[en] The first objective of this work consisted in the selection and characterization of a cotton collection of 48 commercial and experimental varieties with potential for improvement (especially Upland and Pima). Through the use of 67 microsatellite markers (SSR), a subsequent study of the phylogeny and the taking of field data on morphological characters, productive potential and fiber quality, we found an important genetic and phenotypic diversity contained in this vegetal collection, both inter and intra species. Some varieties were interesting as a donor parent of certain characters (e.g.: Fantom or WC-19NSSL) or as recurrent genetic background (e.g.: Elpida, TM-1, Campo or GW-4269) for future selection and improvement processes. The previous results also served to guide the second objective of this thesis: to initiate a crossings program for the future obtaining of ELS hybrids with less vigor than the commercial witnesses Intercott-211 and Intercott-670. Although in the phenotypic characterization of the 19 experimental combinations of hybrids the specific combining ability (SCA) has been less important than the general combining ability (GCA), it was shown that it is possible to obtain better adapted hybrids than the controls to the Andalusian climatic conditions (less vigor, shorter cycles and good performance). Lider variety (Upland) has been shown to be the female parent with the best GCA, as its offspring have generally shown lower vigor, shorter cycles and good yields due to the large number and weight of their fruits, compared to commercial controls. So Lider variety should be taken into account in new hybrid combinations, in addition to making new assessments of these and other hybrids in different years or locations to confirm the results of this thesis. In conclusion, the genetic improvement of new varieties of Upland cotton adapted to European farming conditions, would increase productivity, improve the price of fiber, and also in the case of new ELS hybrids, would reduce economic losses resulting from the lack of water and pests attacks, given the greater tolerance and resistance of the hybrids to different environmental stresses. Therefore, the varietal improvement would allow an increase in crop profitability, and a better competitiveness and sustainability of the cotton sector.

[es] El primer objetivo de este trabajo consisti&oacute; en la selecci&oacute;n y caracterizaci&oacute;n de una colecci&oacute;n de 48 variedades comerciales y experimentales de algod&oacute;n (sobre todo Upland y Pima) con potencial para la mejora. Para conocer la diversidad gen&eacute;tica contenida en la colecci&oacute;n, se emple&oacute; una bater&iacute;a de 67 marcadores microsat&eacute;lites (SSR) cuyos datos permitieron un posterior estudio de las relaciones filogen&eacute;ticas entre variedades. Estos datos moleculares fueron acompa&ntilde;ados con datos de campo sobre caracteres morfol&oacute;gicos, de potencial productivo y de calidad de la fibra, obtenidos de ensayos con dise&ntilde;os en bloques al azar con tres repeticiones. Con estos datos fenot&iacute;picos se realizaron an&aacute;lisis estad&iacute;sticos y de componentes principales para determinar las diferencias significativas entre variedades. Los resultados obtenidos, guiaron el segundo objetivo de esta tesis: iniciar un programa de cruzamientos para la futura obtenci&oacute;n de h&iacute;bridos ELS interespec&iacute;ficos con menor vigor que los testigos comerciales Intercott-211 e Intercott-670. Para ello realiz&oacute; un esquema de cruzamientos North Carolina II entre los 4 parentales femeninos (Upland) y los 5 parentales masculinos (Pima), para obtener finalmente 19 combinaciones experimentales de h&iacute;bridos. De nuevo, estos h&iacute;bridos fueron llevados a campo en ensayos en bloques al azar con tres repeticiones y se tomaron anotaciones fenot&iacute;picas de 29 caracteres relacionados con caracteres morfol&oacute;gicos, de potencial productivo, de vigor y de calidad de la fibra. Con estos datos se realizaron comparaciones de medias con los testigos, an&aacute;lisis de la varianza y an&aacute;lisis de aptitud combinatoria general y espec&iacute;fica.