1,721,106 research outputs found
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Using Genomic Resources to Breed Cowpeas With Larger Seeds
Full text linkCowpea (Vigna unguiculata) is a warm-season legume that is primarily cultivated for protein rich grain. Seed size is an important breeding target that distinguishes most domesticated crops from their wild relatives and is a particularly important trait for the grain legumes. This dissertation describes efforts to breed cowpea varieties with larger seeds using marker-assisted approaches to breeding. The first chapter of this dissertation describes the development of a consensus genetic map of 1,107 molecular markers which was constructed by analyzing bead-assay genotype data from 13 experimental populations. The content and organization of the cowpea genome was also compared to the genome of soybean (Glycine max) to describe regions of synteny. The second chapter utilizes the genetic map, legume synteny, and phenotypic information collected from field and greenhouse trials to develop associations between allelic variation and the inheritance of seed size. Many of the regions of the cowpea genome important for seed size were found to be syntenic with regions of the soybean genome that were previously associated with the inheritance of seed size. These marker-trait associations are applied in the third chapter to breed cowpea varieties with up to 52% larger seeds which was accomplished by introgressing a rare Mozambican haplotype into the genetic background of a California blackeyed pea. Preliminary field screening identified introgression lines that also performed well for other important agronomic traits including yield, maturity, and plant architecture. The introgression lines developed in this work could be used as parents for deploying large seed size in other pedigrees and could be studied to better understand the impact of seed size on nutritional content and agronomic performance
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Genetics of Consumer-Related Traits in Cowpea (Vigna unguiculata [L.] Walp.)
Full text linkCowpea (Vigna unguiculata [L.] Walp.) is a crop with a rising profile. Today, cowpea is mostly grown as a subsistence crop by smallholder farmers in marginal conditions. Over 90% of cowpea production occurs in a sub-Saharan Africa, where it serves as an important source of calories, protein, and micronutrients. Despite its importance in developing countries, few resources have been invested in researching the genetic control of consumer- and agronomic-related traits in cowpea. Long considered an orphan crop, as new genetic and genomic resources are developed, new opportunities arise for research into genetic control of traits. Research into the genetics of cowpea dates to the early twentieth century when researchers made crosses to identify factors controlling various traits. New resources made available in recent years facilitate examination of the mechanisms of control over these traits. In this dissertation, I present findings demonstrating mapping of black seed coat and purple pod color, seed coat pattern, and leaf aspect ratio. The mapping of these traits identifies the physical locations of genetic factors identified over the past century, including the Black Color (Bl), Color Factor (C), Holstein (H), Watson (W), and various leaf shape loci. Further, genetic markers have been developed for use in marker assisted selection for these traits. Adding insight into how the seed coat develops, I present a system following seed coat development which explains some of the observed variation in seed coat patterns. Finally, to assist breeders in determining what traits should be focused on for breeding purposes, I present a consumer-preference analysis performed in Ghana during August and September 2018. In combination, the findings presented in this thesis will facilitate breeders’ efforts to develop new varieties for changing conditions
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Mapping Domestication-Related Traits and QTL Pyramiding in Cowpea [Vigna unguiculata (L.) Walp]
Full text linkCowpea (Vigna unguiculata [L.] Walp) is one of the most important food and nutritional security crops. It is one of the main sources of dietary protein and folic acid for millions of people in sub-Saharan Africa and other parts of the developing world. Cowpea is a diploid (2n = 22) with a genetically diverse gene-pool composed of wild and cultivated forms. Cowpea was domesticated in Africa, from where it spread into all continents and now is commonly grown in many parts of Asia, Europe, United States and Central and South America. Domestication of cowpea has, in general, resulted in a determinate growth habit, increased pod and seed size, early flowering, and reduction of pod shattering. However, the genetic control of these traits is largely unknown. This lack of domestication-related knowledge in cowpea has limited the utilization of broad germplasm for crop improvement. This dissertation investigates the genetic basis of domestication traits using recently developed genetic and genomic resources available for cowpea and studies the effect of two seed size loci in a different genetic background. In the first chapter, regions of the cowpea genome that played an important role in cowpea domestication were identified. A total of 215 recombinant inbred lines derived from a cross between a cultivated and a wild cowpea accession were used to evaluate nine domestication-related traits (pod shattering, peduncle length, flower color, days to flowering, 100-seed weight, pod length, leaf length, leaf width and seed number per pod). A high-density genetic map containing 17,739 single nucleotide polymorphisms was constructed and used to identify 16 quantitative trait loci (QTLs) for these nine traits. Four regions were identified showing QTL clustering for these traits, including one region on Vu08 where four QTLs related to increased organ size (seed weight, pod length, leaf length and leaf width) were mapped. Using sequence homology comparison with common bean, a candidate gene (Vigun08g217000) for increased organ size was identified. This gene codes for a histidine kinase 2 and the Arabidopsis ortholog AHK2 (AT5G35750.1) has been shown to regulate, among other things, plant organ size. The second chapter investigates the genetic basis of seed size, which is a main domestication target and one of the key yield determinants. A “mini-core” panel of 368 genetically diverse cowpea accessions, mainly landraces, was used to evaluate four