124,589 research outputs found
Identification of metabolites involved in the cold stress tolerance promoted by psychrotolerant bacteria in plants
No full textCold stress causes serious negative impacts on growth and yield of economically valuable crops. While some plants are adapted to cold environments, crops originating from sub-tropical regions, such as tomato, are more sensitive to cold stress. The efficacy of plant-associated microorganisms to protect plants against cold stress was reported, but scarce information is available on the molecular mechanisms underlying this process. The aim of this project is to understand the physiological mechanisms activated by psychrotolerant bacteria on tomato plants and to identify plant and/or bacterial metabolites and genes responsible for cold stress tolerance. Antarctic plants are a possible understudied source of psychrotolerant endophytic bacteria to be exploited in the plant protection against cold stress and four isolates were selected on a bacterial collection for their ability to promote tomato plant growth at low temperatures. The four bacterial isolates are currently being tested for their ability to stimulate plant physiological responses related to cold stress adaptation. In particular, the content of proline and malondialdehyde (MDA) was previously associated to cold stress in tomato plants and it will be analysed in bacterized and non-bacterized plants exposed to cold stress (7 days at 0°C) and recovery condition (0, 2 and 4 days at 25°C) using two different biochemical assays. Metabolomic and transcriptomic changes will be then analysed in bacterized and non-bacterized plants exposed to cold stress. In particular, amino acids, sugars and sugar alcohols previously associated with cold tolerance will be assessed in bacterized and non-bacterized plants using gas chromatography mass spectrometry (GC-MS) and hydrophobic interaction liquid chromatography (HILIC)-MS. The outcome of this project will provide a deeper knowledge in the mechanisms of cold adaptation enhanced by endophytic bacteria in plants
First evidence of Pantoea ananatis infections on strawberry in Italy
No full textRecently, symptoms resembling fire blight such as brownish lesions, necrosis, and production of exudates were observed on a new cold-resistant strawberry variety (Ania®). Thus, the aim of this study was to isolate, identify and characterize the causative agents. Bacterial isolation was carried out from symptomatic plant tissues (leaves and stems) collected from four strawberry plants. Tissues were surface-sterilized, homogenized in 0.85% (w/v) NaCl and serially diluted onto Nutrient Agar. One hundred twenty bacterial isolates were tested for the induction of the hypersensitive response (HR) in tobacco leaves. Bacterial isolates with yellow colonies able to induce HR were identified as Pantoea ananatis by 16S rDNA gene sequencing. PCRs using the primer pair PANA_1080 specific for P. ananatis species validated these results. Subsequently, pathogenicity tests were carried out by wounding detached ripe pseudo-fruits from strawberry plants (Ania®) and inoculating five μL of bacterial cell suspension (∼1×108 CFU/mL) of a selected P. ananatis strain. Distilled water and Escherichia coli DH5were used as control treatments. Strawberries were incubated in the dark at 27°C and 90% RH and appearance of symptoms was monitored daily. No symptoms were observed on the control treatments. On P. ananatis inoculated strawberries, symptoms appeared after five days and the bacterial strain was re-isolated from the sympotmatic pseudo-frutits. Furthermore, P. ananatis strains were evaluated for the production of plant cell wall degrading enzymes (i.e. cellulases). To the best of our knowledge, this is the first report of P. ananatis on strawberry in Italy
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Ecology and potential functions of plant-associated microbial communities in cold environments
No full textComplex microbial communities are associated with plants and can improve their resilience under harsh environmental conditions. In particular, plants and their associated communities have developed complex adaptation strategies against cold stress. Although changes in plant-associated microbial community structure have been analysed in different cold regions, scarce information is available on possible common taxonomic and functional features of microbial communities across cold environments. In this review, we discuss recent advances in taxonomic and functional characterization of plant-associated microbial communities in three main cold regions, such as alpine, Arctic and Antarctica environments. Culture-independent and culture-dependent approaches are analysed, in order to highlight the main factors affecting the taxonomic structure of plant-associated communities in cold environments. Moreover, biotechnological applications of plant-associated microorganisms from cold environments are proposed for agriculture, industry and medicine, according to biological functions and cold adaptation strategies of bacteria and fungi. Although further functional studies may improve our knowledge, the existing literature suggest that plants growing in cold environments harbor complex, host-specific and cold-adapted microbial communities, which may play key functional roles in plant growth and survival under cold conditions
