Temperature induced non directed heritable changes in virulence of an unstable avirulent strain of Ralstonia solanacearum*

Unidirectional, stable and rapid shift from high virulence to avirulence is common in strains of heterogeneous species group Ralstonia solanacearum. In contrast, an Indian isolate, under study produced unstable avirulent variants both in in vitro and in vivo and the variants, while multiplying at 30°C, dissociate to spontaneously produce highly virulent revertants at frequency of 3.4 per cent. The instability, avirulence and dissociation perpetuate in variants in subsequent generations. Conversion to virulence was not found directed by the host factors. However, stress incubation at 35 and 37°C for 84 and 168 h, respectively increased conversions to virulence by 4–6.4 fold. High temperature induced virulence was heritable. The isolate also produced sub population growing faster at 40°C as against optimum growth temperature of 30°C.