1,721,053 research outputs found
Exploring recessive resistance to the powdery mildew disease
Full text linkThe powdery mildew disease, caused by obligate biotrophic fungi belonging to the Ascomycete order of Erysiphales, is common among higher plants and represents one of the most important threats for the cultivation of many crop species. Although powdery mildew resistance is usually a dominant trait, recessively inherited resistance has been reported to occur in Arabidopsis, barley, tomato and pea. In <strong>Chapter 1</strong> of this thesis, we provide a state of the art on the understanding of mechanisms underlying plant immunity and review monogenic dominant and recessive sources used in breeding in order to develop resistant cultivars. In <strong>Chapter 2 and 3,</strong> we describe a successful homology-based cloning approach for the isolation of the recessive ol-2 gene, naturally occurring in a tomato accession collected in Ecuador and conferring broad-spectrum resistance to the powdery mildew fungus Oidium neolycopersici. We realized that ol-2 resistance shares striking similarities with well-known barley and Arabidopsis mlo powdery mildew resistance, originating from loss-of-function mutations of genes encoding for specific seven transmembrane domains MLO isoforms. The following chain of evidence was provided demonstrating that ol-2 resistance is due to the loss of the tomato MLO homolog SlMLO1: a) Ol-2 and SlMLO1 loci share the same genetic and cytogenetic position; b) resistant ol-2/ol-2 lines are homozygous for a loss-of-function deletion in the sequence of SlMLO1; c) a molecular marker developed on the mutation site co-segregates with resistant individuals in an F<sub>2</sub>population; d) SlMLO1 transgenic expression in ol-2/ol-2 individuals results in disease susceptibility; e) SlMLO1 virus-induced silencing in Ol-2/Ol-2 individuals is associated to increased powdery mildew resistance. In <strong>Chapter 4</strong>, we first illustrate a chemical mutagenesis program allowing the identification of a pea line showing recessive resistance towards the powdery mildew fungus Erysiphe pisi. Histological and genetic analyses revealed that the mutated gene is allelic to er1, commonly used in pea breeding for the development of resistant cultivars. As defense mechanisms associated to er1 resistance are reminiscent of mlo immunity, we sequenced the pea MLO homolog PsMLO1 and found a loss-of-function point mutation characterizing the resistant line. A polymorphic CAPS marker was developed on the mutation site and found to be fully co-segregating with resistance in a large F<sub>2</sub>population. Finally, PsMLO1 sequencing in three er1 resistant cultivars also resulted in the identification of aberrant alleles, further substantiating the identification of another case of mlo-based immunity. In <strong>Chapter 5</strong>, we report the identification (in vitro and in silico) of a series of MLO homolog sequences in five cultivated Solanaceae species affected by the powdery mildew disease. Comparative analyses using a dataset of several dicot MLO proteins allowed the identification of candidate isoforms for disease susceptibility and the detection of cluster-specific transmembrane amino acid motifs. In <strong>Chapter 6</strong>, we look at disease resistance as a condition due to the lack of susceptibility genes like MLO. We review several susceptibility genes isolated in crop species and in Arabidopsis, with respect to their molecular characterization, their role in plant-pathogen interactions and the resistant phenotype deriving from their loss-of-function mutations/silencing. A breeding strategy based on the lack of plant susceptibility genes is discussed.  
Phenotypic and pomological diversity of selected native walnut (Juglans regia) populations: implications for breeding and cultivation programs
No full textThere is a significant genetic diversity among Iranian local populations of Persian walnut (Juglans regia L.). Therefore the walnut cultivated for nut production provided a good opportunity for the identification of genotypes with desirable traits. In the present study, the pomological and phenological diversity traits of a total of 167 seed-originated walnut genotypes were investigated based on International Plant Genetic Resources Institute and the International Union for the Protection of New Varieties of Plants descriptors for two consecutive years. Considerable variations were found among the studied genotypes for all the evaluated traits. Nut weights, kernel weights, and kernel percentages among the selected genotypes ranged from 5.78 to 18.04 g, 2.4 to 10.78 g, and 18.33 to 78.20 respectively. Lateral bearing (LaBe) was positively and significantly correlated with yield (Yi) (r = 0.88). In addition, a negative correlation was observed between chilling damage and either LaBe or Yi. According to principal component analysis, the first two components explained 56% of the total variance among the studied genotypes. Phenological traits such as bud break date, first (FPSh), and last pollen shedding date (LPSh) were the most important traits contributing to the first component (PC1). PC2 was mainly contributed by nut weight (NuWe), kernel weight (KeWe), and kernel percentage (KePe). Cluster analysis divided the genotypes under study into 3 main groups. After 2-year evaluation, promising genotypes with lateral bearing habit, light kernel color, high yield, and late-leafing have been identified, including 22Fa-BC167, 22Fa-BC93, 22Fa-BC162, 22Fa-BC105, and 22Fa-BC163. These genotypes showed great potential for direct introduction into commercial cultivation in the orchards or as parental candidates for future walnut breeding programs
CAPS technology as a tool for the development of genic and functional markers: Study in peas
No full textDNA markers linked to economically important alleles are often used in plant breeding in order to replace/assist traditional phenotypic selection. Thanks to growing advances in agricultural genetics and genomics, it is possible today to develop genic markers and functional markers, the latter targeting polymorphisms, within a certain gene, directly responsible for the phenotype. It is known that allelic variation is commonly due to single nucleotide polymorphisms (SNPs) and small insertion/deletions (In/Del). In both cases restriction endonucleases recognition sites can be created or disrupted. Thus, cleaved amplified polymorphic sequence (CAPS) technology is particularly suitable for the development of genic and functional markers. In recent activities, we developed a series of CAPS and derived CAPS (dCAPS) functional markers which target all SNP mutations in a gene of cultivated pea (Pisum sativum L.) known to determine resistance to the powdery mildew pathogen Erysiphe pisi. Molecular markers other than CAPS, including those based on next generation sequencing methods, can be today used to target SNPs and In/Del polymorphisms. However, considering their ease of obtainment without the need of costly equipment, CAPS might be still the markers of choice for breeding programs which do not make use of genome-wide screenings and for species whose genetic/genomic information is limited
Exploitation of recessive mlo-mutants for durable powdery mildew resistance in vegetable crops
No full textCAPS technology as a tool for the development of genic and functional markers: study in peas
No full textDNA markers linked to economically important alleles are often used in plant breeding in order to replace/assist traditional phenotypic selection. Thanks to growing advances in agricultural genetics and genomics, it is possible today to develop so-called genic markers, designed on the DNA sequence of genes having a known effect on the phenotype, and functional markers, targeting, within the same genes, polymorphisms directly responsible for the phenotype. It is known that allelic variation is commonly due to single nucleotide polymorphisms (SNPs) and small insertion/deletions (In/Del), which in many cases can be associated to the creation or disruption of restriction endonucleases recognition sites. Thus, cleaved amplified polymorphic sequence (CAPS) technology is particularly suitable for the development of genic and functional markers. In recent activities, we developed a series of CAPS and derived CAPS (dCAPS) functional markers which target all SNP mutations in a gene of cultivated pea (Pisum sativum L.) known to determine resistance to the powdery mildew pathogen Erysiphe pisi. Molecular markers other than CAPS, including those based on next generation sequencing methods, can be today used to target SNPs and In/Del polymorphisms. However, considering their ease of obtainment without the need of costly equipment, CAPS might be still the markers of choice for breeding programs which do not make use of genome-wide screenings and for species whose genetic/genomic information is limited
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
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