Characterisation of Pectobacterium wasabiae and Pectobacterium carotovorum subsp. carotovorum isolates from diseased potato plants in Finland

Abstract

To identify bacteria causing soft rot and blackleg in potato in Finland, pectinolytic enterobacteria were isolated from diseased potato stems and tubers. In addition to isolates identified as Pectobacterium atrosepticum and Dickeya sp., many of the isolated strains were identified as Pectobacterium carotovorum subsp. carotovorum. Phylogenetic analysis and biochemical tests indicated that one of the isolates from potato stems resembled Pectobacterium wasabiae. Furthermore, two blackleg-causing P. carotovorum strains recently isolated in Europe clustered with P. wasabiae, suggesting that at least some of these isolates were originally misidentified. All the other Finnish P. carotovorum isolates resembled the subsp. carotovorum type strain in biochemical tests but could be clustered into two distinct groups in the phylogenetic analysis. One of the groups mainly contained strains isolated from diseased tubers, whereas the other mainly included isolates from potato stems. In contrast to the tuber isolates, the stem isolates lacked genes in Type III secretion genes, were not able to elicit a hypersensitive response in tobacco leaves and produced only small amounts of autoinducers in the stationary phase in vitro. P. wasabiae isolate was able to cause similar amount of blackleg-like symptoms as P. atrosepticum in a field experiment with vacuum-infiltrated tubers, whereas both P. atrosepticum and P. carotovorum isolates reduced emergence and delayed growth more than P. wasabiae. Our findings confirm the presence of P. wasabiae in Finland and show that the Finnish P. carotovorum subsp. carotovorum isolates can be divided into two groups with specific characteristics and possibly also different ecologies.

Virulence of Pectobacterium carotovorum subsp. brasiliense on potato compared with that of other Pectobacterium and Dickeya species under climatic conditions prevailing in the Netherlands

“…In both years, disease expression was slower with tubers inoculated with P. wasabiae than with D. solani , suggesting that P. wasabiae was less aggressive. In field experiments in Finland, P. wasabiae isolates were able to cause similar disease incidences as P. atrosepticum , but P. atrosepticum isolates reduced emergence and delayed growth of potatoes more than P. wasabiae (Pasanen et al ., ). Slow development of disease can also be a risk as, in field inspections, infections may remain unnoticed if the haulms are destroyed before symptom expression becomes visible.…”

“…Previous reports of blackleg‐causing strains of P. carotovorum subsp. carotovorum can probably be attributed to a misidentification of strains that were actually P. wasabiae (de Haan et al ., ; Pasanen et al ., ). Reports from the USA make clear that P. carotovorum subsp.…”

“…Field experiments in Finland have shown that seed tubers inoculated with P. carotovorum subsp. carotovorum reduced growth, although no blackleg developed (Pasanen et al ., ).…”

“…Pectobacterium wasabiae was recognized for the first time as a potato blackleg‐causing agent in New Zealand (Pitman et al ., ). Since then, it has been detected in potatoes in many potato‐growing regions in the world (de Haan et al ., ; De Boer et al ., ; Moleleki et al ., ; Pasanen et al ., ; Waleron et al ., ). From the work of Nykyri et al .…”

Evaluation of a diagnostic microarray for the detection of major bacterial pathogens of potato from tuber samples

“…Potato is infected by at least 10 bacterial pathogens which cause diseases of economic importance (Czajkowski et al ., , and references therein). For example, currently at least three species of Pectobacterium ( Pectobacterium atrosepticum , Pectobacterium carotovorum and Pectobacterium wasabiae ) and two species of Dickeya ( Dickeya solani and Dickeya dianthicola ) are known to cause blackleg and soft rot complex in Finland (Hukkanen et al ., ; Aittamaa et al ., ; Laurila et al ., , ; Degefu et al ., ; Pasanen et al ., ). This diversity of causal agents makes identification and management of disease relatively more complex and costly since independent tests have to be carried out.…”