Several fast-growing strains nodulating Vicia faba in Peru, Spain and Tunisia formed a cluster related to Rhizobium leguminosarum. The 16S rRNA gene sequences were identical to that of R. leguminosarum USDA 2370 T , whereas rpoB, recA and atpD gene sequences were phylogenetically distant, with sequence similarities of less than 96 %, 97 % and 94 %, respectively. DNA-DNA hybridization analysis showed a mean relatedness value of 43 % between strain FB206 T and R. leguminosarum USDA 2370 T . Phenotypic characteristics of the novel strains also differed from those of the closest related species of the genus Rhizobium. Therefore, based on genotypic and phenotypic data obtained in this study, we propose to classify this group of strains nodulating Vicia faba as a novel species of the genus Rhizobium named Rhizobium laguerreae sp. nov. The type strain is FB206 T (5LMG 27434 T 5CECT 8280 T ).
In this work, we analysed the core and symbiotic genes of rhizobial strains isolated from Vicia sativa in three soils from the Northwest of Spain, and compared them with other Vicia endosymbionts isolated in other geographical locations. The analysis of rrs, recA and atpD genes and 16S-23S rRNA intergenic spacer showed that the Spanish strains nodulating V. sativa are phylogenetically close to those isolated from V. sativa and V. faba in different European, American and Asian countries forming a group related to Rhizobium leguminosarum. The analysis of the nodC gene of strains nodulating V. sativa and V. faba in different continents showed they belong to a phylogenetically compact group indicating that these legumes are restrictive hosts. The results of the nodC gene analysis allow the delineation of the biovar viciae showing a common phylogenetic origin of V. sativa and V. faba endosymbionts in several continents. Since these two legume species are indigenous from Europe, our results suggest a world distribution of strains from R. leguminosarum together with the V. sativa and V. faba seeds and a close coevolution among chromosome, symbiotic genes and legume host in this Rhizobium-Vicia symbiosis.
In this study 17 isolates from effective nodules of Vicia faba and Pisum sativum var. macrocarpum growing in different soils from Peru were isolated and characterized. The isolates, presenting 11 different RAPD profiles, were distributed in three groups on the basis of their 16S-RFLP patterns. The 16S rRNA gene sequences of strains from 16S-RFLP groups I, II and III were closely related (identities higher than 99.5%) to Rhizobium leguminosarum bv. trifolii DSM 30141 (=ATCC 14480), R. leguminosarum bv. viciae DSM 30132(T) and Rhizobium etli CFN42(T) (=USDA 9032(T)), respectively. The analysis of the 16S-23S intergenic spacer (ITS) and two housekeeping genes, atpD and recA, confirmed the identification of strains from group I, however those from groups II and III were phylogenetically divergent to strains DSM 30132(T) and CFN42(T). These results support the fact that the 16S rRNA gene is not adequate for identification at species level within genus Rhizobium and suggest the existence of putative new species within the phylogenetic group of R. leguminosarum. They also confirm the need of a taxonomic revision of R. leguminosarum since the reference strains of the three biovars included in this study are phylogenetically divergent according to their ITS, atpD and recA gene sequences.
ResumenEl presente estudio se realizó con el objetivo de evaluar el efecto de 19 cepas de Rhizobium en la germinación y en el crecimiento de plantas de Lycopersicon esculentum. El efecto de los rizobios sobre la germinación de las semillas se determinó inoculando las semillas con suspensiones densas de rizobio y dejándolas germinar en arena esterilizada. El efecto sobre el crecimiento del cultivo se estudió en condiciones de cámara de crecimiento, utilizando suelo franco arenoso, con pH 7.3. El diseño utilizado fue completamente al azar con 21 tratamientos (19 cepas, un control sin inocular y un control con fertilización química) y cuatro repeticiones. Las cepas PEVF02, PEVF03, PEVF05, PEVF08, PEVF09, PEVF10, PEPSM12, PEPSM15 y PEPSM17 estimularon la germinación de las semillas de tomate, mientras que las cepas PEVF01, PEVF02, PEVF03, PEVF04, PEVF05, PEVF08 y PEPSM14 promovieron el crecimiento de plantas de tomate (Lycopersicon esculentum). Las cepas PEVF02 y PEVF08 tuvieron un efecto significativo positivo en la germinación y en el crecimiento de las plantas de tomate, por lo cual podrían recomendarse como potenciales PGPR en este cultivo, como alternativa para reducir el uso de fertilizantes químicos. Palabras claves: Rhizobium, rizobacterias promotoras del crecimiento de plantas (PGPR), Lycopersicon esculentum. AbstracThe aim of the present study was to evaluate the effect of 19 Rhizobium strains on seed germination and growth of Lycopersicon esculentum plants. The effect of Rhizobium on germination was determined by inoculating the seeds with dense suspensions of Rhizobium and germinating them in sterilized sand. The effect of Rhizobium on tomato plants was studied in growth chamber conditions using a sandy loam soil, with pH 7.3. A completely random design was used with 21 treatments (19 strains, a control without inoculating nor chemical fertilization and a control with only chemical fertilization) and four repetitions. Strains PEVF02, PEVF03, PEVF05, PEVF08, PEVF09, PEVF10, PEPSM12, PEPSM15 and PEPSM17 stimulated the germination of tomato seeds, whereas strains PEVF01, PEVF02, PEVF03, PEVF04, PEVF08 and PEPSM14 promoted the growth of tomato plants (Lycopersicon esculentum). Strains PEVF02 and PEVF08 had a significant positive effect on germination and growth of tomato plants; thus these strains could be recommended as potential PGPR for this crop, as an alternative for reducing the use of chemical fertilizers.
This study enlarges our knowledge on plant-microbial interactions in high altitude mountains and provides new applications for PGPR inoculation in purple amylaceum corn, which is part of the staple diet for the native Quechua communities.
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