Preliminary genomic characterization of Ralstonia solanacearum strain isolated from tomato in Italy.

Twenty strains of Ralstonia solanacearum, the causal agent of bacterial wilt of solanaceous crops, collected during systematic monitoring of greenhouse tomato cultivations in 2007 and 2009 in Sardinia from tomato plants, soil and water, were characterized using different approaches. The disease occurred on ungrafted tomato plants of cvs Arawak, Cuore di Bue and Ikram, and on Cuore di Bue grafted onto the interspecific hybrids “Beaufort” and “He-Man”. Affected plants showed collapse and wilting, stunting and chlorosis and the presence of adventitious roots on the stem. Fluidal colonies were isolated on SMSA and Kelman’s tetrazolium media and selected for their typical morphology. The twenty selected strains were pathogenic to tomato and geranium plantlets, and were identified by Biolog, IFAS and by conventional PCR using the primers OLI-1 and Y-2. Phylotype characterization performed following Fegan and Prior (2005) scheme revealed that all strains belonged to phylotype II, which comprises strains belonging to biovar 1, 2 and 2T of R. solanacearum. It contains also R. solanacearum race 3, a of potato and tomato pathogen, and race 2, a banana pathogen. Phylotype II strains had considerable phylogenetic diversity, including 10 different sequevars. Amplification and sequencing of the endoglucanase gene (egl) of these strains and phylogenetic analysis performed with known egl sequence, showed that these Sardinian strains falls in sequevar 1. Further genomic characterization of these strains was performed by amplification and sequencing of the endoglucanase gene, by rep-PCR and by M13-PCR fingerprinting. These preliminary results showed similarity among R. solanacearum strains used in this work.