Diversity of Rhizobium-Phaseolus vulgaris symbiosis: overview and perspectives
ABSTRACT Common bean (Phaseolus vulgaris) has become a cosmopolitan crop, but was originally domesticated in the Americas and has been grown in Latin America for several thousand years. Consequently an enormous diversity of bean nodulating bacteria have developed and in the centers of origin the predominant species in bean nodules is R. etli. In some areas of Latin America, inoculation, which normally promotes nodulation and nitrogen fixation is hampered by the prevalence of native strains. Many other species in addition to R. etli have been found in bean nodules in regions where bean has been introduced. Some of these species such as R. leguminosarum bv. phaseoli, R. gallicum bv. phaseoli and R. giardinii bv. phaseoli might have arisen by acquiring the phaseoli plasmid from R. etli. Others, like R. tropici, are well adapted to acid soils and high temperatures and are good inoculants for bean under these conditions. The large number of rhizobia species capable of nodulating bean supports that bean is a promiscuous host and a diversity of bean-rhizobia interactions exists. Large ranges of dinitrogen fixing capabilities have been documented among bean cultivars and commercial beans have the lowest values among legume crops. Knowledge on bean symbiosis is still incipient but could help to improve bean biological nitrogen fixation.
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ABSTRACT: Alterations on growth, amino acids metabolism and some antioxidant enzyme activities as result of imazamox treatment were examined in determinate and indeterminate nodules, formed by Phaseolus vulgaris and Vicia sativa, respectively. Young seedlings of both legumes were inoculated with their respective microsymbionts and grown under controlled conditions. At vegetative growth, plants were treated with imazamox (250μM) in the nutrient solution and harvested 7days after. Imazamox was mainly accumulated in V. sativa where concentrations were more than six fold higher than those detected in P. vulgaris. Nodule dry weight and total nitrogen content were reduced by the herbicide treatment: the highest decrease of nodule biomass (50%) and nitrogen content (40%) were registered in V. sativa and P. vulgaris, respectively. The concentration of branched-chain amino acids (BCAA) did not change in neither determinate nor indeterminate nodules even though the acetohydroxyacid synthase activity decreased in root and nodules of both symbioses with the herbicide application. Based on this last result and taking into account that total free amino acids increased in roots but not in nodules of common vetch, a possible BCAA translocation from root to nodule could occur. Our results suggest that the maintenance of BCAA balance in nodule become a priority for the plant in such conditions. The involvement of activities glutathione-S-transferase, guaiacol peroxidase and superoxide dismutase in the response of the symbioses to imazamox are also discussed.Pesticide Biochemistry and Physiology 05/2014; DOI:10.1016/j.pestbp.2014.04.005 · 2.01 Impact Factor
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ABSTRACT: The common bean, Phaseolus vulgaris is an important crop for food security and nitrogen fixation through Rhizobium symbiosis. Commercial Rhizobium inoculants are being promoted to fix nitrogen and enhance bean production in the Lake Victoria basin. Rhizobium symbiosis depends on nutrients, especially phosphorus, which is widely applied as diammonium phosphate (DAP) in the Lake Victoria basin. Water hyacinth, Eichornia crassipes (Mart.) Solms-Laubach (Pontederiaceae) is being developed into compost, with perceived benefits of improving crop production and limiting its disastrous spread in Lake Victoria. High nutrient content in water hyacinth compost can stimulate Rhizobium nodulation and nitrogen fixation, consequently improving plant growth and pest resistance. However, it is not yet established whether Rhizobium inoculants and water hyacinth composts are compatible options for plant growth promotion and pest suppression in beans. A field experiment with two trials was conducted to assess the compatibility of commercial Rhizobium inoculant, DAP, cattle farmyard manure (FYM), and four formulations of water hyacinth compost i.e., water hyacinth only (H), with molasses (H+Mol), cattle manure culture (H+CMC) or effective microbes (H+EM). Rhizobium inoculated plants had high number of root nodules when grown with H+CMC and H+EM. Plants were large in size with short development period when grown with the composts, especially H+CMC and H+EM. Those grown with H+EM produced high number of flowers. Rhizobium inoculated plants had high anthracnose incidence than non-inoculated ones when grown with H+CMC. Those grown with H+EM had low anthracnose incidence, but was high in FYM. During flowering, Rhizobium inoculated plants had higher Aphis fabae population than non-inoculated ones when grown in FYM or without fertilizer. Those grown with H+EM had the lowest A. fabae population. Yields in water hyacinth compost were improved, especially for H+CMC in the second trial. DAP treated plants had more flowers and pods having heavy seeds, with low anthracnose and A. fabae infestations; but had low germination rates that reduced the yields. In conclusion, the commercial Rhizobium inoculant is predominantly compatible with water hyacinth compost formulations containing effective microbes and cattle manure culture, which could enhance tolerance of bean plants to aphids and possibly to anthracnose disease. These two water hyacinth compost formulations need further investigation for their potential in enhancing food production and alleviating the water hyacinth problem in the Lake Victoria basin.Applied Soil Ecology 04/2014; 76:68–77. DOI:10.1016/j.apsoil.2013.12.011 · 2.21 Impact Factor
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ABSTRACT: Three common bean strains, 23C2 (Tunisia), Gr42 (Spain) and IE4868 (Mexico), which were identified previously as representing a genomic group closely related to Rhizobium gallicum, are further studied here. Their 16S rRNA gene sequence showed 98.5%-99% of similarity respectively with Rhizobium loessense CCBAU 7190BT, R. gallicum R602spT, R. mongolense USDA 1844T and R. yanglingense CCBAU 71623T. Phylogenetic analysis based on recA, atpD, dnaK and thrC showed that these strains were closely related and could be distinguished from the four type strains. Strains 23C2, Gr42 and IE4868 could be also differentiated from their closest phylogenetic neighbors by their phenotypic and physiological properties and their fatty acid contents. All three strains harbored symbiotic genes specific of biovar gallicum. Levels of DNA/DNA relatedness between strain 23C2 and the type strains of R. loessense, R. mongolense, R. gallicum and R. yanglingense ranged from 58.1-61.5%. The G+C content of the genomic DNA of strain 23C2 was 59.52%. On the basis of these data, strains 23C2, Gr42 and IE4868 were considered as a novel species of the genus Rhizobium for which the name Rhizobium azibense is proposed. Strain 23C2T (=CCBAU 101087= HAMBI3541) was designated as the type strain.International Journal of Systematic and Evolutionary Microbiology 01/2014; 64. DOI:10.1099/ijs.0.058651-0 · 2.80 Impact Factor