Identification, genetic diversity, and pathogenicity of Ralstonia pseudosolanacearum causing cigar tobacco bacterial wilt in China

Ralstonia pseudosolanacearum, previously known as R. solanacearum species complex (RSSC) phylotypes I and III, is a plant pathogenic bacterium causing significant yield losses in economical crops. In the May of 2020 and 2021, cigar tobacco bacterial wilt was first observed in fields in Danzhou, Hainan Province, China. A total of eight bacterial isolates were isolated and identified as R. pseudosolanacearum with race 1, biovar III by 16S rRNA gene sequencing, Biolog, and host identification. The amino acid sequence showed that Hainan strains and 15 R. pseudosolanacearum reference strains from flue-cured tobacco in Shandong and Guizhou Provinces, all belonged to RS1000 type containing the avrA gene, only Guizhou strains also had the popP1 gene. On the basis of phylotype-specific multiplex PCR amplification, mismatch repair gene and endoglucanase gene-base tree, Hainan strains were identified as phylotype I sequevar 70, and showed stronger pathogenic capabilities on three different varieties than those reference strains. This is the first report of cigar tobacco bacterial wilt caused by R. pseudosolanacearum sequevar 70. The results revealed the diversity of RSSC in Nicotiana tabacum in China and provided useful information regarding the epidemiology of cigar tobacco wilt disease, as well as the breeding for disease resistance in local cigar tobacco. This is the first report of cigar tobacco bacterial wilt caused by Ralstonia pseudosolanacearum sequevar 70, and moreover contribute to the epidemiology of cigar tobacco wilt in China.