An overview of the metabolic differences between Bradyrhizobium japonicum 110 bacteria and differentiated bacteroids from soybean (Glycine max) root nodules: an in vitro 13C- and 31P-nuclear magnetic resonance spectroscopy study.

Bradyrhizobium japonicum is a symbiotic nitrogen-fixing soil bacteria that induce root nodules formation in legume soybean (Glycine max.). Using (13)C- and (31)P-nuclear magnetic resonance (NMR) spectroscopy, we have analysed the metabolite profiles of cultivated B. japonicum cells and bacteroids isolated from soybean nodules. Our results revealed some quantitative and qualitative differences between the metabolite profiles of bacteroids and their vegetative state. This includes in bacteroids a huge accumulation of soluble carbohydrates such as trehalose, glutamate, myo-inositol and homospermidine as well as Pi, nucleotide pools and intermediates of the primary carbon metabolism. Using this novel approach, these data show that most of the compounds detected in bacteroids reflect the metabolic adaptation of rhizobia to the surrounding microenvironment with its host plant cells.

QTLs for resistance to soybean cyst nematode, races 3, 9, and 14 in cultivar Hartwig

The objective of this work was to identify major and minor-effect quantitative trait loci (QTL) for resistance to races 3, 9, and 14 of soybean cyst nematode (SCN) in Hartwig cultivar; to map new resistance QTLs for these races; and to check for the existence of epistatic interactions between QTLs. Cultivar Hartwig is an important resistance source to SCN. Recombinant inbred lines (RIL) obtained from a cross between 'Hartwig' (resistant) and Y23 (susceptible) were evaluated regarding resistance to the three races. New genomic regions for resistance to SCN were identified by microsatellites. Four QTLs, which explained between 12 and 34% of phenotypic variance, were detected for resistance to race 3 in linkage groups (LG) A2, G, J, and M. The QTL in LG G is also important for resistance to race 9. Epistatic interactions were detected between loci, which indicate resistance to races 9 and 14. There are high and low-effect resistance QTLs to SCN.

Cover crops and herbicide timing management on soybean yield under no-tillage system

The objective of this work was to evaluate the effect of cover crops and timing of pre-emergence herbicide applications on soybean yield under no-tillage system. The experiment consisted of four cover crops (Panicum maximum, Urochloa ruziziensis, U. brizantha, and pearl millet) and fallow, in addition to four herbicide timings (30, 20, 10, and 0 days before soybean sowing), under no-tillage system (NTS), and of two control treatments under conventional tillage system (CTS). The experimental design was a completely randomized block, in a split-plot arrangement, with three replicates. Soybean under fallow, P. maximum, U. ruziziensis, U. brizantha, and pearl millet in the NTS and soybean under U. brizantha in the CTS did not differ significantly regarding yield. Soybean under fallow in the CTS significantly reduced yield when compared to the other treatments. The amount of straw on soil surface did not significantly affect soybean yield. Chemical management of P. maximum and U. brizantha near the soybean sowing date causes significant damage in soybean yield. However, herbicide timing in fallow, U. ruziziensis, and pearl millet does not affect soybean yield.

Biometric analysis of protein and oil contents of soybean genotypes in different environments

The objective of this work was to identify by biometric analyses the most stable soybean parents, with higher oil or protein contents, cultivated at different seasons and locations of the state of Minas Gerais, Brazil. Forty-nine genotypes were evaluated in the municipalities of Viçosa, Visconde do Rio Branco, and São Gotardo, in the state of Minas Gerais, from 2009 to 2011. Protein and oil contents were analyzed by infrared spectrometry using a FT-NIR analyzer. The effects of genotype, environment, and genotype x environment interaction were significant. The BARC-8 soybean genotype is the best parent to increase protein contents in the progenies, followed by BR 8014887 and CS 3032PTA276-3-4. Selection for high oil content is more efficient when the crossings involve the Suprema, CD 01RR8384, and A7002 genotypes, which show high mean phenotypic values, wide adaptability, and greater stability to environmental variation.

