A comprehensive study of the (2√3 × 2√3)R30° structure of silicene on Ag(111)

International audienceThe deposition of one silicon monolayer on Ag(1 1 1) gives rise to a set of superstructures depending on growth conditions. These superstructures are correlated to the epitaxy between the honeycomb structure of silicon (so called silicene) and the silver substrate. In this paper, from a detailed re-analysis of experimental results, obtained by scanning tunneling microscopy and by low energy electron diffraction on the (2√3  ×  2√3)R30° structure, we propose a new atomic model of the silicene layer based on periodic arrangements of perfect areas of (2√3  ×  2√3)R30° surrounded by defect areas. A generalization of this model explains the main experimental observations: deviation of the average direction, Moiré patterns and apparent global disorder. In the frame of the proposed model, the apparent disorders observed on the STM images, would be topological effects, i.e. the silicene would keep a quasi-perfect honeycomb structure

Growth of silicene layers on Ag(111): unexpected effect of the substrate temperature

The deposition of one silicon monolayer on the silver (111) substrate in the temperature range 150-300$^\circ$C, gives rise to a mix of (4$\times$4), ($2\sqrt{3}\times 2\sqrt{3}$)R30$^\circ$ and ($\sqrt{13}\times\sqrt{13}$)R13.9$^\circ$ superstructures which strongly depends on the substrate temperature. We deduced from a detailed analysis of the LEED patterns and the STM images that all these superstructures are given by a quasi identical silicon single layer with a honeycomb structure (i.e. a silicene-like layer) with different rotations relatively to the silver substrate. The STM images morphology are explained from the relative position of the silicon atoms relative to the silver atoms. A complete analysis of all possible rotations of the silicene layer predicts also a ($\sqrt{7}\times\sqrt{7}$)R19.1$^\circ$ superstructure which has not been observed so far.Comment: This manuscript has been withdrawn as it will soon be published on-line in the Journal of Physics: Condensed Matte

Markers associated with stalk number and suckering in sugarcane colocate with tillering and rhizomatousness QTLs in sorghum

Two important factors influencing sugar yield, the primary focus of sugarcane plant breeding programs, are stalk number and suckering. Molecular markers linked to both of these traits are sought to assist in the identification of high sugar yield, high stalk number, low-suckering sugarcane clones. In this preliminary mapping study, 108 progeny from a biparental cross involving two elite Australian sugarcane clones were evaluated at two sites for two years for both stalk number and suckering. A total of 258 DNA markers, including both restriction fragment length polymorphisms (RFLPs) and radio-labelled amplified fragments (RAFs), were scored and evaluated using single-factor analysis. Sixteen (7 RFLPs and 9 RAFs) and 14 (6 RFLPs and 8 RAFs) markers were identified that were significantly associated (P < 0.01) with stalk number and suckering, respectively, across both years and sites. The seven and six RFLP markers associated with stalk number and suckering, respectively, were generated by eight different RFLP probes, of which seven had been mapped in sorghum and (or) sugarcane. Of significant interest was the observation that all seven RFLP probes could be shown to be located within or near QTLs associated with tillering and rhizomatousness in sorghum. This observation highlights the usefulness of comparative mapping between sorghum and sugarcane and suggests that the identification of useful markers for stalk number and suckering in sugarcane would be facilitated by focussing on sorghum QTLs associated with related traits

Experimental assessment of the accuracy of genomic selection in sugarcane

The authors wish to thank T. Dumont, C. Lallemand, I. Promi, R. Tibere, M. Carbel, J. M. Coupan, O. Calvados and N. Lubin for field work, M. Hoarau for lab work. This study was funded by the eRcane company, by CIRAD (Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement) ATP-SEPANG project grant, by the Conseil Regional de la Reunion, by the European Union (European regional development fund-ERDF), by ANR (Agence Nationale de la Recherche) Delicas project grant ANR-08-GENM-001, ANR Grass biofuel project grant ANR-07-GPLA-018-005 and by the ANRT (Association Nationale de la Recherche et de la Technologie) through the CIFRE Ph.D grant No600/2012 of M. Gouy.International audienceSugarcane cultivars are interspecific hybrids with an aneuploid, highly heterozygous polyploid genome. The complexity of the sugarcane genome is the main obstacle to the use of marker-assisted selection in sugarcane breeding. Given the promising results of recent studies of plant genomic selection, we explored the feasibility of genomic selection in this complex polyploid crop. Genetic values were predicted in two independent panels, each composed of 167 accessions representing sugarcane genetic diversity worldwide. Accessions were genotyped with 1,499 DArT markers. One panel was phenotyped in Reunion Island and the other in Guadeloupe. Ten traits concerning sugar and bagasse contents, digestibility and composition of the bagasse, plant morphology, and disease resistance were used. We used four statistical predictive models: bayesian LASSO, ridge regression, reproducing kernel Hilbert space, and partial least square regression. The accuracy of the predictions was assessed through the correlation between observed and predicted genetic values by cross validation within each panel and between the two panels. We observed equivalent accuracy among the four predictive models for a given trait, and marked differences were observed among traits. Depending on the trait concerned, within-panel cross validation yielded median correlations ranging from 0.29 to 0.62 in the Reunion Island panel and from 0.11 to 0.5 in the Guadeloupe panel. Cross validation between panels yielded correlations ranging from 0.13 for smut resistance to 0.55 for brix. This level of correlations is promising for future implementations. Our results provide the first validation of genomic selection in sugarcane