97 research outputs found
Magnetotransport in polycrystalline LaSrMnO thin films of controlled granularity
Polycrystalline LaSrMnO (LSMO) thin films were
synthesized by pulsed laser ablation on single crystal (100) yttria-stabilized
zirconia (YSZ) substrates to investigate the mechanism of magneto-transport in
a granular manganite. Different degrees of granularity is achieved by using the
deposition temperature (T) of 700 and 800 C. Although no
significant change in magnetic order temperature (T) and saturation
magnetization is seen for these two types of films, the temperature and
magnetic field dependence of their resistivity ((T, H)) is strikingly
dissimilar. While the (T,H) of the 800 C film is comparable to that
of epitaxial samples, the lower growth temperature leads to a material which
undergoes insulator-to-metal transition at a temperature (T 170
K) much lower than T. At T T, the resistivity is characterized by
a minimum followed by ln \emph{T} divergence at still lower temperatures. The
high negative magnetoresistance ( 20) and ln \emph{T} dependence
below the minimum are explained on the basis of Kondo-type scattering from
blocked Mn-spins in the intergranular material. Further, a striking feature of
the T = 700 C film is its two orders of magnitude larger anisotropic
magnetoresistance (AMR) as compared to the AMR of epitaxial films. We attribute
it to unquenching of the orbital angular momentum of 3d electrons of Mn ions in
the intergranular region where crystal field is poorly defined.Comment: 26 pages, 7 figure
Strain induced magnetic domain evolution and spin re-orientation transition in epitaxial manganite films
The evolution of magnetic domain structure in epitaxial
LaCaMnO films on (001) NdGaO is monitored as a
function of temperature and magnetic field using Magnetic Force Microscopy. We
see two distinct regions of magnetic orientational order; one in-plane
displaying contrast-less image and the other tilted away from the film plane
forming a distinct stripe pattern. A strong domain splitting is observed at the
boundary of two regions, which is resilient to reorientation with temperature
and magnetic field. We propose a model magnetic free energy functional to
explain the mechanism of domain splitting seen in manganite films
Interface driven reentrant superconductivity in HoNi-NbN-HoNi nanostructures
Superconductivity (S) and ferromagnetism (F) are probed through transport and
magnetization measurements in nanometer scale HoNi-NbN (F-S) bilayers and
HoNi-NbN-HoNi (F-S-F) trilayers. The choice of materials has been made
on the basis of their comparable ordering temperatures and strong magnetic
anisotropy in HoNi. We observe the normal state reentrant behavior in
resistance vs. temperature plots of the F-S-F structures just below the
superconducting transition in the limited range of HoNi layer thickness
d (20 nm d 80 nm) when d is fixed at 10
nm. The reentrance is quenched by increasing the out-of-plane (H)
magnetic field and transport current where as in-plane (H) field
of 1500 Oe has no effect on the reentrance. The thermally activated flux
flow characteristics of the S, F-S and F-S-F layers reveal a transition from
collective pinning to single vortex pinning as we place F layers on both sides
of the S film. The origin of the reentrant behavior seen here in the range of
0.74 T/T 0.92 is attribute to a delicate balance
between the magnetic exchange energy and the condensation energy in the
interfacial regions of the trilayer.Comment: 13 pages and 5 figure
Identification of wheat cultivars for low nitrogen tolerance using multivariable screening approaches
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). A set of thirty-six wheat cultivars were grown for two consecutive years under low and high nitrogen conditions. The interactions of cultivars with different environmental factors were shown to be highly significant for most of the studied traits, suggesting the presence of wider genetic variability which may be utilized for the genetic improvement of desired trait(s). Three cultivars, i.e., RAJ 4037, DBW 39 and GW 322, were selected based on three selection indices, i.e., tolerance index (TOL), stress susceptibility index (SSI), and yield stability index (YSI), while two cultivars, HD 2967 and MACS 6478, were selected based on all four selection indices which were common in both of the study years. According to Kendall’s concordance coefficient, the consistency of geometric mean productivity (GMP) was found to be highest (0.778), followed by YSI (0.556), SSI (0.472), and TOL (0.200). Due to the high consistency of GMP followed by YSI and SSI, the three selection indices could be utilized as a selection tool in the identification of high-yielding genotypes under low nitrogen conditions. The GMP and YSI selection indices had a positive and significant correlation with grain yield, whereas TOL and SSI exhibited a significant but negative correlation with grain yield under both high and low nitrogen conditions in both years. The common tolerant genotypes identified through different selection indices could be utilized as potential donors in active breeding programs to incorporate the low nitrogen tolerant genes to develop high-yielding wheat varieties for low nitrogen conditions. The study also helps in understanding the physiological basis of tolerance in high-yielding wheat genotypes under low nitrogen conditions
