Aung Zaw Htwe

Phylogeny and nitrogen fixation potential of Bradyrhizobium species isolated from the legume cover crop Pueraria phaseoloides (Roxb.) Benth. in Eastern Cameroon

Abstract Pueraria is an herbaceous, perennial legume crop originating in Asia. Pueraria phaseoloides (Roxb.) Benth. (tropical kudzu) is frequently introduced into production systems and is used as green manure, a cover crop and a forage plant, making it important economically. We used P. phaseoloides as a trap crop to study and characterize soil rhizobia in Eastern Cameroon. Bacteria were isolated from fresh nodules collected from field-grown P. phaseoloides roots. The 16S-23S rRNA internal transcribed spacer (ITS) sequences from 30 bacterial isolates were amplified by polymerase chain reaction (PCR) and the reaction products were sequenced. Phylogenetic analysis revealed that all isolates were ascribed to the genus Bradyrhizobium and were grouped into three clusters of Bradyrhizobium sp. strains, one cluster of B. yuanmingense strains, and one cluster of B. elkanii strains. Acetylene reduction assay (ARA) results indicated that the B. yuanmingense strains had significantly higher nitrogen fixation potential and that they could be used as inoculants to enhance nitrogen fixation in Pueraria grown in Eastern Cameroon.

Enhanced plant growth and/or nitrogen fixation by leguminous and non-leguminous crops after single or dual inoculation of Streptomyces griseoflavus P4 with Bradyhizobium strains

Plant growth-promoting endophytic bacteria have been widely used during crop production for either single inoculation or co-inoculation with nitrogen-fixing bacteria. The effect of Streptomyces griseoflavus P4 on growth of various crops was studied and the effects of co-inoculation on plant growth, nodulation and nitrogen fixation by soybean was investigated. Pot experiments were conducted in an environmentally controlled room. Nitrogen fixation was evaluated based on acetylene reduction activity (ARA). Significant increases in soybean and maize growth performance were observed after inoculation with S. griseoflavus P4, although some growth parameters were not significant in some crops. S. griseoflavus P4 was co-inoculated with high nitrogen-fixing strains. Co-inoculation of Bradyrhizobium elkanii AHY3-1 with P4 into the Yezin-6 (non-Rj) soybean cultivar resulted in significantly increased root dry weight. Nitrogenase activity also increased due to co-inoculation of B. elkanii AHY3-1 with P4 when compared with single inoculation of this strain. Co-inoculation of Bradyrhizobium japonicum SAY3-7 and B. elkanii AHY3-1 with S. griseoflavus P4 into the Yezin-11 (Rj4) soybean cultivar increased nitrogen fixation significantly by 45 and 31%, respectively, when compared with single inoculation of these strains. Moreover, single or dual inoculation of bradyrhziobial strains resulted in significantly higher shoot biomass than that in the control and P4 alone. These results show that plant growth was promoted by S. griseoflavus P4 and that plant growth and nitrogen fixation were enhanced in soybean after co-inoculation of S. griseoflavus P4 with the Bradyrhizobium strains, B. japonicum SAY3-7 and B. elkanii AHY3-1. Key words: Co-inoculation, growth, nitrogenase activity, single inoculation, soybean, Streptomyces griseoflavus P4.

Effects of co-inoculation of Bradyrhizobium japonicum SAY3-7 and Streptomyces griseoflavus P4 on plant growth, nodulation, nitrogen fixation, nutrient uptake, and yield of soybean in a field condition

ABSTRACT Co-inoculation of nitrogen-fixing bacteria with plant growth-promoting bacteria has become more popular than single inoculation of rhizobia or plant-growth-promoting bacteria because of the synergy of these bacteria in increasing soybean yield and nitrogen fixation. This study was conducted to investigate the effects of Bradyrhizobium japonicum SAY3-7 and Streptomyces griseoflavus P4 co-inoculation on plant growth, nodulation, nitrogen fixation, nutrient uptake, and seed yield of the ‘Yezin-6’ soybean cultivar. Nitrogen fixation was measured using the acetylene reduction assay and ureide methods. Uptake of major nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)] was also measured. This study showed that single inoculation of SAY3-7 significantly increased shoot biomass; nodulation; Relative Ureide Index (RUI %), percent nitrogen derived from N fixation (% Ndfa); N, P, K, Ca, and Mg uptakes; during the later growth stages (R3.5 and R5.5), compared with control. These observations indicate that SAY3-7 is an effective N-fixing bacterium for the plant growth, nodulation, and nitrogen fixation with an ability to compete with native bradyrhizobia. Co-inoculation of SAY3-7 and P4 significantly improved nodule number; nodule dry weight; shoot and root biomass; N fixation; N, P, K, Ca, and Mg uptake; at various growth stages and seed yield in ‘Yezin-6’ soybean cultivar compared with the control, but not the single inoculation treatments. Significant differences in plant growth, nodulation, N fixation, nutrient uptake, and yield between co-inoculation and control, not between single inoculation and control, suggest that there is a synergetic effect due to co-inoculation of SAY3-7 and P4. Therefore, we conclude that Myanmar Bradyrhizobium strain SAY3-7 and P4 will be useful as effective inoculants in biofertilizer production in the future.