Soybean (Glycine max. L.) and bacteroid glyoxylate cycle activities during nodular senescence.

Soybean (Glycine max. L.) nodular senescence results in the dismantling of the peribacteroid membrane (PBM) and in an increase of soybean isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (MS; EC 4.1.3.2) mRNA and protein levels. This suggests that in senescing soybean nodular cells, the specific glyoxylate cycle enzyme activities might be induced to reallocate carbon obtained from the PBM degradation. In order to evaluate as well the carbon metabolism of the nitrogen-fixing Bradyrhizobium japonicum endosymbiotic bacteroids during nodular senescence, their glyoxylate cycle activities were also investigated. To this end, partial DNA sequences were isolated from their icl and ms genes, but the corresponding mRNAs were not detected in the microorganisms. It was also observed that the bacteroid ICL and MS activities were negligible during nodular senescence. This suggests that glyoxylate cycle activities are not reinitiated in the bacteroids under these physiological conditions. In case the microorganisms nevertheless feed on the PBM degradation products, this might occur via the citric acid cycle exclusively.

An overview of the metabolic differences between Bradyrhizobium japonicum 110 bacteria and differentiated bacteroids from soybean (Glycine max) root nodules: An in vitro 13C-and 31P-nuclear magnetic resonance spectroscopy study

Bradyrhizobium japonicum is a symbiotic nitrogen-fixing soil bacteria that induce root nodules formation in legume soybean (Glycine max.). Using 13C- and 31P-nuclear magnetic resonance (NMR) spectroscopy, we have analysed the metabolite profiles of cultivated B.japonicum cells and bacteroids isolated from soybean nodules. Our results revealed some quantitative and qualitative differences between the metabolite profiles of bacteroids and their vegetative state. This includes in bacteroids a huge accumulation of soluble carbohydrates such as trehalose, glutamate, myo-inositol and homospermidine as well as Pi, nucleotide pools and intermediates of the primary carbon metabolism. Using this novel approach, these data show that most of the compounds detected in bacteroids reflect the metabolic adaptation of rhizobia to the surrounding microenvironment with its host plant cells.

Soybean (Glycine max. L.) and bacteroid glyoxylate cycle activities during nodular senescence

Soybean (Glycine max. L.) nodular senescence results in the dismantling of the peribacteroid membrane (PBM) and in an increase of soybean isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (MS; EC 4.1.3.2) mRNA and protein levels. This suggests that in senescing soybean nodular cells, the specific glyoxylate cycle enzyme activities might be induced to reallocate carbon obtained from the PBM degradation. In order to evaluate as well the carbon metabolism of the nitrogen-fixing Bradyrhizobium japonicum endosymbiotic bacteroids during nodular senescence, their glyoxylate cycle activities were also investigated. To this end, partial DNA sequences were isolated from their icl and ms genes, but the corresponding mRNAs were not detected in the microorganisms. It was also observed that the bacteroid ICL and MS activities were negligible during nodular senescence. This suggests that glyoxylate cycle activities are not reinitiated in the bacteroids under these physiological conditions. In case the microorganisms nevertheless feed on the PBM degradation products, this might occur via the citric acid cycle exclusively.

Metabolic and structural rearrangement during dark-induced autophagy in soybean (Glycine max L.) nodules: An electron microscopy and P-31 and C-13 nuclear magnetic resonance study

The effects of dark-induced stress on the evolution of the soluble metabolites present in senescent soybean (Glycine max L.) nodules were analysed in vitro using C-13- and P-31-NMR spectroscopy. Sucrose and trehalose were the predominant soluble storage carbons. During dark-induced stress, a decline in sugars and some key glycolytic metabolites was observed. Whereas 84% of the sucrose disappeared, only one-half of the trehalose was utilised. This decline coincides with the depletion of Gln, Asn, Ala and with an accumulation of ureides, which reflect a huge reduction of the N-2 fixation. Concomitantly, phosphodiesters and compounds like P-choline, a good marker of membrane phospholipids hydrolysis and cell autophagy, accumulated in the nodules. An autophagic process was confirmed by the decrease in cell fatty acid content. In addition, a slight increase in unsaturated fatty acids (oleic and linoleic acids) was observed, probably as a response to peroxidation reactions. Electron microscopy analysis revealed that, despite membranes dismantling, most of the bacteroids seem to be structurally intact. Taken together, our results show that the carbohydrate starvation induced in soybean by dark stress triggers a profound metabolic and structural rearrangement in the infected cells of soybean nodule which is representative of symbiotic cessation.

