Effects of Plant Growth-Promoting Rhizobacteria and Rhizobium on Mycorrhizal Development and Growth of Paraserianthes falcataria (L.) Nielsen Seedlings in Two Types of Soils with Contrasting levels of pH

An investigation was carried out on the effects of two plant growth-promoting rhizobacteria and Rhizobium on the seedling growth of Paraseriathes falcataria (l.) Nielsen and mycorrhizal development in two soils with contrasting level of pH (5 and 6) in a greenhouse. The results show that inoculation of Paraserianthes seeds with Pseudomonas sp ‘‘Proradix’’ (DSMZ 13134) and Bacillus amyloliquefaciens FZB42 in single or combined application significantly increased root and shoot dry weight, mycorrhizal root colonization, and nutrient concentration (P. Zn and Cu) in the shoots of Paraseriathes seedlings compared to untreated control. Only in the soil with pH 5, an inoculation with P. sp. ”Proradix®“ in addition to Rhizobium inoculation led to a further increase of all measured variables compared to Rhizobium inoculation alone. In all other treatments, inoculation with PGPRs in addition to Rhizobium inoculation did not lead to a significant increase of any of the measured variables. The results demonstrate that plant growth-promoting rhizobacteria have the potential to promote the indigenous arbuscular mycorrhizal fungi establishment and the growth of Paraseriathes seedling

Effects of Pseudomonas sp. ”Proradix” and Bacillus amyloliquefaciens FZB42 on the Establishment of AMF Infection, Nutrient Acquisition and Growth of Tomato Affected by Fusarium oxysporum Schlecht f.sp. radicis-lycopersici Jarvis and Shoemaker

The fungus Fusarium oxysporum Schlecht f. sp. radicis-lycopersici Jarvis and Shoemaker (FORL) causes crown and root rot in tomato (Lycopersicon esculentum Mill.), which is a serious problem for field and greenhouse production causing significant losses. The main objective of this study was to test the efficacy of two commercial bacteria strains Pseudomonas sp. ”Proradix” (DSMZ 13134) (Proradix®, Sourcon Padena, Tübingen-Germany) and Bacillus amyloliquefaciens FZB42 (RhizoVital® 42 TB, ABiTEP, Berlin, Germany) in improving mycorrhization, nutrient status and plant growth of tomato affected by FORL. Soil inoculation with P. sp. ”Proradix” and B. amyloliquefaciens FZB42 in single and combined application significantly improved root and shoot biomass production of tomato, and P, Mn and Zn shoot concentrations in pathogen-infested soil. After application of the bacteria strains, roots of tomato were healthier and showed a significantly higher colonization by arbuscular mycorrhizal fungi if the latter was inoculated too. Combined inoculationd with the bacteria strains and arbuscular mycorrhizal fungi increased the observed effects on dry matter and shoot nutrient concentrations. However, clear synergistic effects could not be detected. The results obtained suggest an important role of rhizosphere interactions for the expression of bio-control mechanisms by inoculation with effective Pseudomonas and Bacillus strains in addition to simple antagonistic effects

Effects of Plant Growth-Promoting Rhizobacteria and Rhizobium on Mycorrhizal Development and Growth of Paraserianthes falcataria (L.) Nielsen Seedlings in Two Types of Soils with Contrasting levels of pH

An investigation was carried out on the effects of two plant growth-promoting rhizobacteria and Rhizobium on the seedling growth of Paraseriathes falcataria (l.) Nielsen and mycorrhizal development in two soils with contrasting level of pH (5 and 6) in a greenhouse. The results show that inoculation of Paraserianthes seeds with Pseudomonas sp ‘‘Proradix’’ (DSMZ 13134) and Bacillus amyloliquefaciens FZB42 in single or combined application significantly increased root and shoot dry weight, mycorrhizal root colonization, and nutrient concentration (P. Zn and Cu) in the shoots of Paraseriathes seedlings compared to untreated control. Only in the soil with pH 5, an inoculation with P. sp. ”Proradix®“ in addition to Rhizobium inoculation led to a further increase of all measured variables compared to Rhizobium inoculation alone. In all other treatments, inoculation with PGPRs in addition to Rhizobium inoculation did not lead to a significant increase of any of the measured variables. The results demonstrate that plant growth-promoting rhizobacteria have the potential to promote the indigenous arbuscular mycorrhizal fungi establishment and the growth of Paraseriathes seedling

