Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Using photorespiratory oxygen response to analyse leaf mesophyll resistance
    Yin, Xinyou ; Putten, Peter E.L. van der; Belay, Daniel ; Struik, Paul C. - \ 2020
    Photosynthesis Research 144 (2020). - ISSN 0166-8595 - p. 85 - 99.
    CO compensation point - CO transfer - Internal conductance - O response - Re-assimilation - Resistance

    Classical approaches to estimate mesophyll conductance ignore differences in resistance components for CO2 from intercellular air spaces (IAS) and CO2 from photorespiration (F) and respiration (Rd). Consequently, mesophyll conductance apparently becomes sensitive to (photo)respiration relative to net photosynthesis, (F + Rd)/A. This sensitivity depends on several hard-to-measure anatomical properties of mesophyll cells. We developed a method to estimate the parameter m (0 ≤ m ≤ 1) that lumps these anatomical properties, using gas exchange and chlorophyll fluorescence measurements where (F + Rd)/A ratios vary. This method was applied to tomato and rice leaves measured at five O2 levels. The estimated m was 0.3 for tomato but 0.0 for rice, suggesting that classical approaches implying m = 0 work well for rice. The mesophyll conductance taking the m factor into account still responded to irradiance, CO2, and O2 levels, similar to response patterns of stomatal conductance to these variables. Largely due to different m values, the fraction of (photo)respired CO2 being refixed within mesophyll cells was lower in tomato than in rice. But that was compensated for by the higher fraction via IAS, making the total re-fixation similar for both species. These results, agreeing with CO2 compensation point estimates, support our method of effectively analysing mesophyll resistance.

    Effects of extreme rainfall events are independent of plant species richness in an experimental grassland community
    Padilla, Francisco M. ; Mommer, Liesje ; Caluwe, Hannie de; Smit-Tiekstra, Annemiek E. ; Visser, Eric J.W. ; Kroon, Hans de - \ 2019
    Oecologia 191 (2019)1. - ISSN 0029-8549 - p. 177 - 190.
    Biodiversity - Climate change - Drought - Overyielding - Resistance - Roots - Stability

    Global climate models predict more frequent periods of drought stress alternated by heavier, but fewer rainfall events in the future. Biodiversity studies have shown that such changed drought stress may be mitigated by plant species richness. Here, we investigate if grassland communities, differing in species richness, respond differently to climatic extremes within the growing season. In a 3-year outdoor mesocosm experiment, four grassland species in both monoculture and mixture were subjected to a rainfall distribution regime with two levels: periods of severe drought in the summer intermitted by extreme rainfall events versus regular rainfall over time. Both treatments received the same amount of water over the season. Extreme rainfall combined with drought periods resulted in a 15% decrease in aboveground biomass in the second and third year, compared to the regular rainfall regime. Root biomass was also reduced in the extreme rainfall treatment, particularly in the top soil layer (− 40%). All species developed higher water use efficiencies (less negative leaf δ13C) in extreme rainfall than in regular rainfall. These responses to the rainfall/drought treatment were independent of species richness, although the mixtures were on an average more productive in terms of biomass than the monocultures. Our experimental results suggest that mixtures are similarly able to buffer these within-season rainfall extremes than monocultures, which contrasts with findings in the studies on natural droughts. Our work demonstrates the importance of investigating the interactions between rainfall distribution and drought periods for understanding effects of climate change on plant community performance.

    Editorial: Plant responses to phytophagous mites/thrips and search for resistance
    Sperotto, Raul A. ; Grbic, Vojislava ; Pappas, Maria L. ; Leiss, Kirsten A. ; Kant, Merijn R. ; Wilson, Calum R. ; Santamaria, Estrella M. ; Gao, Yulin - \ 2019
    Frontiers in Plant Science 10 (2019). - ISSN 1664-462X
    Defense - Mites - Plant responses - Resistance - Thrips - Tolerance
    Darwinian black box selection for resistance to settled invasive Varroa destructor parasites in honey bees
    Blacquière, Tjeerd ; Boot, Willem ; Calis, Johan ; Moro, Arrigo ; Neumann, Peter ; Panziera, Delphine - \ 2019
    Biological Invasions 21 (2019)8. - ISSN 1387-3547 - p. 2519 - 2528.
    Apis mellifera - Honey bee - Host parasite relationship - Natural selection - Resistance - Sustainable apiculture - Tolerance - Varroa destructor