Germination, senescence and pathogenic attack in soybean (Glycine max. L.): Identification of the cytosolic aconitase participating in the glyoxylate cycle

During our study of the glyoxylate cycle in soybean (Glycine max. L. var. Maple arrow), two mitochondrial and three cytosolic aconitase molecular species (EC 4.2.1.3) were detected, designated as M1, M2, C1, C2 and C3 isoforms, respectively, according to their intracellular locations and electrophoretic mobilities. Using the glyoxylate cycle marker enzymes isocitrate lyase (ICL, EC 4.1.3.1) and malate synthase (MS, EC 4.1.3.2), the activity of this pathway providing the essential link between P-oxidation and gluconeogenesis was confirmed during germination (cotyledons) and senescence (leaves). It was then established that, in both cases, the activity of the CI aconitase isoform developed concomitantly with the transcription and translation levels of the icl and ms genes. This strongly suggests that C1 aconitase is constitutive of the glyoxylate cycle. In addition, the same isoform was found to be active during pathogenic attack as well (hypocotyls). It might be assumed that in such a case the glyoxylate cycle is reinitiated as a part of a carbon reallocation system feeding on the diseased tissue cellular components.

Pathogenic attack and carbon reallocation in soybean leaves (Glycine max. L.): Reinitiation of the glyoxylate cycle as a defence reaction

Pathogenic attack by the fungus Botrytis cinerea (primary pathogen) on soybean leaves (Glycine max. L.; cv. Maple arrow) results in a hypersensitive response (necrotising infected leaves), in the establishment of local acquired resistance, as well as in the systemic induction of genes coding for pathogenesis-related proteins. It now appears that, concomitantly with these already well documented defence reactions, the pathogenic attack also induces the carbon reallocation mechanism based on the reinitiation of the glyoxylate cycle (pseudo-senescence of the infected leaves).

Cultural practices and genetic resistance as factors affecting soybean stem canker and plant yield in the Cerrado

Field experiments were conducted in the 1995-96 soybean (Glycine max) growing season to evaluate the effects of cultural practices and host genetic resistance on the intensity of soybean stem canker, caused by Diaporthe phaseolorum f.sp. meridionalis (Dpm). Experiments were conducted in a commercial field severely infected in the previous (1994-95) season. In one study, minimum tillage (MT) and no-tillage (NT) cropping systems were investigated for their effects on disease development and on plant yields in cvs. FT-Cristalina (susceptible) and FT-Seriema (moderately resistant). Another study evaluated the effects of plant densities (8, 15, 21 and 36 plants/m) on disease development in cvs. FT-Cristalina, FT-101 (moderately resistant) and FT-104 (resistant). Disease incidence and severity were consistently lower in NT than in MT, and plant yields were increased by 23% and 14% in the NT system for the susceptible and moderately resistant cultivars, respectively, compared to the yields in the MT system. The Gompertz and Logistic models described well the disease progress curves in all situations. For both susceptible and moderately resistant cultivars, disease severity increased proportionately to the increase in plant densities. At the end of the season, 100% of the plants of cv. FT-Cristalina were infected by Dpm, at all plant densities. Disease levels on cv. FT-101 were intermediate while only very low disease levels were recorded on cv. FT-104. There was a consistent negative correlation between stem canker severity and yield. Some practices demonstrated potential for direct application in disease control, and could be combined considering their additive effects.

