Wide genetic diversity of Ralstonia solanacearum strains affecting tomato in Trinidad, West Indies

The genetic diversity of Ralstonia solanacearum causing bacterial wilt of tomato in Trinidad was assessed using the hierarchical phylotyping scheme and rep-PCR DNA fingerprinting. Seventy-one isolates were collected in 2003 on infected tomato crops in the four main vegetable cropping areas of Trinidad (North, Central, South-East and South). Two phylotypes were present, with phylotype II being much more prevalent (66%) than phylotype I (34%). Phylotype II strains consisted mainly of sequevar 7 in Central and South-East, and sequevar 35 in North, South-East and South. This is the first report of sequevar 7 outside south-eastern USA. In contrast, no brown rot (phylotype IIB/1, race 3 biovar 2) or emerging strains of phylotype IIB/4NPB were identified. Rep-PCR data were used to assess population genetic structure. No significant clustering by geographical distance was found, suggesting regular gene flow among cropping areas (via waterways, plant or soil). However, the population from Central was significantly differentiated from the others, containing only phylotype II/seq 7 strains, with a high degree of clonality, suggesting a possible recent introduction from abroad. The South population was less aggressive and more genetically diverse, suggesting horizontal gene transfers within the population, even among isolates of different phylotypes. Phylotype I and phylotype II populations differed slightly in clonality levels, with indications of more frequent recombination events within phylotype I populations. Possible factors influencing genetic diversity and distribution within the island are discussed.