Banca de DEFESA: ISABELLY SANTOS ROSADO DE OLIVEIRA

Discussing the host specificity of forest legumes

Forest legumes; Host specificity; Nodulation; Rhizobia; Taxonomy.

Legumes (Leguminosae) constitute the third-largest family of flowering plants, playing crucial roles from an ecological and economic perspective. They are distinguished by their diversity and global distribution, possessing the ability to form symbiosis with nitrogen-fixing bacteria known as rhizobia and can be employed in the restoration of degraded areas. Following advances in the phylogeny of Leguminosae, the family underwent reclassification, identifying six subfamilies. However, the nodulation capacity is restricted to the Caesalpinioideae subfamily (including the Mimosoid clade) and Papilionoideae. The interaction between legumes and rhizobia is typically species-strain-specific, known as host specificity, warranting attention, and studies on this interaction are essential for elucidating the processes determining the establishment and efficiency of symbiosis.The aim of this study was to compare symbiotic efficiency data of rhizobia in forest legume species within different tribes and clades of the aforementioned subfamilies, correlating host specificity with the taxonomy of both bacteria and plants. The study relied on a table compiling basic nodulation data and associating them with colors to facilitate visualization of the nodulation pattern within tribes and clades. The phylogeny of the 16SrRNA gene of isolated strains from host legume species was conducted to identify and/or confirm the bacterial genus identity. The phylogenetic tree revealed the presence of genera such as Bradyrhizobium, Rhizobium, Sinorhizobium, Mesorhizobium, Azorhizobium, and Paraburkholderia. The nodulation pattern indicated the formation of two relevant clusters: the Mimosa Clade, where species exhibited specificity with the Paraburkholderia genus, and the Millettioids Clade, where species nodulated with different genera, indicating promiscuity. The performance of strains BR 3617, BR 5609, and BR6205 stood out due to symbiotic efficiency in species from different tribes and clades. Based on the results, the nodulation process was contextualized, and the observed counterpoint between the Mimosa and Millettioids Clades was discussed. Suggestions for genomic sequencing analysis of isolated strains and identification of nodulation-related genes were proposed for more accurate inferences regarding host specificity.