Tomato cultivation in the tropics is hampered by bacterial wilt, a devastating soil~borne disease caused by Ra/slonia solanacearum (Smith). The disease is wide spread in India, causing yield losses to the extent of 90 per cent and is the main limiting factor for tomato cultivation in Kerala. The warm, humid tropical climate and acidic soil prevailing in Kerala favours the incidence of bacteri,lI wilt. This soil~borne pathogen has different races and wide host range of over 200 plant species (Buddenhagen et al., 1962). Breeding of resistant varieties is considered as the optimum strategy to control this disease. However, the stability of BW resistance in tomato is highly affected by pathogen density, pathogen strains, temperature, soil moisture and presence of root~knot
nematode.