Pectobacterium atrosepticum (van Hall) Gardan et al. as a Causal Agent of Potato Blackleg in Greenland

As a part of a blackleg and soft rot survey on potato plants cultivated in the agricultural region of Southern Greenland during the growing season of 2019 diseased potato plants and tubers were collected at six localities. Samples of plants and tubers with typical blackleg and soft rot symptoms were cut into parts weighing ca. 10–15 g each and incubated in potato enrichment broth (PEB) under anaerobic conditions for 4–7 days at ca. 20–22 °C (conditions during shipment of the samples from Greenland to Poland). After enrichment plant extracts were plated on crystal violet pectate (CVP) medium to isolate individual cavity-forming bacterial colonies. The inoculated plates were incubated at 22, 25 and 28 °C to maximize the chance of finding pectinolytic bacteria with different growth temperature optima. Cavity-forming isolates were collected and purified to pure cultures on tryptone soya agar (TSA). Ten cavity-forming isolates, named Green1 – Green10, representing isolates from symptomatic plants from different locations, were selected for analyses. The isolates gave a 434 bp. product in Pectobacterium spp.-specific PCR and a 439 bp. product in P. atrosepticum (Pba) -specific PCR. These isolates were Gram (−) rods, facultative anaerobic, catalase positive, oxidase and indole negative, grew in TSB + 5% NaCl, produced acid from lactose, maltose and raffinose. BlastN analyses of the ca. 1300 bp. 16S rDNA sequences of all 10 strains indicated a 99–100% similarity to the 16S rDNA of Pectobacterium atrosepticum. All 10 isolates caused soft rot of potato tuber slices after 72 h at 28 °C. Phylogenetic analysis based on the recA gene sequence grouped the isolates together with P. atrosepticum strains CFBP1526T and SCRI1043. This is the first report on isolation of P. atrosepticum from blackleg-diseased potato plants in Greenland. The presence of P. atrosepticum and its possible impact on potato cultivation in Greenland is discussed.