Genetic Diversity and Pathogenicity of Ralstonia solanacearum E.F. Smith in Tomato (Lycopersicon esculentum Mill.) in Kandy, Matale, and Monaragala Districts

Bacterial wilt, caused by Ralstonia solanacearum E.F. Smith, is one of the most destructive diseases of tomato (Lycopersicon esculentum Mill) in Sri Lanka. Twenty isolates of R. solanacearum from tomato plants grown in eleven different agro climatic zones from selected districts (Kandy, Matale, Monaragala) were characterized in terms of pathogenicity on susceptible check variety Marglobe and in molecular level using random amplified polymorphic DNA (RAPD) method. Each isolate was inoculated to ten Marglobe plants using root inoculation method. Plants were inoculated with 50 ml of 48 hours old cultures with 10 CFU by pouring into the root zone. Data collection was done at 3 days intervals up to 30 days. Sixteen isolates were highly virulent and four isolates were moderately virulent on Marglobe under green house conditions. Isolate collected from Hanguranketa (Maoya) area showed the highest relative pathogenicity value (5) where the lowest value was recorded by the isolate collected from Randenigala area (3.8). It is suggested that the isolate collected from Hanguranketa could be used for screening of existing tomato germplasm in Sri Lanka for bacterial wilt resistance. Genetic diversity of isolates was assessed using RAPD method with ten selected decamer Operon primers, namely OPA-02, OPA-03, OPA-04, OPA-14, OPC–15, OPD-07, OPD-08, OPD-10, OPD–15, and OPF-12. A higher degree of polymorphism was observed even in the isolates collected from the same agroecological zone. RAPD data did not reveal clear relationship between genetic differences and the virulence of the pathogen, but indicated that a higher genetic diversity of the pathogen existed in the three districts considered.