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Descripción
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| Lupinus mariae-josephae (Lmj) is a lupine species endemic of a small area in Valencia region (Eastern Spain) where the lupine plants thrive in alkaline-limed soils, a unique habitat for lupines that preferentially grow in acid or neutral soils. When this work was initiated, the extension of the endemic area of Lmj was of about 700 squared kilometers confined to the Valencia province. In this area, Lmj thrives in small, isolated patches containing a reduced number of plants, and points to an endemism that can easily became endangered or extinct. Consequently, the Valencia Community authorities gave a ?microreserve? status for conservation of the species. All efforts, using classical strategies directed to extend the area of Lmj growth and ensure its conservation have been so far unsuccessful. The work presented here is directed to improve our knowledge of Lmj ecology and it is centered in the characterization of their symbiotic rhizobia by phenotypic, phylogenetic and genomic analysis as well as in the investigation of the potential contribution of the symbiosis to improve its conservation. To this end, different topics have been studied, and results are briefly described here. The first topic deals with the indigenous rhizobial symbionts of the Lmj endemism, and their genetic diversity was investigated. The Lmj root symbionts belong to the Bradyrhizobium genus, and phylogenetic analysis based on core genes identified a large diversity of Bradyrhizobium strains with phenotypic and symbiotic characteristics different from rhizobia nodulating other Lupinus spp. native of Spain (ISLU strains). The strains were split in two clades. Clade I included Lmj strains that define a new lineage, close to other Bradyrhizobium species as B. jicamae and B. elkanii. Clade II contained ISLU strains close to classical B. canariense and B. japonicum lineages that establish symbioses with lupines in acid soils of the Mediterranean area. The phylogenetic analysis based on symbiotic genes identified only two distinct clusters. The singularity and large diversity of these strains in such a small geographical area makes this an attractive system for studying the evolution and adaptation of the rhizobial symbiont to the plant host. Additionally, the presence of bacteria able to nodulate Lmj in basic soils from Chiapas, Mexico was investigated. Surprisingly, these soils contain bacteria able to effectively nodulate and fix nitrogen with Lmj plants in greenhouse assays. In a second topic, the taxonomic status of the endosymbiotic bacteria of Lmj from Valencia endemism and Chiapas was investigated. Results from phylogenetic analysis of core genes and Average Nucleotide Identity (ANIm) using draft genomic sequences identified new Bradyrhizobium species within strains of Clade I of Lmj endosymbiotic bacteria. Only one of these potentially new species has been defined, meanwhile the others are under process of characterization. The name ?Bradyrhizobium valentinum? sp. nov. was proposed for the defined species (type strain LmjM3T= CECT 8364T, LMG 2761T). The third topic was directed to conservation of endangered Lmj in its natural habitat. The relevant conclusion of this experimentation is that the symbiosis should be considered as a relevant factor in the conservation strategies for endangered legumes. First, we showed absence of bacteria able to nodulate Lmj in all the inspected ?terra rossa? or alkaline red soils of the Iberian Peninsula and Balearic Islands. Then, two efficient nitrogen-fixing strains with Lmj plants, LmjC and LmjM3T, were selected as inoculum for seed coating. Two planting experiments were carried out in consecutive years under natural conditions in areas with edapho-climatic characteristics identical to those sustaining natural Lmj populations, and successful reproduction of the plant was achieved. The relevant conclusion from these assays was that the successful reproductive cycle was absolutely dependent on seedling inoculation with | |
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Internacional
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Si |
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ISBN
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Tipo de Tesis
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Doctoral |
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Calificación
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Sobresaliente cum laude |
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Fecha
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