Preliminary survey on Ralstonia solanacearum strains isolated from tomato in Italy

Tomato wilting caused by Ralstonia solanacearum (RS) to tomato cultivars Arawak, Cuore di Bue and Ikram growing in greenhouses in Southern Sardinia was observed in February and April 2007. Tomato plants were grown in the soil and in soil-less culture in five greenhouses. The percentage of affected plants was up to 70%. Isolations from symptomatic plants and from water used for irrigation onto SMSA and TZCA media gave fluid white colonies with a red centre. Pathogenicity tests were done by inoculating six isolates each on 9 plants of tomato, eggplant and tobacco. Only tomato and eggplant plants wilted within two weeks and died; no symptoms were observed in tobacco and in control plants. Isolates obtained originally and from artificially inoculated plants were characterized by biochemical and physiological tests, BIOLOGTM system and IFAS. FAME analysis, performed on two isolates, confirmed the similarity with RS. PCR with primers OLY-1 and Y-2, specific for RS, gave the expected band of 288 bp. Digestion of PCR products with AvaII restriction endonuclease gave the same pattern as the reference strain. Rep-PCR and SDS-PAGE of whole-cell proteins confirmed the similarity of our isolates with RS reference strain. Furthermore, partial 16S rDNA gene sequences of several isolates were compared with known sequences of RS and their similarity was 100%. Sequences were deposited in GenBank (Accession numbers from AM690474 to AM690480). In conclusion, it was ascertained that the bacteria isolated from tomato in Sardinia have the same characteristics of race 3 of R. solanacearum.