Mycoparasitism by Pythium oligandrum and P. acanthicum

Isolates of the reported mycoparasites Pythium oligandrum, P. acanthicum and P. periplocum markedly reduced growth and cellulolysis by Botryotrichum piluliferum, grew rapidly across agar plates precolonized by Phialophora radicicola var radicicola (sensu Deacon) and, where tested (not P. periplocum), were non-pathogenic towards higher plants. Isolates of P. echinulatum, P. mamillatum. P. megalacanthum, P. spinosum, P. ultimum and one isolate of P. acanthicum behaved differently from the mycoparasites and could, themselves, be placed in two groupings in these tests. It is suggested that the ability or otherwise to grow on Phialophora-precolonized agar plates may help to distinguish broad biological groupings within the genus Pythium, but these groupings may cut across conventional taxonomic ones.One isolate of P. acanthicum was tested for its effects on a range of cellulolytic fungi: it reduced their growth to different extents, as did P. oligandrum.Plates of potato-dextrose agar precolonized by Phialophora radicicola were used to isolate selectively P. oligandrum and similar fungi from soils, but the use of hemp seed baits in conjunction with precolonized plates was less selective for these fungi.Straw pieces precolonized by P. oligandrum and buried in soil decomposed at the same rate as virgin straws or those precolonized by P. ultimum or Mucor hiemalis. Subsequently, Stachyholrys atra appeared to colonize straws more frequently from soil, and Fusarium spp. less so, in the presence of P. oligandrum than in its absence. In the laboratory, P. oligandrum was antagonized by Slachyholrys, whereas Fusarium spp. were frequently overgrown by the Pythium.     

Seaweed Extracts: A Promising Source of Antibiofilm Agents with Distinct Mechanisms of Action against Pseudomonas aeruginosa

The organization of bacteria in biofilms is one of the adaptive resistance mechanisms providing increased protection against conventional treatments. Thus, the search for new antibiofilm agents for medical purposes, especially of natural origin, is currently the object of much attention. The objective of the study presented here was to explore the potential of extracts derived from three seaweeds: the green Ulva lactuca, the brown Stypocaulon scoparium, and the red Pterocladiella capillacea, in terms of their antibiofilm activity against P. aeruginosa. After preparation of extracts by successive maceration in various solvents, their antibiofilm activity was evaluated on biofilm formation and on mature biofilms. Their inhibition and eradication abilities were determined using two complementary methods: crystal violet staining and quantification of adherent bacteria. The effect of active extracts on biofilm morphology was also investigated by epifluorescence microscopy. Results revealed a promising antibiofilm activity of two extracts (cyclohexane and ethyl acetate) derived from the green alga by exhibiting a distinct mechanism of action, which was supported by microscopic analyses. The ethyl acetate extract was further explored for its interaction with tobramycin and colistin. Interestingly, this extract showed a promising synergistic effect with tobramycin. First analyses of the chemical composition of extracts by GC–MS allowed for the identification of several molecules. Their implication in the interesting antibiofilm activity is discussed. These findings suggest the ability of the green alga U. lactuca to offer a promising source of bioactive candidates that could have both a preventive and a curative effect in the treatment of biofilms.     

A methodological approach for ecotoxicological characterization of non-hazardous sediments for their beneficial reuse

Purpose

In France, the beneficial reuse of sediments is conditioned upon a demonstration of environmental acceptability for each scenario. Such evidence has to be provided in application of the NF EN 12920 +A1 standard methodologies. Before the application of risk assessment methodology, the HP14 hazard property must be measured using specific bioassays. However, sediments may have ecotoxicological impacts despite a non-hazardous classification. The application of a battery of bioassays sensitive to non-hazardous sediments could allow to select sediments before choosing the beneficial reuse option.

Materials and methods

First, HP14 methodologies were applied on the studied sediments. These sediments had to be managed on shore according to French legislation. Then, following recommendations from a previous study, other ecotoxicological tests and modified ecotoxicological tests from HP14 methodology were selected. Ostracods mortality and growth tests were selected as a complement because its sensitivity to sediment ecotoxicity is known. To take into account the effects of extraction method and liquid/solid ratio on ecotoxicological impact of sediments, ecotoxicological tests have been applied to percolates. They have been obtained from up-flow percolation tests following the standard NF EN 14405. For each percolate, the rotifer clones reproduction test and the ostracod mortality and growth tests were performed.

