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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    Can traits predict individual growth performance? A test in a hyperdiverse tropical forest
    Poorter, Lourens ; Castilho, Carolina V. ; Schietti, Juliana ; Oliveira, Rafael S. ; Costa, Flávia R.C. - \ 2018
    New Phytologist 219 (2018)1. - ISSN 0028-646X - p. 109 - 121.
    acclimation - Amazon - defense - functional traits - growth - plant strategies - plasticity - tropical rainforest
    The functional trait approach has, as a central tenet, that plant traits are functional and shape individual performance, but this has rarely been tested in the field. Here, we tested the individual-based trait approach in a hyperdiverse Amazonian tropical rainforest and evaluated intraspecific variation in trait values, plant strategies at the individual level, and whether traits are functional and predict individual performance. We evaluated > 1300 tree saplings belonging to > 383 species, measured 25 traits related to growth and defense, and evaluated the effects of environmental conditions, plant size, and traits on stem growth. A total of 44% of the trait variation was observed within species, indicating a strong potential for acclimation. Individuals showed two strategy spectra, related to tissue toughness and organ size vs leaf display. In this nutrient- and light-limited forest, traits measured at the individual level were surprisingly poor predictors of individual growth performance because of convergence of traits and growth rates. Functional trait approaches based on individuals or species are conceptually fundamentally different: the species-based approach focuses on the potential and the individual-based approach on the realized traits and growth rates. Counterintuitively, the individual approach leads to a poor prediction of individual performance, although it provides a more realistic view on community dynamics.
    Naturally selected honey bee (Apis mellifera) colonies resistant to Varroa destructor do not groom more intensively
    Kruitwagen, Astrid ; Langevelde, Frank van; Dooremalen, Coby van; Blacquière, Tjeerd - \ 2017
    Journal of Apicultural Research 56 (2017)4. - ISSN 0021-8839 - p. 354 - 365.
    cage - colony collapse - defense - density-dependent behavior - dust removal - natural selection - resistance behavior
    The ectoparasitic mite Varroa destructor is an important cause of high colony losses of the honey bee Apis mellifera. In The Netherlands, two resistant A. mellifera populations developed naturally after ceasing varroa control. As a result, mite infestation levels of the colonies of these populations are generally between 5–10%. However, the mechanisms behind mite resistance are still unclear. Since grooming behavior is a typical resistance trait that occurs in A. mellifera, we compared grooming between colonies of these two resistant populations and control colonies that had been treated against varroa twice a year in previous years. Grooming was investigated by measuring mite fall in broodless colonies in the field and in small cages with a fixed number of mites and bees in the lab. Furthermore, grooming was investigated at the individual level by measuring the effectiveness to remove dust by individual bees from the resistant and control colonies. We found that the grooming behavior of resistant colonies was unexpectedly equally or even less effective than that of control colonies. These results were supported by the effectiveness of individual bees to remove dust. Based on our results, we discuss that the trigger for grooming behavior may be density-dependent: grooming may be only beneficial at high mite infestation levels. Other resistance mechanisms than grooming are more likely to explain the varroa resistance of our two populations.
    Trading direct for indirect defense? Phytochrome B inactivation in tomato attenuates direct anti-herbivore defenses whilst enhancing volatile-mediated attraction of predators
    Cortés, Leandro E. ; Weldegergis, Berhane T. ; Boccalandro, Hernán E. ; Dicke, Marcel ; Ballaré, Carlos L. - \ 2016
    New Phytologist 212 (2016)4. - ISSN 0028-646X - p. 1057 - 1071.
    defense - indirect defense - jasmonate - phytochrome - R : FR ratio - tomato (Solanum lycopersicum) - tritrophic interaction - volatile

    Under conditions of competition for light, which lead to the inactivation of the photoreceptor phytochrome B (phyB), the growth of shade-intolerant plants is promoted and the accumulation of direct anti-herbivore defenses is down-regulated. Little is known about the effects of phyB on emissions of volatile organic compounds (VOCs), which play a major role as informational cues in indirect defense. We investigated the effects of phyB on direct and indirect defenses in tomato (Solanum lycopersicum) using two complementary approaches to inactivate phyB: illumination with a low red to far-red ratio, simulating competition, and mutation of the two PHYB genes present in the tomato genome. Inactivation of phyB resulted in low levels of constitutive defenses and down-regulation of direct defenses induced by methyl jasmonate (MeJA). Interestingly, phyB inactivation also had large effects on the blends of VOCs induced by MeJA. Moreover, in two-choice bioassays using MeJA-induced plants, the predatory mirid bug Macrolophus pygmaeus preferred VOCs from plants in which phyB was inactivated over VOCs from control plants. These results suggest that, in addition to repressing direct defense, phyB inactivation has consequences for VOC-mediated tritrophic interactions in canopies, presumably attracting predators to less defended plants, where they are likely to find more abundant prey.

