In vitro Evaluation of Plant Growth-Promoting Endophytes from Bambara Groundnut Nodules in Côte d’Ivoire

Abstract

In the modern farming process, the misuse of synthetic fertilizers has led to significant pollution of soil, air and water. The excessive use of these chemicals has deleterious effects on soil microorganisms, affects soil fertility and also pollutes the environment. Now, one of the main challenges of agriculture in West Africa, particularly in Côte d’Ivoire, is to be able to ensure high agricultural productivity while preserving the environment. Therefore, the use of PGPR endophytic bacteria presents itself as an alternative to the use of chemical fertilizers to improve crop productivity. Some endophytes which are considered as PGPR can promote plant growth trough mobilization of nutrients in soils, production of plant growth regulators, protection of plants from hytopathogens by controlling or inhibiting them, and improvement of soil structure. In order to select the most effective endophytic bacteria to be used as biofertilizers, the objective of this study is to evaluate the PGPR potential of bacteria isolated from Bambara groundnut nodules in vitro. To accomplish this, 34 endophytic bacteria isolated from the nodules of 5 varieties of Bambara groundnut in soils from 5 localities of Daloa, which had been the subject of molecular characterization, were tested to evaluate their capacity to produce AIA and siderophores, to solubilize phosphate. The AIA production test was carried out on YEM supplemented with L-tryptophan, that of phosphate solubilization on Pikovskaya medium (PVK) and that of siderophore production on Chrome Azurol S medium (CAS medium). Generally, all strains were able to produce a detectable amount of IAA which ranged from 16.3 to 275.5µg/ml, to solubilize phosphate in amounts ranging from 16 to 453,45µg/ml and produce siderophore with indexes ranged from 1,08 to 5,36. In total, 19 strains showed multi-PGP traits and could be promising biofertilizers. These endophytic bacteria have the potential to be used in sustainable agriculture as biofertilizers and can help reduce the dependence on synthetic chemicals, which contributes to the preservation of the environment. In perspective, it would be interesting to test the 19 strains with multi-PGPR traits under field conditions to determine the effectiveness of bacterial strains on the development and yield of Bambara pea plants in order to select the most efficient bacterial strains and propose them as biofertilizers.