Pattern and causes of the establishment of the invasive bacterial potato
pathogen Dickeya solani and of the maintenance of the resident
pathogen D. dianthicola
Abstract
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 ability 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 caused a higher symptom incidence on aerial parts of potato
plants than D. solani, while D. solani was more aggressive on tubers
(i.e. with more severe symptoms). In co-infection assays, D. dianthicola
outcompeted D. solani in aerial parts, while the two species co-existed
in tubers. A comparison of 76 D. solani genomes (56 of which having been
sequenced here) revealed balanced frequencies of two previously
uncharacterized alleles, VfmBPro and VfmBSer, at the vfmB virulence
gene. Experimental inoculations showed that the VfmBSer population was
more aggressive on tubers while the VfmBPro population outcompeted the
VfmBSer population in stem lesions, suggesting an important role of the
vfmB virulence gene in the ecology of the pathogens. 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 the endemic D.dianthicola nevertheless persisted.