Phylogenetic and phenotypic analyses on Dickeya spp. isolated from different host plants in Taiwan

Dickeya spp. cause severe diseases in many crops. Most previous studies in Taiwan identified these pathogens as a single species (Erwinia chrysanthemi), and little is known about their genetic and phenotypic diversity. This study collected 40 Dickeya strains isolated from different host plants in Taiwan and conducted a series of phylogenetic and phenotypic analyses. Reconstruction of maximum likelihood trees revealed that the isolated strains belonged to D. dadantii, D. chrysanthemi, D. undicola, and D. fangzhongdai. Among the 40 tested strains, 32 collected from Phalaenopsis orchids and Welsh onions were classified as D. fangzhongdai, while those isolated from the other hosts were assigned to D. dadantii, D. chrysanthemi, and D. undicola, suggesting that some of these bacteria exhibit host preferences. Inoculation of representative strains of the four Dickeya species onto potato, Phalaenopsis and African violet showed that the maceration potentials varied inter‐ and intra‐specifically and that the differential infection patterns were host‐dependent. Phenotypic assays also revealed that strain‐level variation in maceration potential was associated (in part) with the pathogens' tolerance to hostile pH and temperature or regulation of indigoidine production. Although comparisons of colony morphology and pigment production were not sufficient to differentiate Dickeya species, Biolog analyses identified several nutrients and chemicals potentially capable of differentiating among different species. Overall, our data revealed the genetic diversity and phenotypic characteristics of Dickeya spp. in Taiwan and provided information useful for their identification. The study also presented the first evidence showing that D. undicola, a recently identified species inhabiting surface waters, could naturally infect plants.