Pattern and causes of the establishment of the invasive bacterial potato
pathogen Dickeya solani and of the maintenance of the resident
pathogen D. dianthicola
Invasive pathogens can be a threat when they affect human health, food
production or ecosystem services, by displacing resident species, and we
need to understand the cause of their establishment. We studied the
patterns and causes of the establishment of the pathogen Dickeya solani
that recently invaded potato agrosystems in Europe by assessing its
invasion dynamics and its competitive advantages or disadvantages
against the closely-related resident D.dianthicola species.
Epidemiological records over one decade in France revealed the
establishment of D.solani and the maintenance of the resident
D.dianthicola in potato fields exhibiting blackleg symptoms. Using
experimentations, we showed that D.dianthicola was more aggressive than
D.solani on aerial parts, while D.solani was more aggressive on tubers.
In co-infection assays, D.dianthicola outcompeted D.solani in aerial
parts, while D.solani and D.dianthicola co-existed in tubers. A
comparison of 76 D.solani genomes (56 of which having been sequenced
here) revealed balanced frequencies of two uncharacterized alleles,
VfmBPro and VfmBSer, at the vfmB virulence gene. Experimental
inoculations showed that the VfmBSer population was more aggressive on
tubers, while VfmBPro and VfmBSer populations exhibited a similar
aggressiveness on stems. In stem co-infections, the VfmBPro population
outcompeted the VfmBSer population, while they co-existed in tubers.
This study thus brings novel insights allowing a better understanding of
the pattern and causes of the D.solani invasion into potato production
agrosystems, and the reasons why D.dianthicola nevertheless persisted.
More broadly, this study contributes to our understanding the ecological
determinants of pathogen invasion and of the conditions for the
maintenance of endemic competitors.