Impact of a genetically modified Rhizobium strain with improved nodulation competitiveness on the early stages of arbuscular mycorrhiza formation

Arbuscular mycorrhizal (AM) fungi and the AM symbiosis are key components in agroecosystems, thus, they have been used as biosensors to evaluate the impact of a Rhizobium meliloti strain, that was genetically modified to improve its nodulation competitiveness, when applied as inoculant. It was found that such a rhizobial strain did not interfere with any of a series of processes related to mycorrhiza formation by the representative AM fungus Glomus mosseae. The parameters tested include spore germination, mycelial growth from the mycorrhizal propagules and AM entry point formation on the developing root system of the common host plant Medicago sativa L. Indeed, the genetically modified Rhizobium increased the number of AM colonization units and the nutrient acquisition ability in the mycorrhizal plant, with respect to the wild type rhizobial strain.