1,721,009 research outputs found
The puzzle of bakanae disease through interactions between Fusarium fujikuroi and rice
Full text linkBakanae disease, one of the most noteworthy seedborne rice diseases, is caused by Fusarium fujikuroi, a member of the Gibberella fujikuroi species complex. The decreasing availability of chemical seed-dressing products over the last few years has raised the concerns of rice seed companies regarding bakanae disease. Therefore, new research trends require a deeper investigation into the main aspects of bakanae disease through interactions between rice and F. fujikuroi, in order to find new resistant or tolerant cultivars and alternative bakanae disease control strategies, as well as to develop more sensitive molecular diagnostic techniques. Here, some new aspects of F. fujikuroi epidemiology and pathogenicity, as well as its interactions with rice, are reported, and recent approaches applied to control bakanae disease are summarized
Antagonistic yeasts and thermotherapy as seed treatments to control Fusarium fujikuroi on rice
No full textBakanae disease, caused by Fusarium fujikuroi, is the most important seedborne disease of rice. Biological
control and physical treatments can be effective tools to control seedborne diseases. Sixty-two isolates of
yeasts and yeast-like fungi were obtained from different rice seeds. Four yeast isolates were selected in
dual culture assays for mycelial growth inhibition, and in seed tests for reduction of infection rate. The
isolates R23 and R26 were identified as Metschnikowia pulcherrima, the isolate R9 as Pichia guilliermondii,
and the isolate SB1 as Sporidiobolus pararoseus. Rice seeds treated with P. guilliermondii R9, M. pulcherrima
R23 and R26 significantly reduced the infection rate of F. fujikuroi, compared to some commercial biofungicides.
The four selected yeasts reduced the bakanae disease severity in rice plants grown in greenhouse
trials. Antagonist seed dressing resulted in reduction of the disease index from 93.0% in the untreated
control to 20.0% in P. guilliermondii R9 treated seeds, and to 28.5% in M. pulcherrima R23 treated seeds.
Selected antagonists were also used in combination with thermotherapy, which contributed to increase
their efficacy. Thus, P. guilliermondii R9 and M. pulcherrima R23 combined with thermotherapy at 60 C for
10 min decreased the bakanae disease index below 5%, and improved the seed germination rate compared
to the single treatments, showing a seed priming effect. This is the first report about the use of
antagonistic yeasts for seed dressing of rice to control F. fujikuroi on rice seeds, and biological treatment
may be improved through combination with thermotherapy
Differentiation of Pythium spp. from vegetable crops with molecular markers and sensitivity to azoxystrobin and mefenoxam
Full text linkBackground: Pythium species attack various vegetable crops causing seed, stem and root rot, and 'damping-off' after germination. Pythium diseases are prevalently controlled by two classes of fungicides, QoIs with azoxystrobin and phenlyamides with mefenoxam as representatives. The present study aimed to test the sensitivity of six Pythium species from different vegetable crops to azoxystrobin and mefenoxam and differentiating species based on ITS, cytochrome b and RNA polymerase I gene sequences.
Results: The inter- and intra-species sensitivity to azoxystrobin was found to be stable, with the exception of one Pythium paroecandrum isolate, which showed reduced sensitivity and two cytochrome b amino acid changes. For mefenoxam, the inter-species sensitivity was quite variable and many resistant isolates were found in all six Pythium species, but no RNA polymerase I amino acid changes were observed in them. ITS and cytochrome b phylogenetic analyses permitted a clear separation of Pythium species corresponding to globose- and filamentous-sporangia clusters.
Conclusion: The results document the necessity of well-defined chemical control strategies adapted to different Pythium species. Since the intrinsic activity of azoxystrobin among species was stable and no resistant isolates were found, it may be applied without species differentiation, provided it is used preventatively to also control highly aggressive isolates. For a reliable use of mefenoxam, precise identification and sensitivity tests of Pythium species are crucial because its intrinsic activity is variable and resistant isolates may exist. Appropriate mixtures and/or alternation of products may help to further delay resistance development
Development and validation of a TaqMan real time PCR assay for the specific detection and quantification of Fusarium fujikuroi in rice plants and seeds
Full text link Bakanae disease, which is caused by the seedborne pathogen Fusarium fujikuroi, is found throughout the world on rice. A TaqMan real-time PCR has been developed on the TEF 1-α gene to detect F. fujikuroi in different rice tissues. Three primer/probe sets were tested. The selected set produced an amplicon of 84 bp and was specific for F. fujikuroi with respect to eight Fusarium species of rice and six other rice common pathogens. The assay was validated for specificity, selectivity, sensitivity, repeatability, and reproducibility. The detection limit was set at 27.5 fg of DNA, which is approximately equivalent to one haploid genome of F. fujikuroi. The developed TaqMan real-time assay was able to efficiently detect and quantify F. fujikuroi from rice culms, leaves, roots, and seeds. At 1 week post-germination (wpg), the pathogen was more diffused in the green tissues, while at 3 wpg it was uniformly spread also in the roots. The highest concentration of F. fujikuroi was measured in the M6 cultivar, which showed around 1,450 fungal cells/g. The assay was sufficiently sensitive to detect a few genomic equivalents in the rice seeds, corresponding to 9.89 F. fujikuroi cells/g. The assay permitted bakanae disease to be detected in asymptomatic tissues at the early rice development stages. </jats:p
Fast and Sensitive Detection of Soil-Borne Cereal Mosaic Virus in Leaf Crude Extract of Durum Wheat
Full text linkSoil-borne cereal mosaic virus (SBCMV) is a furovirus with rigid rod-shaped particles containing an ssRNA genome, transmitted by Polymyxa graminis Led., a plasmodiophorid that can persist in soil for up to 20 years. SBCMV was reported on common and durum wheat and it can cause yield losses of up to 70%. Detection protocols currently available are costly and time-consuming (real-time PCR) or have limited sensitivity (ELISA). To facilitate an efficient investigation of the real dispersal of SBCMV, it is necessary to develop a new detection tool with the following characteristics: no extraction steps, very fast results, and high sensitivity to allow pooling of a large number of samples. In the present work, we have developed a reverse transcription loop-mediated isothermal amplification (RT-LAMP) protocol with such characteristics, and we have compared it with real-time PCR. Our results show that the sensitivity of LAMP and real-time PCR on cDNA and RT-LAMP on crude extracts are comparable, with the obvious advantage that RT-LAMP produces results in minutes rather than hours. This paves the way for extensive field surveys, leading to a better knowledge of the impact of this virus on wheat health and yield
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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