1. Introduction
Ralstonia solanacearum is the causal agent of bacterial wilt, one of the most important bacterial diseases worldwide. Hundreds of different plant species, including many important agricultural crops such as potato, tomato, banana, and pepper plants, as well as trees, such as eucalyptus, are affected by this vascular pathogen ( Hayward 1991). During infection, the pathogen bacteria become motile and travel throughout the vascular system of the plant. As the cell density increases, virulence genes are expressed and the cells become undergo proliferation and secrete exopolysaccharide and pectin-degrading enzymes, leading to the death of the plant ( Clough et al., 1997 and Saile et al., 1997). Bacterial wilt disease is widespread causing substantial crop losses in most areas of the world.