Symbiotic effectiveness of different indigenous Bradyrhizobium strains on selected Rj-genes harboring Myanmar soybean cultivars

Many scientists are working to identify effective strains of rhizobia to increase nitrogen fixation and reduce nitrogen fertilizer application. Symbiotic nitrogen fixation of leguminous crops has become an alternative to nitrogenous fertilizer, due to its higher efficiency for nitrogen fixation. This experiment was conducted to select strains for improved nitrogen fixation of soybean (Glycine max L.). Bradyrhizobium strains isolated from Myanmar were evaluated for symbiotic efficacy, using the cultivar Yezin-6 (non-Rj). Five Bradyrhizobium strains, B. japonicum SAY3-7, B. elkanii AHY3-1, B. liaoningense SMY3-1, Bradyrhizobium spp. AHY3-6 and B. yuanmingense SMY6-10 were shown to have superior nitrogenase activity. These five strains were evaluated for their effectiveness on different Rj-genes in soybean cultivars. The nitrogen fixation of B. japonicum SAY3-7, B. elkanii AHY3-1 and B. liaoningense SMY3-1 were higher than other indigenous strains and the standard strain, B. japonicum USDA110. This was particularly the case for the cultivars Yezin-6 (non-Rj) and Yezin-11 (Rj4), but not for the cultivarsYezin-9 (Rj3) and Yezin-10 (Rj2Rj3). Bradyrhizobium japonicum SAY3-7, B. elkanii AHY3-1 and B. liaoningense SMY3-1 were also evaluated on Yezin-8 (non-Rj) and Yezin-3 (Rj4). Bradyrhizobium japonicum SAY3-7 had significantly higher nitrogenase activity on Yezin-8 (non-Rj), although B. japonicum SAY3-7 was not significantly different than B. elkanii AHY3-1 and B. liaoningense SMY3-1 on Yezin-3 (Rj4). Therefore, B. japonicum SAY3-7, which was the most effective nitrogen fixing strain in all the experiments, was selected for inoculant production. According to this study, it can be concluded that the strains were specific to cultivars and,thus, selection of a strain compatible to a specific cultivar is necessary to increase symbiotic nitrogen fixation. Key words: Bradyrhizobium strains, Myanmar, nitrogenase activity, Rj-genes, soybean.

Draft Genome Sequences of Bradyrhizobium elkanii Strains BLY3-8 and BLY6-1, Which Are Incompatible with Rj3 Genotype Soybean Cultivars

ABSTRACT We report here the draft genome sequences of Bradyrhizobium elkanii strains BLY3-8 and BLY6-1, which are incompatible with Rj3 genotype soybean cultivars. The genome sequences of these strains will be useful to identify a causal gene for this incompatibility.

Selection of type A and type B strains for improving symbiotic effectiveness on non-Rj and Rj4 genotype soybean varieties

