Effects of soybean variety and Bradyrhizobium strains on yield,protein content and biological nitrogen fixation under cool growing conditions in Germany

Soybean (Glycine max (L.) Merr.) is able to fix atmospheric nitrogen in symbiosis with the bacteria Bradyrhizobium japonicum. Because these bacteria are not native in European soils, soybean seeds must be inoculated with Bradyrhizobium strains before sowing to fix nitrogen and meet their yield potential. In Central Europe soybean cultivation is still quite new and breeding of early maturing soybean varieties adapted to cool growing conditions has just started.Under these low temperature conditions in Central Europe the inoculation with different, commercially available Bradyrhizobium inoculants has resulted in unsatisfactory nodulation. The aim of this study was: (i) to test the ability of commercially available inoculants to maximize soybean grain yield, protein content and protein yield, (ii) to study the interaction of different inoculants with different soybean varieties for two different sites in Germany under cool growing conditions over three years and (iii) to determine the variability of biological nitrogen fixation. Field trials were set up on an organically managed site at the Hessische Staatsdomäne Frankenhausen (DFH) and on a conventionally managed site in Quedlinburg (QLB) for three consecutive seasons from 2011 to 2013. Three early maturing soybean varieties—Merlin, Bohemians, Protina—were tested in combination with four different Bradyrhizobium inoculants—Radicin No.7, NPPL-Hi Stick, Force 48, Biodoz Rhizofilm—and compared with a non-inoculated control. Effective inoculation with Bradyrhizobium strains increased grain yield, protein content and protein yield by up to 57%, 26% and 99%, respectively. Grain yield, protein content and protein yield were generally higher in DFH. Average grain yield was 1634 kg ha⁻¹ in QLB (2012–2013) and 2455 kg ha⁻¹ in DFH (2011–2013), average protein content was 386 g kg⁻¹ in QLB and 389 g kg⁻¹ in DFH and average protein yield was 650 kg ha⁻¹ in QLB and 965 kg ha⁻¹ in DFH. The percentage of nitrogen derived from air (Ndfa) ranged between 40% and 57%. Soybeans inoculated with Radicin No. 7 failed to form nodules, and crop performance was identical to the non-inoculated control. Biodoz Rhizofilm, NPPL Hi-Stick and Force 48 are suitable for soybean cultivation under cool growing conditions in Germany. Interactions between soybean variety and inoculant were significant for protein content and protein yield at both sites, but not for nodulation, grain yield, thousand kernel weight and Ndfa. The variety Protina in combination with the inoculant Biodoz Rhizofilm can be recommended for tofu for both tested sites, while Merlin and Protina in combination with Biodoz Rhizofilm are recommended for animal fodder production in DFH. Animal fodder production was not profitable in QLB due to low protein yields.     

EFFECTS OF pH ON GROWTH AND NODULATION OF TWO FORAGE LEGUMES

A study was conducted to compare the responses to acid pH of Medicago sativa and Lotus glaber, two forage legumes with different environmental requirements, either supplied with inorganic nitrogen (N) or inoculated with different strains of their nodule bacteria. Medicago sativa showed, in both treatments, a significant reduction in total dry weight at pH below 6.0. In contrast, Lotus glaber grew equally well at all the pHs assayed in the presence of adequate N. Under inoculated conditions, in the absence of N supply, plant growth was dependent on the bacterial strain used. When the ability of each strain to multiply in culture medium was examined, it was observed that Sinorhizobium meliloti strains showed a pH-sensitive response that inhibited growth at pH 4.0, whereas Mesorhizobium loti strains showed normal growth at this pH. These results suggest that for the effectiveness of Mesorhizobium loti–Lotus glaber symbiosis in acid soils the major factor to be considered is the tolerance of the bacterial strain to acid conditions, while the limiting factors for the Sinorhizobium meliloti–Medicago sativa symbiosis are the sensitivity to low pH of both the plant and its bacteria.     

Effects of sludge on germination and initial growth performance of Leucaena leucocephala seedlings in the nursery

A study was carried out to determine the influence of different types of sludges （municipal, industrial and residential） on field germination, growth and nodulation of L. leucocephala seedlings in the nursery. Before sowing of seeds, different combinations of sludges were incorporated with the nutrient deficient natural forest soils. Field germination, nodulation status and physical growth parameters of seedlings （shoot and root length, vigor index, collar diameter, leaf number, fresh and dry weight of shoot and root and total dry biomass increment） were recorded after three and six months of seed sowing. Field germination, nodulation status and growth parameters were varied significantly in the soil amended with sludges in comparison to control. The highest number of nodule was recorded from soil amended with residential sludge （ 1：1 ） and highest fresh and dry nodule weight was also found from the same combination in both three and six month old seedlings. In case of growth parameters, the highest growth was recorded from soil and residential sludge （ 1：1 ） combination compared to control. From the study, it can be recommended that soil amended with residential sludge （ 1：1 ） provide better field germination, growth and nodule formation of L. leucocephala in degraded soil.     