    Established invasive species can pose a continuous threat to biodiversity and food security, thereby calling for sustainable mitigation. There is a consensus that the ubiquitous ecto-parasitic mite Varroa destructor, an invasive species from Asia, is the main biological threat to global apiculture with Apis mellifera. V. destructor has almost completely wiped out wild European honey bee (Apis mellifera) populations. The only remedy for apiculture, to date, is frequent control measures against the mite throughout the season, which prevents possible adaptations. While targeted breeding efforts have, so far, not achieved the selection of tolerant or resistant bees, natural selection approaches have succeeded at least seven times. Here, we propose to take advantage of natural selection for honey bee resistance by stopping mite treatment in managed colonies. The main principles are within population mating of the colonies’ own virgin queens and drones and selection based on survival and proliferous development of colonies. Being used for 10 years, it has shown to result in grosso modo ‘normal’ colonies with a high level of resistance to V. destructor. Here, we call for local groups of beekeepers and scientists to join a novel natural selection program that has started so far on three locations. This will eventually lead to several locally adapted V. destructor resistant honey bee populations around the world, and help global apiculture becoming more sustainable.

    Genetic variation in Sorghum bicolor strigolactones and their role in resistance against Striga hermonthica
    Mohemed, Nasreldin ; Charnikhova, Tatsiana ; Fradin, Emilie F. ; Rienstra, Juriaan ; Babiker, Abdelgabar G.T. ; Bouwmeester, Harro J. - \ 2018
    Journal of Experimental Botany 69 (2018)9. - ISSN 0022-0957 - p. 2415 - 2430.
    Germination stimulant - Parasitic weed - Resistance - Sorghum - Striga - Strigolactones

    Sorghum is an important food, feed, and industrial crop worldwide. Parasitic weeds of the genus Striga constitute a major constraint to sorghum production, particularly in the drier parts of the world. In this study we analysed the Striga germination stimulants, strigolactones, in the root exudates of 36 sorghum genotypes and assessed Striga germination and infection. Low germination-stimulating activity and low Striga infection correlated with the exudation of low amounts of 5-deoxystrigol and high amounts of orobanchol, whereas susceptibility to Striga and high germination- stimulating activity correlated with high concentrations of 5-deoxystrigol and low concentrations of orobanchol. Marker analysis suggested that similar genetics to those previously described for the resistant sorghum variety SRN39 and the susceptible variety Shanqui Red underlie these differences. This study shows that the strigolactone profile in the root exudate of sorghum has a large impact on the level of Striga infection. High concentrations of 5-deoxystrigol result in high infection, while high concentrations of orobanchol result in low infection. This knowledge should help to optimize the use of low germination stimulant-based resistance to Striga by the selection of sorghum genotypes with strigolactone profiles that favour normal growth and development, but reduce the risk of Striga infection.

    Resistance to tomato yellow leaf curl virus in tomato germplasm
    Yan, Zhe ; Pérez-de-Castro, Ana ; Díez, Maria J. ; Hutton, Samuel F. ; Visser, Richard G.F. ; Wolters, Anne-Marie A. ; Bai, Yuling ; Li, Junming - \ 2018
    Frontiers in Plant Science 9 (2018). - ISSN 1664-462X
    Begomovirus - Resistance - S. chilense - S. peruvianum - Solanum lycopersicum - Tomato - TYLCV

