1,721,045 research outputs found
Cell wall digestibility of perennial ryegrass : an association mapping approach
Full text linkLolium perenne L. (perennial ryegrass) is the most prevalent grass species on dairy farms in temperate regions of the world. Its energy content is among the highest of forage grasses, but not as high as that of more expensive concentrate, which is an essential part of a cow's diet to opti-mize milk yields. Increasing the available energy content of ryegrass, measured as the total digestibility (OMD), would be economically beneficial for the farmer, as it would reduce the amount of concentrate to be added. Moreover, ryegrass often contains an excess in protein, resulting in nitrogen pollution, which would also be reduced if OMD were higher. Past breeding efforts have been successful in increasing the content of water-soluble carbohydrates at the expense of the cell wall portion (NDF), with a consequential positive impact on OMD. However, NDF is important for rumen functioning and the cow's health, and for this reason, we focus on breeding for an improved cell wall digestibility (NDFD).
The cell wall is rich in energy, under the form of cellulose and hemicellu-lose. These structural carbohydrates are partially digested by rumen microorganisms. However, these microorganisms cannot break down lignin, a polymer that functions as a glue in the cell wall, and cannot access cellulose and hemicellulose easily. Therefore, decreasing the lignin content or modifying the lignin composition could improve the digestibility of the carbohydrate fraction of the cell wall, and would vastly increase the energy released per gram ryegrass forage. Reducing the amount of ferulic acids, which can cross-link lignin to hemicellulose, may have a similar effect. Here, we present a study that considers both phenotypic and marker-assisted selection (MAS) to improve the cell wall digestibility of perennial ryegrass. In order to obtain useful molecular markers for MAS, an association mapping is conducted where genetic variation in single-nucleotide polymorphisms (SNPs) is correlated with phenotypic variation in lignin content and NDFD.
It is known that NDFD decreases with the maturity of the plant. There-fore, we harvested a diverse set of genotypes at a fixed maturity stage, namely at heading. A large variability in NDFD was found at this stage. However, the cell wall of blade, and to a lesser extent stem, is still harder to digest when harvest (and thus heading) occurs later. This is due to vegetative tillers being older when harvested later. To select plants with the highest NDFD independent from this confounder, a harvest-date (HD) correction was applied. Although the genetic diversity and heritability are lower than for NDF, NDFD has a relatively larger impact on OMD. As a result, the response to selection is similar for both traits. As NDF has been successfully used as criterion for improving OMD in the past, we expect the same for NDFD. We conclude that NDFD is a relevant trait for breeding. Our estimates predict a potential to increase milk yields by 2% by selecting the highest-NDFD genotypes in the studied material.
A strong relationship was found between lignin content and NDFD, mak-ing it a worthy substitute for phenotypic selection if ruminal fluid (used for NDFD analysis) is not readily available. For phenotypic selection at the plant level, selecting on HD-corrected KL (Klason lignin) is equivalent to selecting on HD-corrected NDFD. For TL (total lignin), even a higher breeding efficiency is expected than for NDFD. For phenotypic selection, separation of organs is considered infeasible, however, for association mapping, organ-specific HD-corrected TL content is recommended as trait, for its high accuracy and high expected heritability. The effects of esterified ferulates (estFA) and diferulates (diFA) on plant NDFD are lim-ited after NIRS prediction, and these traits are therefore not recommend-ed for breeding purposes. Nevertheless, the effect of ferulates should be investigated further.
To conduct association mapping, we selected and sequenced 127 genes from 22 gene families related to lignin or ferulic acid biosynthesis. How-ever, gene families contain many genes (paralogs) coding for structurally similar enzymes with possibly different functions. Based on a literature study, we prioritized ryegrass genes in four monolignol biosynthesis gene families, namely 4CL, COMT, CAD and CCR, each containing a large num-ber of genes in ryegrass. Considering the conservation of essential resi-dues in protein sequences, we were able to put forward hypotheses on functional redundancy of paralogs within each gene family. We later used this information for prioritizing genes for marker development.
Six molecular markers were significantly associated with NDFD or (pro-tein-corrected) KL and were selected as candidates for validation. Alleles with a large beneficial effect were discovered in the following genes: LpHCALDH1, LPHCALDH11, LpWRKY5, LpCAD1, LpC4H3 and LpLAC1. Once validated, priority should go to finding these beneficial alleles in current elite material. Increasing the frequency of beneficial alleles in a popula-tion is feasible, but pyramiding and fixing several beneficial alleles in a single genotype will not be a sinecure. Nevertheless, in order to develop an elite ryegrass variety with an improved cell wall digestibility, only a few markers may suffice, in combination with phenotypic or genomic selection
Enhancement of biomass production and accessibility of the cell wall for fermentation in Brachypodium distachyon as a model and Zea mays as a crop
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Genetic analysis of crown rust resistance in ryegrasses (Lolium spp.) using molecular markers
Full text linkDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Impact of hop terroir on beer flavour characteristics
No full textHops are one of the key ingredients in beer production and mainly impart bitterness, aroma, and the final flavour to beer. The specific hop characteristics of beer largely depend on the hop variety (or combination of varieties) used and the type of hop addition and technologies applied. However, the hop characteristics could also be affected by the growing conditions and the cultivation practices used, in general terms referred to as ‘terroir’. In this study, the impact of hop terroir on the aroma- and flavour-related characteristics in beer was comprehensively investigated for a broad set of commercially relevant hop varieties. By combining the generated genetic and biochemical data, the specific effects of both variety and terroir on the hop brewing characteristics and, consequently, on the sensory attributes of beer were elucidated. The knowledge and insights gained in the course of this study, as well as the tools developed for genetic and biochemical differentiation of hop batches, are ready for use in further research and for exploitation by the hop and brewing industries
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