Abstract
Lotus spp. are widely used as a forage to improve pastures, and inoculation with elite rhizobial strains is a common practice in many countries. However, only a few Lotus species have been studied in the context of plant-rhizobia interactions. In this study, forty highly diverse bacterial strains were isolated from root nodules of wild Lotus parviflorus plants growing in two field locations in Portugal. However, only 10% of these isolates could nodulate one or more legume hosts tested, whereas 90% were thought to be opportunistic nodule associated bacteria. Phylogenetic studies place the nodulating isolates within the Bradyrhizobium genus, which is closely related to B. canariense and other Bradyrhizobium sp. strains isolated from genistoid legumes and Ornithopus spp. Symbiotic nodC and nifH gene phylogenies were fully consistent with the taxonomic assignment and host range. The non-nodulating bacteria isolated were alpha- (Rhizobium/Agrobacterium), beta- (Massilia) and gamma-proteobacteria (Pseudomonas, Lysobacter, Luteibacter, Stenotrophomonas and Rahnella), as well as some bacteroidetes from genera Sphingobacterium and Mucilaginibacter. Some of these nodule-associated bacteria expressed plant growth promotion (PGP) traits, such as production of lytic enzymes, antagonistic activity against phytopathogens, phosphate solubilization, or siderophore production. This argues for a potential beneficial role of these L. parviflorus nodule-associated bacteria.
Highlights
Lotus is the largest genus of the Loteae tribe, which includes more than 180 species of perennial and annual herbs and small shrubs distributed in the Mediterranean region and in the Western USA [1,2]
We found a great diversity of bacteria inside nodules of wild L. parviflorus plants growing in two different locations in Portugal
Only four of these isolates (10%) were able to nodulate the original host L. parviflorus. These four isolates are slow growers, and phylogenetically related to B. canariense and other Bradyrhizobium strains isolated from legumes, such as L. uliginosus, Ornithopus and other genistoid legumes (e.g., Lupinus) root nodules
Summary
Lotus is the largest genus of the Loteae tribe, which includes more than 180 species of perennial and annual herbs and small shrubs distributed in the Mediterranean region and in the Western USA [1,2]. (Lotus uliginosus, Lotus corniculatus, Lotus tenuis, and Lotus subbiflorus) have forage value and are widely used to improve pastures [2]. Lotus spp. can establish nitrogen-fixing symbioses with certain soil bacteria collectively known as rhizobia. Lotus can either form specific interactions with the intermediate growing Mesorhizobium genus (group I: L. corniculatus and L. tenuis, e.g., [5,6,7]) or with the slow growing, Bradyrhizobium genus (group II: L. uliginosus (Lotus pedunculatus), Lotus angustissimus and L. subbiflorus, e.g., [8,9,10]). It has been found that certain non-cultivated Lotus species interact with rhizobia of the genus Ensifer [12,13,14]. It seems that a lot is to be discovered about Lotus root nodule microsymbionts, especially regarding uncultivated species [15]
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