Abstract
Groundnut is an economically important N2-fixing legume that can contribute about 100–190kgNha−1 to cropping systems. In this study, groundnut-nodulating native rhizobia in South African soils were isolated from root nodules. Genetic analysis of isolates was done using restriction fragment length polymorphism (RFLP)-PCR of the intergenic spacer (IGS) region of 16S-23S rDNA. A total of 26 IGS types were detected with band sizes ranging from 471 to 1415bp. The rhizobial isolates were grouped into five main clusters with Jaccard's similarity coefficient of 0.00–1.00, and 35 restriction types in a UPGMA dendrogram. Partial sequence analysis of the 16S rDNA, IGS of 16S rDNA-23S rDNA, atpD, gyrB, gltA, glnII and symbiotic nifH and nodC genes obtained for representative isolates of each RFLP-cluster showed that these native groundnut-nodulating rhizobia were phylogenetically diverse, thus confirming the extent of promiscuity of this legume. Concatenated gene sequence analysis showed that most isolates did not align with known type strains, and may represent new species from South Africa. This underscored the high genetic variability associated with groundnut Rhizobium and Bradyrhizobium in South African soils, and the possible presence of a reservoir of novel groundnut-nodulating Bradyrhizobium and Rhizobium in the country.
Highlights
The use and cultivation of groundnut (Arachis hypogaea L.) dates back to 350 BC in its native South America where it has been used for thousands of years [1]
A total of 71 bacterial isolates were obtained from the root nodules of groundnut planted in South African soils, and 46 of the isolates elicited nodulation in groundnut under glasshouse conditions
The intergenic spacer (IGS) polymerase chain reaction (PCR)-amplified product yielded polymorphic bands in the rhizobial isolates tested from groundnut
Summary
The use and cultivation of groundnut (Arachis hypogaea L.) dates back to 350 BC in its native South America where it has been used for thousands of years [1]. Traders were responsible for spreading groundnut from South America to Asia and Africa [18]. The Spanish and Portuguese explorers brought groundnut on their voyages to Africa. West Africa Portuguese traders in the 16th century introduced the crop. Nitrogen fixation by legume-rhizobia symbiosis plays a major role in sustaining soil health for crop production. This process is influenced by many factors, which include geographic location, soil type and host-plant genotypes, as well as the rhizobial symbiont itself [36].
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