Identification by HS-SPME/GC-MS and activity testing of Trichoderma spp. volatile organic compounds against grapevine downy mildew
No full textDowny mildew, caused by the biotrophic oomycete Plasmopara viticola, is one of the most destructive diseases of the grapevine [1]. Fungi of the genus Trichoderma are economically important biocontrol agents since they play a crucial role in plantgrowth promotion, mycoparasitism of plant pathogens and priming of plant defence. Trichoderma spp. also release a high diversity of volatile organic compounds (VOCs), which play a decisive role against plant pathogens [2]. However, the possible contribution of Trichoderma VOCs in antagonistic processes against grapevine downy mildew has not yet been investigated. In this work, VOC emission profiles of three Trichoderma strains belonging to T. asperellum, T. atroviride and T. harzianum were analysed using headspace-solidphase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS). Total ion current chromatograms were processed by an open source software [3], and statistical analysis on the obtained raw data was carried out using an in-house R-script. VOCs emitted by the Trichoderma strains at specific time-points were selected, and pure compounds were tested against downy mildew by leaf disks assays on susceptible grapevines. The development of downy mildew symptoms was reduced on leaf disks exposed to air treated with two sesquiterpenes, one hydrocarbon, or one heterocyclic compound, indicating the efficacy of these VOCs against downy mildew in plant tissues. Our data suggest that VOCs emitted by the Trichoderma strains under study can effectively be detected and identified by HS-SPME/GC-MS, and can inhibit the development of downy mildew symptoms on susceptible grapevine
Identification of Trichoderma spp. volatile organic compounds (VOCs) by HS-SPME/GC-MS analysis
No full textIntroduction
Trichoderma spp. are among the most widespread soil microorganisms and have been widely used as biological control agents against numerous phytopathogens [1]. Trichoderma biological control mechanisms are based on the production of antimicrobial substances, lytic enzymes, competition with other microorganisms for nutrients and/or space, mycoparasitism, and plant resistance induction [2]. Moreover, Trichoderma spp. are known to produce numerous volatile organic compounds (VOCs) [3] that play crucial roles in the inter-kingdom communications and biological control mechanisms [4]. Three Trichoderma strains, such as T. asperellum T34 (T34), T. atroviride SC1 (SC1), T. harzianum T39 (T39) are well documented for their ability to cope with a broad spectrum of phytopathogens and are commercialised as biofungicides. Several studies highlighted the importance of Trichoderma spp. as an alternative strategy against grapevine pathogens [5], but no information is available on the possible biological control mechanism mediated by Trichoderma VOCs against grapevine downy mildew (caused by Plasmopara viticola). The aim of this study was to identify VOCs produced by T34, SC1 and T39 using headspace-solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-MS) analysis.
Materials and Methods
Volatile-mediated effects of Trichoderma strains were assessed on grapevine leaf disks incubated with uninoculated potato dextrose agar (PDA) Petri dishes (Control) and dishes with PDA-grown T34, SC1 or T39 colonies without contact with leaf tissues. Leaf disks were inoculated with a suspension of P. viticola sporangia and downy mildew severity was assessed at six days post inoculation (dpi).
For headspace analysis of Trichoderma spp. VOCs, 20 μL of the conidial suspension of the respective Trichoderma strain were inoculated on PDA poured into sterile 20 mL-HS vials. VOCs produced by Trichoderma strains were measured using HS-SPME/GC-MS analysis at 48 or 72 h of incubation at 25°C. For compound identification, deconvoluted mass spectra were compared with an in-house library obtained with authentic reference standards. Compound annotation was achieved imposing a relative deviation of retention index (RI) value lower than 2% from the reference value published in the NIST14 database, and according to the mass spectrum similarity score set higher than 70%. Two independent experiments were carried out. Five of the identified VOCs were selected according to their emission profiles and pure compounds were tested against P. viticola by leaf disk assay.