    Tomato yellow leaf curl virus (TYLCV) is a virus species causing epidemics in tomato (Solanum lycopersicum) worldwide. Many efforts have been focused on identification of resistance sources by screening wild tomato species. In many cases, the accession numbers were either not provided in publications or not provided in a consistent manner, which led to redundant screenings. In the current study, we summarized efforts on the screenings of wild tomato species for TYLCV resistance from various publications. In addition, we screened 708 accessions from 13 wild tomato species using different inoculation assays (i.e., whitefly natural infection and Agrobacterium-mediated inoculation) from which 138 accessions exhibited no tomato yellow leaf curl disease (TYLCD) symptoms. These symptomless accessions include 14 accessions from S. arcanum, 43 from S. chilense, 1 from S. chmielewskii, 28 from S. corneliomulleri, 5 from S. habrochaites, 4 from S. huaylasense, 2 from S. neorickii, 1 from S. pennellii, 39 from S. peruvianum, and 1 from S. pimpinellifolium. Most of the screened S. chilense accessions remained symptomless. Many symptomless accessions were also identified in S. arcanum, S. corneliomulleri, and S. peruvianum. A large number of S. pimpinellifolium accessions were screened. However, almost all of the tested accessions showed TYLCD symptoms. Further, we studied allelic variation of the Ty-1/Ty-3 gene in few S. chilense accessions by applying virus-induced gene silencing and allele mining, leading to identification of a number of allele-specific polymorphisms. Taken together, we present a comprehensive overview on TYLCV resistance and susceptibility in wild tomato germplasm, and demonstrate how to study allelic variants of the cloned Ty-genes in TYLCV-resistant accessions.

    Spaces for participation and resistance : gendered experiences of oil palm plantation development
    Vos, Rosanne de; Delabre, Izabela - \ 2018
    Geoforum 96 (2018). - ISSN 0016-7185 - p. 217 - 226.
    Gender - Micro-politics - Palm oil - Positionality - Resistance - Spaces for participation

    In this paper, we explore the gendered experiences of, and responses to, socio-economic and environmental change evoked by processes of land acquisition for oil palm plantation development. Drawing upon ethnographic fieldwork in West Kalimantan, Indonesia, we examine the heterogeneous and differentiated nature of women's lived experiences in resisting, accepting and enacting agrarian change. We find that impacts stretch beyond livelihood opportunities, access to land and resources, and labour conditions: plantation development also affects and changes social relations, leading to insecurity and anxiety and new forms of solidarity. Using an analytical framework of ‘spaces for participation’ we highlight how women are excluded from participation during negotiations and contestations around land acquisition for the development of oil palm plantations. Yet, women also challenge their exclusion by claiming space for participation in different ways, including by engaging in alternative, more subtle forms of resistance that frequently go unnoticed by policies and practices that aim to empower women.

    The Sw-5 gene cluster : Tomato breeding and research toward orthotospovirus disease control
    Oliveira, Athos S. de; Boiteux, Leonardo S. ; Kormelink, Richard ; Resende, Renato O. - \ 2018
    Frontiers in Plant Science 9 (2018). - ISSN 1664-462X
    NB-LRR - NLR - Orthotospovirus - Resistance - Sw-5 - Sw-5b - Tomato

    The Sw-5 gene cluster encodes protein receptors that are potentially able to recognize microbial products and activate signaling pathways that lead to plant cell immunity. Although there are several Sw-5 homologs in the tomato genome, only one of them, named Sw-5b, has been extensively studied due to its functionality against a wide range of (thrips-transmitted) orthotospoviruses. The Sw-5b gene is a dominant resistance gene originally from a wild Peruvian tomato that has been used in tomato breeding programs aiming to develop cultivars with resistance to these viruses. Here, we provide an overview starting from the first reports of Sw-5 resistance, positional cloning and the sequencing of the Sw-5 gene cluster from resistant tomatoes and the validation of Sw-5b as the functional protein that triggers resistance against orthotospoviruses. Moreover, molecular details of this plant–virus interaction are also described, especially concerning the roles of Sw-5b domains in the sensing of orthotospoviruses and in the signaling cascade leading to resistance and hypersensitive response.

