Virus - vector relationships in the transmission of tospoviruses

Tomato spotted wilt virus (TSWV), member of the genus Tospovirus within the family Bunyaviridae, ranks among the top ten of economically most important plant viruses. Tospoviruses cause significant yield losses in agricultural crops such as tomato, lettuce, pepper, tobacco, potato and groundnut, but also in ornamentals like chrysanthemum, alstroemeria, gloxinia and impatiens. Currently, more than 650 different plant species belonging to more than 70 distinct botanical families are known to be susceptible to tospoviruses. Following the introduction of the vector Frankliniella occidentalis from the United states in Europe, TSWV and impatiens necrotic spot virus (INSV), a tospovirus mainly occurring in ornamentals, are prevailing in the Netherlands, especially in greenhouse cultivations.To gain more insight in the epidemiology of tospoviruses, information is needed on the kinetics of their transmission. The experiments described in this thesis were done to analyze some of the parameters involved.An efficient local lesion assay was developed to facilitate transmission studies using leaf disks of Petunia x hybrida "Blue Magic". In this assay, transmission could be scored reliably within 2 to 3 days on the basis of local lesion formation. This assay also enabled easy handling of large numbers of thrips. Besides petunia, leaf disks of other plant hosts were found to be suitable as substrate in transmission studies as well.Using this assay it was established that F. occidentalis could acquire and transmit the virus in periods of 5 min. Longer periods were required for more efficient transmission. To quantify virus transmission the median acquisition (AAP 50 ) and inoculation access periods (IAP 50 ), i.e. the periods needed for 50% of the thrips to respectively acquire or inoculate the virus were determined. The value for the AAP 50 was 67 min whereas an IAP 50 of 59 min was found. The leaf disk assay was also employed to determine the efficiency of transmission and the latent period (LP), the period between acquisition and inoculation of the virus, for both TSWV and INSV. The majority of thrips already transmitted virus at the end of the second larval stage at transmission rates for TSWV or INSV of 52.8 % or 80.0%, respectively.The fate of the virus in the thrips after ingestion was studied in different developmental stages of F. occidentalis. The accumulation of two viral proteins, the nucleocapsid (N) and a non-structural (NS S ) protein, as monitored by ELISA en Western blot analyses, increased within two days above the levels initially ingested. Immunocytology of infected adults confirmed that viral products were present in high amounts, especially, in the salivary glands. Electron microscopic studies revealed the presence of many virus particles in the salivary ducts. These results unequivocally demonstrated that TSWV replicated in its insect vector and that the salivary glands were a major site of multiplication. This multiplication was not accompanied by pathological effects on the vector. No effect of virus infection was found on development time, reproduction rate and survival . This study al so revealed that no transovarial transmission of virus to the progeny took place.The vector competence was determined for four thrips and four tospovirus species. The results showed that specificity of transmission, as occurring for other insect-transmitted plant viruses, also exists for tospovirus transmission by thrips. F. occidentalis appeared to be the most efficient vector for all 4 viruses tested, i.e. TSWV, INSV, tomato chlorotic spot virus (TCSV) and groundnut ringspot virus (GRSV). Frankliniella schultzei transmitted three (TSWV, TCSV and GRSV) of the four tospoviruses, whereas Frankliniella intonsa, not yet reported as tospovirus vector, transmitted TSWV and TCSV. Of Thripstabaci, previously known as an important vector for TSWV, only one out of four populations tested was able to transmit TSWV at, moreover, a low efficiency.Finally, the transmission of mutant tospoviruses, which were generated after successive mechanical transfers of virus, was studied. Defective interfering mutants were found to be transmittable by thrips, albeit at a frequency 10 to 20 times lower than the wild type virus. In contrast, envelope deficient mutants were not transmitted by thrips, indicating the importance of the envelope glycoproteins in virus-vector relationships

