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

Abstract

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.

Two species with a peculiar evolution within the genus Pectobacterium suggest adaptation to a new environmental niche

“…Some of these species initially recorded in water have also been found on plants. For example, Dickeya undicola was isolated from diseased carrots in Taiwan (Wei et al, 2021) and Dickeya lacustris was isolated from the rhizosphere of asymptomatic pond‐dwelling plants (Hugouvieux‐Cotte‐Pattat et al, 2019a). However, potential host plants remain to be discovered for many water‐isolated species.…”

Insight into biodiversity of the recently rearranged genus Dickeya

“…dieffenbachiae strains were nearly all isolated from ornamentals of the genus Dieffenbachia ( Araceae family). With the isolation of new Asiatic strains of D. dadantii ( Fujikawa et al., 2019 ; Wei et al., 2021 ; Tan et al., 2022 ), the heterogeneity within this species may increase. The strain S3-1 isolated from an Araceae ( Zantedeschia aethiopica ) in Taiwan ( Wei et al., 2021 ) is distinct from members of both D. dadantii subspecies, with 96.3-96.7 ANI values and 68-72% dDDH values.…”

Colonization by orchid mycorrhizal fungi primes induced systemic resistance against a necrotrophic pathogen

“…Infected leaves (diameter 4 mm) were excised at the site of initial infection and macerated in 1 mL liquid selective enhancement medium containing 3.75 g/L MgSO 4 ·7H 2 O, 1 g/L (NH 4 ) 2 SO 4 , 1 g/L K 2 HPO 4 , 0.2 mL/L 5N NaOH, and 1.7 g/L pectin at pH 7.2 (Wako Pure Chemicals, Osaka, Japan) for 24 h at 28°C (Hélias et al ., 2012). Because of the ability of this pathogen to produce indigoidine (Lee and Yu, 2006; Alič et al ., 2019; Wei et al ., 2021), we used a selective nutrient agar medium containing crystal violet, 70 mg/mL glutamine, and 4 mg/mL MnCl 2 ·2H 2 O at pH 6.5–6.8. Plates were incubated at 28°C for 1 day and bluish colonies were selected for counting.…”

“…On the basis of the arguments that colonization by AM fungi primes host defense responses against pathogens (Marquez et al, 2018) and major molecular components of AM symbiosis signaling are also present in OM (Miura et al, 2018), here we hypothesized that colonization by OM fungi (OMF) also causes ISR in orchids just as in AM plants. We used a necrotrophic, pectinolytic Gram-negative bacterium known to cause leaf soft rot in orchids (Cating and Palmateer, 2011;Joko et al, 2014;Wei et al, 2021). As recommended by Eck et al (2022), we also investigated the relationship between mycorrhizal colonization rate and ISR.…”