Assessing host range, symbiotic effectiveness, and photosynthetic rates induced by native soybean rhizobia isolated from Mozambican and South African soils

Abstract

Host range and cross-infectivity studies are important for identifying rhizobial strains with potential for use as inoculants. In this study, 10 native soybean rhizobia isolated from Mozambican and South African soils were evaluated for host range, symbiotic effectiveness and ability to induce high rates of photosynthesis leading to enhanced plant growth in cowpea (Vigna unguiculata L. Walp.), Bambara groundnut (Vigna subterranean L. Verdc.), Kersting’s groundnut (Macrotyloma geocarpum Harm) and soybean (Glycine max L. Merr). The test isolates had different growth rates and colony sizes. Molecular analysis based on enterobacterial repetitive intergenic consensus (ERIC)-PCR revealed high genetic diversity among the test isolates. The results further showed that isolate TUTLBC2B failed to elicit nodulation in all test plants, just as TUTNSN2A and TUTDAIAP3B were also unable to nodulate cowpea, Kersting’s bean and Bambara groundnut. Although the remaining strains formed ineffective nodules on cowpea and Kersting’s bean, they induced effective nodules on Bambara groundnut and the two soybean genotypes. Bacterial stimulation of nodule numbers, nodule dry weights and photosynthetic rates was generally greater with isolates TUTRSRH3A, TUTM19373A, TUTMCJ7B, TUTRLR3B and TUTRJN5A. As a result, these isolates elicited significantly increased accumulation of biomass in shoots and whole plants of Bambara groundnut and the two soybean genotypes. Whole-plant symbiotic nitrogen (N) of soybean and Bambara groundnut was highest for the commercial strains CB756 and WB74, as well as for TUTRLR3B, TUTMCJ7B and TUTRSRH3A, suggesting that the three native rhizobial isolates have potential for use as inoculants.

Symbiotic N2 Fixation and Grain Yield of Endangered Kersting's Groundnut Landraces in Response to Soil and Plant Associated Bradyrhizobium Inoculation to Promote Ecological Resource-Use Efficiency

“…Even the B values obtained from inoculation of landraces Puffeun and Funsi with the commercial Bradyrhizobium strain CB756 differed for whole plants, though similar at the organ level. These findings are consistent with earlier reports which showed variable response of legume genotypes to rhizobial inoculation under both field and glasshouse conditions (Gyogluu et al, 2017 ; Kyei-Boahen et al, 2017 ; Mbah and Dakora, 2017 ). In this study, an increase in nodulation, whether by native soil rhizobia or the introduced strain CB756, did not always translate into better plant growth, higher N 2 fixation, and/or greater grain yield.…”

“…Thus, the success of rhizobial inoculation in the field is often measured by the extent of nodulation, N 2 fixation, plant growth and grain yield when compared to uninoculated control (Kyei-Boahen et al, 2017 ). Of the many techniques available, the 15 N natural abundance has been very successful in quantifying N 2 fixation by grain legumes under field conditions (Mohale et al, 2014 ; Mapope and Dakora, 2016 ; Gyogluu et al, 2017 ).…”

Widespread Distribution of Highly Adapted Bradyrhizobium Species Nodulating Diverse Legumes in Africa

“…B. elkanii is also reported to be the major microsymbiont nodulating soybean in Malawian and Kenyan soils (Herrmann et al, 2014; Parr, 2014). Jaiswal et al (2016), Naamala et al (2016), and Gyogluu et al (2018) have similarly found B. elkanii and some native Bradyrhizobium species to be the dominant symbionts species nodulating soybean in South Africa, Mozambique and Ethiopia. Geographically speaking, an earlier study by Abaidoo et al (2000) also indicated that B. elkanii and B. japonicum were the most dominant bacterial symbionts isolated from root nodules of soybean in Benin, Cameroon, Ghana, Nigeria, Togo, and Uganda.…”

“…These so-called promiscuous TGx soybean genotypes can fix more N 2 than the strict nodulating varieties from North America due to their ability to form more effective symbiosis with indigenous Bradyrhizobium strains in African soils (Mpepereki et al, 2000). The TGx soybean varieties also seem to have the ability to attract diverse indigenous bradyrhizobia in African soils as shown by B. japonicum, B. diazoefficiens , and B. elkanii which were recently identified as the dominant strains nodulating soybean in South Africa, Ethiopia, and Mozambique (Jaiswal et al, 2016; Naamala et al, 2016; Chibeba et al, 2017; Gyogluu et al, 2018). B. elkanii is also reported to be the major microsymbiont nodulating soybean in Malawian and Kenyan soils (Herrmann et al, 2014; Parr, 2014).…”

Insights into the Phylogeny, Nodule Function, and Biogeographic Distribution of Microsymbionts Nodulating the Orphan Kersting’s Groundnut [ Macrotyloma geocarpum (Harms) Marechal & Baudet] in African Soils

“…During the symbiotic process, which commences via intricate molecular dialogue between legumes and their compatible rhizobia, bacteroids in root nodules exchange fixed N for C compounds from photosynthesis (23). As a result, photosynthetic rates and shoot biomass accumulation are often used as measures of N 2 -fixing efficiency in purely symbiotic systems (14).…”