Combining ability analysis for yield and protein content in bread wheat (Triticum aestivum)
The experiment was conducted with 10 parents and their 45 F1s (half diallel) during crop seasons (2008/09 and 2009/10) under normal and heat-stress environment to find out combining ability effects. The analysis of variance showed highly significant differences for all the traits at genotypic level under both normal and heat-stress environment. The significant additive variance (D) and dominance variance (H1) indicated that, expression of these traits is controlled by both additive and non-additive gene action. Among the parents, there was asymmetrical distribution of positive and negative dominant genes and preponderance of over-dominance gene action for all the traits under both the environment. Estimates of narrow-sense heritability were higher for days to 50% flowering; days to maturity; plant height and spike length. Our results also indicated that only three parents (HD 2285 for grain filling duration and thousand grains weight; PBW 373 for the days to maturity and plant height and UP 2425 for number of tillers and grain yield) had favorable general combining ability (GCA) effects under normal sown environment. While under heat-stress environment, cultivar HD 2285 showed highest GCA effect for days to 50% flowering, grain filling duration and thousand grain weight; HD 2733 for plant height and protein content; and PBW 373 for number of tillers and grain yield. Five cross combinations showed contrasting favorable specific combining ability (SCA) effect for more than one trait under both normal and heat-stress environment. Attempting combinations involving parents with high GCA for desirable yield components could be useful. The traits showing more than 35 percent narrow-sense heritability could be rewarding for further improvement of grain yield and protein content in wheat (Triticum aestivum L.)
Genomic Selection for Wheat Blast in a Diversity Panel, Breeding Panel and Full-Sibs Panel
Wheat blast is an emerging threat to wheat production, due to its recent migration to South Asia and Sub-Saharan Africa. Because genomic selection (GS) has emerged as a promising breeding strategy, the key objective of this study was to evaluate it for wheat blast phenotyped at precision phenotyping platforms in Quirusillas (Bolivia), Okinawa (Bolivia) and Jashore (Bangladesh) using three panels: (i) a diversity panel comprising 172 diverse spring wheat genotypes, (ii) a breeding panel comprising 248 elite breeding lines, and (iii) a full-sibs panel comprising 298 full-sibs. We evaluated two genomic prediction models (the genomic best linear unbiased prediction or GBLUP model and the Bayes B model) and compared the genomic prediction accuracies with accuracies from a fixed effects model (with selected blast-associated markers as fixed effects), a GBLUP + fixed effects model and a pedigree relationships-based model (ABLUP). On average, across all the panels and environments analyzed, the GBLUP + fixed effects model (0.63 +/- 0.13) and the fixed effects model (0.62 +/- 0.13) gave the highest prediction accuracies, followed by the Bayes B (0.59 +/- 0.11), GBLUP (0.55 +/- 0.1), and ABLUP (0.48 +/- 0.06) models. The high prediction accuracies from the fixed effects model resulted from the markers tagging the 2NS translocation that had a large effect on blast in all the panels. This implies that in environments where the 2NS translocation-based blast resistance is effective, genotyping one to few markers tagging the translocation is sufficient to predict the blast response and genome-wide markers may not be needed. We also observed that marker-assisted selection (MAS) based on a few blast-associated markers outperformed GS as it selected the highest mean percentage (88.5%) of lines also selected by phenotypic selection and discarded the highest mean percentage of lines (91.8%) also discarded by phenotypic selection, across all panels. In conclusion, while this study demonstrates that MAS might be a powerful strategy to select for the 2NS translocation-based blast resistance, we emphasize that further efforts to use genomic tools to identify non-2NS translocation-based blast resistance are critical
