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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    Soilless Cultivation Through an Intensive Crop Production Scheme. Management Strategies, Challenges and Future Directions
    Tzortzakis, Nikolaos ; Nicola, Silvana ; Savvas, Dimitrios ; Voogt, Wim - \ 2020
    Frontiers in Plant Science 11 (2020). - ISSN 1664-462X
    abiotic stress - biofortification - hydroponics - induced resistance - nutrient management
    Plant growth promotion by Pseudomonas fluorescens : mechanisms, genes and regulation
    Cheng, X. - \ 2016
    Wageningen University. Promotor(en): Francine Govers; J.M. Raaijmakers, co-promotor(en): M. van der Voort. - Wageningen : Wageningen University - ISBN 9789462578753 - 192
    soil bacteria - pseudomonas fluorescens - plants - growth stimulators - soil suppressiveness - plant diseases - induced resistance - biochemistry - biosynthesis - plant-microbe interactions - transcriptomics - bodembacteriën - pseudomonas fluorescens - planten - groeistimulatoren - bodemweerbaarheid - plantenziekten - geïnduceerde resistentie - biochemie - biosynthese - plant-microbe interacties - transcriptomica

    Pseudomonas fluorescens is a Gram-negative rod shaped bacterium that has a versatile metabolism and is widely spread in soil and water. P. fluorescens strain SBW25 (Pf.SBW25) is a well-known model strain to study bacterial evolution, plant colonization and biocontrol of plant diseases. It produces the biosurfactant viscosin, a lipopeptide that plays a key role in motility, biofilm formation and activity against zoospores of Phytophthora infestans and other oomycete pathogens. In addition to viscosin, Pf.SBW25 produces other metabolites with activity against plant pathogens. The production of these yet unknown metabolites appeared to be regulated by the GacS/GacA two-component regulatory system (the Gac-system). The second P. fluorescens strain SS101 (Pf.SS101) studied in this thesis is known for its plant growth-promoting activities but the underlying mechanisms and genes are largely unknown. Therefore, in this study, we aimed to identify novel metabolites and biosynthetic genes in Pf.SBW25 and Pf.SS101, and to investigate their role in plant growth promotion and biocontrol. To this end, a multidisciplinary approach involving bioinformatic analysis of the genome sequences of strains Pf.SBW25 and Pf.SS101, microarray-based expression profiling, screening of genomic libraries, bioactivity assays, mass spectrometric image analysis (MALDI-IMS) and GC/MSMS analysis was adopted. In conclusion, we showed that the GacS/GacA two-component system as a global regulator of the expression of genes play important roles in antagonism of Pseudomonas fluorescens toward plant pathogenic microbes as well as in plant growth promotion and ISR. Growth promotion by P. fluorescens is associated with alterations in auxin biosynthesis and transport, steroid biosynthesis, carbohydrate metabolism and sulfur assimilation. Moreover, advanced chemical profiling allowed us to compare the metabolite profiles of free-living P. fluorescens and P. fluorescens living in association with plant roots. A better understanding of yet unknown mechanisms exploited by the various Pseudomonas fluorescens strains will lead to new opportunities for the discovery and application of natural bioactive compounds for both industrial and agricultural purposes.

    Regulation of cucumber (Cucumis sativus) induced defence against the two-spotted spider mite (Tetranychus urticae
    He, J. - \ 2016
    Wageningen University. Promotor(en): Harro Bouwmeester; Marcel Dicke, co-promotor(en): Iris Kappers. - Wageningen : Wageningen University - ISBN 9789462576810 - 211
    cucumis sativus - cucumbers - induced resistance - plant pests - tetranychus urticae - mites - defence mechanisms - herbivore induced plant volatiles - herbivory - metabolomics - terpenoids - genomics - cucumis sativus - komkommers - geïnduceerde resistentie - plantenplagen - tetranychus urticae - mijten - verdedigingsmechanismen - herbivoor-geinduceerde plantengeuren - herbivorie - metabolomica - terpenen - genomica

    Plants have evolved mechanisms to combat herbivory. These mechanisms can be classified as direct defences which have a negative influence on the herbivores and indirect defence that attracts natural enemies of the attacking herbivores. Both direct and indirect defences can be constantly present or induced upon attack. This study, using cucumber (Cucumis sativus) and the two-spotted spider mite (Tetranychus urticae) as model, aimed to reveal the molecular mechanisms underlying the induced defence during herbivory, with emphasis on transcriptional changes and the involved TFs, the enzymatic function of the genes associated with volatile biosynthesis, and their promoters which regulate their expression.

    Getting prepared for future attack : induction of plant defences by herbivore egg deposition and consequences for the insect community
    Pashalidou, F.G. - \ 2015
    Wageningen University. Promotor(en): Marcel Dicke; Joop van Loon, co-promotor(en): Nina Fatouros. - Wageningen : Wageningen University - ISBN 9789462574120 - 168
    insect-plant relaties - planten - insectenplagen - herbivorie - verdedigingsmechanismen - geïnduceerde resistentie - herbivoor-geinduceerde plantengeuren - ovipositie - natuurlijke vijanden - brassica - pieris brassicae - trofische graden - sluipwespen - hyperparasitoïden - insectengemeenschappen - insect plant relations - plants - insect pests - herbivory - defence mechanisms - induced resistance - herbivore induced plant volatiles - oviposition - natural enemies - brassica - pieris brassicae - trophic levels - parasitoid wasps - hyperparasitoids - insect communities

