Success and failure of invasive races of plant pathogens: The case of Puccinia striiformis f. sp. tritici in France

Invasions of new races can have contrasting consequences on populations of Puccinia striiformis f. sp. tritici, causing yellow rust of wheat. For example, the emergence of PstS7 (Warrior race) had major impacts in Europe and in France. By contrast, PstS2 had no impact in France, while it significantly affected other parts of the world. The objective of this study was to better understand factors that govern the success of an invasive race, taking the contrasting history of PstS7 and PstS2 in France as a case study. We compared these two races for three key factors driving invasive potential: (a) virulence against local cultivars, (b) aggressiveness in local environmental conditions, and (c) competitiveness against local races. During the period when PstS2 was detected, 70% of the grown wheat area was protected against this race by at least one known Yr resistance gene. By contrast, we found that only 15% of the wheat area had a low risk of infection by PstS7. In planta competition experiments suggested a higher competitiveness of PstS7 against local isolates compared to PstS2 in optimal thermal conditions. In silico experiments, based on thermal performance curves, suggested a high competitiveness of PstS7 considering infection efficiency. PstS2 was extremely competitive against local races in all considered environments (20 French sites × 15 years) due to its short latency period. Our findings highlight the importance of considering adaptation to environmental conditions, particularly temperature, in addition to virulence spectrum, in order to understand the evolutionary trajectories of emerging strains in pathogen populations.     

Toxicity survey of Canadian Arctic marine sediments

Purpose

This paper reports a toxicity survey of Canadian Arctic marine sediments. During the Amundsen scientific cruise, eight sites distributed across the Canadian Arctic and sub-Arctic regions were selected to highlight sensitive areas affected by either atmospheric deposition, ocean current, river drainage, or anthropogenic activities. As part of the Canadian-led ArcticNet research program, this study aims to monitor and to better understand potential changes likely to impact the Arctic.

Materials and methods

Surface sediments were investigated with bioanalytical tests to assess sediment toxicity. Testing of sediment elutriates was undertaken with the ARTOXKIT M, Microtox liquid phase (MLPA), and ROTOXKIT M toxicity assays, while whole sediment testing was carried out with the Microtox solid phase assay (MSPA) toxicity test procedure. Sediment mercury (Hg) content was also determined in each sample since Hg transport and toxicity is specifically an important issue in the Arctic and is generally a key indicator of the pollution status in many aquatic ecosystems.

Results and discussion

Based on bioassay results and sediment granulometric criteria, these Arctic sediments must be considered nontoxic. However, based on MSPA half maximal inhibitory concentrations (IC50s) and/or MLPA threshold effect concentration (TEC) values, some degree of toxicity may be measureable particularly in the sediments located in southern and northeast Hudson Bay. The Hudson Bay watershed drains 30% of Canadian rivers and extends to northern USA. Despite the large Hg concern in the Arctic, the input of local or long-range Hg sources does not appear to be a contributing factor to sediment toxicity.

Conclusions

These initial results are valuable in that they set baseline quality levels for these sediments as of 2005. As such, future comparisons can be made to assess temporal and spatial trends. Human activity and climate change is expected to impact these regions in the future, resulting in further reduction of sea ice extent, access to new Arctic seaways, and drilling associated with the exploitation of natural resources.     

Cultivated einkorn wheat (Triticum monococcum L. subsp. monococcum): the long life of a founder crop of agriculture

The first cultivated wheat, cultivated einkorn (Triticum monococcum L. subsp. monococcum), was domesticated in South-East Turkey during the Pre-Pottery Neolithic period. It then spread to the Middle-East, the Balkans and Caucasus, Turkmenistan, Central and Mediterranean Europe, North-Africa, and finally to Western and Northern Europe. In all these regions, it played an important role in the development of agriculture and was cultivated for several centuries before being replaced by free-threshing wheats. Today, cultivated einkorn is only present in isolated, mountainous areas of a few countries. However, there is renewed interest for this crop due to the nutritional qualities of its grain, its adaptation to low-input agriculture and high level of resistance to pests and diseases that represent advantages for organic farming. Cultivated einkorn is also a valuable reservoir of genes for wheat improvement. Its utilization, limited by its hulledness, low yield and especially by a poor knowledge of its diversity and its low crossability with bread and durum wheat, is expected to increase in the future, particularly with the need for wheat breeding to face newly emerging diseases through the use of genetic resistances. Considering these perspectives, the present review attempts to analyse the current and historical importance of einkorn cultivation and utilization in wheat breeding, tracing back to its origin and diffusion. The main traits of resistance to pest and diseases, and the nutritional qualities and technological characteristics of the grain are described. Einkorn genetic resources diversity exploration is reviewed and successful examples of introgression of useful einkorn traits into cultivated wheat are reported. Lastly, perspectives of einkorn cultivation development in low-input agriculture and use for wheat enhancement are discussed.     

