Early Emergence of Dickeya solani Revealed by Analysis of Dickeya Diversity of Potato Blackleg and Soft Rot Causing Pathogens in Switzerland.

Jacques Pédron,Isabelle Kellenberger,Frédérique Van Gijsegem,Santiago Schaerer

doi:10.3390/microorganisms9061187

Abstract

Blackleg and soft rot in potato caused by Pectobacterium and Dickeya enterobacteral genera are among the most destructive bacterial diseases in this crop worldwide. In Europe, over the last century, Pectobacterium spp. were the predominant causal agents of these diseases. As for Dickeya, before the large outbreak caused by D. solani in the 2000s, only D. dianthicola was isolated in Europe. The population dynamics of potato blackleg causing soft rot Pectobacteriaceae was, however, different in Switzerland as compared to that in other European countries with a high incidence (60 up to 90%) of Dickeya species (at the time called Erwinia chrysanthemi) already in the 1980s. To pinpoint what may underlie this Swiss peculiarity, we analysed the diversity present in the E. chrysanthemi Agroscope collection gathering potato isolates from 1985 to 2000s. Like elsewhere in Europe during this period, the majority of Swiss isolates belonged to D. dianthicola. However, we also identified a few isolates, such as D. chrysanthemi and D. oryzeae, two species that have not yet been reported in potatoes in Europe. Interestingly, this study allowed the characterisation of two “early” D. solani isolated in the 1990s. Genomic comparison between these early D. solani strains and strains isolated later during the large outbreak in the 2000s in Europe revealed only a few SNP and gene content differences, none of them affecting genes known to be important for virulence.

Highlights

Besides bacterial wilt caused by Ralstonia solanacearum and, to a lesser degree, bacterial ring rot and wilt caused by Clavibacter sepedonicus, the most destructive bacterial diseases are blackleg and soft rot provoked by the genera Pectobacterium and Dickeya [1]
The population dynamics of potato blackleg causing soft rot Pectobacteriaceae (SRP) is different in Switzerland as compared to in other European countries with a high incidence (60 up to 90%) of Dickeya species already in the 1980s [15]
Agroscope collection gathering isolates from 1985 to 1990 and identified the majority of isolates as D. dianthicola, and a few isolates as D. chrysanthemi and D. oryzeae and, interestingly, two “early” D. solani isolated in the 1990s from potato seeds imported from

Summary

Introduction

Potatoes are cultivated all over the world, as far north as Finland near the Arctic. Circle and far south as New Zealand, and in various environmental conditions from the South American Altiplano to the Neguev Desert in Israel; it is the fourth main food crop worldwide. Besides bacterial wilt caused by Ralstonia solanacearum and, to a lesser degree, bacterial ring rot and wilt caused by Clavibacter sepedonicus, the most destructive bacterial diseases are blackleg and soft rot provoked by the genera Pectobacterium and Dickeya [1]. In several European countries, these soft rot Pectobacteriaceae (SRP) are responsible for most of the declassifications and rejections of potato seed lots [2]. The main route of infection is via contaminated potato seeds, where the bacteria may remain latently at a low level until the environmental conditions become favourable for expression of the virulence factors and extensive bacterial multiplication

Methods

Results

Conclusion