1,721,012 research outputs found
A New <i>Phytophthora</i> sp. causing root and collar rot on <i>Pistacia lentiscus</i> in Italy
No full textLentisk (Pistacia lentiscus L., Anacardiaceae) is an evergreen shrub that is widespread over the Mediterranean Region. The species is also cultivated as an ornamental plant in Italy. In August 2008, a survey carried out in a forest nursery in Sardinia (39°57′N, 9°13′E) revealed the presence of symptoms such as wilting and desiccation of foliage associated with root and collar rot on 1- to 3-year-old potted seedlings of lentisk. Approximately 30% of 1,500 potted plants were affected. A Phytophthora sp. was consistently isolated from infected roots on synthetic mucor agar medium. Colonies on carrot agar (CA) were stellate to slightly radiate with low aerial mycelium
Diplodia africana causing dieback disease on Juniperus phoenicea: a new host and first report in the northern hemisphere
No full text<i>Phytophthora</i>:an ancient, historic, biologically and structurally cohesive and evolutionarily successful generic concept in need of preservation
Full text linkThe considerable economic and social impact of the oomycete genus Phytophthora is well known. In response to evidence that all downy mildews (DMs) reside phylogenetically within Phytophthora, rendering Phytophthora paraphyletic, a proposal has been made to split the genus into multiple new genera. We have reviewed the status of the genus and its relationship to the DMs. Despite a substantial increase in the number of described species and improvements in molecular phylogeny the Phytophthora clade structure has remained stable since first demonstrated in 2000. Currently some 200 species are distributed across twelve major clades in a relatively tight monophyletic cluster. In our assessment of 196 species for twenty morphological and behavioural criteria the clades show good biological cohesion. Saprotrophy, necrotrophy and hemi-biotrophy of woody and non-woody roots, stems and foliage occurs across the clades. Phylogenetically less related clades often show strong phenotypic and behavioural similarities and no one clade or group of clades shows the synapomorphies that might justify a unique generic status. We propose the clades arose from the migration and worldwide radiation ~ 140 Mya (million years ago) of an ancestral Gondwanan Phytophthora population, resulting in geographic isolation and clade divergence through drift on the diverging continents combined with adaptation to local hosts, climatic zones and habitats. The extraordinary flexibility of the genus may account for its global 'success'. The 20 genera of the obligately biotrophic, angiosperm-foliage specialised DMs evolved from Phytophthora at least twice via convergent evolution, making the DMs as a group polyphyletic and Phytophthora paraphyletic in cladistic terms. The long phylogenetic branches of the DMs indicate this occurred rather rapidly, via paraphyletic evolutionary 'jumps'. Such paraphyly is common in successful organisms. The proposal to divide Phytophthora appears more a device to address the issue of the convergent evolution of the DMs than the structure of Phytophthora per se. We consider it non-Darwinian, putting the emphasis on the emergent groups (the DMs) rather than the progenitor (Phytophthora) and ignoring the evolutionary processes that gave rise to the divergence. Further, the generic concept currently applied to the DMs is narrower than that between some closely related Phytophthora species. Considering the biological and structural cohesion of Phytophthora, its historic and social impacts and its importance in scientific communication and biosecurity protocol, we recommend that the current broad generic concept is retained by the scientific community.</p
Soil- and waterborne Phytophthora species linked to recent outbreaks in Northern California restoration sites
Full text linkMany studies around the globe have identified plant production facilities as major sources of plant pathogens that may be released in the wild, with significant consequences for the health and integrity of natural ecosystems. Recently, a large number of soilborne and waterborne species belonging to the plant pathogenic genus Phytophthora have been identified for the first time in California native plant production facilities, including those focused on the production of plant stock used in ecological restoration efforts. Additionally, the same Phytophthora species present in production facilities have often been identified in failing restoration projects, further endangering plant species already threatened or endangered. To our knowledge, the identification of Phytophthora species in restoration areas and in plant production facilities that produce plant stock for restoration projects is a novel discovery that finds many land managers unprepared, due to a lack of previous experience with these pathogens. This review summarizes some of the key knowledge about the genus Phytophthora in general and lists some of the many soilborne and waterborne species recently recovered from some California restoration sites and plant production facilities
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
Endemic and emerging pathogens threatening cork oak trees: Management options for conserving a unique forest ecosystem
No full textCork oak (Quercus suber) forests are unique in being largely anthropogenic, and representing both an important source of income and a great reservoir of biodiversity. Because of changes in the Mediterranean climate and developments in the way farming is conducted, the semi-natural cork-oak forests have become ecologically fragile and more susceptible to pathogens.
There is evidence that climate is selecting for thermophilic or thermotolerant pathogen strains that produce a larger biomass. A high infectivity (massive propagule pressure) is a major determinant in the spread of pathogens to as yet uncontaminated areas. We describe the role and effect of these pathogens with the aim to identify strategies for curtailing diseases and safeguarding the forests.
This report gives an overview of the most harmful pathogens of cork-oak and provides a critical evaluation of how cork-oak stands are currently managed, suggesting new ways of management and also outlining future research necessary to keep the disease agents under control.
A knowledge of the effect of climate change on the growth and survival of pathogens, and on tree-parasite interactions as a result, has become fundamental for making informed decisions and managing cork oak forests properly
Multiple Phytophthora species associated with declining wild olive trees in Sardinia, Italy
No full textWild olive represents one of the most iconic woody plants in the Mediterranean Basin. This slow-growing evergreen tree is characteristic of sclerophyll vegetation, extremely tolerant to drought, salinity and diseases, thus is commonly used as rootstock for grafting cultivated olive varieties. Since 2022, extensive dieback and mortality of wild olive trees have been observed in Sardinia, Italy. Affected plants showed leaf chlorosis, wilting, defoliation, shoot blight and epicormic shoots, often associated with root rot and necroses on the feeder roots, initially associated with Phytophthora bilorbang and P. pseudocryptogea. A 2-year study was thereafter conducted to clarify the aetiology of this unusual disease. Using a baiting technique, 10 Phytophthora taxa from three phylogenetic clades (2, 6, 8) were isolated from 53 of 87 rhizosphere soil samples collected, including P. asparagi, P. bilorbang, P. crassamura, P. inundata, P. kelmanii, P. oleae, P. pseudocryptogea, P. sansomeana and P. syringae. Additionally, some isolates that showed several polymorphisms in rDNA internal transcribed spacer (ITS) sequences compared with closely related known species are reported here as P. taxon paulensis. Pathogenicity tests on 1-year-old wild olive seedlings showed that nine out of 10 Phytophthora taxa significantly reduced root length of inoculated seedlings compared to controls. P. inundata and P. oleae caused the greatest reduction, while root length of seedlings inoculated with P. kelmanii did not differ from the controls. This study provides insights into the role of Phytophthora taxa in the wild olive decline in Sardinia, indicating the urgent need to expand monitoring and implement effective management strategies to mitigate the disease
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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