Results
VOCs produced by T34, SC1 or T39 reduced downy mildew symptoms on grapevine leaf disks. HS-SPME/GC-MS analysis revealed a total of 26 and 21 Trichoderma VOCs found in the first and second experiments, respectively. Trichoderma VOCs included alkenes, ketones, pyrones, furanes and terpenes. Terpenes were successfully identified using manual inspection of extracted ion current (EIC) chromatograms at m/z 136 for monoterpenes, m/z 202 and 204 for sesquiterpenes, and m/z 272 for diterpenes. VOC profiles differed according to the Trichoderma strains and T39 was the highest producer of VOCs and terpenes compared to T34 and SC1. Five metabolite groups were identified according to changes in abundance among the three Trichoderma strains: VOCs with consistent changes in both experiments at both (Group 1), or at one time point (Group 2); VOCs with different changes in abundance in both experiments (Group 3); VOCs detected only in the first (Group 4) or second (Group 5) experiment. Five VOCs (two sesquiterpenes, one alkene, one furan and one pyrone) were tested against P. viticola and each VOC was applied to a filter paper disk on the lid of the Petri dish without contact with leaf tissues. Three VOCs slightly reduced the development of downy mildew symptoms at dosages of 50 mg/L in air volume. Two pure VOCs significantly reduced downy mildew symptoms at the dosage of 10 mg/L in air volume.
Discussion/Conclusions
HS-SPME/GC-MS analysis is a powerful tool to detect and identify Trichoderma VOCs. VOC profiles differed in the three Trichoderma strains and T39 was the highest producer of terpenes, followed by T34 and SC1, indicating genotypic determinants of VOC production. Five VOCs (two sesquiterpenes, one alkene, one furan and one pyrone) reduced downy mildew symptoms on grapevine leaf disks. Preliminary results suggest that two most effective VOCs enhanced the grapevine defence responses against P. viticola. These results indicate that Trichoderma VOCs are promising molecules that could be further developed to naturally control grapevine downy mildew. Further transcriptomic and metabolomic studies are required to shed light on the grapevine defence mechanisms activated by Trichoderma VOCs against downy mildew
The good, the bad and the ugly: how volatile organic compounds (VOCs) produced by Trichoderma spp. protect grapevine plants against downy mildew
No full textTrichoderma spp. are among the most widespread soil microorganisms and have been widely used as biological control agents against phytopathogens. Trichoderma spp. are known to produce volatile organic compounds (VOCs) that play crucial roles in the inter-kingdom communications and biological control mechanisms. Several studies highlighted the importance of Trichoderma spp. as an alternative strategy against grapevine pathogens, but no information is available on the possible biological control mechanisms mediated by Trichoderma VOCs against grapevine downy mildew (caused by Plasmopara viticola). The aim of this study was to characterize VOCs produced by three Trichoderma strains and to investigate their effects against grapevine downy mildew. VOCs produced by Trichoderma asperellum T34, T. harzianum T39, and T. atroviride SC1 reduced downy mildew symptoms on grapevine leaf disks. A head space–solid phase microextraction gas chromatography–mass spectrometry analysis revealed 31 VOCs in two independent experiments, including alkenes, ketones, pyrones, furanes and terpenes. Five reduced downy mildew symptoms on grapevine leaf disks. In particular, 6-pentyl-2H-pyran-2-one and 2-pentylfuran increased the accumulation of callose and enhanced the modulation of defense-related genes after P. viticola inoculation, indicating an induction of grapevine defense mechanisms. Moreover, one 6-pentyl-2H-pyran-2-one activated the hypersensitive response after P. viticola inoculation to reinforce the grapevine defense reaction. These results indicate that Trichoderma VOCs can induce grapevine resistance and these molecules will be further characterized to better clarify the mode of action against grapevine downy mildew
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
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