Native legumes of the Farrapos protected area in Uruguay establish selective associations with rhizobia in their natural habitat

Abstract

The area known as Farrapos wetlands is a Protected Natural Area of Uruguay and is a RAMSAR site. It is characterized for being one of the most extensive fluvial wetlands of the country, with an important heterogeneity of environments. The aim of this work was to survey native legumes and the nodulating rhizobial symbionts present in this protected area in order to contribute to the conservation of native biological resources. Nodules of legumes growing in their natural habitat were collected for the isolation of rhizobia. Interestingly, each legume species presented nodules with distinct morphologies reinforcing the idea that nodule phenotype can be included as additional information in legume taxonomy studies. Nodulation ability of selected isolates was assessed in gnotobiotic conditions. Isolates were identified by analysing 16S rRNA sequences and characterized by phylogenetic analysis. Papilionoideae legumes harbour rhizobia from the Bradyrhizobium, Rhizobium, Azorhizobium and Ensifer genera, while nodules from the Caesalpinoideae, including the mimosoid clade, harbour Alpha-rhizobia belonging to the Rhizobium, Bradyrhizobium and Mesorhizobium genera, as well as Beta-rhizobia from the Cupriavidus and Paraburkholderia genera. We found that the Farrapos protected area possess a great diversity of rhizobia, with high host specificity in their natural environment.