Elemental Composition and Chemical Evolution of Geologic Materials in Gale Crater, Mars: APXS Results From Bradbury Landing to the Vera Rubin Ridge

The Alpha Particle X-ray Spectrometer (APXS) on the rover Curiosity has analyzed the composition of geologic materials along a >20-km traverse in Gale crater on Mars. The APXS dataset after 6.5 Earth years (2,301 sols) includes 712 analyses of soil, sand, float, bedrock, and drilled/scooped fines. We present the APXS results over this duration and provide stratigraphic context for each target. We identify the best APXS measurement of each of the 22 drilled and scooped samples that were delivered to the instruments Chemistry and Mineralogy (CheMin; X-ray diffractometer) and Sample Analysis at Mars (SAM; mass spectrometer and gas chromatograph) during this period. The APXS results demonstrate that the basaltic and alkali-rich units in the Bradbury group (sols 0-750) show minimal alteration indicating an arid climate. In contrast, the Murray formation of the Mount Sharp group (sols ∼750-2,301) has compositions indicating pervasive alteration. Diagenetic features are common and show fluid interaction with the sediment after (and possibly during) lithification. A sandstone unit, the Stimson formation, overlies part of the Murray formation. This has a composition similar to the basaltic sand and soil, suggesting a shared source. Cross-cutting, fracture-associated haloes are evidence of late-stage fluid alteration after lithification of the sediment. The APXS dataset, evaluated in concert with the full science payload of Curiosity, indicates that Gale crater was habitable, and that liquid water was stable for extended periods.We are indebted to NASA-JPL, the Canadian Space Agency, and Australian Research Council (DP150104604) for supporting our work and the MSL mission. A portion of this study was conducted at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration

Grain quality in breeding

Grain characteristics (hardness, protein content/quality, starch properties, enzymatic activity, etc.) play an important role in the definition of end use quality for wheat-based products. Among them, gluten strength and extensibility, mostly determined by glutenin and gliadin composition, are two of the main factors that determine gluten quality. The complex inheritance of most quality traits has led to the development of indirect tests used in breeding for early and advanced generation selection. The main focus of breeders is adding resistance to biotic stress (fungi, insects, nematodes, etc.) and increasing grain yield while selection for quality often occurs in later generations. This often results in the propagation of poor quality lines that must be later discarded. Evaluation of quality in early generations requires suitable tests, preferably non-destructive. Increasing knowledge of the genes involved in quality will facilitate more precise and effective selection. Recent advances in wheat genome sequencing and the extensive genotyping of mapping populations has led to a precise molecular characterization of high molecular weight (HMW) and low molecular weight (LMW) glutenins, as well as the discovery of genes associated with quality traits like grain hardness, starch composition (e.g., waxy genes), etc. Massive genomic data will impact in breeding programs allowing quality fine tuning by precise selection of glutenins, starch, hardness and other traits, for specific end uses through marker assisted selection, genomic selection, etc. This chapter will describe different methods used for quality selection in breeding programs and research, and some examples of integration of local breeding programs with the extremely diverse end-uses of wheat based on a series of case-studies. Current and potential approaches to quality evaluation in durum wheat, wild relatives and synthetic wheat breeding programs will be also presented