First report of Pectobacterium aroidearum causing soft rot disease of white calla lily in Taiwan.
Production of white calla lily (Zantedeschia aethiopica) in Taiwan has been severely threatened by bacterial soft rot. Dickeya sp. (syn. Erwinia chrysanthemi) was previously identified to cause soft rot of white calla lily. However, this disease has still seriously occurred in Yang-Ming-Shan, Taipei, Taiwan. In April 2019, white calla lily tubers exhibiting symptoms of discolored rot were observed in a commercial nursery and a greenhouse of Chinese Culture University in Yang-Ming-Shan, and 50% of the plants exhibited symptoms. A bacterium was isolated on nutrient agar from different surface-sterilized rotted tuber tissues. Three representative isolates, CL1904-1, CL1904-2, and CL1904-3, were obtained. Based on the results of PCR assay, sequence comparison and phylogenetic analysis of 16S rDNA sequence, gapA, gyrB, and mdh genes, the isolates were identified as P. aroidearum. To confirm the pathogenicity of the isolates, both tubers of white calla lily plants and detached leaf petioles were inoculated with a bacterial suspension according to the method of Lee et al. (2002). Sterile water was used as the control. After incubation at 28°C for 2 days in sealed plastic boxes (>95% relative humidity), dark brown soft rot symptoms developed on the inoculated tubers and detached petioles. The same bacterium was repeatedly isolated from the inoculated tissues of white calla lily exhibiting soft rot symptoms and identified by PCR with primers Y1/Y2 and gapA-sequencing. The control tubers and petioles remained symptom-free. P. aroidearum SCRI 109T was originally isolated from the same plant host in South Africa. This is thought to be the first report of P. aroidearum causing bacterial soft rot of white calla lily in Taiwan.