Symbiotic diversity, specificity and distribution of rhizobia in native legumes of the Core Cape Subregion (South Africa)

• DOI: 10.1093/femsec/fiu024
• Publication Date: 2015-01-09T19:54:02Z
• Authors: Benny Lemaire; Oscar Dlodlo; Samson Chimphango; Charles Stirton; Brian Schrire; James S. Boatwright; Olivier Honnay; Erik Smets; Janet Sprent; Euan K. James; Abraham M. Muasya
• Keywords: 0301 basic medicine; 570; host preference; Burkholderia; root nodulation; 630; Host Specificity; South Africa; 03 medical and health sciences; Bacterial Proteins; RNA, Ribosomal, 16S; Fynbos legumes; Bradyrhizobium; Symbiosis; Phylogeny; Base Sequence; Mesorhizobium; in situ immunogold labelling; Fabaceae; Biodiversity; 15. Life on land; Rec A Recombinases; Oxidoreductases; Root Nodules, Plant; Acyltransferases; Rhizobium

Rhizobial diversity and host preferences were assessed in 65 native Fynbos legumes of the papilionoid legume tribes Astragaleae, Crotalarieae, Genisteae, Indigofereae, Millettieae, Phaseoleae, Podalyrieae, Psoraleeae and Sesbanieae. Sequence analyses of chromosomal 16S rRNA, recA, atpD and symbiosis-related nodA, nifH genes in parallel with immunogold labelling assays identified the symbionts as alpha- (Azorhizobium, Bradyrhizobium, Ensifer, Mesorhizobium and Rhizobium) and beta-rhizobial (Burkholderia) lineages with the majority placed in the genera Mesorhizobium and Burkholderia showing a wide range of host interactions. Despite a degree of symbiotic promiscuity in the tribes Crotalarieae and Indigofereae nodulating with both alpha- and beta-rhizobia, Mesorhizobium symbionts appeared to exhibit a general host preference for the tribe Psoraleeae, whereas Burkholderia prevailed in the Podalyrieae. Although host genotype was the main factor determining rhizobial diversity, ecological factors such as soil acidity and site elevation were positively correlated with genetic variation within Mesorhizobium and Burkholderia, respectively, indicating an interplay of host and environmental factors on the distribution of Fynbos rhizobia.