ABSTRACT The selection of effective rhizobia for higher efficiency nitrogen fixation is one of the most important steps for inoculant production. Therefore, this experiment was conducted to select the most effective type A and type B strains for specific Rj-gene harboring soybean varieties and to test the symbiotic effectiveness of selected strains on different Rj-gene harboring soybean varieties. Screening experiments using the specific soybean varieties were done with a completely randomized design and three replications in this study. Evaluation of the effective Myanmar Bradyrhizobium strains for plant growth, nodulation and N2 fixation were studied in pot experiments using sterilized vermiculite in the Phytotron (controlled-environmental condition). Then, a pot experiment was conducted using Futsukaichi soil in the screen house (natural environmental condition). The N2 fixation ability of soybean was evaluated by acetylene reduction activity (ARA) and the relative ureide index method. In the first screening experiment, type A and type B strains with higher nitrogen fixation and proper nodulation on their respective soybean cultivars were selected for the next screening. In the second screening, Bradyrhizobium elkanii AHY3-1 (type A), Bradyrhizobium japonicum SAY3-7 (type A), B. elkanii BLY3-8 (type B) and B. japonicum SAY3-10 (type B) isolates, which showed higher nitrogen fixation and nodulation in Yezin-3 (Rj4) and Yezin-6 (non-Rj), were selected for the next experiment. In the third screening experiment, SAY3-7 and BLY3-8, which had higher nitrogen fixing potential and proper nodulation, were selected as effective isolates. These two isolates were compatible with non-Rj and Rj4 soybean varieties for nodulation and nitrogen fixation. Based on the results of the screening experiment, these two strains were tested for their symbiotic efficacy in Futsukaichi soil. This study shows that inoculation treatment of SAY3-7 and BLY3-8 significantly increased plant growth, nodulation, and N2 fixation at the V6, R3.5 and R8 stages in Yezin-3 (Rj4) and/or Yezin-6 (non-Rj), and the seed yield at R8 stage, in Yezin-3 (Rj4) and Yezin-6 (non-Rj) soybean varieties compared with the control treatment. It can be concluded that SAY3-7 and BLY3-8 are suitable for inoculant production because of their higher nitrogen fixation ability, proper nodulation and better productivity of Myanmar soybean cultivars.

Effects of co-inoculation of Bradyrhizobium elkanii BLY3-8 and Streptomyces griseoflavus P4 on Rj4 soybean varieties

ABSTRACT Co-inoculation of selected nitrogen-fixing bacteria with plant growth-promoting bacteria is the promising way for the improvement of soybean production through enhancing plant growth, nodulation, and N2 fixation. Therefore, this experiment was conducted to study the effects of co-inoculation of Bradyrhizobium elkanii BLY3-8 with Streptomyces griseoflavus P4 on plant growth, nodulation, N2 fixation, N uptake, and seed yield of Rj4 soybean varieties. Two experiments with completely randomized design and three replicates were done in this study. N2-fixation ability of soybean was evaluated by acetylene reduction activity (ARA) and relative ureide method. In the first experiment, synergetic effect in N2 fixation and nodulation was occurred in co-inoculation treatment (BLY3-8 + P4) in Yezin-3 and Fukuyutaka. Based on these results, co-inoculation effect of BLY3-8 and P4 was assessed on Yezin-3 and Fukuyutaka varieties at three different growth stages, using Futsukaichi soil under natural environmental conditions. This study shows that co-inoculation of BLY3-8 and P4 significantly increased N2 fixation at V6 stage; plant growth, nodulation, N2 fixation, and N uptake at R3.5 stage; and shoot growth, N uptake, and seed yield at R8 stage, in Rj4 soybean varieties compared with the control. Significant difference in plant growth, nodulation, N2 fixation, N uptake, and yield between co-inoculation and control, not between single inoculation and control, suggests that there is a synergetic effect due to co-inoculation of BLY3-8 and P4.

Effects of Fermented Nori ( Pyropia yezoensis ) Seaweed Liquid Fertilizers on Growth Characteristics, Nutrient Uptake, and Iodine Content of Komatsuna ( Brassica rapa L.) Cultivated in Soil

We investigated the effects of fermented nori (Pyropia yezoensis) liquid fertilizers on plant growth, soil plant analysis development (SPAD) values, and nutrient uptake of komatsuna (Brassica rapa L. var. wakana komatsuna) plants. The four types of fermented nori seaweed liquid fertilizers (SLFs) evaluated in this study were prepared by anaerobic fermentation of unwashed nori (SLF1), aerobic fermentation of unwashed nori (SLF2), anaerobic fermentation of washed nori (SLF3), and aerobic fermentation of washed nori (SLF4). In Experiment 1, the highest plant growth, SPAD, and nutrient uptake values were obtained from treatment with SLF2 and SLF4. There were no significant differences between the effects of basal and foliar application of SLFs, except for iodine (I) content; plants treated with SLF1 had the highest I content. In Experiment 2, plant growth and nutrient uptake decreased with higher concentrations of SLFs. Plants treated with 25% SLF2 + 75% chemical fertilizer (CF) or 25% SLF4 + 75% CF exhibited significantly higher plant growth and nutrient uptake. The highest I content resulted from treatment with 75% SLF1 + 25% CF or 100% SLF1. Taken together, our results showed that 25% SLF + 75% CF produced the best plant growth characteristics, nutrient uptake, and I content relative to the controls. Therefore, basal application of these liquid organic fertilizers can be used to increase productivity, nutrient uptake, and I content and to reduce nitrate-nitrogen content in komatsuna production.