Studies on plant to plant transmission of Clavibacter michiganensis subsp. sepedonicus
The spread of potato ring rot (Clavibacter michiganensis subsp. sepedonicus – EPPO A2 quarantine pest) is essentially due to infected seed potatoes and contaminated potato handling equipment. In Denmark, a seed certification programme had been implemented by 1986, but the disease was sporadically found in seed potatoes from 1988 to 1994. As disease incidence could not be related to known sources of inoculum, other means of transmission were envisaged, such as transmission from plant to plant, insect vectors. Field trials were conducted in Denmark over a period of three years on plant-to-plant transmission. Healthy and infected seed potatoes were planted 35 cm apart. To study whether transmission could occur through leaves or roots, a subsurface barrier was placed between healthy and infected seed tubers in one treatment of the experiment. Indirect immunofluorescence antibody staining (IFAS) with monoclonal antibodies was used to detect the presence of the bacterium at harvest (in samples of stem and progeny tubers). In the treatment with subsurface barrier, none of the plants grown from the healthy seed tubers was found infected. In the other experiment without subsurface barrier, 2 plants (out of 368) grown from healthy seed tubers were infected at harvest (0.5%). The author concluded that very little, if any, plant-to-plant transmission (probably through soil) may occur in the field. He also pointed out that in Denmark, since his study was initiated, legislation and recommendation for potato ring rot control were re-evaluated. The required prophylactic measures were strengthened, and in particular it is now prohibited for all seed potato growers to share production equipment with ware potato growers (this was only required in the past for the growers involved in the production of the first four generations of seed potatoes), and equipment must be disinfected if shared between seed potato growers. As a result of these more stringent measures, no ring rot was found in seed potatoes in the harvests of 1995 and 1996.
Sources
Mansfeld-Giese, K. (1997) Plant-to-plant transmission of the bacterial ring rot pathogen Clavibacter michiganensis subsp. sepedonicus.
Potato Research 40(2), 229-235.