Saharan wheats: before they disappear

Wheat landraces cultivated in the Saharan oases have been submitted during centuries to drought, heat and salinity and are expected to have developed tolerance to these constraints. The different forms present in the oases of Libya, Algeria and Morocco have been collected and described by several authors who highlighted the peculiarity and diversity of this germplasm, on the basis of spike and grain morphology. The origin, date and way of introduction of wheat in the Saharan oases are however largely unknown. Most landraces may have been introduced from Egypt, possibly during wet climatic episodes. Spike morphological traits of some landraces suggest an Asiatic origin (Iran, Turkestan and Afghanistan). More recent introductions have also probably occurred. This lack of information as well as the potential interest of this germplasm for wheat improvement would merit further studies. Marker-based diversity analysis of Saharan wheats and comparison with North-African and Asian wheats might permit to precise their classification and confirm their origin. Evaluation for tolerance to abiotic constraints would allow a better understanding of their adaptation to the oases environments and identification of potential progenitors to be used by wheat breeders. Such studies are urgent considering the quick genetic erosion of this germplasm due to drastic ecological and socio-economic changes affecting Saharan oases and their cropping systems.     

Liquid carbon, carbon-glass beads, and the crystallization of carbon nanotubes

The formation of carbon nanotubes in a pure carbon arc in a helium atmosphere is found to involve liquid carbon. Electron microscopy shows a viscous liquid-like amorphous carbon layer covering the surfaces of nanotube-containing millimeter-sized columnar structures from which the cathode deposit is composed. Regularly spaced, submicrometer-sized spherical beads of amorphous carbon are often found on the nanotubes at the surfaces of these columns. Apparently, at the anode, liquid-carbon drops form, which acquire a carbon-glass surface due to rapid evaporative cooling. Nanotubes crystallize inside the supercooled, glass-coated liquid-carbon drops. The carbon-glass layer ultimately coats and beads on the nanotubes near the surface.     

Seismic detection of the lunar core

Despite recent insight regarding the history and current state of the Moon from satellite sensing and analyses of limited Apollo-era seismic data, deficiencies remain in our understanding of the deep lunar interior. We reanalyzed Apollo lunar seismograms using array-processing methods to search for the presence of reflected and converted seismic energy from the core. Our results suggest the presence of a solid inner and fluid outer core, overlain by a partially molten boundary layer. The relative sizes of the inner and outer core suggest that the core is ~60% liquid by volume. Based on phase diagrams of iron alloys and the presence of partial melt, the core probably contains less than 6 weight % of lighter alloying components, which is consistent with a volatile-depleted interior.     

Missing mass in collisional debris from galaxies

Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.     

Live-cell imaging of enzyme-substrate interaction reveals spatial regulation of PTP1B

Endoplasmic reticulum-localized protein-tyrosine phosphatase PTP1B terminates growth factor signal transduction by dephosphorylation of receptor tyrosine kinases (RTKs). But how PTP1B allows for RTK signaling in the cytoplasm is unclear. In order to test whether PTP1B activity is spatially regulated, we developed a method based on F?rster resonant energy transfer for imaging enzyme-substrate (ES) intermediates in live cells. We observed the establishment of a steady-state ES gradient across the cell. This gradient exhibited robustness to cell-to-cell variability, growth factor activation, and RTK localization, which demonstrated spatial regulation of PTP1B activity. Such regulation may be important for generating distinct cellular environments that permit RTK signal transduction and that mediate its eventual termination.     

Expression of myelin-associated glycoprotein by small neurons of the dorsal root ganglion in chickens

Biochemical and immunocytochemical investigations have shown that myelin-associated glycoprotein (MAG) is exclusively related to myelin and myelin-forming cells in mammals. In the present study it was found that dorsal root ganglia in young chickens display MAG-immunoreactive material in most small sensory neurons. The presence of MAG at the surface of small sensory neurons raises the question of whether this glycoprotein acts as a cell adhesion molecule in lower vertebrates.     

Shape and temperature memory of nanocomposites with broadened glass transition

Shape-memory polymers can revert to their original shape when they are reheated. The stress generated by shape recovery is a growing function of the energy absorbed during deformation at a high temperature; thus, high energy to failure is a necessary condition for strong shape-memory materials. We report on the properties of composite nanotube fibers that exhibit this particular feature. We observed that these composites can generate a stress upon shape recovery up to two orders of magnitude greater than that generated by conventional polymers. In addition, the nanoparticles induce a broadening of the glass transition and a temperature memory with a peak of recovery stress at the temperature of their initial deformation.