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Tar Spot of Corn: A Diagnostic and Methods Guide
No full textTar spot of corn is an emerging plant disease in the continental United States and Canada caused by the fungal pathogen Phyllachora maydis Maubl. Tar spot has been known to occur in Mexico, the Caribbean, and Central and South America since the early to mid-1900s. In 2015, it was reported for the first time in the continental United States. Since that time, tar spot has spread across corn-producing areas in the United States with epidemics as recent as 2021 resulting in significant yield losses. Although tar spot has been known to affect corn for over a century in the Americas, the biology of the pathogen, etiology, and epidemiology of the disease are not well understood. Additionally, symptoms and signs of tar spot resemble other foliar diseases and abiotic disorders of corn, which may lead to misdiagnosis. In this paper, we provide a brief description of current knowledge about tar spot of corn, including pathogen taxonomy, host range, symptoms and signs, specimen storage, pathogenicity testing, diagnostic protocols, and geographic distribution. This information will be useful to diagnosticians, researchers, and other professionals working with this disease.Minnesota Invasive Terrestrial Plants and Pests Center through the Minnesota Environment and Natural Resources Trust FundSolórzano, José E.; Cruz, C. D.; Arenz, Brett E.; Malvick, Dean K.; Kleczewski, Nathan M.. (2023). Tar Spot of Corn: A Diagnostic and Methods Guide. Retrieved from the University Digital Conservancy, 10.1094/PHP-04-22-0033-DG
Identifying loci conferring quantitative disease resistance in sorghum and maize against fungal foliar pathogens
Full text linkThere are multiple mechanisms by which hosts defend themselves against pathogens. Broadly disease resistance can be split into qualitative and quantitative resistance. In qualitative resistance the presence of a single resistance gene (R gene) confers complete resistance against the pathogen. R proteins can interact directly as receptors or indirectly as guardees/decoys with pathogen Avr proteins. R genes are generally race specific. Quantitative disease resistance (QDR) is genetically complex with a partial phenotype conferred by multiple small effect genes. In some instances genes and loci associated with QDR confer broad spectrum resistance against multiple of pathogens (Singh et al., 2011a). Many QDR genes are not directly associated with host defense responses but with host morphology and development, signal transduction, and the general defense response, among other mechanisms. The mechanisms underlying qualitative resistance are well understood through many detailed analyses (Spoel and Dong, 2012; Song et al., 2015; Balint-Kurti, 2019; Dievart et al., 2020; Sun et al., 2020). By contrast the mechanisms associated with QDR remains largely elusive.
The deployment of resistant germplasm is an economically efficient means to manage disease. However, high selection pressure on pathogens with high evolutionary potential can lead to pathogens overcoming host resistance. Durability of resistance can be maintained through genetic complexity. Genetic complexity is established by stacking both R genes and QDR genes through pyramiding (Mundt, 2018). As complexity increases, pathogens are required to evade multiple forms of detection.
Maize is a model organism and has been studied for resistance to a variety of diseases. Northern corn leaf blight and sorghum leaf blight are both caused by the hemibiotrophic fungus Exserohilum turcicum. Both qualitative and quantitative resistance against E. turcicum have been described in maize. In contrast, the genetic architecture of resistance against E. turcicum in sorghum is poorly understood. Maize and sorghum are closely related C4 grass species, and likely share mechanisms of resistance to E. turcicum. Identification of resistance in sorghum against E. turcicum can enhance management strategies and understanding of the pathosystem.
By definition, emerging diseases are not as well understood. Phyllachora maydis, the causal agent of tar spot in maize was identified in the United States in 2015. The role of environmental conditions is important in the P. maydis pathosystem. Resistance has been identified in tropical germplasm but not in temperate-adapted germplasm. Accessions developed by the Germplasm Enhancement of Maize (GEM) project contain introgressions from landraces in elite backgrounds. Screening exotic-derived germplasm will aid in the identification of donors for alleles contributing towards resistance to tar spot.
Chapter 1 is a literature review of disease resistance in crops, specifically on quantitative and qualitative disease resistance in maize. Chapter 2 is a QTL mapping study that identifies loci for resistance to E. turcicum in two sorghum recombinant inbred line populations. The distribution of resistance loci in sorghum is non-random. The relationship of resistance to E. turcicum between maize and sorghum is examined, and maize genes for resistance colocalize within the sorghum leaf blight resistance loci. Sorghum and maize likely utilize similar mechanisms of resistance against E. turcicum. The main objective of Chapter 3 is to identify sources of resistance to tar spot in exotic-derived germplasm. Environmental conditions have a strong influence on disease severity, but consistent phenotypic responses are observed across environments. Disease symptoms vary between juvenile and adult plants. Accessions with potential for use in breeding for tar spot resistance are described. Chapter 4 summarizes the findings from Chapters 2 and 3 and discusses implications for future research goals of confirming a QTL on chromosome 3 in sorghum associated with resistance against E. turcicum. Chapter 4 also discusses implications of environmental modeling for predicating disease development and further identifying sources of resistance to tar spot in maize.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2023-05-01The student, Sarah Lipps, accepted the attached license on 2021-04-21 at 07:45.The student, Sarah Lipps, submitted this Thesis for approval on 2021-04-21 at 07:49.This Thesis was approved for publication on 2021-04-28 at 15:36.DSpace SAF Submission Ingestion Package generated from Vireo submission #16457 on 2021-09-16 at 20:11:33Made available in DSpace on 2021-09-17T04:04:41Z (GMT). No. of bitstreams: 2
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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
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