    Two different R gene loci co-evolved with Avr2 of Phytophthora infestans and confer distinct resistance specificities in potato
    Aguilera-Galvez, C. ; Champouret, N. ; Rietman, H. ; Lin, X. ; Wouters, D. ; Chu, Z. ; Jones, J.D.G. ; Vossen, J.H. ; Visser, R.G.F. ; Wolters, P.J. ; Vleeshouwers, V.G.A.A. - \ 2018
    Studies in Mycology 89 (2018). - ISSN 0166-0616 - p. 105 - 115.
    Avr gene - Co-evolution - Late blight - Phytophthora infestans - Potato - R gene - Resistance - Solanum
    Late blight, caused by the oomycete pathogen Phytophthora infestans, is the most devastating disease in potato. For sustainable management of this economically important disease, resistance breeding relies on the availability of resistance (R) genes. Such R genes against P. infestans have evolved in wild tuber-bearing Solanum species from North, Central and South America, upon co-evolution with cognate avirulence (Avr) genes. Here, we report how effectoromics screens with Avr2 of P. infestans revealed defense responses in diverse Solanum species that are native to Mexico and Peru. We found that the response to AVR2 in the Mexican Solanum species is mediated by R genes of the R2 family that resides on a major late blight locus on chromosome IV. In contrast, the response to AVR2 in Peruvian Solanum species is mediated by Rpi-mcq1, which resides on chromosome IX and does not belong to the R2 family. The data indicate that AVR2 recognition has evolved independently on two genetic loci in Mexican and Peruvian Solanum species, respectively. Detached leaf tests on potato cultivar ‘Désirée’ transformed with R genes from either the R2 or the Rpi-mcq1 locus revealed an overlapping, but distinct resistance profile to a panel of 18 diverse P. infestans isolates. The achieved insights in the molecular R – Avr gene interaction can lead to more educated exploitation of R genes and maximize the potential of generating more broad-spectrum, and potentially more durable control of the late blight disease in potato.
    Seagrass ecosystem trajectory depends on the relative timescales of resistance, recovery and disturbance
    O'Brien, Katherine R. ; Waycott, Michelle ; Maxwell, Paul ; Kendrick, Gary A. ; Udy, James W. ; Ferguson, Angus J.P. ; Kilminster, Kieryn ; Scanes, Peter ; McKenzie, Len J. ; McMahon, Kathryn ; Adams, Matthew P. ; Samper-Villarreal, Jimena ; Collier, Catherine ; Lyons, Mitchell ; Mumby, Peter J. ; Radke, Lynda ; Christianen, Marjolijn J.A. ; Dennison, William C. - \ 2018
    Marine Pollution Bulletin 134 (2018). - ISSN 0025-326X - p. 166 - 176.
    Colonizing - Opportunistic - Persistent - Recovery - Resilience - Resistance - Seagrass - Trajectory
    Seagrass ecosystems are inherently dynamic, responding to environmental change across a range of scales. Habitat requirements of seagrass are well defined, but less is known about their ability to resist disturbance. Specific means of recovery after loss are particularly difficult to quantify. Here we assess the resistance and recovery capacity of 12 seagrass genera. We document four classic trajectories of degradation and recovery for seagrass ecosystems, illustrated with examples from around the world. Recovery can be rapid once conditions improve, but seagrass absence at landscape scales may persist for many decades, perpetuated by feedbacks and/or lack of seed or plant propagules to initiate recovery. It can be difficult to distinguish between slow recovery, recalcitrant degradation, and the need for a window of opportunity to trigger recovery. We propose a framework synthesizing how the spatial and temporal scales of both disturbance and seagrass response affect ecosystem trajectory and hence resilience.
    The NSm proteins of phylogenetically related tospoviruses trigger Sw-5b–mediated resistance dissociated of their cell-to-cell movement function
    Leastro, Mikhail Oliveira ; Oliveira, Athos Silva De; Pallás, Vicente ; Sánchez-Navarro, Jesús A. ; Kormelink, Richard ; Resende, Renato Oliveira - \ 2017
    Virus Research 240 (2017). - ISSN 0168-1702 - p. 25 - 34.
    Avr - Hypersensitive response - NS protein - Resistance - Sw-5b gene - Tospovirus