    Functional Divergence of Two Secreted Immune Proteases of Tomato
    Ilyas, M. ; Hörger, A.C. ; Bozkurt, T.O. ; Burg, H.A. van den; Kaschani, F. ; Kaiser, M. ; Belhaj, K. ; Smoker, M. ; Joosten, M. ; Kamoun, S. ; Hoorn, R.A.L. van der - \ 2015
    Current Biology 25 (2015)17. - ISSN 0960-9822 - p. 2300 - 2306.
    cf-2-dependent disease resistance - pathogen effectors - transcription factors - provides insights - genome sequence - plant-pathogens - gene - defense - target - specialization
    Rcr3 and Pip1 are paralogous secreted papain-like proteases of tomato. Both proteases are inhibited by Avr2 from the fungal pathogen Cladosporium fulvum, but only Rcr3 acts as a co-receptor for Avr2 recognition by the tomato Cf-2 immune receptor [ 1, 2, 3 and 4]. Here, we show that Pip1-depleted tomato plants are hyper-susceptible to fungal, bacterial, and oomycete plant pathogens, demonstrating that Pip1 is an important broad-range immune protease. By contrast, in the absence of Cf-2, Rcr3 depletion does not affect fungal and bacterial infection levels but causes increased susceptibility only to the oomycete pathogen Phytophthora infestans. Rcr3 and Pip1 reside on a genetic locus that evolved over 36 million years ago. These proteins differ in surface-exposed residues outside the substrate-binding groove, and Pip1 is 5- to 10-fold more abundant than Rcr3. We propose a model in which Rcr3 and Pip1 diverged functionally upon gene duplication, possibly driven by an arms race with pathogen-derived inhibitors or by coevolution with the Cf-2 immune receptor detecting inhibitors of Rcr3, but not of Pip1.
    Parasitism overrides herbivore identity allowing hyperparasitoids to locate their parasitoid host using herbivore-induced plant volatiles
    Zhu, F. ; Broekgaarden, C. ; Weldegergis, B.T. ; Harvey, J.A. ; Vosman, B. ; Dicke, M. ; Poelman, E.H. - \ 2015
    Molecular Ecology 24 (2015)1. - ISSN 0962-1083 - p. 2886 - 2899.
    cabbage brassica-oleracea - time rt-pcr - nicotiana-attenuata - insect herbivores - gene-expression - trophic levels - defense - responses - specialist - generalist
    Foraging success of predators profoundly depends on reliable and detectable cues indicating the presence of their often inconspicuous prey. Carnivorous insects rely on chemical cues to optimize foraging efficiency. Hyperparasitoids that lay their eggs in the larvae or pupae of parasitic wasps may find their parasitoid hosts developing in different herbivores. They can use herbivore-induced plant volatiles (HIPVs) to locate parasitized caterpillars. Because different herbivore species induce different HIPV emission from plants, hyperparasitoids may have to deal with large variation in volatile information that indicates host presence. In this study, we used an ecogenomics approach to first address whether parasitized caterpillars of two herbivore species (Pieris rapae and P. brassicae) induce similar transcriptional and metabolomic responses in wild Brassica oleracea plants and, second, whether hyperparasitoids Lysibia nana are able to discriminate between these induced plant responses to locate their parasitoid host in different herbivores under both laboratory and field conditions. Our study revealed that both herbivore identity and parasitism affect plant transcriptional and metabolic responses to herbivory. We also found that hyperparasitoids are able to respond to HIPVs released by wild B. oleracea under both laboratory and field conditions. In addition, we observed stronger attraction of hyperparasitoids to HIPVs when plants were infested with parasitized caterpillars. However, hyperparasitoids were equally attracted to plants infested by either herbivore species. Our results indicate that parasitism plays a major role in HIPV-mediated plant-hyperparasitoid interactions. Furthermore, these findings also indicate that plant trait-mediated indirect interaction networks play important roles in community-wide species interactions.
