Dynamique des interactions entre Dickeya dianthicola, Dickeya solani et leur hôte Solanum tuberosum

Abstract : In potato plant (Solanum tuberosum), blackleg and soft rot are diseases caused by bacterial populations associating one or more species of the genus Pectobacterium and Dickeya. For several decades in Europe, the involvement of the genus Dickeya has increased, notably with the recent emergence of D. solani in the 2000s. No effective control exists against these plant pathogens; only prophylactic approaches are set up by the production industry. In this work, analysis of the structure of pathogenic populations in potato fields of northern France shows that D. dianthicola and D. solani dominate populations of Pectobacterium in relative abundance, while D. dianthicola dominates D. solani when both populations coexist. In a second part, artificial populations of D. dianthicola and D. solani isolates have allowed to assessed their aggressiveness and competitiveness in a greenhouse experiment. While the D. dianthicola population confirms its strongest aggressiveness and competitiveness when whole plants of S. tuberosum are infected, D. solani population is more aggressive and competitive when infecting Hyacinthus orientalis, as well as in rich and minimal liquid mediums. The individual analysis of the isolates of the artificial populations of D. dianthicola and D. solani shows that different aggressiveness in the host S. tuberosum is a distinctive trait of these pathogenic species; which reinforces the hypothesis of a recent host transfer (bulb plants to potato plants) of D. solani. Remarkably, in infected tissues of S. tuberosum (stem and tubers), the virulence genes pelD and pelE are highly expressed and more heterogeneously among D. solani isolates than those of D. dianthicola. A comparative transcriptomic analysis confirms the variability of the expression of virulence functions between 3 isolates of D. solani. All this work reveals that D. solani is still in adaptation phase to the host S. tuberosum, with less competitiveness against D. dianthicola during co-infection but an expression of the virulence functions in maceration condition greater that D. dianthicola. Thus, under the condition of selection of favorable genetic variations to its establishment on S. tuberosum host plant and the improvement of its competitiveness against D. dianthicola, D. solani represents a medium-term major risk for potato cultivation.
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Pauline Blin. Dynamique des interactions entre Dickeya dianthicola, Dickeya solani et leur hôte Solanum tuberosum. Bactériologie. Université Paris-Saclay, 2017. Français. ⟨NNT : 2017SACLS267⟩. ⟨tel-02299932⟩

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