seed size-related traits (seed weight, length, width, and density). A genome-wide association study (GWAS) and meta-analysis identified 17 loci associated with seed size. One locus was common to weight, width and length, suggesting pleiotropy. By integrating synteny based-analysis with common bean, six candidate genes (Vigun05g036000, Vigun05g039600, Vigun05g204200, Vigun08g217000, Vigun11g187000, and Vigun11g191300) which are implicated in multiple functional categories related to seed size were identified. In the third chapter, two seed size QTLs were targeted for introgression in the background of a popular cultivar from Senegal “Pakau”. Four combinations of the positive (large seed size) alleles of the two QTL were observed in the backcross progenies and were analyzed to test the effect on seed phenotype of these QTL in the Pakau genetic background: no positive QTL alleles, positive allele of Css-1 only, positive allele of Css-4 only, and positive alleles of both QTL.The results of this dissertation provide a basis for further fine mapping of genes controlling domestication traits and a foundation for the utilization and exploitation of diverse landraces and wild relatives in cowpea breeding programs
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
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Characterization of Root-Knot Nematode Resistance in Cowpea and Utilization of Cross-Species Platforms in Legume Genomics
Full text linkCowpea (Vigna unguiculata L. Walp) is an important food and fodder legume worldwide. Cowpea is grown extensively in sub-Saharan Africa where it is an important staple. Root-knot nematode (RKN, Meloidogyne spp.) is a significant pest in cowpea. Several sources of resistance to RKN have been identified in cowpea, including the widely used Rk gene. As part of a study to elucidate the mechanism of Rk -mediated resistance, the histological response to avirulent M. incognita feeding of a resistant cowpea cultivar CB46 was compared with a susceptible near-isogenic line. It was found that the Rk-mediated resistance is a delayed response which lacked an early hypersensitive reaction (HR). Typically in pathogen resistance HR is closely associated with an oxidative burst (OB) in infected tissue. Following a basal OB during early infection in both susceptible and resistant cowpea roots no significant OB was detected, a profile consistent with the histological observations of a delayed resistance response. As cowpea does not have a microarray platform, a readily available soybean (Glycine max) genome array was used to identify single feature polymorphisms (SFP) in cowpea. An algorithm called Robustified Projection Pursuit was used for data analysis and RNA was used as a surrogate for DNA to detect SFPs between two genetically diverse cowpea genotypes. Cowpea genomic amplicon sequencing was performed for SFP validation and a 71% validation rate was observed. This study demonstrated that the soybean genome array is a satisfactory platform for identification of SFPs in cowpea. Furthermore, this study provided an example of a method to extend genomic resources from well supported species to "orphan" crops like cowpea.Transcriptome profiles of incompatible and compatible cowpea-RKN interactions for two time points using the Affymetrix soybean GeneChip were generated. The profiles indicated that the RKN resistance pathway was still partially suppressed at 9 days post-inoculation in resistant cowpea roots. Subtle variation of ROS concentration, induction of toxins and other defense related genes were indicated to play a role in this unique resistance mechanism. Further functional analysis of these differentially expressed genes will advance understanding of this intriguing plant-nematode interaction in a more precise manner
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
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Genetic Mapping of Fusarium oxysporum f.sp. tracheiphilum Race 3 and Race 4, Macrophomina phaseolina Resistance and Other Traits in Cowpea (Vigna unguiculata [L.] Walp).
Full text linkCowpea (Vigna unguiculata) is a legume crop which is grown in many warm regions around the world. Genomic resources have been developed for cowpea which has enabled the identification of QTL and candidate genes which can be utilized in trait improvement.Fungal diseases cause significant constraints to cowpea yield. Fusarium oxysporum f.sp. tracheiphilum (Fot) race 3 and race 4 cause vascular wilt disease and are problematic in California. Genetic mapping identified the Fot3-1 locus which confers resistance to Fot race 3 in the CB27 x 24-125B-1 population. Fot3-1 was identified on BAC clone CH093L18, which carries leucine-rich repeat serine/threonine protein kinases. QTLs were identified which confer resistance against Fot race 4. Fot4-1 was identified in the IT93K-503-1 x CB46 population and Fot4-2 was identified in the CB27 x 24-125B-1 and CB27 x IT82E-18(Big Buff) populations. The syntenic loci for Fot4-1 and Fot4-2 were examined with Glycine max, where several disease resistance candidate genes were identified. Macrophomina phaseolina is a fungal pathogen which causes diseases under high temperatures and drought-stress. QTLs, Mac-10, Mac-11, Mac-12 and Mac-13, were identified in the Sanzi x Vita 7 population. The Mac-11 locus was positioned within BAC clone CH038D17 where an auxin response factor was present. Mac-13 was identified within BAC clones CH062O11 and CH069K06, where an auxin-responsive GH3 family protein was present. Leaf morphology was studied in the cowpea RIL population, Sanzi x Vita 7, in which a QTL was identified for leaf shape, Hls. High co-linearity was observed for the syntenic Hls region in Medicago truncatula and Glycine max where EZA1/SWINGER genes were present. Heat-induced browning of seed coats is caused by high temperatures which discolors the seed coats of cowpea. Three QTL, Hbs-1, Hbs-2, and Hbs-3, were identified using cowpea RIL populations IT93K-503-1 x CB46 and IT84S-2246 x TVu14676. Hbs-1 was identified in BAC clone CM018C23 where ethylene forming enzymes were present. Hbs-3 was identified in BAC clones CH047M01 and CM014K16 where ACC synthase genes were present. Practical outcomes from these studies are the identification of molecular markers which can be used in a Marker Assisted Selection breeding scheme, which should expedite variety development for cowpea
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
Dispelling 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
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