1,720,958 research outputs found
Status of fire blight resistance breeding in Malus
No full textMalus domestica (apple) is one of the most important fruit crops worldwide. Fire blight, caused by Erwinia amylovora, is one of the most destructive bacterial diseases that impacts apple production systems worldwide. Although it is possible to manage fire blight using antibiotics such as streptomycin, kasugamycin or oxytetracycline, the quest for sustainable and eco-friendly production makes breeding for fire blight resistance the most promising and desirable approach. Breeding for resistance is a long, resource-intensive process due to the high susceptibility of most commercial apple cultivars, and the fact that most resistance sources being characterized are from wild genetic backgrounds with unpalatable fruits, and apple’s long generation times. Nevertheless, establishment of pre-breeding materials is crucial. This review highlights the status of breeding for fire blight resistance in Malus, taking into account, 1) major and minor resistance sources and their interaction with E. amylovora, 2) progress and challenges associated with using wild species as resistance sources, 3) progress and challenges associated with using elite cultivars as resistance sources, 4) advances in biotechnology for use in enhancing the production of durable fire blight resistant cultivar
Genetic analysis and fine mapping of the fire blight resistance locus of Malus ×arnoldiana on linkage group 12 reveal first candidate genes
Full text linkMalus ×arnoldiana accession MAL0004 has been found to be resistant to moderately and highly virulent strains of the fire blight causal pathogen – the Gram-negative bacterium, Erwinia amylovora. Genetic analyses with an F1 segregating population derived from crossing the highly susceptible apple cultivar ‘Idared’ and MAL0004 led to the detection and mapping of the fire blight resistance locus of M. ×arnoldiana to linkage group (LG)12 (FB_Mar12). FB_Mar12 mapped at the distal end of LG12 below the apple SSR Hi07f01 in an interval of approximately 6 cM (Centimorgan), where both the fire blight resistance loci of M. floribunda 821 and ‘Evereste’ were located. We fine mapped the region containing FB_Mar12 using 892 progenies. Mining of the region of interest (ROI) on the ‘Golden Delicious’ doubled haploid genome (GDDH13) identified the presence of 2.3 Mb (megabases) in the homologous region. Of 40 primer pairs designed within this region, 20 were polymorphic and nine were mapped, leading to the identification of 24 significant recombinant individuals whose phenotypes were informative in determining the precise position of the locus within a 0.57 cM interval. Analyses of tightly linked marker sequences on the M. baccata draft genome revealed scaffolds of interest putatively harboring the resistance loci of M. ×arnoldiana, a hybrid between M. baccata and M. floribunda. Open reading frame (ORF) analyses led to the prediction of first fire blight resistance candidate genes with serine/threonine kinase and leucine-rich repeat domains, including homologs of previously identified ‘Evereste’ candidate genes. We discuss the implications of these results on breeding for resistance to fire blight
Malus fusca fire blight resistance: identification of a candidate gene on chromosome 10 and a novel minor locus on chromosome 16
No full textFire blight resistance of the wild apple species Malus fusca (accession MAL0045) has been previously reported.
This accession, crossed with the domesticated apple cultivar ‘Idared’, allowed for studies on the genetics of
the resistance of this crabapple with the resultant F1 population. A major fire blight locus (Mfu10), found on
chromosome 10, explained up to 66% of the phenotypic variance amongst the M. fusca × ‘Idared’ progenies.
Although fire blight resistance is strain specific for some Malus accessions, leading to the breakdown of resistance
in few resistance donors by highly aggressive strains of Erwinia amylovora; no strain able to breakdown the
resistance of M. fusca itself or Mfu10 has been found. This makes this wild apple an interesting model for
resistance studies with different wild-type and mutant strains of E. amylovora. A candidate gene (FB_Mfu10),
underlying the major locus, was recently proposed. FB_Mfu10 was predicted on the sequence of a bacterial
artificial chromosome (BAC) clone, spanning the fire blight locus on chromosome 10 and encodes B-lectin and
serine/threonine kinase domains. Preliminary functional analyses showed, that the open reading frame (ORF),
together with its border sequences upstream of the start codon and downstream of the stop codon (~ 6000 bp), is
present only in resistant F1 genotypes with 8bp distinguishing between susceptibility and resistance. Furthermore,
with a dense genetic map of M. fusca and studies with a mutant of an aggressive strain of E. amylovora, a minor
fire blight locus has been identifie
Identification of additional fire blight resistance candidate genes following MinION Oxford Nanopore sequencing and assembly of BAC clone spanning the Malus fusca resistance locus
Full text linkPyramiding different fire blight resistance genes and QTLs in future apple cultivars is the most eco-friendly way to combat this disease. Identification of strong fire blight resistance donors, and introgression of their resistance into apple breeding material are a continuing effort of breeding programs. Thus, enormous effort is been put into breeding research to understand host – pathogen interactions and mechanisms of resistance found in Malus. The crabapple Malus fusca (accession MAL0045) is highly resistant to fire blight, and although resistance is strain-dependent, resistance of MAL0045 is not overcome by any known strain of Erwinia amylovora to date. A strong fire blight resistance locus (FB_Mfu10) was fine mapped to an interval of 0.33 Centimorgan (cM) on linkage group (LG) 10 of MAL0045 using 1888 progenies. Subsequently, a single bacterial artificial chromosome (BAC) clone (46H22), which harbours FB_Mfu10-resistance alleles, was identified in a MAL0045 BAC library and sequenced using MiSeq illumina leading to the assembly of 45 contigs. Analyses of the sequence of 46H22 led to the identification of a receptor-like kinase candidate gene. Here, we report about resequencing 46H22 using MinION Oxford Nanopore and successfully assembled the sequences into a single contig, which allowed for identifying additional candidate genes
Fire blight resistance of Malus ×arnoldiana is controlled by a quantitative trait locus located at the distal end of linkage group 12
No full textErwinia amylovora is the pathogen which incites fire blight - the most devastating bacterial disease affecting pome fruit production worldwide. So far, only one functionally proven gene for resistance to this disease has been reported in Malus, even though several quantitative trait loci (QTLs) have been identified. Since some highly aggressive strains are capable of overcoming described resistances in Malus, including that of the only isolated and functionally-proven resistance gene, it is important to identify more resistance donors useful for the establishment of pyramided and durable resistance. Quantitative trait locus analyses were performed on F1 progenies derived from a cross between the Malus ×domestica cultivar, Idared, and the wild apple species M. ×arnoldiana. Progenies were artificially inoculated with two strains of E. amylovora – the moderately aggressive strain Ea222_JKI, and the highly aggressive Canadian strain, Ea3049. A QTL was identified at the distal end of linkage group (LG) 12 of M. ×arnoldiana explaining over 50% of the phenotypic variation among the progenies inoculated with Ea222_JKI. A significant QTL effect was also identified on LG12 using the phenotypic data of the progenies inoculated with Ea3049. The fire blight resistance QTL of M. ×arnoldiana (FB_Mar12) appeared to be located at a similar position as those of Evereste and/or M. floribunda clone 821 below the SSR marker Hi07f01 on LG12 of the apple genome. The results presented here suggest that this QTL could be allelic with the other reported fire blight QTLs on LG12. Nevertheless, it is imperative to perform more studies aimed at further elucidating the resistance mechanism of this wild apple species since it displays a significant resistance effect to Ea304
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
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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