GEOGRAPHICAL DIFFERENTIATION OF THE POPULATION OF XANTHOMONAS-AXONOPODIS PV. MANIHOTIS IN COLOMBIA

Analyses of DNA polymorphism and virulence variation were used to eval uate the population structure of Xanthomonas axonopodis pv, manihotis, the pathogen causing cassava bacterial blight in Colombia, We collect ed strains from the major cassava-growing regions which can be grouped into different edaphoclimatic zones (ECZs) according to environmental conditions, production constraints, and economic parameters, DNA poly morphism was assessed by a restriction fragment length polymorphism an alysis, using an X. axonopodis pv, manihotis plasmid DNA sequence (pth B) as a probe to evaluate the genetic relatedness among 189 Colombian strains, The sampling intensity permitted the estimation of genetic di fferentiation within and among ECZs, sites, and fields and even within an individual plant, A multiple correspondence analysis indicated tha t the Colombian X. axonopodis pv, manihotis population showed a high d egree of diversity relative to X. axonopodis pv, manihotis populations studied previously, and the entire collection was grouped into seven clusters, A general correlation was observed between the clusters and the geographical origin of the strains, as each cluster was largely co mposed of strains from the same ECZ. Representative strains, identifie d with pthB, were further characterized by ribotyping, hybridization t o two repetitive genomic probes (pBS6 and pBS8), and restriction analy sis of plasmid contents to evaluate the complementarity of these marke rs, Virulence variation was observed within the Colombian collection, Strains of different aggressiveness were found in all ecological zones , but no correlation between virulence variation and DNA polymorphism was observed, The genetic and virulence analyses contribute to underst anding the X. axonopodis pv. manihotis population structure in Colombi a.