacter michiganensis subsp. sepedonicus in potato under European conditions: population development and yield reduction

The population development of Clavibacter michiganensis subsp, sepedonicus (Cms) using fluidal strain (NCPPB 4053) and non-mucoid strain (NCPPB 3898) were monitored by IF cell staining method in potato cultivars 'Hansa' and 'Desiree' under field conditions in Denmark and Finland. The influence of Cms on potato yield in 'Hansa' was also examined under field conditions in Finland. Population development was generally similar in potato fields in Denmark and Finland, but a higher bacterial density and a higher number of symptomatic plants were found in Finland than in Denmark. Inoculation of potato tubers with the fluidal Cms strain NCPPB 4053 resulted in higher densities of Cms in plants during the growing season than inoculation with the non-mucoid strain NCPPB 3898. Population densities of the fluidal Cms strain (4053) increased rapidly in the beginning of the seasons, and reached its maximum ca. 80-100 days from planting in susceptible 'Hansa'. Lower levels of Cms were found in tubers of the more resistant 'Desiree' than in those of the susceptible 'Hansa'. Tuber and stem symptoms emerged 80-100 days after planting in 'Hansa', but no visual symptoms were observed in 'Desiree'. Severe infection reduced the tuber yield of 'Hansa' by 41-56% in Finland.