A new clade of Dickeya spp. plays a major role in potato blackleg outbreaks in North Finland

Abstract

Until recently Dickeya was regarded as a pathogen not established in Finland. As a result the blackleg symptom observed on potato was often associated with Pectobacterium atrosepticum. The occurrence of Dickeya spp. on potato in Finland was first reported in 2004. Since then the prevalence of Dickeya has been monitored through surveys and routine test of seed lots produced in the country. The results of monitoring of Dickeya spp. in seed lots produced in Finland between the years 2004 and 2008 indicated a steady increase in the incidence of Dickeya spp. The highest incidence was observed in samples from the 2006 growing season where about 37% were positive for Dickeya spp. The summer in 2006 was one of the warmest summers recorded in 100 years in Finland. The majority of infected lots were imported varieties. Since recently heavy blackleg outbreaks have occurred in production fields in the High Grade (HG) zone. A detailed study of these incidents of blackleg outbreaks in North Finland during the years 2008 and 2010 indicated that Dickeya spp. was the major component in the observed blackleg complex. It was detected and isolated from almost all symptomatic plants investigated. Repetitive sequences PCR (REP-PCR) and Pulsed Field Gel Electrophoresis (PFGE) analysis of strains isolated in Finland showed identical pattern with those isolated recently in other European countries with a proposed name 'Dickeya solani'. Moreover, the dnaX gene sequence of the representative strains isolated in Finland indicated 100% similarity to the dnaX sequences of 'D. solani'. The study presents the first report of a detailed analysis of bacteria involved in potato blackleg complex from natural field outbreaks in North Finland HG zone and characterisation of the 'D. solani' strains playing the major role in the disease complex.

The effect of temperature on the phenotypic features and the maceration ability of Dickeya solani strains isolated in Finland, Israel and Poland

“…The importance of the geographical orgin and the temperature profiles. This finding confirms the results of Degefu et al (2013) and van der Wolf et al (2014), that also indicated high similarities between D. solani strains of different origin. The variable tandem repeats method applied by Parkinson et al (2015) Parkinson et al (2015).…”

“…The RFLP -PFGE was performed as already described by Degefu et al (2013). After the electrophoresis run was completed, the gels were stained with ethidium bromide solution (0.5 mg ml…”

“…They also possess features which allow for more effective colonization and faster spread through the plant vascular system than in the case of D. dianthicola (Czajkowski et al 2010). All previously characterized D. solani strains indicated identical rep-PCR and PFGE profiles (Degefu et al 2013;Tsror (Lahkim) et al 2013;van der Wolf et al 2014;Potrykus et al 2016). However, the comparison of genome sequences of several D. solani strains indicated the existence of some differences within the studied strains caused probably by the horizontal gene transfer (Khayi et al 2015).…”

“…During last decade, strains from D. solani species were isolated from potatoes across Europe and Israel (Toth et al 2011;van der Wolf et al 2014) undoubtedly more often than the strains of D. dianthicola. Laurila et al (Laurila et al 2008;Laurila et al 2010) and Degefu et al (2013) reported the presence of D. solani strains in Finland. Also, the strains of D. solani were isolated from potato plants with blackleg and soft rot symptoms in France, the Netherlands, Poland, Spain and Switzerland (Palacio-Bielsa et al 2006;Helias 2006;Czajkowski et al 2009;Slawiak et al 2009a;Toth et al 2011;Gill et al 2014;Potrykus et al 2016).…”

“…The question why D. solani has spread throughout Europe and caused more severe losses than D. dianthicola has been raised by researchers across Europe (Czajkowski et al 2009;Toth et al 2011;Degefu et al 2013;Potrykus et al 2016). Studies show that these pathogens are able to induce diseases at the lower inoculum levels, produce more PCWDE and in addition possess an arsenal of T5SS/T6SS secreted proteins exhibiting more diverse functions than just destroying the plant cell-wall (Toth et al 2011;Garlant et al 2013;Pedron et al 2014;Khayi et al 2015;Potrykus et al 2016).…”