Stimulation of Soybean (Glycine max) growth and yield using Bradyrhizobium inoculants in the semi-arid environment of Botswana

Background: Crop yields in the semi-arid regions are low due to climatic and soil related constraints.Soybean as one of the most important legume crops grown worldwide, has a role to contribute nitrogen to improve nutrient poor soils in Africa. A study was conducted to examine the effects of Bradyrhizobium spp inoculations on the growth and yield of soybean varieties in a glasshouse.Method: The study was arranged in a randomized complete block factorial design, with factor A being two soybean varieties (Bimha and Status) while factor B was inoculation using four Bradyrhizobium strains and the uninoculated control. Results: Bradyrhizobium inoculation significantly (P less than 0.001)affected days to 50% flowering, days to emergence, nodule number, root dry weight and grain yield and yield traits. Parameters that were affected by both inoculant strain and variety included days to 50% flowering, days to emergence, number of pods per plant, pod weight and number of seeds per pod. The interaction effect of variety and Bradyrhizobium inoculant strain was observed only on number of pods per plants. Our study shows that soybean grows well when inoculated with Bradyrhizobium inoculants, in semi-arid conditions of Botswana.

Characterization of Bradyrhizobium spp. Nodulating Lupinus cosentinii and L. luteus Microsymbionts in Morocco

In this work, we analyzed the diversity of the nodule-forming bacteria associated with Lupinus luteus and Lupinus cosentinii grown in the Maamora Cork oak forest acidic soils in Morocco. The phenotypic analysis showed the high diversity of the strains nodulating the two lupine's species. The strains were not tolerant to acidity or high alkalinity. They do not tolerate salinity or high temperatures either. The strains isolated from L. luteus were more tolerant to antibiotics and salinity than those isolated from L. cosentinii. The plant growth promoting (PGP) activities of our strains are modest, as among the 28 tested isolates, only six produced auxins, six produced siderophores, whereas three solubilized phosphates. Only two strains possess the three activities. The rrs gene sequences from eight representative strains selected following ARDRA and REP-PCR results revealed that they were members of the genus Bradyrhizobium. Six strains were then retained for further molecular analysis. The glnII, recA, gyrB, dnaK, and rpoB housekeeping gene sequence phylogeny showed that some strains were close to B. lupini LMG28514T whereas others may constitute new genospecies in the genus Bradyrhizobium. The strains were unable to nodulate Glycine max and Phaseolus vulgaris and effectively nodulated L. luteus, L. cosentinii, L. angustifolius, Chamaecytisus albidus, and Retama monosperma. The nodC and nodA symbiotic gene phylogenies showed that the strains are members of the genistearum symbiovar.

Growth and Competitive Infection Behaviors of Bradyrhizobium japonicum and Bradyrhizobium elkanii at Different Temperatures

Growth and competitive infection behaviors of two sets of Bradyrhizobium spp. strains were examined at different temperatures to explain strain-specific soybean nodulation under local climate conditions. Each set consisted of three strains—B. japonicum Hh 16-9 (Bj11-1), B. japonicum Hh 16-25 (Bj11-2), and B. elkanii Hk 16-7 (BeL7); and B. japonicum Kh 16-43 (Bj10J-2), B. japonicum Kh 16-64 (Bj10J-4), and B. elkanii Kh 16-7 (BeL7)—which were isolated from the soybean nodules cultivated in Fukagawa and Miyazaki soils, respectively. The growth of each strain was evaluated in Yeast Mannitol (YM) liquid medium at 15, 20, 25, 30, and 35 °C with shaking at 125 rpm for one week while measuring their OD660 daily. In the competitive infection experiment, each set of the strains was inoculated in sterilized vermiculite followed by sowing surface-sterilized soybean seeds, and they were cultivated at 20/18 °C and 30/28 °C in a 16/8 h (day/night) cycle in a phytotron for three weeks, then nodule compositions were determined based on the partial 16S-23R rRNA internal transcribes spacer (ITS) gene sequence of DNA extracted from the nodules. The optimum growth temperatures were at 15–20 °C for all B. japonicum strains, while they were at 25–35 °C for all B. elkanii strains. In the competitive experiment with the Fukagawa strains, Bj11-1 and BeL7 dominated in the nodules at the low and high temperatures, respectively. In the Miyazaki strains, BjS10J-2 and BeL7 dominated at the low and high temperatures, respectively. It can be assumed that temperature of soil affects rhizobia growth in rhizospheres and could be a reason for the different competitive properties of B. japonicum and B. elkanii strains at different temperatures. In addition, competitive infection was suggested between the B. japonicum strains.

