First report of Dickeya dadantii causing bacterial soft rot of Thaumatophyllum bipinnatifidum in Taiwan

Philodendrons are important foliage ornamentals planted worldwide (Chen et al. 2010). In November 2021, soft rot symptoms were observed on (now known as ; Sakuragui et al. 2018) grown in a nursery in Taichung, Taiwan. On symptomatic plants, the petioles were macerated; leaf lesions were also found on some plants (Figure S1). About 60% of the plants on site were symptomatic; these plants tended to cluster together. Four plants were sampled. Infected tissues were soaked and cut into pieces in 10 mM MgCl (using scalpels); undiluted samples were streak-plated onto nutrient agar (NA) and grown for 24 h at 28°C. Translucent, creamy-white colonies were isolated from all of the tissues examined, and 4 isolates, PHIL1 to PHIL4, were obtained (each from a different plant). All isolates exhibited typical phenotypes of bacteria belonging to ; they could cause maceration symptoms on potato slices, ferment glucose and produce phosphatase (Schaad et al. 2001); they could also produce indigoidine on NGM medium (NA added with glycerol and MnCl ; Lee and Yu. 2006). Polymerase chain reactions using -specific primers 5A and 5B (Chao et al. 2006) amplified the expected amplicon in all 4 isolates. The 16S rDNA of PHIL1 to PHIL4 were amplified using primer pair 27f/1492r (Lane 1991) and the amplicons were sequenced; all 4 isolates shared the same 1,395-bp sequence (accession nos. ON203122, ON479664-ON479666). Among the strains belonging to known species (in GenBank), PHIL1 to PHIL4 shared the highest sequence identity (99.93%) with . 3937; they also shared 98.78% sequence identity with . CFBP 1269 . Multilocus sequence analysis (MLSA) targeting fragments of PHIL1 to PHIL4's A (720 bp), J (672 bp), X (450 bp), B (822 bp), and N (762 bp) genes (Marrero et al. 2013) were conducted. The five-gene concatenated sequences (3,426 bp) of the 4 isolates (accession nos. ON227444-ON227448, ON494509-ON494523) were identical. A maximum-likelihood phylogenetic analysis including these sequences and those of type strains of other known species revealed that PHIL1 to PHIL4 clustered with strains belonging to . (Figure S2). Koch's postulates were fulfilled with an inoculation test conducted on . (17 cm in aboveground height; 7-months-old). Stab inoculation using sterile toothpicks was conducted on petioles. Three plants were tested for each isolate and 2 petioles were inoculated for each plant; all 4 isolates were included in the assay. The pathogen loads inoculated were quantified by the spread