    The cell-to-cell movement protein (NSM) in members of the tospovirus species Tomato spotted wilt virus (TSWV) has been recently identified as the effector of the single dominant Sw-5b resistance gene from tomato (Solanum lycopersicum L.). Although most TSWV isolates shows a resistance-inducing (RI) phenotype, regular reports have appeared on the emergence of resistance-breaking (RB) isolates in tomato fields, and suggested a strong association with two point mutations (C118Y and T120N) in the NSM protein. In this study the Sw-5b gene has been demonstrated to confer not only resistance against TSWV but to members of five additional, phylogenetically-related tospovirus species classified within the so-called “American” evolutionary clade, i.e. Alstroemeria necrotic streak virus (ANSV), Chrysanthemum stem necrosis virus (CSNV), Groundnut ringspot virus (GRSV), Impatiens necrotic spot virus (INSV) and Tomato chlorotic spot virus (TCSV). Remarkably, a member of the species Bean necrotic mosaic virus (BeNMV), a recently discovered tospovirus classified in a distinct American subclade and circulating on the American continent, did not trigger a Sw-5b-mediated hypersensitive (HR) response. Introduction of point mutations C118Y and T120N into the NSM protein of TSWV, TCSV and CSNV abrogated the ability to trigger Sw-5b-mediated HR in both transgenic-N. benthamiana and tomato isolines harboring the Sw-5b gene whereas it had no effect on BeNMV NSM. Truncated versions of TSWV NSM lacking motifs associated with tubule formation, cell-to-cell or systemic viral movement were made and tested for triggering of resistance. HR was still observed with truncated NSM proteins lacking 50 amino acids (out of 301) from either the amino- or carboxy-terminal end. These data altogether indicate the importance of amino acid residues C118 and T120 in Sw-5b-mediated HR only for the NSM proteins from one cluster of tospoviruses within the American clade, and that the ability to support viral cell-to-cell movement is not required for effector functionality.

    High-resolution mapping of genes involved in plant stage-specific partial resistance of barley to leaf rust
    Yeo, F.K.S. ; Bouchon, R. ; Kuijken, R. ; Loriaux, A. ; Boyd, C. ; Niks, R.E. ; Marcel, T.C. - \ 2017
    Molecular Breeding 37 (2017)4. - ISSN 1380-3743
    Barley - High resolution mapping - Puccinia - Quantitative trait locus (QTL) - Resistance

    Partial resistance quantitative trait loci (QTLs) Rphq11 and rphq16 against Puccinia hordei isolate 1.2.1 were previously mapped in seedlings of the mapping populations Steptoe/Morex and Oregon Wolfe Barleys, respectively. In this study, QTL mapping was performed at adult plant stage for the two mapping populations challenged with the same rust isolate. The results suggest that Rphq11 and rphq16 are effective only at seedling stage, and not at adult plant stage. The cloning of several genes responsible for partial resistance of barley to P. hordei will allow elucidation of the molecular basis of this type of plant defence. A map-based cloning approach requires to fine-map the QTL in a narrow genetic window. In this study, Rphq11 and rphq16 were fine-mapped using an approach aiming at speeding up the development of plant material and simplifying its evaluation. The plant materials for fine-mapping were identified from early plant materials developed to produce QTL-NILs. The material was first selected to carry the targeted QTL in heterozygous condition and susceptibility alleles at other resistance QTLs in homozygous condition. This strategy took four to five generations to obtain fixed QTL recombinants (i.e., homozygous resistant at the Rphq11 or rphq16 QTL alleles, homozygous susceptible at the non-targeted QTL alleles). In less than 2 years, Rphq11 was fine-mapped into a 0.2-cM genetic interval and a 1.4-cM genetic interval for rphq16. The strongest candidate gene for Rphq11 is a phospholipid hydroperoxide glutathione peroxidase. Thus far, no candidate gene was identified for rphq16.