豆科木本植物根部特征与结瘤的关系

选取了11种豆科木本植物，比较了它们的根部外部形态和解剖结构特点，分析这些特点与结瘤的关系。结果表明，结瘤豆科植物的根系松软，颜色较浅，为白色或土黄色；不能结瘤的植物根系坚硬，颜色较深，为黑色或深褐色。石蜡切片观察，结瘤豆科植物和非结瘤豆科植物在根的表皮部分存在着明显差异，而在皮层和中柱部分差异不明显。非结瘤豆科植物的表皮细胞排列致密且整齐；而结瘤豆科植物表皮细胞较薄，切片时容易收缩破损。非结瘤豆科植物的根表皮细胞外切向壁的厚度比结瘤豆科植物的要厚，颜色也较深。豆科植物的表皮细胞外切向壁厚度似乎能够反映豆科植物从不结瘤到结瘤的进化过程。     

First indications for the involvement of strigolactones on nodule formation in alfalfa (Medicago sativa)

Strigolactones have recently been suggested to be phytohormones that are present in all plants. Strigolactones are released by roots into the rhizosphere, stimulating the seed germination of parasitic plants such as Striga spp. and Orobanche spp. and play a crucial role in the interaction between plants and symbiotic arbuscular mycorrhizal fungi.By applying different concentrations of the synthetic strigolactone analogue GR24 to alfalfa (Medicago sativa) inoculated with Sinorhizobium meliloti we could show that in alfalfa nodulation is positively affected by the presence of the strigolactone analogue GR24. Moreover, we could show that this increased nodulation cannot be linked with a stimulatory effect of GR24 on the growth or the expression of nod genes of S. meliloti.Putative mechanisms operating in the plant in response to the addition of GR24 and leading to increased nodule formation by rhizobia are discussed.     

Nodule phosphorus requirement and O2 uptake in common bean genotypes under phosphorus deficiency

Abstract

The effect of P deficiency on nodulation, nodule P content, nodule O₂ permeability and N fixation rates in Phaseolus vulgaris–rhizobia symbiosis was studied under glasshouse conditions. Four recombinant inbred lines (L34, L83, L115 and L147) and one variety cultivated in Morocco (Concesa) were inoculated with Rhizobium tropici CIAT 899 in hydroaeroponic culture. Two P levels i.e. 75 (deficient level) and 250 µmol plant^?1 week^?1 P (sufficient level) were applied and the trial was assessed 42 days after transplanting that coincide with plant flowering stage. Under P-deficiency, decrease of plant growth (18%) and nodule biomass (19%) was detected and significantly pronounced in the sensitive line L147 compared with the remaining genotypes. Additionally, under P-deficiency, the efficiency in use of rhizobial symbiosis, estimated by the slope of the regression model of shoot biomass as a function of nodule biomass, was significantly increased in the four lines. This constraint did not significantly influence nodule P content in Concesa, but it was 24 and 41% lower in the tolerant and in the sensitive lines, respectively. Nodule P content was positively correlated to nodule biomass, r=0.75, and shoot N, r=0.92. These genotypic variations were associated with variability in nodule O₂ permeability that was significantly affected by the P level-bean genotype interaction. Under P-deficiency, nodule O₂ permeability was significantly reduced in the tested genotypes and accompanied with a decrease in shoot N content, especially in the sensitive lines (35%). Moreover, the ratios plant N fixed: nodule P content and plant N fixed:nodule dry weight were affected under P-deficiency in four lines with an exception observed in Concesa. Depending on the observed data we concluded that N₂ fixation efficiency could be influenced by nodulation and level of nodule P requirement which depend on both bean genotypes and P level.     

Differential responses of chickpea (Cicer arietinum L.) — Rhizobium combinations to saline soil conditions

Summary Chickpea cultivars (Cicer arietinum L.) and their symbiosis with specific strains of Rhizobium spp. were examined under salt stress. The growth of rhizobia declined with NaCl concentrations increasing from 0.01 to 2% (w : v). Two Rhizobium spp. strains (F-75 and KG 31) tolerated 1.5% NaCl. Of the 10 chickpea cultivars examined, only three (Pusa 312, Pusa 212, and Pusa 240) germinated at 1.5% NaCl. The chickpea — Rhizobium spp. symbiosis was examined in the field, with soil varying in salinity from electrical conductivity (EC) 4.5 to EC 5.2 dSm^-1, to identify combinations giving satisfactory yields. Significant interactions between strains and cultivars caused differential yields of nodules, dry matter, and grain. Four chickpea — Rhizobium spp. combinations, Pusa 240 and F-75 (660 kg ha^-1), Pusa 240 and IC 76 (440 kg ha^-1), Pusa 240 and KG 31 (390 kg ha^-1), and Pusa 312 and KG 31 (380 kg ha^-1), produced significantly higher grain yields in saline soil.     