Oilseed rape (Brassica napus L.) genotypic variation in response to boron deficiency

Boron efficiency of 16 oilseed rape genotypes was tested using both hydroponic and pot-soil growing techniques. From the nutrient solution experiment (0.1 and 10 mu M B), 4 representative contrasting genotypes were selected based on relative root and shoot growth. These were then grown in pots with low-B soil (0.25 mg kg(-1)). From the nutrient solution experiment, 2 genotypes selected as B-inefficient did not show any growth disorders, and the concentration of B in the shoots was above critical. Furthermore, 4 contrasting genotypes were subjected to the stable B-11 isotope-enriched uptake solution for 6 h to verify possible low B-induced active uptake by roots and xylem loading of B. The concentration of B-11 in either root cell sap or xylem exudate was higher than in the external nutrient solution, which indicated the presence of low B-induced active uptake for all tested genotypes, and, to some extent, their efficiency with low B. In conclusion, a combination of different growing techniques under controlled environmental conditions together with different parameters including relative root and shoot weight, shoot B concentration, and B uptake provided reliable B efficiency results in oilseed rape genotypes

Fate of glyphosate stored in weed residues and the potential of phytotoxicity for following crops.

Glyphosate, a broad spectrum, non-selective herbicide, is the world´s most important and widely used herbicide. The globally increasing adoption of no-till or reduced tillage systems is becoming a driving force for enhanced glyphosate use. In such systems, glyphosate is applied pre-sowing for weed control and glyphosate may remain in root and shoot residues. To evaluate potential risks associated with glyphosate residues, a pot experiment was conducted under controlled greenhouse conditions with two contrasting soils: weakly buffered acidic Arenosol and highly buffered Luvisol. Glyphosate was supplied as glyphosate enriched rye grass straw (1.2 g DM kg-1 soil) prior to sowing sunflower as a non-target plant. Several physiological parameters, such as intracellular shikimate accumulation as a metabolic indicator for glyphosate toxicity, biomass production and micronutrient status were analyzed. Detrimental effects on sunflower plants linked to glyphosate toxicity were observed only in the Arenosol but not in the Luvisol. This is most probably related to the difference in soil properties. The detoxification capacity of the fine-textured Luvisol, with a high clay content, was high enough for an adequate immobilization and inactivation of glyphosate. On the sandy Arenosol, the level of glyphosate supply exceeded the detoxification capacity. In addition to the difference in detoxification capacity, differences in nutrient bio-availability might also have aggravated the observed inhibition of nutrient acquisition. Thus, the findings suggest the importance of weed residues in transferring glyphosate from target to non-target plants, particularly in no-till or reduced tillage systems, with the consequence of detrimental effects on following crop plants

Silicon ameliorates manganese toxicity in cucumber by decreasing hydroxyl radical accumulation in the leaf apoplast

This work was focused on the role of silicon (Si) in amelioration of manganese (Mn) toxicity caused by elevated production of hydroxyl radicals (center dot OH) in the leaf apoplast of cucumber (Cucumis sativus L.). The plants were grown in nutrient solutions with adequate (0.5 mu M) or excessive (100 mu M) Mn concentrations with or without Si being supplied. The symptoms of Mn toxicity were absent in the leaves of Si-treated plants subjected to excess Mn, although the leaf Mn concentration remained extremely high. The apoplastic concentration of free Mn2+ and H2O2 of high Mn-treated plants was significantly decreased by Si treatment. Si supply suppressed the Mn-induced increased abundance of peroxidase (POD) isoforms in the leaf apoplastic fluid, and led to a rapid suppression of guaiacol-POD activity under excess Mn. The spin-trapping reagent 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide was used to detect center dot OH by electron paramagnetic resonance spectroscopy. Although supplying Si markedly decreased the accumulation of center dot OH in the leaf apoplast with excess Mn, adding monosilicic acid to the Mn2+/H2O2 reaction mixture did not directly affect the Fenton reaction in vitro. The results indicate that Si contributes indirectly to a decrease in center dot OH in the leaf apoplast by decreasing the free apoplastic Mn2+, thus regulating the Fenton reaction. A direct inhibitory effect of Si on guaiacol-POD activity (demonstrated in vitro) may also contribute to decreasing the POD-mediated generation of center dot OH