    Biofumigation using a wild Brassica oleracea accession with high glucosinolate content affects beneficial soil
    Zuluaga, D.L. ; Ommen Kloeke van, A.E.E. ; Verkerk, R. ; Röling, W.F.M. ; Ellers, J. ; Roelofs, D. ; Aarts, M.G.M. - \ 2015
    Plant and Soil 394 (2015). - ISSN 0032-079X - p. 155 - 163.
    chemical diversity - gene-expression - indian mustard - natural toxin - life-history - isothiocyanates - collembola - release - defense - tissues
    Aims This study explores the biofumigation effects of glucosinolate (GSL) containing Brassica oleracea plant material on beneficial, non-target soil organisms, and aims to relate those effects to differences in GSL profiles. Methods Leaf material of purple sprouting broccoli ‘Santee’, Savoy cabbage ‘Wintessa’, and the wild B. oleracea accession Winspit was analysed for GSL production and used for biofumigation experiments on the beneficial soil invertebrates, Folsomia candida (springtail) and Eisenia andrei (earthworm) and the soil bacterial community. Results When mixed into soil, the Winspit plant material exerted the highest toxic effects on beneficial soil invertebrates by reducing survival and reproduction. Total GSL levels varied substantially between genotypes, in particular the aliphatic GSL (AGSL) sinigrin and gluconapin being highly abundant or exclusively present in Winspit. Differences between the genotypes regarding biofumigation effects on the soil microbial community were only observed on a temporal basis with the largest difference in bacterial community structure after 1 week. Conclusions The high total GSL content in biofumigated soil could explain the toxicity of Winspit for soil invertebrates. These effects are likely to be the results of high AGSL levels in Winspit. The use of wild B. oleracea crops, such asWinspit, for biofumigation practices would need a proper assessment of the overall impact on soil biota before being applied on a wide scale
    The butterfly plant arms-race escalated by gene and genome duplications
    Edger, P.P. ; Heidel-Fischer, H.M. ; Bekaert, K.M. ; Rota, J. ; Glockner, G. ; Platts, A.E. ; Heckel, D.G. ; Der, J.P. ; Wafula, E.K. ; Tang, M. ; Hofberger, J.A. ; Smithson, A. ; Hall, J.C. ; Blanchette, M. ; Bureau, T.E. ; Wright, S.I. ; dePamphilis, C.W. ; Schranz, M.E. ; Conant, G.C. ; Barker, M.S. ; Wahlberg, N. ; Vogel, H. ; Pires, J.C. ; Wheat, C.W. - \ 2015
    Proceedings of the National Academy of Sciences of the United States of America 112 (2015)27. - ISSN 0027-8424 - p. 8362 - 8366.
    evolutionaire genetica - co-evolutie - diversificatie - brassica - pieridae - papilionidae - glucosinolaten - fylogenie - evolutionary genetics - coevolution - diversification - brassica - pieridae - papilionidae - glucosinolates - phylogeny - diversity - defense - cytochrome-p450 - polymorphism - arabidopsis - metabolism - expression - speciation
    Coevolutionary interactions are thought to have spurred the evolution of key innovations and driven the diversification of much of life on Earth. However, the genetic and evolutionary basis of the innovations that facilitate such interactions remains poorly understood. We examined the coevolutionary interactions between plants (Brassicales) and butterflies (Pieridae), and uncovered evidence for an escalating evolutionary arms-race. Although gradual changes in trait complexity appear to have been facilitated by allelic turnover, key innovations are associated with gene and genome duplications. Furthermore, we show that the origins of both chemical defenses and of molecular counter adaptations were associated with shifts in diversification rates during the arms-race. These findings provide an important connection between the origins of biodiversity, coevolution, and the role of gene and genome duplications as a substrate for novel traits.
    Natural loss-of-function mutation of EDR1 conferring resistance to tomato powdery mildew in Arabidopsis thaliana accession C24
    Gao, D. ; Appiano, M. ; Huibers, R.P. ; Loonen, A.E.H.M. ; Visser, R.G.F. ; Wolters, A.M.A. ; Bai, Y. - \ 2015
    Molecular Plant Pathology 16 (2015)1. - ISSN 1464-6722 - p. 71 - 82.
    salicylic-acid - downy mildew - gene - defense - plants - microsatellites - mechanism - evolution - cloning - kinase
    To screen for potentially novel types of resistance to tomato powdery mildew Oidium neolycopersici, a disease assay was performed on 123 Arabidopsis thaliana accessions. Forty accessions were fully resistant, and one, C24, was analysed in detail. By quantitative trait locus (QTL) analysis of an F2 population derived from C24 × Sha (susceptible accession), two QTLs associated with resistance were identified in C24. Fine mapping of QTL-1 on chromosome 1 delimited the region to an interval of 58¿kb encompassing 15 candidate genes. One of these was Enhanced Disease Resistance 1 (EDR1). Evaluation of the previously obtained edr1 mutant of Arabidopsis accession Col-0, which was identified because of its resistance to powdery mildew Golovinomyces cichoracearum, showed that it also displayed resistance to O.¿neolycopersici. Sequencing of EDR1 in our C24 germplasm (referred to as C24-W) revealed two missing nucleotides in the second exon of EDR1 resulting in a premature stop codon. Remarkably, C24 obtained from other laboratories does not contain the EDR1 mutation. To verify the identity of C24-W, a DNA region containing a single nucleotide polymorphism (SNP) unique to C24 was sequenced showing that C24-W contains the C24-specific nucleotide. C24-W showed enhanced resistance to O.¿neolycopersici compared with C24 not containing the edr1 mutation. Furthermore, C24-W displayed a dwarf phenotype, which was not associated with the mutation in EDR1 and was not caused by the differential accumulation of pathogenesis-related genes. In conclusion, we identified a natural edr1 mutant in the background of C24.
    The heat shock transcription factor PsHSF1 of Phytophthora sojae is required for oxidative stress tolerance and detoxifying the plant oxidative burst
    Sheng, Yuting ; Wang, Yonglin ; Meijer, H.J.G. ; Yang, Xinyu ; Hua, C. ; Ye, Wenwu ; Tao, Kai ; Liu, Xiaoyun ; Govers, F. ; Wang, Yuanchao - \ 2015
    Environmental Microbiology 17 (2015)4. - ISSN 1462-2912 - p. 1351 - 1364.
    signal-transduction - in-vivo - pathogen - infestans - expression - sequence - defense - laccase - binding - yeast
    In the interaction between plant and microbial pathogens, reactive oxygen species (ROS) rapidly accumulate upon pathogen recognition at the infection site and play a central role in plant defence. However, the mechanisms that plant pathogens use to counteract ROS are still poorly understood especially in oomycetes, filamentous organisms that evolved independently from fungi. ROS detoxification depends on transcription factors (TFs) that are highly conserved in fungi but much less conserved in oomycetes. In this study, we identified the TF PsHSF1 that acts as a modulator of the oxidative stress response in the soybean stem and root rot pathogen Phytophthora sojae. We found that PsHSF1 is critical for pathogenicity in P.¿sojae by detoxifying the plant oxidative burst. ROS produced in plant defence can be detoxified by extracellular peroxidases and laccases which might be regulated by PsHSF1. Our study extends the understanding of ROS detoxification mechanism mediated by a heat shock TF in oomycetes.
    Greening Flood Protection - An Interactive Knowledge Arrangement Perspective
    Janssen, S.K.H. ; Tatenhove, J.P.M. van; Otter, H.S. ; Mol, A.P.J. - \ 2015
    Journal of Environmental Policy and Planning 17 (2015)3. - ISSN 1523-908X - p. 309 - 331.
