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.