Pathogenicity and Relative Abundance of and Species in Switzerland: An Epidemiological Dichotomy.

and species are the causal agents of blackleg and soft rot diseases in potatoes. The main pathogenic species identified so far on potatoes are , , , , , and . Ten years ago, the most prevalent Soft Rot Pectobacteriaceae in Europe were the species, and , with some variations among countries. Since then, a drastic increase in the abundance of has been observed in most European countries. This shift is difficult to explain without comparing the pathogenicity of all and species. The pathogenicity of all the above-mentioned bacterial species was assessed in field trials and in vitro tuber slice trials in Switzerland. Two isolates of each species were inoculated by soaking tubers of cv. Desiree in a suspension of 10 CFU/mL, before planting in the field. For all trials, the species were the most virulent ones, but long-term strain surveys performed in Switzerland indicate that is currently the most frequent species detected. Our results show that the pathogenicity of the species is not the main factor explaining the high prevalence of and in the Swiss potato fields.