Identification and genomic characterization of Ralstonia pseudosolanacearum strains isolated from pepino melon in China

The Ralstonia solanacearum species complex (RSSC) strains are severely destructive on a wide host range, and caused producing serious economic losses. In 2018, a bacterial wilt on pepino melon was observed in Huizhou city, Guangdong province, China. Identifying the pathogen of the pepino melon bacterial wilt and exploring its pathogenesis might be useful in developing control strategies. Physiological and biochemical, phylotyping, and pathogenicity were carried out. Seventeen isolates of pepino melon were identified as Ralstonia pseudosolanacearum (R. solanacearum phylotype I), race 1, biovar 3. A strain RS24 has a genome of 6.10 Mb that consists of a 3,908,757 bp circular chromosome, a 2,077,399 bp circular megaplasmid and a 118,798 bp circular small plasmid with 5,217 protein-coding genes, 60 transfer RNAs, 5 non-coding RNAs, and 4 rRNAs (5S, 16S, and 23S), and the G + C content of 66.69%. Functional annotation successfully classified 4026 genes into 25 COG categories. Five candidate CRISPRs, 77 genomic islands and 10 prophages were predicted. RS24 contained a small plasmid carrying type IV secretion system (T4SS), and was different from GMI1000 in the number and type of T3SS effectors and the gene encoding T6SS. The genome sequencing and analysis of strain RS24 provided effective reference data for further study of the pathogenic mechanism and exploring the host specificity of R. pseudosolanacearum. This was the first record of pepino melon bacterial wilt caused by R. pseudosolanacearum.