    Functional characterization of the powdery mildew susceptibility gene SmMLO1 in eggplant (Solanum melongena L.)
    Bracuto, Valentina ; Appiano, Michela ; Ricciardi, Luigi ; Göl, Deniz ; Visser, Richard G.F. ; Bai, Yuling ; Pavan, Stefano - \ 2017
    Transgenic Research 26 (2017)3. - ISSN 0962-8819 - p. 323 - 330.
    Eggplant - MLO - Plant breeding - Powdery mildew - Resistance
    Eggplant (Solanum melongena L.) is one of the most important vegetables among the Solanaceae and can be a host to fungal species causing powdery mildew (PM) disease. Specific homologs of the plant Mildew Locus O (MLO) gene family are PM susceptibility factors, as their loss of function results in a recessive form of resistance known as mlo resistance. In a previous work, we isolated the eggplant MLO homolog SmMLO1. SmMLO1 is closely related to MLO susceptibility genes characterized in other plant species. However, it displays a peculiar non-synonymous substitution that leads to a T → M amino acid change at protein position 422, in correspondence of the MLO calmodulin-binding domain. In this study, we performed the functional characterization of SmMLO1. Transgenic overexpression of SmMLO1 in a tomato mlo mutant compromised resistance to the tomato PM pathogen Oidium neolycopersici, thus indicating that SmMLO1 is a PM susceptibility factor in eggplant. PM susceptibility was also restored by the transgenic expression of a synthetic gene, named s-SmMLO1, encoding a protein identical to SmMLO1, except for the presence of T at position 422. This indicates that the T → M polymorphism does not affect the protein role as PM susceptibility factor. Overall, the results of this work are of interest for the functional characterization of MLO proteins and the introduction of PM resistance in eggplant using reverse genetics.
    Next-Generation Sequencing in the Mycology Lab
    Zoll, Jan ; Snelders, Eveline ; Verweij, Paul E. ; Melchers, Willem J.G. - \ 2016
    Current Fungal Infection Reports 10 (2016)2. - ISSN 1936-3761 - p. 37 - 42.
    Clinical mycology lab issues - Mycobiome - Next-generation sequencing - Resistance - Review - Whole genome sequencing

    New state-of-the-art techniques in sequencing offer valuable tools in both detection of mycobiota and in understanding of the molecular mechanisms of resistance against antifungal compounds and virulence. Introduction of new sequencing platform with enhanced capacity and a reduction in costs for sequence analysis provides a potential powerful tool in mycological diagnosis and research. In this review, we summarize the applications of next-generation sequencing techniques in mycology.

    Evaluation of field resistance to Striga hermonthica (Del.) Benth. in Sorghum bicolor (L.) Moench. The relationship with strigolactones
    Mohemed Ahmed Mohamed, Nasr Eldin ; Charnikhova, Tatsiana ; Bakker, Evert J. ; Ast, Aad van; Babiker, Abdelgabar Gt ; Bouwmeester, Harro J. - \ 2016
    Pest Management Science 72 (2016)11. - ISSN 1526-498X - p. 2082 - 2090.
    Resistance - Sorghum - Striga - Strigolactones

    BACKGROUND: Significant losses in sorghum biomass and grain yield occur in sub-Saharan Africa owing to infection by the root-parasitic weed Striga hermonthica (Del.) Benth. One strategy to avoid these losses is to adopt resistant crop varieties. For further delineation of the role of germination stimulants in resistance, we conducted a field experiment employing six sorghum genotypes, in eastern Sudan, and in parallel analysed the strigolactone levels in the root exudates of these genotypes under controlled conditions in Wageningen. RESULTS: The root exudates of these genotypes displayed large differences in strigolactone composition and Striga-germination-inducing activity. Korokollow, Fakimustahi and Wadfahel exuded the highest amounts of 5-deoxystrigol. Fakimustahi was by far the highest sorgomol producer, and Wadbaco and SRN39 produced the highest amount of orobanchol. The concentration of 5-deoxystrigol in the root exudate showed a significant positive correlation with in vitro Striga germination and was positively associated with Striga infection in the field experiments, whereas orobanchol was negatively associated with Striga infection in the field experiments. CONCLUSION: For the first time a close association is reported between strigolactone levels analysed under laboratory conditions and Striga infection in the field in sorghum genotypes. These genotypes may be used for further study of this resistance mechanism and for the introgression of the low germination trait in other sorghum varieties to breed for a strigolactone composition with low stimulant activity. The use of such improved varieties in combination with other Striga management tools could possibly alleviate the current Striga problem on the African continent.

