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

Ramsubhag A., Lawrence D., Cassie D., Fraser R., Umaharan P., Prior P., Wicker E.. 2012. Plant Pathology, 61 (5) : p. 844-857.

DOI: 10.1111/j.1365-3059.2011.02572.x

The genetic diversity of Ralstonia solanacearumcausing bacterial wilt of tomato in Trinidadwas assessed using the hierarchical phylotyping scheme and rep-PCRDNAfingerprinting. Seventy-one isolateswere collected in2003on infected tomato crops in the fourmain vegetable cropping areas ofTrinidad (North, Central, South-East and South).Two phylotypeswere present,with phylotype II being much more prevalent (66%) than phylotype I (34%). Phylotype II strains consistedmainly 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 southeastern 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 Centralwas significantly differentiated fromthe 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 eventswithin phylotype I populations. Possible factors influencing genetic diversity and distributionwithin the island are discussed.

Mots-clés : ralstonia solanacearum; solanum lycopersicum; variation génétique; distance génétique; phylogénie; gène; génétique des populations; trinité-et-tobago; flétrissement bactérien

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