Pathogenicity of Different Rhizobium radiobacter (Agrobacterium tumefaciens) Isolates and Their Identification with Conventional Methods

Rhizobium radiobacter is a significant causal agent that ranks among the top ten bacteria of molecular plant pathology in the world, has the largest range of hosts among plant pathogenic bacteria, and limits production and leads to economic losses in agriculture. The distinctive feature of the causal agent from other bacteria is the Ti plasmid, the extrachromosomal structure present in all virulent types. In this study, virulence of five R. radiobacter isolates (1A, 1B, 2A, 2B and RK 473) isolated from different rootstocks was tested in carrot slices, squash fruits, kalanchoe leaves, tomato and sunflower seedlings, and GF677, M9 and MM106 rootstocks, and hypersensitive response tests were conducted in tobacco plant. The isolates were diagnosed with biochemical and physiological tests by classical methods. All isolates formed tumors in carrot slices and squash fruits. 1A, 1B, 2A and 2B isolates formed tumors in the stem of GF677 peach rootstock, while it did not form any tumors on the stems of M9 and MM106 rootstocks. Tumor formation was observed in 1B isolate in the root application of GF677 peach rootstock, while no tumor formation was observed in other isolates. RK 473 isolate became pathogenic in M9 and MM106 apple rootstocks, while it was observed that the other isolates did not form any tumors. It was seen that none of the isolates became pathogenic in tomato and sunflower root and stem, and kalanchoe leaf applications. According to the virulence test results, 1B isolate was found out to be the most virulent isolate. Biochemical and physiological tests revealed the differences between isolates.