K. L. Bayliss, J. Kuo, K. Sivasithamparam, M. J. Barbetti & E. S. Lagudah

The survival of Ralstonia solanacearum in naturally infested sandy loam soil under irrigated rice culture was investigated in Sankhu village (1400 m above sea level) in central Nepal. The experimental plot had a previous history of bacterial wilt and a range of 1.5 ´ 104±3 ´ 104 colony-forming units (CFU) per g soil was present. The survival of R. solanacearum was monitored in roots of naturally growing aquatic weeds in the rice plot and in soil before and after rice harvest. The incidence of the bacterial infection in the weeds, Dopatrium sp. and Monochoria vaginalis, were 57.5 and 10%, respectively. The bacterial population detected in soil before rice harvest was 1.5 ´ 104 CFU per g soil whereas a range of 7.5 ´ 102±1.5 ´ 103 CFU per g was detected after the rice harvest. Biovar typing of R. solanacearum isolated from potato plants, potato tubers, aquatic weeds, and the soil from the experimental plot yielded the diverse biovars 2 A, 3 and 4. This is the ®rst report of the survival of these biovars in soil, which was under continuous ¯ow of irrigation water for 3 months during rice culture.