Characterising variation in wheat traits under hostile soil conditions in India
Intensive crop breeding has increased wheat yields and production in India. Wheat improvement in India typically involves selecting yield and component traits under non-hostile soil conditions at regional scales. The aim of this study is to quantify G*E interactions on yield and component traits to further explore site-specific trait selection for hostile soils. Field experiments were conducted at six sites (pH range 4.5-9.5) in 2013-14 and 2014-15, in three agro-climatic regions of India. At each site, yield and component traits were measured on 36 genotypes, representing elite varieties from a wide genetic background developed for different regions. Mean grain yields ranged from 1.0 to 5.5 t ha⁻¹ at hostile and non-hostile sites, respectively. Site (E) had the largest effect on yield and component traits, however, interactions between genotype and site (G*E) affected most traits to a greater extent than genotype alone. Within each agro-climatic region, yield and component traits correlated positively between hostile and non-hostile sites. However, some genotypes performed better under hostile soils, with site-specific relationships between yield and component traits, which supports the value of ongoing site-specific selection activities
New Genotypes and Genomic Regions for Resistance to Wheat Blast in South Asian Germplasm
Wheat blast (WB) disease, since its first identification in Bangladesh in 2016, is now an established serious threat to wheat production in South Asia. There is a need for sound knowledge about resistance sources and associated genomic regions to assist breeding programs. Hence, a panel of genotypes from India and Bangladesh was evaluated for wheat blast resistance and a genome-wide association study (GWAS) was performed. Disease evaluation was done during five crop seasons-at precision phenotyping platform (PPPs) for wheat blast disease at Jashore (2018-19), Quirusillas (2018-19 and 2019-20) and Okinawa (2019 and 2020). Single nucleotide polymorphisms (SNP) across the genome were obtained using DArTseq genotyping-by-sequencing platform, and in total 5713 filtered markers were used. GWAS revealed 40 significant markers associated with WB resistance, of which 33 (82.5%) were in the 2NS/2AS chromosome segment and one each on seven chromosomes (3B, 3D, 4A, 5A, 5D, 6A and 6B). The 2NS markers contributed significantly in most of the environments, explaining an average of 33.4% of the phenotypic variation. Overall, 22.4% of the germplasm carried 2NS/2AS segment. So far, 2NS translocation is the only effective WB resistance source being used in the breeding programs of South Asia. Nevertheless, the identification of non-2NS/2AS genomic regions for WB resistance provides a hope to broaden and diversify resistance for this disease in years to come
Identification of Genomic Regions and Sources for Wheat Blast Resistance through GWAS in Indian Wheat Genotypes
Wheat blast (WB) is a devastating fungal disease that has recently spread to Bangladesh and poses a threat to the wheat production in India, which is the second-largest wheat producing country in the world. In this study, 350 Indian wheat genotypes were evaluated for WB resistance in 12 field experiments in three different locations, namely Jashore in Bangladesh and Quirusillas and Okinawa in Bolivia. Single nucleotide polymorphisms (SNPs) across the genome were obtained using DArTseq (R) technology, and 7554 filtered SNP markers were selected for a genome-wide association study (GWAS). All the three GWAS approaches used identified the 2NS translocation as the only major source of resistance, explaining up to 32% of the phenotypic variation. Additional marker-trait associations were located on chromosomes 2B, 3B, 4D, 5A and 7A, and the combined effect of three SNPs (2B_180938790, 7A_752501634 and 5A_618682953) showed better resistance, indicating their additive effects on WB resistance. Among the 298 bread wheat genotypes, 89 (29.9%) carried the 2NS translocation, the majority of which (60 genotypes) were CIMMYT introductions, and 29 were from India. The 2NS carriers with a grand mean WB index of 6.6 showed higher blast resistance compared to the non-2NS genotypes with a mean index of 46.5. Of the 52 durum wheats, only one genotype, HI 8819, had the 2NS translocation and was the most resistant, with a grand mean WB index of 0.93. Our study suggests that the 2NS translocation is the only major resistance source in the Indian wheat panel analysed and emphasizes the urgent need to identify novel non-2NS resistance sources and genomic regions
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