Abstract: The objective of this study was to determine the population structure of some taxa of the genus Xanthomonas based on the hrp gene cluster. Three pairs of oligonucleotide primers specific for different regions of the hrp genes of Xanthomonas spp. were designed to carry out the study. The phylogenetic analysis of the hrp genes revealed a diverse evolutionary relationship for this region of the bacterial genome of the xanthomonads.One of the major findings of this study is the divergence between hrp gene sequence and host specificity. Furthermore, the restriction banding profiles generated for the hrp fragments may be an easy and discriminating approach for identification of plant pathogenic xanthomonads. Dissertation Discovery Company and University of Florida are dedicated to making scholarly works more discoverable and accessible throughout the world. This dissertation, "Genetic and Evolutionary Characterization of Plant Pathogenic Xanthomonads Based on DNA Sequences Related to the Hrp Genes" by Rui Pereira Leite, was obtained from University of Florida and is being sold with permission from the author. A digital copy of this work may also be found in the university's institutional repository, IR@UF. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation.