Effect of Temperature Treatments on the Viability of Clavibacter sepedonicus in Infected Potato Tissue

Abstract

The objective of the present study was to establish whether exposure to temperatures of 55-70 °C results in eradication of the pathogen Clavibacter sepedonicus (Cs) in colonised potato tissue, in order to evaluate the efficiency of composting for disinfection of Cs-infected potato waste. Pre-sprouted potato tubers were inoculated and planted to produce Cs-colonised stem and tuber material. After incubation in temperature-controlled water baths, the infected potato tissue was analysed for the presence of culturable and pathogenic Cs. Additional experiments were performed with Cs-colonised potato stem tissue crushed and deaerated, thus simulating macerated stem tissue in the compost heap. To enable a comparison with bacterial cells that are not enclosed by their natural organic matrix, temperature treatments were applied to non-infected stem tissue crushed and deaerated, and spiked with freshly prepared Cs-suspensions. Cs settled inside colonised potato tissue, as well as Cs present as Cs-suspensions supplemented to potato tissue, was eradicated by exposure to heat, even after a treatment of 1 h at 55 °C, with the exception of one case in which the pathogen present in intact stem material escaped a treatment of 6 h at 60 °C, indicating that incidentally stems may provide niches in which the pathogen is protected against heat.

PM 9/2 (3) Clavibacter sepedonicus

“…• controlled composting according to EPPO Standard PM 3/66 (EPPO, 2022b) at an officially approved composting site. Considering the conflicting information available on heat tolerance of C. sepedonicus in plant material (Steinmöller et al, 2013;Stevens et al, 2021) the resulting compost should not be returned to arable agricultural land. It can be returned to non-agricultural land as well as to e.g.…”

“…Possible means of disposal include: incineration. heat sterilization. industrial processing at a processing plant with appropriate waste facilities with a system of cleaning and disinfection of at least the departing vehicles, except when used for transportation of the same lot. controlled composting according to EPPO Standard PM 3/66 (EPPO, 2022b) at an officially approved composting site. Considering the conflicting information available on heat tolerance of C. sepedonicus in plant material (Steinmöller et al., 2013; Stevens et al., 2021) the resulting compost should not be returned to arable agricultural land. It can be returned to non‐agricultural land as well as to e.g.…”

Bacterial ring rot of potato caused by Clavibacter sepedonicus: A successful example of defeating the enemy under international regulations

“…Viable pathogen cells were extracted after composting potato tubers and debris for 6 days at 70°C, 13 days at 55°C, and a 90 min pasteurization at 70°C, indicating that C. sepedonicus might be disseminated through potato residues from processing industries (Steinmöller et al, 2013). Stevens et al (2021c) noted that the pathogen was eradicated by exposure to heat after a treatment for 60 min at 55°C. Biofilm formation by C. sepedonicus is suspected to play a role in disease but has not been examined methodically.…”

“…sepedonicus might be disseminated through potato residues from processing industries (Steinmöller et al, 2013 ). Stevens et al ( 2021c ) noted that the pathogen was eradicated by exposure to heat after a treatment for 60 min at 55°C. Biofilm formation by C. sepedonicus is suspected to play a role in disease but has not been examined methodically.…”

PM 3/66 (3) Guidelines for the management of plant health risks of biowaste of plant origin

“…For other pests, e.g. Clavibacter sepedonicus , there is conflicting information available on heat tolerance (Steinmöller et al., 2013; Stevens et al., 2021).…”