    Silencing of six susceptibility genes results in potato late blight resistance
    Sun, Kaile ; Wolters, Anne-Marie A. ; Vossen, Jack H. ; Rouwet, Maarten E. ; Loonen, Annelies E.H.M. ; Jacobsen, Evert ; Visser, Richard G.F. ; Bai, Yuling - \ 2016
    Transgenic Research 25 (2016)5. - ISSN 0962-8819 - p. 731 - 742.
    Late blight - Potato - Resistance - RNAi - Susceptibility gene

    Phytophthora infestans, the causal agent of late blight, is a major threat to commercial potato production worldwide. Significant costs are required for crop protection to secure yield. Many dominant genes for resistance (R-genes) to potato late blight have been identified, and some of these R-genes have been applied in potato breeding. However, the P. infestans population rapidly accumulates new virulent strains that render R-genes ineffective. Here we introduce a new class of resistance which is based on the loss-of-function of a susceptibility gene (S-gene) encoding a product exploited by pathogens during infection and colonization. Impaired S-genes primarily result in recessive resistance traits in contrast to recognition-based resistance that is governed by dominant R-genes. In Arabidopsis thaliana, many S-genes have been detected in screens of mutant populations. In the present study, we selected 11 A. thalianaS-genes and silenced orthologous genes in the potato cultivar Desiree, which is highly susceptible to late blight. The silencing of five genes resulted in complete resistance to the P. infestans isolate Pic99189, and the silencing of a sixth S-gene resulted in reduced susceptibility. The application of S-genes to potato breeding for resistance to late blight is further discussed.

    Hydraulic fracturing, energy transition and political engagement in the Netherlands : The energetics of citizenship
    Rasch, Elisabet Dueholm ; Köhne, Michiel - \ 2016
    Energy Research & Social Science 13 (2016). - ISSN 2214-6296 - p. 106 - 115.
    Citizenship - Energy transition - Hydraulic fracturing - Resistance

    This paper analyses how citizens (re)define their relation to the state in the contestation of hydraulic fracturing in the Noordoostpolder (the Netherlands) in the context of energy transition. It approaches citizenship as the negotiations between governments and citizens about in-and exclusion in decision-making processes and argues that these are also produced at the site of energy transition. It focuses on how residents of the Noordoostpolder construct their citizenship, resisting the advent of fracking in their environment while at the same time negotiating their own inclusion in decision-making processes. Our ethnographic material encompasses almost a year of these negotiations starting shortly after the announcement of the Noordoostpolder as a site for exploratory drilling, when people feel highly disempowered and excluded. We closely follow a process of gradual empowerment in the face of energy transition as inhabitants start to produce their own knowledge base and coalesce into unusual partnerships to negotiate their inclusion. Our main argument is that negotiations about hydraulic fracturing in relation to energy transition goes beyond energy issues. It is also -if not mostly -about who gets to decide on energy and land use.

