Potato (Solanum tuberosum) is a major crop in Poland with a value of €3000M in 2007. Blackleg has been causing high economic damage, and during 2005, 116 samples of potato stems and tubers with symptoms of blackleg and soft rot, each representing a crop, were collected from 17 regions of Poland. Sample homogenates were plated on crystal violet pectate medium. After purification on tripticase soy agar medium, 1000 isolates were identified as Pectobacterium sp. or Dickeya spp. on the basis that they were Gram-negative rods, oxidase negative, facultatively anaerobic, grew at 28°C and degraded pectate. Three isolates from one seed-tuber lot, cv. Sante, were identified as Dickeya spp. (syn. Erwinia chrysanthemi, Pectobacterium chrysanthemi). The seed lot had been grown in the region of Podlaskie in the northeast of Poland, and multiplied at least once in Poland. The isolates grew at 37°C, were sensitive to erythromycin, positive for phosphatases, negative for acid production from α-methyl-glucoside and caused soft rot in potato tuber slices (Samson et al., 2005). They were also positive in a PCR amplification procedure using pelADE specific primers which are specific for E. chrysanthemi (Nassar et al., 1996).
The test isolates were further identified by biochemical assays as biovar 3 (Palacio-Bielsa et al., 2006). Isolates were identical to Dickeya spp. strains recently isolated from potato in the Netherlands and Finland according to RFLP-patterns of recA sequences (Waleron et al., 2002), rep-PCR patterns, 16S rDNA and dnaX sequence analysis. In a field experiment in the Netherlands in 2008, potato tubers (cv. Kondor) vacuum-infiltrated with a test isolate from Poland resulted in 49% blackleg-diseased plants, whereas the water-inoculated plants were all symptomless, indicating the high aggressiveness of the test isolate.
This is the first report of potato blackleg caused by Dickeya spp. in Poland. The pathogen may have been introduced via seed potato tubers from the Netherlands, where the pre-basic seed of the infected seed lot had been produced. In the last three years, Dickeya spp. have been causing high economic losses to seed potato production in the Netherlands of up to €30M annually. Further spread of the pathogen in potato production in Poland is expected to have a high economic impact.