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.