Occurrence, Characteristics, and PCR-Based Detection of Causing Soft Rot of Chinese Cabbage in China.

Bacterial soft rot is an important disease of Chinese cabbage ( L. ssp. ) in China and many other countries. Four pectinolytic bacterial strains (WBC1, WBC6, WBC9, and WBC11) were isolated from soft-rotted Chinese cabbage in Beijing, China. Based on 16S rDNA and gene sequence analyses, multilocus sequence analysis (MLSA), and genomic average nucleotide identity (ANI) analysis, these four strains were identified as . This species, previously reported from potato in countries not including China, is a new soft rot pathogen of Chinese cabbage in China. Biochemical characteristics of these strains tested by Biolog were mostly consistent with those of NIBIO1006. Their pathogenicity on Chinese cabbage is temperature dependent, with all four strains as well as the type strain exhibiting high pathogenicity at 23°C and 28°C. These four strains infected , , , and by artificial inoculation. Specific polymerase chain reaction (PCR) and quantitative PCR (qPCR) primers for were developed on the basis of its specific gene sequences (determined by genome comparison methods). Both PCR and qPCR detected not only genomic DNA of but also the pathogen from diseased plant tissues even before external symptoms appeared. Their detection sensitivities were as low as 1 pg and 100 pg genomic DNA of , respectively. To our knowledge, this study is the first to both report the emergence of on Chinese cabbage in China and provide rapid and accurate PCR/qPCR-based detection systems specific for .