Time-course of nitrogen fixation in two bambara groundnut (Vigna subterranea L. Verdc.) cultivars

TheA-value method, involving the application of a higher¹⁵N rate to a reference non-N₂-fixing plant, was used to assess the magnitude of N₂ fixation in two bambara groundnut cultivars at four growth stages [vegetative, 0–47 days after planting (DAP); early pod-filling, 47–99 DAP; mid-pod-filling, 99–120 DAP; physiological maturity, 120–148 DAP). The cultivars were Ex-Ada, a bunchy type, and CS-88-11, a slightly spreading type. They were grown on a loamy sand. Uninoculated Ex-Ada and CS-88-11 were used as reference plants to measure the N₂ fixed in the inoculated bambara groundnuts. In this greenhouse study, soil was the major source of N in bambara groundnuts during vegetative growth, and during this period it accounted for over 80% of the N accumulaed in the plants. However, N₂ fixation became the major source of plant N during reproductive growth. There were significant differences between the two cultivars in the ability to fix N₂, and at physiological maturity, almost 75% of the N in CS-88-11 was derived from the atmosphere compared to 55% in Ex-Ada. Also, the total N fixed in CS-88-11 at physiological maturity was almost double that in Ex-Ada. Our data indicate that the higher N₂ fixation in CS-88-11 was due to two factors, a higher intensity of N₂ fixation and a longer active period of N₂ fixation. The results also suggest that bambara groundnut genotypes could be selected for higher N₂ fixation in farining systems.     

Nitrogen fixation,biomass production,and nutrient uptake by annual Sesbania species in an alkaline soil

Summary In three field trials conducted during the summer season of 1986, 1987 and 1989 in an alkaline soil, 17 accessions of annual Sesbania spp. were evaluated for nodulation, N₂ fixation (acetylene reduction assay), dry weight of roots and shoots, woody biomass production, and nutrient uptake. At 50 days after sowing all the accessions were effectively nodulated (average 36.4 root nodules plant^-1) with a high nodule score (3.4). There was a lot of variation in nodule volume and mass and in acetylene reduction activity but not in N content (5.2%). N uptake in shoots, roots and nodules averaged 639, 31, and 13 mg plant^-1, respectively, and much of the fixed N remained in shoots. Accessions of S. cannabina complex performed better than others. S. rostrata had poor root nodulation but exhibited excellent stem nodulation (300 nodules plant^-1) even though not inoculated with Azorhizobium sp. Average concentrations of N, P, K, S, Ca, and Mg in the shoots were high, at 3.2, 0.28, 1.5, 0.28, 1.5, and 0.4% respectively, and Na was low (0.15%), reflecting the usefulness of Sesbania spp. as an integrated biofertilizer source. Green matter production was 26.0 Mg ha^-1 (5.9 Mg dry matter) and N uptake was 158 kg ha^-1, 54 days after sowing. Average woody biomass of six accessions at maturity, 200 days after sowing, was high (19.9 Mg ha^-1), showing its potential for shortterm firewood production. Total nutrient uptake for production of woody biomass (200 days of growth) was no more demanding than growing the plant to the green-manuring stage of 50–60 days' growth.     

Effect of root temperature on nodule development of bean, lentil and pea

The rhizobia-legume symbiosis is the main source of fixed nitrogen for many agricultural systems. However, it is inhibited by low soil temperature. To date, research on nodulation has involved either qualitative or destructive analyses. The use of computer-based image analysis potentially allows nodules to be followed during the course of development. Seedlings of bean (Phaseolus vulgaris L.), lentil (Lens culinaris Medik.) and pea (Pisum sativum L.) were transplanted into plastic growth pouches suspended in water baths maintained at 10, 15, 20 or 25 °C. Two days after transplanting, all plants were inoculated with appropriate rhizobial strains. Seven days after inoculation, plant roots were scanned; this was repeated weekly for 7 weeks. Data on nodule length were collected through image analysis. Nodule length was correlated with nodule size and development. There were increases in the precision of estimates of environmental effects through observation of individual nodule development, as opposed to averages for populations of nodules. The effects of root temperature on nodulation and nodule development were observed both in the delayed onset of nodulation and in reduced subsequent nodule growth rate, resulting in effects on final nodule size.