Identification and distribution of microsymbionts associated with soybean nodulation in Mozambican soils

Cynthia Gyogluu,Sanjay K Jaiswal,Stephen Kyei-Boahen,Felix D Dakora

doi:10.1016/j.syapm.2018.05.003

Cynthia Gyogluu, Sanjay K Jaiswal + Show 2 more

Open Access

https://doi.org/10.1016/j.syapm.2018.05.003

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Abstract

Indigenous soybean rhizobial strains were isolated from root nodules sampled from farmers’ fields in Mozambique to determine their identity, distribution and symbiotic relationships. Plant infection assays revealed variable nodulation and symbiotic effectiveness among the 43 bacterial isolates tested. Strains from Ruace generally promoted greater whole-plant growth than the others. 16S rRNA-RFLP analysis of genomic DNA extracted from the rhizobial isolates produced different banding patterns, a clear indication of high bacterial diversity. However, the multilocus sequence analysis (MLSA) data showed alignment of the isolates with B. elkanii species. The 16S rRNA sequences of representative soybean isolates selected from each 16S rRNA-RFLP cluster showed their relatedness to B. elkanii, as well as to other Bradyrhizobium species. But a concatenated phylogeny of two housekeeping genes (glnII and gyrB) identified the soybean nodulating isolates as Bradyrhizobium, with very close relatedness to B. elkanii. The nifH and nodC sequences also showed that the majority of the test soybean isolates were closely related to B. elkanii, albeit the inconsistency with some isolates. Taken together, these findings suggest that the B. elkanii group are the preferred dominant microsymbiont of soybean grown in Mozambican soils. Furthermore, the distribution of soybean rhizobia in the agricultural soils of Mozambique was found to be markedly influenced by soil pH, followed by the concentrations of plant-available P and Mn. This study suggested that the identified isolates TUTMJM5, TUTMIITA5A and TUTLBC2B can be used as inoculants for increased soybean production in Mozambique.

Highlights

Interest in soybean cultivation in Africa is increasing due to its high protein content of grain for human consumption and for use as animal feed
Ernment interest in promoting soybean production in Mozambique necessitates the creation of new knowledge for increasing the grain yield of this legume
Understanding the genetic diversity of soybean rhizobia is important for discovering new genera, species and strains for developing new technologies, including the production of inoculants, for increased soybean yield

Summary

Introduction

Interest in soybean cultivation in Africa is increasing due to its high protein content of grain for human consumption and for use as animal feed. In Mozambique, there is an increasing demand for soybean, driven largely by the poultry industry and for exportation. This has led to many farmers switching to soybean production [42], as it offers them an income opportunity for their livelihood [19]. Soybean cultivation in Mozambique is dominated by smallholder farmers who use little or no inputs. The increase was due to the application of inputs such as bacterial

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