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

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.

The metabolic shift in highly and weakly virulent Dickeya solani strains is more affected by temperature than by mutations in genes encoding global virulence regulators

ABSTRACT Global warming may shortly increase the risk of disease development on plants. Significant differences in the metabolic activity screened with Phenotype Microarray at 22°C and 28°C were observed between D. solani strains with high and low virulence level. Highly virulent D. solani was characterized by a higher number of metabolized compounds and a faster metabolism and was more tolerant to non-favorable pH and osmolarity. Metabolic phenotyping showed for the first time that the mutation in pecT gene, which encodes a global repressor of virulence, affects several pathways of the basic cell metabolism. PecT mutants had a higher maceration capacity of potato tissue and showed a higher pectinolytic activity than the wild-type strains. On the contrary, mutation in expI gene, which encoded the signaling molecules synthase crucial for quorum sensing, had an insignificant effect on the cell metabolism, although it slightly reduced the potato tissue maceration. The ability to utilize most of the tested compounds was higher at 28°C, while the survival at non-favorable pH and osmolarity was higher at 22°C. These results proved that the temperature of incubation had the most significant impact on the D. solani metabolic profiles.

Understanding the Properties of Starch in Potatoes (Solanum tuberosum var. Agria) after Being Treated with Pulsed Electric Field Processing

The purpose of this study was to investigate the properties of starch in potatoes (Solanum tuberosum cv. Agria) after being treated with pulsed electric fields (PEF). Potatoes were treated at 50 and 150 kJ/kg specific energies with various electric field strengths of 0, 0.5, 0.7, 0.9 and 1.1 kV/cm. Distilled water was used as the processing medium. Starches were isolated from potato tissue and from the PEF processing medium. To assess the starch properties, various methods were used, i.e., the birefringence capability using a polarised light microscopy, gelatinisation behaviour using hot-stage light microscopy and differential scanning calorimetry (DSC), thermal stability using thermogravimetry (TGA), enzyme susceptibility towards α-amylase and the extent of starch hydrolysis under in vitro simulated human digestion conditions. The findings showed that PEF did not change the properties of starch inside the potatoes, but it narrowed the temperature range of gelatinisation and reduced the digestibility of starch collected in the processing medium. Therefore, this study confirms that, when used as a processing aid for potato, PEF does not result in detrimental effects on the properties of potato starch.