Anomalous direction for skyrmion bubble motion

Magnetic skyrmions are localized topological excitations that behave as particles and can be mobile, with great potential for novel data storage devices. In this work, the current-induced dynamics of large skyrmion bubbles is studied. When skyrmion motion in the direction opposite to the electron flow is observed, this is usually interpreted as a perpendicular spin current generated by the spin Hall effect exerting a torque on the chiral N\'{e}el skyrmion. By designing samples in which the direction of the net generated spin current can be carefully controlled, we surprisingly show that skyrmion motion is always against the electron flow, irrespective of the net vertical spin-current direction. We find that a negative bulk spin-transfer torque is the most plausible explanation for the observed results, which is qualitatively justified by a simple model that captures the essential behaviour. These findings demonstrate that claims about the skyrmion chirality based on their current-induced motion should be taken with great caution

What characterizes an excellent social worker? Perceptions of teachers in contrast to the working field

The Hanze University Groningen offers more than 60 different honours programmes for students who want to do more than the regular programme offers them. In these programmes, students are guided to become an excellent professional. Competencies defining an excellent professional were assessed in a previous research by means of focus group discussions and Delphi survey with professionals and experts in the social worker field, resulting in a profile of the excellent social worker consisting of 6 domains. Our aim is to investigate the opinions of the teachers at the faculty Social Work regarding the profile of the excellent Social Worker. In addition, we aim to explore how teachers recognize, acknowledge and encourage excellence among their students. The Delphi method was used to investigate the opinions of the teachers. All teachers of Social Work Department were invited to fill in a survey giving their opinion on the excellent social worker profile as stated by the professionals. The teachers were asked to choose whether each domain was “essential”, “important but not essential” or “not needed” for an excellent Social Worker. Currently, 35 teachers answered the survey. Teachers agree that the competencies of the profile are essential for an excellent professional, with exception of ‘coaching and supporting your colleagues’. Over 50% of the respondents think that this is important but not essential. More than 90% of the teachers agree that “thinking out of the box” and “having the courage to think of different and innovative solutions” are essential competencies for excellence. In addition, teachers indicated that ethics, internationalization and entrepreneurship are missing in the profile. To conclude, the profile is acknowledged by teachers with broad support. In the next stage of the research, teachers will be asked about how they stimulate these competences by students. The research will be completed in June

Characterisation of detachment in the MAST-U Super-X divertor using multi-wavelength imaging of 2D atomic and molecular emission processes

In this work, we provide the first 2D spatially resolved description of radiative detachment in MAST-U Super-X L-mode divertor plasmas. The Super-X magnetic configuration was designed to achieve reduced heat- and particle loads at the divertor target compared to conventional exhaust solutions. We use filtered camera imaging to reconstruct 2D emissivity profiles in the poloidal plane for multiple atomic and molecular emission lines and bands. A set of deuterium fuelling scans is discussed that, together, span attached to deeply detached divertor states observed in MAST-U. Emissivity profiles facilitate separate analysis of locked-mode induced split branches of the scrape-off layer. Molecular deuterium Fulcher band emission front tracking reveals that the deuterium electron-impact ionisation front, for which it serves a proxy, detaches at different upstream electron densities in the split branches. Upon detachment of this ionisation front, Balmer emission attributed to molecular activated recombination appears near-target. We report a simultaneous radial broadening of the emission leg, consistent with previous SOLPS-ITER modelling. With increased fuelling this emission region detaches, implying electron temperatures below ∼ 1 eV. In this phase, 2D Balmer line ratio reconstruction indicates an onset of volumetric direct electron-ion recombination near-target. At the highest fuelling rates this emission region moves off-target, suggesting a drop in near-wall electron density accompanying the low temperatures.</p

Non-structural proteins of arthropod-borne bunyaviruses: roles and functions

Viruses within the Bunyaviridae family are tri-segmented, negative-stranded RNA viruses. The family includes several emerging and re-emerging viruses of humans, animals and plants, such as Rift Valley fever virus, Crimean-Congo hemorrhagic fever virus, La Crosse virus, Schmallenberg virus and tomato spotted wilt virus. Many bunyaviruses are arthropod-borne, so-called arboviruses. Depending on the genus, bunyaviruses encode, in addition to the RNA-dependent RNA polymerase and the different structural proteins, one or several non-structural proteins. These non-structural proteins are not always essential for virus growth and replication but can play an important role in viral pathogenesis through their interaction with the host innate immune system. In this review, we will summarize current knowledge and understanding of insect-borne bunyavirus non-structural protein function(s) in vertebrate, plant and arthropod