3.3 Dickeya dianthicola exhibited a fitness advantage over D. solani in potato plants with wounded roots.
To evaluate whether plant wounding could benefit to the D. dianthicola resident or to the D. solani invader, pathogen mixtures were inoculated in pots containing plants with wounded roots. At 61 dpi, symptomatic and asymptomatic plants were counted among 15 plants per treatment. The assay was duplicated (2 x 15 plants per treatment). Kruskal-Wallis test revealed differences between the three treatments, i.e., D. solani strain mixture, D. dianthicolastrain mixture and species mixture (k=29.2; DF=2; p=4.6x10-7). Pairwise comparisons (post-hoc Tukey tests) showed that the number of plants with symptoms differed following inoculation by D. solani from inoculation by D. dianthicola (F=-4.5; p=1.9x10-5) and by a mixture ofD. dianthicola and D. solani (F=6.1; p=2.7x10-9). Mean ± SE of the percentage of symptomatic plants reached 33% ± 0 for D. solani , 83% ± 10 forD. dianthicola and 93% ± 7 for a mix of D. dianthicolaand D. solani , indicating a stronger virulence of D. dianthicola as compared to D. solani (Figure S4a) . Pairwise comparisons (post-hoc Tukey tests) of the areas under the disease curves also confirmed that D. solani was less virulent than D. dianthicola (F=-386; p<10-11) and than a mixture of D. dianthicola and D. solani (F=386; p<10-11) (Figure S3c-d) . Because the virulence measured using symptom incidence at the final time point (61 dpi) and area under disease progress curve (from 1 to 61 dpi) gave similar results when comparing the two pathogens, only the final point of symptom incidence was retained for the analysis of the following plant assays, in order to facilitate the presentation of the data.
In the 27 emerging lesions collected from co-infected plants, qPCR quantification of the pathogens revealed an excess of D. dianthicola with a CI median value of 10-5. These CI values were different from one (Kruskal-Wallis test: k=19.5; DF=1; p=10-5; Figure S3b) .
Altogether, these experimental data revealed that the resident D. dianthicola was more effective at exploiting unwounded and wounded potato host plants than the D. solani invader, i.e. D. dianthicola had a higher fitness regarding this component of its ecological niche.