Distribution, incidence and variability of Ralstonia solanacearum, causal agent of bacterial wilt of potato, in Mérida state, Venezuela.
The distribution and incidence of R. solanacearum pathogenic variants was investigated in the main potato production zone of Venezuela from 1992 to 1996. Thirty-eight localities were evaluated, using samples of soil, tissues and tubers. A trifenil tetrazolium chloride medium was used to determine cultural traits and the biovars were determined using biochemistry oxidation tests and/or by their utilization of sugars. The percentage infested area per farm and percentage infested farms per locality were determined. R. solanacearum had spread to 24 of the sampled localities, in zones between 1167 and 3000 m above sea level. R. solanacearum was not found in 14 localities of the Rangel and Miranda municipalities; most of these localities were paramo zones located at >3000 m above sea level. Bacterial wilt disease incidence increased from 22% in 1992 to 37% in 1996, with a variable infestation percentage area per farm ranging between 5 and 75%. The proportion of biovars I, II and III were 6, 82 and 12%, respectively. Variant II, found with the greatest frequency and in most of the affected areas, is specific for potato.