Diversity of Ralstonia solanacearum in the Southeastern United States

Summary Bacterial (Granville) wilt, caused by Ralstonia solanacearum is a major disease of tobacco in both North and South Carolina. In contrast, Granville wilt rarely occurs on tobacco in Georgia and Florida. This difference was documented over fifty years ago and, today, it is still not understood. Isolates of R. solanacearum from tobacco and tomato were collected from Florida, Georgia, North and South Carolina. All isolates were identified as race 1, biovar 1. The polymerase chain reaction (PCR)-based fingerprinting technique, rep-PCR, was used to generate genomic fingerprints that were used to assess the genetic diversity of the R. solanacearum isolates. Bands were scored as present or absent and converted to band-sharing distances. A similarity matrix was generated and used to produce neighbor-joining trees. A highly branched tree that is indicative of the heterogeneity of the isolates in each of the states was constructed. South Carolina isolates segregated from Georgia, North Carolina and Florida isolates. Additionally, South Carolina isolates clustered as a function of the host from which they were isolated. Two isolates from tobacco and two from tomato, from both Georgia and South Carolina, were evaluated for aggressiveness on the susceptible tobacco cultivar, K 326, under controlled environment conditions. Five aggressiveness groups were defined. The tobacco isolates caused the most severe wilt symptoms, however one tobacco isolate was only weakly virulent. Only two of the four tomato isolates were pathogenic on tobacco. There was no correlation between genotypic and aggressiveness groupings. [Beitr. Tabakforsch. Int. 19 (2001) 323-331]