    ecosystem-based management - sustainable development - coastal management - water management - policy - science - netherlands - defense - adaptation - dynamics
    In flood protection, the dominant paradigm of ‘building hard structures’ is being challenged by approaches that integrate ecosystem dynamics and are ‘nature-based’. Knowledge development and policy ambitions on greening flood protection (GFP) are rapidly growing, but a deficit remains in actual full-scale implementation. Knowledge is a key barrier for implementation. To analyse conditions for the implementation of GFP, a knowledge-arrangement perspective is developed. The knowledge-arrangement perspective is applied on a case study of successful implementation of GFP in the Netherlands, the pilot Sand Engine Delfland, a large-scale (21.5 Mm3) sand nourishment project. This project confirms that an integrated knowledge arrangement enables GFP as it allows for multifunctionality. Effectiveness of the integrated arrangement in this project is explained by its ‘flexible’ nature providing ample design space. This was possible because core values in flood protection and nature were not part of the integrated arrangement. More generally the case study demonstrates the difficulties of implementing GFP in existing mainstream flood protection routines. These are not (yet) geared to incorporate uncertainty, dynamics and multifunctionality, characteristics associated with GFP. The Sand Engine project can be regarded as a ‘field laboratory’ of physical and institutional learning and an innovation for mainstream flood protection.
    Diversity of pyrrolizidine alkaloids in native and invasive Senecio pterophorus (Asteraceae): Implications for toxicity
    Castells, E. ; Mulder, P.P.J. ; Perez -Trujillo, M. - \ 2014
    Phytochemistry 108 (2014). - ISSN 0031-9422 - p. 137 - 146.
    increased competitive ability - mass-spectrometry - enemy release - chemical diversity - hypothesis - plants - biosynthesis - evolution - metabolism - defense
    Changes in plant chemical defenses after invasion could have consequences on the invaded ecosystems by modifying the interactions between plants and herbivores and facilitating invasion success. However, no comprehensive biogeographical studies have yet determined the phenotypic levels of plant chemical defenses, as consumed by local herbivores, covering large distributional areas of a species. Senecio pterophorus is a perennial shrub native to Eastern South Africa, expanded into Western South Africa and introduced into Australia and Europe. As other Asteraceae, S. pterophorus contains pyrrolizidine alkaloids (PAs) toxic to vertebrate and invertebrate herbivores. Here we analyzed S. pterophorus PAs by LC–MS/MS on foliage sampled across its entire distributional range, including the native and all non-native areas. PA concentrations and diversity was very high: we found 57 compounds belonging to 6 distinct necine base-types, including the highly toxic 1,2-unsaturated PAs (retronecine and otonecines) and the less toxic 1,2-saturated PAs (platynecine and rosmarinecines). Plants from different origins diverged in their PA absolute and relative concentrations. Rosmarinine was the most abundant compound in Australia and South Africa, but it was nearly absent in Europe. We characterized three plant chemotypes: retrorsine–senkirkine chemotype in Eastern South Africa, rosmarinine chemotype in Australia and Western South Africa, and acetylseneciphylline chemotype in Europe. PA absolute concentrations were highest in Australia. The increased absolute and relative concentrations of retronecine PAs from Australia and Europe, respectively, indicate that S. pterophorus is potentially more toxic in the invasive range than in the native range.
    Chemical ecology of phytohormones: how plants integrate responses to complex and dynamic environments
    Dicke, M. ; Loon, J.J.A. van - \ 2014
    Journal of Chemical Ecology 40 (2014)7. - ISSN 0098-0331 - p. 653 - 656.
    multitrophic interactions - insect herbivores - jasmonate - defense - resistance - immunity - eggs - arabidopsis - modulation - evolution
    Plant volatiles and the environment
    Loreto, F. ; Dicke, M. ; Schnitzler, J.P. ; Turlings, T.C.J. - \ 2014
    Plant, Cell & Environment 37 (2014)8. - ISSN 0140-7791 - p. 1905 - 1908.
    herbivorous insects - floral scent - isoprene - perception - evolution - emissions - aerosols - defense - enemies - stress
    Volatile organic compounds emitted by plants represent the largest part of biogenic volatile organic compounds (BVOCs) released into our atmosphere. Plant volatiles are formed through many biochemical pathways, constitutively and after stress induction. In recent years, our understanding of the functions of these molecules has made constant and rapid progress. From being considered in the past as a mere waste of carbon, BVOCs have now emerged as an essential element of an invisible language that is perceived and exploited by the plants' enemies, the enemies of plant enemies, and neighbouring plants. In addition, BVOCs have important functions in protecting plants from abiotic stresses. Recent advances in our understanding of the role of BVOC in direct and indirect defences are driving further attention to these emissions. This special issue gathers some of the latest and most original research that further expands our knowledge of BVOC. BVOC emissions and functions in (1) unexplored terrestrial (including the soil) and marine environments, (2) in changing climate conditions, and (3) under anthropic pressures, or (4) in complex trophic communities are comprehensively reviewed. Stepping up from scientific awareness, the presented information shows that the manipulation and exploitation of BVOC is a realistic and promising strategy for agricultural applications and biotechnological exploitations.
    Social networking in territorial great tits: slow explorers have the least central social network positions
    Snijders, L. ; Rooij, E.P. van; Burt, J.M. ; Hinde, C.A. ; Oers, K. van; Naguib, M. - \ 2014
    Animal Behaviour 98 (2014). - ISSN 0003-3472 - p. 95 - 102.
    risk-taking behavior - parus-major - avian personalities - exploratory-behavior - reproductive success - prisoners-dilemma - dear enemies - neighbors - wild - defense
    In various animal species individuals differ consistently in their behaviour, often referred to as personality. In several species these personality differences also correlate with differences in social behaviour. This is important as the social environment is a key selection pressure in many animal populations, mediated, for example, via competition or access to social information. Using social network analysis, recent studies have furthered our understanding of the role of personality in the social environment, usually by focusing on swarming or flocking populations. However, social associations in such populations are fundamentally different from those in territorial populations, where individuals meet less frequently and where the costs and benefits of spatial associations differ from those for swarming or flocking species. In this study we therefore tested whether social network position is related to individual differences in exploration behaviour, an established measure of an avian personality trait, using a wild, territorial, personality-typed great tit, Parus major, population. By means of novel, large-scale, automated tracking (Encounternet) we show, while controlling for average territory distance, that slower exploring males had less central social network positions. Yet, slower explorers overall did not travel shorter distances than faster explorers, indicating that a less central social network position was not merely a consequence of lower activity. Finally, males with less central social network positions did not have reduced breeding success compared to males with more central positions. Our results suggest that territorial individuals influence the structuring of their own social environment in relation to their personality. This is relevant, because the establishment of social relations and familiarity with possible competitors is predicted to be important in many territorial populations.
    PIRIN2 stabilizes cysteine protease XCP2 and increases susceptibility to the vascular pathogen Ralstonia solanacearum in Arabidopsis
    Zhang, B. ; Tremousaygue, D. ; Denancé, N. ; Esse, H.P. van; Hörger, A.C. ; Dabos, P. ; Goffner, D. ; Thomma, B.P.H.J. ; Hoorn, R.A.L. van der; Tuominen, H. - \ 2014
    The Plant Journal 79 (2014)6. - ISSN 0960-7412 - p. 1009 - 1019.
    programmed cell-death - nf-kappa-b - disease resistance - phytophthora-infestans - gene-expression - plants - xylem - thaliana - effector - defense
    PIRIN (PRN) is a member of the functionally diverse cupin protein superfamily. There are four members of the Arabidopsis thaliana PRN family, but the roles of these proteins are largely unknown. Here we describe a function of the Arabidopsis PIRIN2 (PRN2) that is related to susceptibility to the bacterial plant pathogen Ralstonia solanacearum. Two prn2 mutant alleles displayed decreased disease development and bacterial growth in response to R. solanacearum infection. We elucidated the underlying molecular mechanism by analyzing PRN2 interactions with the papain-like cysteine proteases (PLCPs) XCP2, RD21A, and RD21B, all of which bound to PRN2 in yeast two-hybrid assays and in Arabidopsis protoplast co-immunoprecipitation assays. We show that XCP2 is stabilized by PRN2 through inhibition of its autolysis on the basis of PLCP activity profiling assays and enzymatic assays with recombinant protein. The stabilization of XCP2 by PRN2 was also confirmed in planta. Like prn2 mutants, an xcp2 single knockout mutant and xcp2 prn2 double knockout mutant displayed decreased susceptibility to R. solanacearum, suggesting that stabilization of XCP2 by PRN2 underlies susceptibility to R. solanacearum in Arabidopsis.
    Identification of candidate genes required for susceptibility to powdery or downy mildew in cucumber
    Schouten, H.J. ; Krauskopf, J. ; Visser, R.G.F. ; Bai, Y. - \ 2014
    Euphytica 200 (2014)3. - ISSN 0014-2336 - p. 475 - 486.
    quantitative trait loci - sativus l. - disease resistance - mlo-gene - qtl analysis - cell-death - arabidopsis - defense - protein - barley
    Powdery mildew (PM, caused by Podosphaera fusca) and downy mildew (DM, caused by Pseudoperonospora cubensis) are important diseases of cucumber (Cucumis sativus). Breeding for resistance has been undertaken since the 1940s, but underlying resistance genes have not been functionally analysed yet. The published genome sequence of cucumber catalyses the search for such genes. Genetic studies have indicated that resistances to PM and DM in cucumber are often inherited recessively, which indicates the presence of susceptibility genes (S-genes). Therefore we analyzed the cucumber genome for homologs of functionally proven S-genes known from other plant species. We identified 13 MLO-like genes in cucumber, three of which cluster in Clade V, the clade that contains all known MLO-like susceptibility genes to powdery mildews in other dicots. The expression of one of these three genes, CsaMLO1, located on chromosome 1, was upregulated after PM inoculation. It co-localizes with a QTL for PM resistance previously identified. Also homologs of the susceptibility genes PMR4 and PMR5 are located at this QTL. The second MLO-like gene from Clade V (CsaMLO8) resides in a recessively inherited major QTL for PM resistance at the bottom of chromosome 5, together with a PMR6-like gene. Two major QTL for DM recessive resistance at the top of chromosome 5 co-localize with CsaDMR6-2, which is homologous to the DMR6 susceptibility gene in Arabidopsis. This study has identified several candidate genes for susceptibility to PM and DM in cucumber that may explain QTL for recessively inherited resistance, reported earlier.
    Green adaptation by innovative dike concepts along the Dutch Wadden Sea coast
    Loon-Steensma, J.M. van; Schelfhout, H.A. ; Vellinga, P. - \ 2014
    Environmental Science & Policy 44 (2014). - ISSN 1462-9011 - p. 108 - 125.
    flood risk-management - salt marshes - netherlands - defense - protection - robust
    This paper describes the development and application of an approach to adapt the existing flood defences along the Dutch Wadden Sea coast to the effects of climate change and sea level rise in the context of other uncertainties and developments. It starts with the development of a dike-portfolio with traditional as well as new flood protection concepts. Next these concepts are evaluated by means of a multi-criteria analysis by local experts. The objective is to identify realistic adaptation options that use or enable natural processes to strengthen ecological resilience and facilitate sustainable human use in the Wadden region. In our analyses Eco-engineering concepts (in rural areas) as well as a Multifunctional dike (in built-up areas) received the highest scores. Multifunctional dikes are robust and offer space for other functions and values. However, their performance in an integral assessment strongly depends on the applied functions and the weight per evaluation criterion. Eco-engineering concepts can potentially contribute to nature and landscape values, but implementation may lead to tension with nature legislation. For the Wadden Sea landscape, which is characterised by the presence of semi-natural salt marshes, the application of vegetated foreshores for flood protection comes forward as being particularly attractive. For every specific stretch of the 227 km long coastline the study has identified the most promising dike concept. The result of this study has been adopted by the national government and the regional water boards as a basis for more detailed analysis and design per stretch of coast. Additional modelling studies and cost benefit analyses will be required at this stage to verify the outcome of our studies and to optimise the design.