Results and discussion

Contaminant analyses of sediments studied reveal differences in contamination between non-hazardous sediments. The majority of ecotoxicological tests carried out in the HP14 test batteries do not differentiate between non-hazardous sediments with low ecotoxicity. However, inhibition of rotifer reproduction and inhibition of plant germination and growth tests can be used. Among the complementary bioassays performed, the ostracods growth inhibition and multigenerational Daphnia reproduction inhibition tests are especially sensitive. Bioassays performed on percolates reveal low ecotoxicities that were not detected with conventional bioassays. For these tests, maximum ecotoxicities are observed on the first percolates for most of the tested sediments, and ecotoxicity effects decrease with the increase in the liquid/solid ratio.

Conclusions

The results enable us to propose a bioassay battery able to highlight the intrinsic toxicity of non-hazardous sediments. This is achieved through bioassays and using up-flow percolation columns to detect low ecotoxicity. This battery can be integrated into the SEDIMATERIAUX approach to ensure the choice of the beneficial reuse option for such sediment. As some of the proposed bioassays remain unsuitable for marine sediments, future studies will adapt the methodology to the presence of marine salts.

     

Precision farming uses typology in arable crop-oriented farms in northern France

The adoption of precision farming techniques (PFTs) has been widely studied targeting specific PFT or farming systems along with the potential benefits of these PFTs in terms of yield or input use. However, few studies have examined how PFTs are adopted and used at the farm level. In this study a preliminary investigation was made of on-farm PFT uses in the Oise region (northern France). Three main PFTs were identified in the area: Global Navigation Satellite Systems (GNSS) guidance, section control, and variable rate (VR) application. For each farm, the use of every PFT was defined by the technical characteristics of the equipment, the field operation(s) concerned, the targeted crop(s), the aim of the use, the PFT adoption drivers, and the perceived impacts by the farmers. These different variables were combined into a typology of PFT uses. The results show that most of the farms combined GNSS guidance for all technical operations and section control, whereas VR application was less common. Section control was largely used by farmers for liquid fertilizers and phytochemical spraying. The typology shows three to five types of use for each PFT, which differ in terms of technique adoption drivers, e.g. reducing on-farm work or adaptation to field morphology. According to literature, economic impacts were found to be the most frequent, however farmers seemed unable to quantify them. Social impacts such as reduced work time and fatigue were also frequent and are becoming the main motivation for using PFT on farms studied. Further research is needed to assess the use trajectories of PFT along with the motivations of each PFT use.

     

Effects of irrigation and nitrogen rates on foliar mineral composition of bell pepper

Irrigation and nitrogen fertilization are two important aspects of bell pepper production. Yet, limited information is available on the effect of irrigation on foliar nutrient content. Bell pepper were grown on bare ground under two nitrogen fertilization rates (11 and 19 kg N week^‐1) and irrigated according to an irrigation scheduling model based on weather data and crop age. Eight irrigation rates ranged between 36 and 148% of the model rate. Leaf samples were taken at first bloom (62 days after transplanting, DAT) and after final harvest (84 DAT). Yield response and the foliar content of all essential elements determined [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), boron (B), copper (Cu), iron (Fe), molybdenum (Mo), manganese (Mn), zinc (Zn)] responded linearly or quadratically to irrigation rates and most foliar nutrient contents remained within or above the sufficiency range. Foliar mineral content tended to be lower at 84 DAT as compared to 62 DAT. Only Ca became deficient under high irrigation rates on 84 DAT. Current fertilization recommendations for bell pepper and 100% of the model irrigation rate resulted in highest yield. These results suggest that the high N rate supplied as calcium nitrate should be used when multiple bell pepper harvests are expected.     

Hierarchical genetic organization of human cortical surface area

Surface area of the cerebral cortex is a highly heritable trait, yet little is known about genetic influences on regional cortical differentiation in humans. Using a data-driven, fuzzy clustering technique with magnetic resonance imaging data from 406 twins, we parceled cortical surface area into genetic subdivisions, creating a human brain atlas based solely on genetically informative data. Boundaries of the genetic divisions corresponded largely to meaningful structural and functional regions; however, the divisions represented previously undescribed phenotypes different from conventional (non-genetically based) parcellation systems. The genetic organization of cortical area was hierarchical, modular, and predominantly bilaterally symmetric across hemispheres. We also found that the results were consistent with human-specific regions being subdivisions of previously described, genetically based lobar regionalization patterns.