Bradyrhizobium spp. inoculation associated with nitrogen application enhances the quality of soybean seeds

ABSTRACT The physiological seed quality can be altered by nutritional management of the soybean crop, especially by the fertilization with nitrogen (N), which is a structural component of several organic compounds, including proteins, and has an important catalytic role in the activation of several enzymes. The aim of this research was to investigate the effects of sources and application rates of mineral N fertilizer associated with inoculation of Bradyrhizobium spp. on physiological quality of soybean seeds. The treatments were arranged in a completely randomized block design, in a 3 × 5 factorial arrangement [three N fertilizer sources (Bradyrhizobium spp. inoculation; Bradyrhizobium spp. inoculation + urea application; and, Bradyrhizobium spp. inoculation + ammonium sulfate application) and five N application rates (0, 50, 100, 150 and 200 kg N ha-1)], with four replicates. Nitrogen fertilizer was applied in topdressing at R2 stage when soybean plants were in full flowering. The quality parameters evaluated in soybean seeds were: 1,000-seed mass, seed protein content, germination, first germination count test, seedling emergence, emergence speed index, accelerated aging, electrical conductivity, vigor and viability of seeds by tetrazolium test. The application of 50 kg N ha-1 of mineral fertilizer (ammonium sulfate or urea) associated with the Bradyrhizobium spp. inoculation enhanced the physiological quality of soybean seeds, resulting in higher seed germination percentage and higher emergence and seedling emergence speed index. The application of ammonium sulfate or urea (50 kg N ha-1) at full flowering of soybean plants inoculated with Bradyrhizobium spp. can improve the physiological quality of soybean seeds.

Effect of fungicides on the symbiosis between Bradyrhizobium strains and peanut

ABSTRACT Seed treatment with fungicides is an important practice for the control of phytopathogens in peanut crops. However, these products can harm rhizobacteria (Bradyrhizobium) and inhibit processes such as biological nitrogen fixation. This study aimed to verify the effects of the treatment of peanut seeds cv. BR1 inoculated with Bradyrhizobium spp. with fungicides. The experiment was conducted in a greenhouse, using two combinations of fungicides [C1: carboxin (200 g L-1) + tiram (200 g L-1); C2: pyraclostrobin (25 g L-1) + thiophanate methyl (225 g L-1) + fipronil (250 g L-1)] and one control without fungicide; two inoculants based on Bradyrhizobium spp. (SEMIA 6144 and ESA 123) and one control with a nitrogen chemical source (ammonium nitrate). The experimental design was completely randomized, in a 3 (2 with fungicide and 1 without fungicide) x 4 (2 inoculations based on rhizobia, 1 N mineral source and 1 without N) x 2 (1 or 2 inoculants applications) factorial scheme, with 5 replications. The root and shoot dry mass, plant height, nodulation and leaf nitrogen accumulation were evaluated. The application of both combinations reduced the number of nodules on plant roots, mainly for C1. The vegetative growth and nitrogen in the leaves were affected by C1, whereas, for C2, there were increments higher than for the control without fungicides. ESA 123 was more tolerant to the effects of fungicides on nodulation. Regarding the number of inoculations, there was an increase in the nitrogen rate with two inoculations. C2, despite affecting the nodulation, was less toxic to the inoculants SEMIA 6144 and ESA 123.