Management of bacterial wilt disease of tomato and potato: genetic variability of Ralstonia solanacearum strains isolated in Emilia Romagna Region

Ralstonia solanacearum (Rs), the causal agent of tomato southern bacterial wilt and of potato brown rot, affects more than 250 plant species and it is included in the EPPO list of quarantine pathogens (QP). On tomato, the disease is characterized by a general wilting of the plant due to the colonization of its vascular system. Rs is a species complex with a high genetic variability and, based on the host plants, is currently divided into 5 races. In Emilia-Romagna Region (Northern Italy), during the last 15 years, Rs presence has been detected in potatoes, tomatoes and in superficial waters in nearby cultivated areas. 27 Rs strains (belonging to races 1 and 3) were characterised by Rep-PCR (BOX, ERIC, REP). The binary matrices from PCR profiles were used for UPGMA analysis in single or concatenated way. PD 2762 Rs and DISTAL 9081 Xanthomonas axonopodis pv. vitians strains were used as race 3 reference and as outgroup, respectively. From the concatenated profiles, the 27 Rs strains were divided in the two macro-groups of races 3 and 1 with a 15% similarity. The 6 strains race 3 were subdivided in 2 groups with a 50% similarity and 5 of them were more similar to each other than the PD 2762 strain. The 21 strains race 1 were subdivided into 4 groups with more than 60% similarity. The high degree of genetic variability particularly among the strains of race 1 (isolated in Parma and Ferrara provinces) suggests the presence of different haplotypes probably due to the movement of non-symptomatic infected material.