Rhizobial diversity in shrub-tree legume-based silvopastoral systems

Abstract

Silvopastoral systems based on tree legumes intercropped with forage grasses can harbor a high diversity of rhizobia, and these bacteria are good indicators of soil quality in several management systems. The objective of this work was to evaluate the morphophysiological, genetic and symbiotic diversity of cowpea [Vigna unguiculata (L.) Walp] rhizobia from soils under silvopastoral systems based on shrub-tree legumes. The experiment was performed in a randomized block design with three treatments and three replications, consisting of signalgrass (Urochloa decumbens Stapf.) intercropped with sabia (Mimosa caesalpiniaefolia); signalgrass intercropped with gliricidia (Gliricidia sepium) and single signalgrass. The samples were collected in the legume row (0 meter) and 4 and 8 meters away.Later, cowpea was used as a trap plant to capture the rhizobia. All strains were phenotypically characterized, authenticated, and genetically identified. Phenotypical characterization of the 431 isolates showed high diversity forming 69 groups at 100% similarity, of which 60 were able to nodulate cowpea during the authentication, and 36 presented relative efficiency superior or equal to the recommended bacteria for the crop. Most of the sequenced strains belonged to Bradyrhizobium (67%) and Methylobacterium (9%). Leifsonia (9%), Cohnella (6%), Rhizobium (3%), Burkholderia (3%), and Paenibacillus (3%) were also represented. Soils under silvopastoral systems harbor efficient rhizobia populations in cowpea with a high genetic diversity, which can be recommended for agronomic efficiency assays.