Showing papers by "Silvia Restrepo published in 1997"

Geographical Differentiation of the Population of Xanthomonas axonopodis pv. manihotis in Colombia.

Abstract: Analyses of DNA polymorphism and virulence variation were used to evaluate the population structure of Xanthomonas axonopodis pv. manihotis, the pathogen causing cassava bacterial blight in Colombia. We collected 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 polymorphism was assessed by a restriction fragment length polymorphism analysis, using an X. axonopodis pv. manihotis plasmid DNA sequence (pthB) as a probe to evaluate the genetic relatedness among 189 Colombian strains. The sampling intensity permitted the estimation of genetic differentiation within and among ECZs, sites, and fields and even within an individual plant. A multiple correspondence analysis indicated that the Colombian X. axonopodis pv. manihotis population showed a high degree 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 composed of strains from the same ECZ. Representative strains, identified with pthB, were further characterized by ribotyping, hybridization to two repetitive genomic probes (pBS6 and pBS8), and restriction analysis of plasmid contents to evaluate the complementarity of these markers. 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 understanding the X. axonopodis pv. manihotis population structure in Colombia.

Répartition géographique de la bactériose vasculaire du manioc en Colombie et variabilité de l'agent pathogène

Abstract: Le manioc est une culture importante en Colombie puisqu'elle couvre environ 196 000 ha. L'un des facteurs limitants de la production est une maladie causee par une bacterie : #Xanthomonas axonopodis# pv. #manihotis# (Xam). La distribution geographique de la maladie et son incidence sont precisees dans les differentes zones ecologiques de la Colombie. Les souches de cette bacterie collectees dans trois zones ont ete caracterisees selon une approche moleculaire, leur agressivite etant evaluee sur la plante. Vingt-six groupes de souches de Xam ont pu etre definis et leur repartition dans les 3 zones ecologiques analysee. Dans une zone de haute altitude, la variabilite de l'agent pathogene est tres faible. L'impact de cette etude pour l'amelioration varietale vis-a-vis de la resistance a la bacteriose est discute. Les perspectives d'etude sur les genes de resistance sont egalement abordes. (Resume d'auteur)