ABSTRACT
Ralstonia solanacearum causes wilt of tomato and huge economic loses worldwide. This disease causes very heavy loss varying from 2% to 90% in different climates and seasons in India. R. solanacearum is a soil-borne bacterium that enters in plants through roots, invades xylem vessels, and spreads rapidly to aerial parts of the plants through the vascular system where its high level of multiplication obstructs the xylem vessel and leads to wilting symptoms, ultimately, plant death. It grows well at 28–32°C strictly in an aerobic condition. Race 3 biovar 2 is most severe between 24 and 35°C in plants and however decreases in aggressiveness when temperatures exceed 35°C or fall below 16°C. R. solanacearum strains present an extensive genetic diversity and are divided into four phylotypes corresponding to the strains’ geographic origin: Asia (phylotype I), America (II), Africa (III), and Indonesia (IV). Several quantitative virulence factors contribute to wilt disease development. The virulence factors for pathogenicity of R. solanacearum include production of extracellular polysaccharide (EPS), a consortium of plant cell wall-degrading enzymes, twitching and swimming motility, taxis, and several dozen effectors secreted by a type 3 secretion system. hrp genes, encoding type III secretion machinery, have been shown 86to be the key determinants for pathogenicity in the vascular phytopathogenic bacterium—R. solanacearum.
