Nondestructive determination of subsurface grain morphology

Recent progress in experimental and numerical methods enables to scrutinize simulated polycrystal surface micromechanics at high spatial resolution. For the correct interpretation of similarities and deviations between experiment and simulation, the consideration of subsurface grain morphology is imperative because of its significant impact on the surface layer boundary condition. A novel method is presented that coarsely scans a relatively large area for subsurface crystallite orientation up to depths of ~0.2 mm by means of differential aperture X-ray microscopy. The resulting point set is categorized into grains according to proximity in physical and orientation space. Reconstruction of the subsurface grain structure starts with a Voronoi tessellation using the categorized set as seed points. Progressive smoothing of the resulting ragged grain boundary surfaces is achieved through mean curvature flow. As it turns out that the reconstruction quality of the bulk and on the surface are related, the latter can serve as guidance for optimum subsurface reconstruction

Grain growth of Pennisetum glaucum (L.) R.Br. under well-watered and drought-stressed conditions

The objective of this study was to investigate the possibility of relationships between grain growth parameters and drought response. Grain growth parameters of more than 70 millet lines were assessed under well-watered and postflowering drought-stress conditions in two field trials at the ICRISAT Sahelian Center, Sadoré, Niger. All the grain growth parameters based on thermal time varied more than two-fold between lines in both moisture environments. Single grain mass of the lines ranged from 4.3–10.9 mg under well-watered conditions and 3.4–9.4 mg under drought stress. When averaged across trials, 51% of the accounted variance of final grain mass could be explained by differences in the grain growth rate under well-watered conditions, while differences in the duration of the linear grain growth phase accounted for 37% of the variation in final grain mass. Drought stress reduced the linear grain growth phase and, as a consequence, reduced final grain mass by up to 25%. Lines with long grain filling periods under well-watered conditions had larger reductions in the grain filling period and in final grain mass under stress. In general, there was little effect of drought stress on the grain growth rate. However, because of the negative correlation of grain growth rate and linear grain growth phase, lines with higher grain growth rates in well-watered conditions had smaller reductions in grain filling period under stress. Grain growth rate accounted with 38% for the major part of the variation in grain mass under stress conditions. Grain growth parameters in well-watered and drought-stress conditions were unrelated to drought tolerance as expressed by a drought response index, and were indicators of neither susceptibility nor tolerance to stress. However final grain mass was highly correlated to yield under stress. A feasible risk-reducing strategy in the likelihood of postflowering stress is to select pearl millet lines for drought escape with a high grain growth rate combined with a relatively short grain filling period

Crop physiology and breeding for drought tolerance: research and development

This paper presents an example of the research and development function of a physiology group within a cereal breeding program: an evaluation of the possibility of incorporating selection for tolerance to drought stress during the flowering and grain-filling period in pearl millet. It includes a review of the problem and possible solutions, and a report of two experiments conducted to identify phenotypic characteristics associated with yield differences under stress which could be used as selection criteria in breeding for tolerance. Differences among genotypes in yield under stress during flowering and grain-filling were partitioned into differences in yield potential, drought escape, and droughttolerance; the drought response accounted for more than 40% of the observed yield differences. Phenotypic traits related to yield under stress were divided into those reflecting drought escape and those reflecting droughttolerance. Droughttolerance was found to be primarily expressed in traits relating to the ability to maintain grain numbers under stress (grain number per panicle and per unit area, and grain yield per panicle). Drought escape, in contrast, was expressed in terms of greater grain biomass and higher harvest index. However, the field data also indicated that considerable progress in yield under stress should be possible by selection for earlier flowering and improved yield potential alon