Development of a real-time PCR method for the differential detection and quantification of four solanaceae in GMO analysis: potato (Solanum tuberosum), tomato (Solanum lycopersicum), eggplant (Solanum melongena), and pepper (Capsicum annuum)

The labeling of products containing genetically modified organisms (GMO) is linked to their quantification since a threshold for the presence of fortuitous GMOs in food has been established. This threshold is calculated from a combination of two absolute quantification values: one for the specific GMO target and the second for an endogenous reference gene specific to the taxon. Thus, the development of reliable methods to quantify GMOs using endogenous reference genes in complex matrixes such as food and feed is needed. Plant identification can be difficult in the case of closely related taxa, which moreover are subject to introgression events. Based on the homology of beta-fructosidase sequences obtained from public databases, two couples of consensus primers were designed for the detection, quantification, and differentiation of four Solanaceae: potato (Solanum tuberosum), tomato (Solanum lycopersicum), pepper (Capsicum annuum), and eggplant (Solanum melongena). Sequence variability was studied first using lines and cultivars (intraspecies sequence variability), then using taxa involved in gene introgressions, and finally, using taxonomically close taxa (interspecies sequence variability). This study allowed us to design four highly specific TaqMan-MGB probes. A duplex real time PCR assay was developed for simultaneous quantification of tomato and potato. For eggplant and pepper, only simplex real time PCR tests were developed. The results demonstrated the high specificity and sensitivity of the assays. We therefore conclude that beta-fructosidase can be used as an endogenous reference gene for GMO analysis.     

Catabolic response and phospholipid fatty acid profiles as microbial tools to assess soil functioning

Microbial properties may help to provide an integrated view of changes in soil functioning associated with soil management or soil status. The fatty acid profiles of membrane phospholipids (PLFA) can give the composition of ecophysiological groups of soil microbial communities, while catabolic response profiles (CRP) estimate the heterotrophic functional diversity in soils, both relevant to the understanding of the role of micro‐organisms in the functioning of the soil. The objectives of this study were (i) to evaluate the CRP and PLFA as microbial tools to characterize changes in soil functioning and (ii) clarify the relation among these microbial measurements, with other physical, chemical and biochemical soil properties. We compare the same soil subjected to different managements and degrees of erosion. An undisturbed soil (UN), an old pasture soil (OP) and soils under continuous cultivation (NT) with four different depth of A horizon: 25 cm (NT 25), 23 cm (NT 23), 19 cm (NT 19) and 14 cm (NT 14) were tested. Substrate‐induced respiration of most substrates diminished when cropping pressure increased (UN > OP > NT), and soil catabolic evenness, as a diversity index, decreased by increasing production pressure and soil erosion. The correlation found among most of the measured physical, chemical and biochemical soil properties with the catabolic evenness showed the potential of this measurement to provide an integrated view of soil functioning. The PLFA analysis showed that the composition of microbial community denoting a partial recovery after 10 yr under grazed grassland. The stress indicators showed that farming practices increased microbial stress with the highest values found in the most eroded soils.     

Lime application to reduce phosphorus release in different textured intact and small repacked soil columns

Purpose

Phosphorus (P) losses from agricultural fields through leaching are the main contributors to eutrophication of lakes and rivers in North America. Adoption of P-retaining strategies is essential to improve the environmental quality of water bodies. The main objective of this study is to evaluate lime as a soil amendment in reducing phosphorus concentration in the leachate from three common soil textures with neutral to alkaline pH.

Materials and methods

Phosphorus leaching from undisturbed soil columns (10 cm in diameter and 20 cm deep) as well as small repacked columns was investigated and compared in this study. Lime (high calcium hydrated lime) at the rate of 1% by air-dried soil mass was applied to the topsoil of the columns. Both sets of experiments followed a full factorial design with two factors of soil texture at three levels (sandy loam, loam, and clay loam) and treatment at two levels (control and limed) with three replicates. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy was performed on the control and limed soil samples to confirm the formation of calcium phosphate compounds.

Results and discussions

For both intact and repacked columns, dissolved reactive phosphorus (DRP) concentrations in the leachates from limed sandy loam and limed loam soil columns was significantly reduced, while DRP in the limed clay loam column leachates was not changed. Elemental mapping demonstrated that in limed sandy loam and loam soils, the calcium loadings on the soil surface were always linked with phosphorus. The formation of calcium phosphate compounds and the increased phosphate adsorption on the soil surface through Ca bridging could be the two main phosphorus-lime retention mechanisms. Total dissolved phosphorus (TDP) in the leachates of limed loam and limed clay loam indoor intact and repacked columns was reduced, while there was no change in that of the sandy loam soil. In finer textured soils, lime can increase TDP retention through the immobilization of organic phosphates.

Conclusions

The impact of lime application on DRP and TDP varied with the soil texture. The lime-induced reduction in the DRP and TDP was variable between the intact and repacked columns demonstrating the importance of soil structure on phosphorus and lime interactions in the soil. Overall, lime application at the studied rate can be considered a promising soil amendment in mitigating phosphorus loss from non-calcareous neutral to alkaline soils.

     

Multivariate evaluation by quality indicators of no-tillage system in Argiudolls of rolling pampa (Argentina)

The purpose of this study was to develop operationally important soil quality indicators to evaluate long-term sustainability, at the farm scale, for no-tillage systems in Argiudolls of rolling pampa (Argentina). The soil was classified as series Arroyo Dulce (Typic Argiudoll), a fertile dark, deep and well-drained soil of the hills. Three situations were considered: pristine soil with grass vegetation, grassland soil (also considered as a reference situation); and 15 years no-tillage soils from four production plots. Physical, physico-chemical, chemical and biochemical indicators were considered. Data were analyzed by principal components analysis (PCA) with canonical discriminant analysis (CDA). The first three components explained 90% of the overall variation. For pristine undisturbed soil, the main variables selected by PCA were particulate C, pH, respiration and total organic C, and in the case of grassland they were C stock (mass of C in the 0–10 cm soil horizon), water-soluble C, and % silt. The no-tillage area was separated in different plots according to the degree of erosion with different depths of the A horizon. Clay content and bulk density were the main variables in the less degraded no tillage plots. Cluster analysis was applied to construct an average linkage distance dendrogram.     

Total and mineralizable soil carbon as affected by tillage in the Argentinean Pampas

This study was carried out in experimental plots established at Marcos Juárez, in the Pampean Region (center of Argentina) on Typic Argiudolls, with high silt content. The aim of this work was to study the effects of two tillage systems (reduced tillage and no-tillage) on the amount of total organic C, potentially mineralizable C, C released by respiration, and C stock in the topsoil of a corn (Zea mays L.)–wheat (Triticum aestivum L.)/soybean (Glycine max L. Merr.)–soybean rotation. No-tillage showed C stock greater than reduced tillage only at 0–5 cm depth, but not at 0–20 cm, even though in situ respiration was lower. As a consequence, no tillage did not show a differential capacity for C sequestration in comparison with reduced tillage.