Isotopologue ratios of N2O emitted from microcosms with NH4+ fertilized arable soils under conditions favoring nitrification

Soils represent the major source of the atmospheric greenhouse gas nitrous oxide (N2O) and there is a need to better constrain the total global flux and the relative contribution of the microbial source processes. The aim of our study was to determine variability and control of the isotopic fingerprint of N2O fluxes following NH4+-fertilization and dominated by nitrification. We conducted a microcosm study with three arable soils fertilized with 0-140 mg NH4+-N kg(-1). Fractions of N2O derived from nitrification and denitrification were determined in parallel experiments using the N-15 tracer and acetylene inhibition techniques or by comparison with unfertilized treatments. Soils were incubated for 3-10 days at low moisture (30-55% water-filled pore space) in order to establish conditions favoring nitrification. Dual isotope and isotopomer ratios of emitted N2O were determined by mass spectrometric analysis of 6180, average delta N-15 (delta N-15 bulk) and N-15 site preference (SP = difference in delta N-15 between the central and peripheral N positions of the asymmetric N2O molecule). N2O originated mainly from nitrification (> 80%) in all treatments and the proportion of NH4+ nitrified that was lost as N2O ranged between 0.07 and 0.45%. delta O-18 and SP of N2O fluxes ranged from 15 to 28.4 parts per thousand and from 13.9 to 29.8 parts per thousand, respectively. These ranges overlapped with isotopic signatures of N2O from denitrification reported previously. There was a negative correlation between SP and delta O-18 which is opposite to reported trends in N2O from denitrification. Variation of average N-15 signatures of N2O (delta N-15(bulk)) did not supply process information, apparently because a strong shift in precursor signatures masked process-specific effects on delta N-15(bulk). Maximum SP of total N2O fluxes and of nitrification fluxes was close to reported SP of N2O from NH4+ or NH2OH conversion by autotrophic nitrifiers, suggesting that SP close to 30 parts per thousand is typical for autotrophic nitrification in soils following NH4+-fertilization. The results suggest that the delta O-18/SP fingerprint of N2O might be used as a new indicator of the dominant source process of N2O fluxes in soils. (C) 2008 Elsevier Ltd. All rights reserved.Deutsche Forschungsgemeinschaft (DFG

Influence of nitrogen rate on micronutrient density in grain of winter wheat (Triticum aestivum L.)

Agricultural approaches are suggested to increase micronutrients in cereal grain and then to alleviate human malnutrition. A long-term (1999-2007) field experiment was conducted to investigate the effect of three nitrogen (N) fertilization rates (0, 130 and 300 kg N/ha) on micronutrient density in wheat grain and its milling fractions. There were three N rates in this trail: 0, 130 and 300 kg N/ha. At maturity, grains were harvested and fractionated into flour, shorts and bran for micronutrients, N and protein analysis. The results showed that N fertilization increased iron (Fe), zinc (Zn) and copper (Cu) density in wheat grain compared to the control. Increase of N application rate from 130 to 300 kg N/ha, however, didn't further increase the three micronutrient density in grain. Most micronutrients were accumulated in bran while the lowest micronutrient concentrations were found in the flour. High N application increased Zn and Cu densities in three fractions while for Fe, its density in shorts and bran were increased, not in flour. Manganese (Mn) concentration in grain was not influenced by N application. It is concluded that nitrogen plays an important role in micronutrient accumulation in wheat grain. Proper nitrogen fertilizer management has a potential to enhance both micronutrients and grain protein