    Brassicacea-based management strategies as an alternative to combat nematode pests : A synopsis
    Fourie, Hendrika ; Ahuja, Preeti ; Lammers, Judith ; Daneel, Mieke - \ 2016
    Crop Protection 80 (2016). - ISSN 0261-2194 - p. 21 - 41.
    Biofumigation - Brassicaceae - Cover/green manure crop - PPN - Resistance - Soil amendments

    Nematode pests parasitise and cause substantial crop yield and quality losses to a wide range of crops worldwide. To minimize such damage, the exploitation and development of alternative nematode control strategies are becoming increasingly important, particularly as a result of global efforts to conserve the ozone layer as well as our soil and water substrates. Inclusion of Brassicaceae crops in cropping systems is one such alternative and has been demonstrated in most cases to be effective in managing the top-three rated economically important nematode pests, viz. root-knot (Meloidogyne), cyst (Heterodera and Globodera) and lesion (Pratylenchus) nematodes as well as others. In the past nematode pests were and still are generally managed successfully by the use of synthetically-derived nematicides, which are progressively being removed from world markets. However, fragmented and limited information about the use of Brassicaceae crops as a nematode management tool exists in various countries. The need thus arose to summarize, compare and discuss the vast amount of information that has been generated on this topic in a concise article. This paper therefore represents a comprehensive, practical and critical review of the use and effect(s) of Brassicaceae-based management strategies and the biofumigation and cover-crop/rotation characteristics of Brassicaceae in reducing nematode-pest population levels in global cropping systems.

    Species-rich semi-natural grasslands have a higher resistance but a lower resilience than intensively managed agricultural grasslands in response to climate anomalies
    Keersmaecker, Wanda De; Rooijen, Nils van; Lhermitte, Stef ; Tits, Laurent ; Schaminée, Joop ; Coppin, Pol ; Honnay, Olivier ; Somers, Ben - \ 2016
    Journal of Applied Ecology 53 (2016)2. - ISSN 0021-8901 - p. 430 - 439.
    Biomass stability - Grasslands - Normalized Difference Vegetation Index - Plant diversity - Remote sensing - Resilience - Resistance - The Netherlands

    The stable delivery of ecosystem services provided by grasslands is strongly dependent on the stability of grassland ecosystem functions such as biomass production. Biomass production is in turn strongly affected by the frequency and intensity of climate extremes. The aim of this study is to evaluate to what extent species-poor intensively managed agricultural grasslands can maintain their biomass productivity under climate anomalies, as compared to species-rich, semi-natural grasslands. Our hypothesis is that species richness stabilizes biomass production over time. Biomass production stability was assessed in response to drought and temperature anomalies using 14 years of the Normalized Difference Vegetation Index (NDVI), temperature and drought index time series. More specifically, vegetation resistance (i.e. the ability to withstand the climate anomaly) and resilience (i.e. the recovery rate) were derived using an auto-regressive model with external input variables (ARx). The stability metrics for both grasslands were subsequently compared. We found that semi-natural grasslands exhibited a higher resistance but lower resilience than agricultural grasslands in the Netherlands. Furthermore, the difference in stability between semi-natural and agricultural grasslands was dependent on the physical geography: the most significant differences in resistance were observed in coastal dunes and riverine areas, whereas the differences in resilience were the most significant in coastal dunes and fens. Synthesis and applications. We conclude that semi-natural grasslands show a higher resistance to drought and temperature anomalies compared to agricultural grasslands. These results underline the need to reassess the ways agricultural practices are performed. More specifically, increasing the plant species richness of agricultural grasslands and lowering their mowing and grazing frequency may contribute to buffer their biomass production stability against climate extremes.

    Peasantry in the Twenty-First Century
    Ploeg, Jan Douwe van der - \ 2015
    In: International Encyclopedia of the Social & Behavioral Sciences / Wright, J.D., Elsevier Inc. Academic Press - ISBN 9780080970868 - p. 664 - 668.
    Agroecology - Food sovereignty - Labor migration - Low external input agriculture - Multifunctionality - Multiple job holding - Peasant agriculture - Pluriactivity - Repeasantization - Resistance - Rural livelihoods - Transnational agrarian movements

    The deregulation of markets and the increasingly interlinked global markets make it very difficult for small farmers to survive. Thus, small primary agricultural producers must search for new ways to continue farming and earn a reasonable income. In many places, this has triggered a process of repeasantization that is reversing the once seemingly inevitable processes of modernization and urbanization. This article argues that this process occurs through six mechanisms that together have a strong impact on the nature and dynamics of the process of agricultural development.

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