Use of semi-seletive media for detection of Sclerotinia sclerotiorum on bean and soybean seeds

This work was aimed at evaluating the possibility of using bromophenol blue as an indicator for detecting the presence of Sclerotinia sclerotiorum in the seeds of dry-beans (Phaseolus vulgaris) and soybean (Glycine max), through incubation of the seeds on an agar medium and "blotter" substrates. The seeds were artificially inoculated with four S. sclerotiorum isolates, plated on the agar medium, named Neon, and on modified Neon agar media all incubated at 14 and 20 ºC for seven days in the dark. Half of the seeds inoculated were surface desinfested prior to plating on the medium. The seeds showing change of colour in the medium, from blue to light yellow, as well as formation of typical mycelium and sclerotia in some cases, were considered to be infected or contaminated by S. sclerotiorum. The two incubation temperatures compared did not show significant (P<0.05) differences in detection level for most of the isolates tested on the different media. According to results obtained in this study, the Neon agar medium with incubation at 14 or 20 ºC has proved to be a reliable and quick method for the detection of S. sclerotiorum mycelium in naturally infected seeds of bean and soybean.

Uptake and translocation of nitrogen, phosphorus and calcium in soybean infected with Meloidogyne incognita and M. javanica

Two soybean (Glycine max) cultivars were used in this study, Ocepar 4, rated as moderately resistant to Meloidogyne incognita race 3 but susceptible to M. javanica, and 'BR 16', susceptible to both nematodes. The effect of nematodes infection on the uptake and transport of N, P and Ca to the shoot was studied in plants growing in a split root system. The upper half was inoculated with 0, 3,000, 9,000 or 27,000 eggs/plant while the lower half received 15N, 32P or 45Ca. Infected plants showed an increase of root but a decrease of shoot mass with increasing inoculum levels. In general, total endogenous nutrients increased in the roots and tended to decrease in the shoots with increasing inoculum levels. When concentrations were calculated, there was an increase in the three nutrients in the roots, and an increase of Ca but no significant variation of N and P was observed in the shoots. The total amount of 15N in the roots increased at the highest inoculum levels but 32P and 45Ca decreased. In the shoots there was a reduction of 32P and 45Ca. The specific concentrations of the labelled nutrients (abundance or radioactivity/tissue mass) also showed a decrease of 32P and 45Ca in the shoots and roots of infected plants and an increase of 15N in the shoots. Considering that overall nutrient concentrations reflect cumulative nutrient uptake and the data from labelled elements gave information at a specific moment of the infection, thus nematodes do interfere with nutrient uptake and translocation.

Effect of population densities of Heterodera glycines race 3 on leaf area, photosynthesis and yield of soybean

The effect of Heterodera glycines on photosynthesis, leaf area and yield of soybean (Glycine max) was studied in two experiments carried out under greenhouse condition. Soybean seeds were sown in 1.5 l (Experiment 1) or 5.0 l (Experiment 2) clay pots filled with a mixture of field soil + sand (1:1) sterilized with methyl bromide. Eight days after sowing, seedlings were thinned to one per pot, and one day later inoculated with 0; 1.200; 3.600; 10.800; 32.400 or 97.200 J2 juveniles of H. glycines. Experiment 1 was carried out during the first 45 days of the inoculation while Experiment 2 was conducted during the whole cycle of the crop. Measurements of photosynthetic rate, stomatic conductance, chlorophyll fluorescence, leaf color, leaf area, and chlorophyll leaf content were taken at ten-day intervals throughout the experiments. Data on fresh root weight, top dry weight, grain yield, number of eggs/gram of roots, and nematode reproduction factor were obtained at the end of the trials. Each treatment was replicated ten times. There was a marked reduction in both photosynthetic rate and chlorophyll content, as well as an evident yellowing of the leaves of the infected plants. Even at the lowest Pi, the effects of H. glycines on the top dry weight or grain yield were quite severe. Despite the parasitism, soybean yield was highly correlated with the integrated leaf area and, accordingly, the use of this parameter was suggested for the design of potential damage prediction models that include physiological aspects of nematode-diseased plants.