    Characterization of the MLO gene family in Rosaceae and gene expression analysis in Malus domestica
    Pessina, S. ; Pavan, S.N.C. ; Catalano, D. ; Gallotta, A. ; Visser, R.G.F. ; Bai, Y. ; Malnoy, M. ; Schouten, H.J. - \ 2014
    BMC Genomics 15 (2014). - ISSN 1471-2164
    powdery mildew resistance - barley - identification - protein - defense - genome - orthologs - evolution - prunus - plants
    Background Powdery mildew (PM) is a major fungal disease of thousands of plant species, including many cultivated Rosaceae. PM pathogenesis is associated with up-regulation of MLO genes during early stages of infection, causing down-regulation of plant defense pathways. Specific members of the MLO gene family act as PM-susceptibility genes, as their loss-of-function mutations grant durable and broad-spectrum resistance. Results We carried out a genome-wide characterization of the MLO gene family in apple, peach and strawberry, and we isolated apricot MLO homologs through a PCR-approach. Evolutionary relationships between MLO homologs were studied and syntenic blocks constructed. Homologs that are candidates for being PM susceptibility genes were inferred by phylogenetic relationships with functionally characterized MLO genes and, in apple, by monitoring their expression following inoculation with the PM causal pathogen Podosphaera leucotricha. Conclusions Genomic tools available for Rosaceae were exploited in order to characterize the MLO gene family. Candidate MLO susceptibility genes were identified. In follow-up studies it can be investigated whether silencing or a loss-of-function mutations in one or more of these candidate genes leads to PM resistance.
    Salt-marsh erosion and restoration in relation to flood protection on the Wadden Sea barrier island Terschelling
    Loon-Steensma, J.M. van; Slim, P.A. ; Decuyper, M. ; Hu, Zhan - \ 2014
    Journal of Coastal Conservation 18 (2014)4. - ISSN 1400-0350 - p. 415 - 430.
    north norfolk - vegetation - succession - herbivory - estuary - defense - field
    This paper explores the impact of erosion and restoration measures on habitat development and on wave damping by a small salt marsh nestled alongside a dike on the Wadden island of Terschelling. The aim is to advance knowledge about the benefits and possible side-effects of salt-marsh restoration. Analysis of a time series of aerial photographs from 1944 to 2010 indicates that the salt marsh decreased steadily in size after maintenance of accretion works was terminated. In the western part of the marsh, which is accessible to sheep, vegetation is low (5–15 cm) and dominated by Salicornia europaea and by Spartina anglica. In the most intensively grazed parts, vegetation is very scarce. The eastern, inaccessible part of the salt marsh is covered by dense patches of the shrubby perennial Atriplex portulacoides and Spartina anglica (15–25 cm in height). SWAN wave models show that wave height at this location is significantly affected by the areal extent of the salt marsh as well as by the vegetation. High or dense vegetation are in the models nearly as effective in damping waves (with an initial height of 0.15 and 0.5 m) as widening the salt-marsh area by 350 m. A low density of low plants, as observed in the grazed part of the marsh, has almost no wave-damping effect. Even under conditions of sea level rise, a broader salt marsh vegetated with high plants significantly affects modelled wave height. Therefore, salt-marsh restoration is an adaptation measure worth exploring, though an array of effect types must be considered.
    Dendrochronology of Atriplex portulacoides and Artemisia maritima in Wadden Sea salt marshes
    Decuyper, M. ; Slim, P.A. ; Loon-Steensma, J.M. van - \ 2014
    Journal of Coastal Conservation 18 (2014)3. - ISSN 1400-0350 - p. 279 - 284.
    wood anatomy - chenopodiaceae - competition - succession - herbivory - defense
    The study uses a rather unusual method, dendrochronology, to investigate the growth and survival of Atriplex portulacoides L. and Artemisia maritima L. on salt marshes at two field sites on the Dutch North Sea barrier islands of Terschelling and Ameland. By providing information on longevity of these typical salt-marsh shrubs, dendrochronology offers an indirect way to investigate the influence of management regime – grazing in this case – on marsh quality and areal extent. Diminishment of salt marshes is a continuing concern in the northern Netherlands. The two shrub species studied here, A. portulacoides and A. maritima, are common to salt marshes. With their extensive roots and branches, they facilitate sedimentation and stabilize salt marshes. Using dendrochronology, this study found that annual growth rings could be identified to determine shrub age and growth. In A. portulacoides these rings took the form of a narrow band of terminal parenchyma. In A. maritima they were made up of unlignified marginal parenchyma together with higher vessel density at the beginning of the growing season. Growth rings indicated that intense grazing was clearly detrimental to the survival of A. portulacoides at the Terschelling site. However, grazing facilitated survival of A. maritima at the Ameland site by reducing light and nutrient competition from grasses. No growth trends could be found, however, as the lifespan for both species is short and many other influences on shrub growth could be identified.
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