    Plants have evolved intriguing defences against insect herbivores. Compared to constitutive Plants have evolved intriguing defences against insect herbivores. Compared to constitutive defences that are always present, plants can respond with inducible defences when they are attacked. Insect herbivores can induce phenotypic changes in plants and consequently these changes may differentially affect subsequent attackers and their associated insect communities. Many studies consider herbivore-feeding damage as the first interaction between plants and insects. The originality of this study was to start with the first phase of herbivore attack, egg deposition, to understand the consequences of plant responses to eggs on subsequently feeding caterpillars and their natural enemies. The main plant species used for most of the experiments was Brassica nigra (black mustard), which occurs naturally in The Netherlands. The main herbivore used was the lepidopteran Pieris brassicae, which lays eggs in clusters and feeds on plants belonging to the Brassicaceae family. This study investigated plant-mediated responses to oviposition and their effects on different developmental stages of the herbivore, such as larvae and pupae. Furthermore, the effects of oviposition were extended to four more plant species of the same family, and to higher trophic levels including parasitoids and hyperparasitoids. The experiments were conducted under laboratory, semi-field and field conditions. This study shows that B. nigra plants recognize the eggs of P. brassicae and initiate resistance against subsequent developmental stages of the herbivore. Interestingly, plant responses to oviposition were found to be species specific. Plants did not respond to egg deposition by another herbivore species, the generalist moth Mamestra brassicae. Moreover, most of the Brassicaceae species tested were found to respond to P. brassicae eggs, which indicates that plant responses against oviposition are more common among the family of Brassicaceae. To assess effects on other members of the food chain, the effects of oviposition on plant volatile emission and the attraction of parasitic wasps, such as the larval parasitoid Cotesia glomerata, were tested. It was shown that the wasps were able to use the blend of plant volatiles, altered by their hosts’ oviposition, to locate young caterpillars just after hatching from eggs. The observed behaviour of the wasps was associated with higher parasitism success and higher fitness in young hosts. Similar results were obtained in a field experiment, where plants infested with eggs and caterpillars attracted more larval parasitoids and hyperparasitoids and eventually produced more seeds compared to plants infested with caterpillars only. This study shows that an annual weed like B. nigra uses egg deposition as reliable information for upcoming herbivory and responds accordingly with induced defences. Egg deposition could influence plant-associated community members at different levels in the food chain and benefit seed production. As the importance of oviposition on plant-herbivore interactions is only recently discovered, more research is needed to elucidate the mechanisms that underlie such plant responses and how these interactions affect the structure of insect communities in nature.

    Synergism in the effect of prior jasmonic acid application on herbivore-induced volatile emission by Lima bean plants: transcription of a monoterpene synthase gene and volatile emission
    Menzel, T.R. ; Weldegergis, B.T. ; David, A. ; Boland, W. ; Gols, R. ; Loon, J.J.A. van; Dicke, M. - \ 2014
    Journal of Experimental Botany 65 (2014)17. - ISSN 0022-0957 - p. 4821 - 4831.
    induced resistance - arabidopsis-thaliana - brassica-oleracea - phytoseiulus-persimilis - attract parasitoids - signaling pathway - methyl salicylate - predatory mite - corn plants - host-plant
    Jasmonic acid (JA) plays a central role in induced plant defence e.g. by regulating the biosynthesis of herbivore-induced plant volatiles that mediate the attraction of natural enemies of herbivores. Moreover, exogenous application of JA can be used to elicit plant defence responses similar to those induced by biting-chewing herbivores and mites that pierce cells and consume their contents. In the present study, we used Lima bean (Phaseolus lunatus) plants to explore how application of a low dose of JA followed by minor herbivory by spider mites (Tetranychus urticae) affects transcript levels of P. lunatus (E)-ß-ocimene synthase (PlOS), emission of (E)-ß-ocimene and nine other plant volatiles commonly associated with herbivory. Furthermore, we investigated the plant’s phytohormonal response. Application of a low dose of JA increased PlOS transcript levels in a synergistic manner when followed by minor herbivory for both simultaneous and sequential infestation. Emission of (E)-ß-ocimene was also increased, and only JA, but not SA, levels were affected by treatments. Projection to latent structures-discriminant analysis (PLS-DA) of other volatiles showed overlap between treatments. Thus, a low-dose JA application results in a synergistic effect on gene transcription and an increased emission of a volatile compound involved in indirect defence after herbivore infestation.
    Reciprocal crosstalk between jasmonate and salicylate defence-signalling pathways modulates plant volatile emission and herbivore host-selection behaviour
    Wei, J. ; Loon, J.J.A. van; Gols, R. ; Menzel, T.R. ; Li, N. ; Kang, L. ; Dicke, M. - \ 2014
    Journal of Experimental Botany 65 (2014)12. - ISSN 0022-0957 - p. 3289 - 3298.
    mediated interactions - specialist herbivore - tetranychus-urticae - induced resistance - parasitic wasps - cotton plants - spider-mites - insect - acid - pathogen
    The jasmonic acid (JA) and salicylic acid (SA) signalling pathways, which mediate induced plant defence responses, can express negative crosstalk. Limited knowledge is available on the effects of this crosstalk on host-plant selection behaviour of herbivores. We report on temporal and dosage effects of such crosstalk on host preference and oviposition-site selection behaviour of the herbivorous spider mite Tetranychus urticae towards Lima bean (Phaseolus lunatus) plants, including underlying mechanisms. Behavioural observations reveal a dynamic temporal response of mites to single or combined applications of JA and SA to the plant, including attraction and repellence, and an antagonistic interaction between SA- and JA-mediated plant responses. Dose-response experiments show that concentrations of 0.001mM and higher of one phytohormone can neutralize the repellent effect of a 1mM application of the other phytohormone on herbivore behaviour. Moreover, antagonism between the two signal-transduction pathways affects phytohormone-induced volatile emission. Our multidisciplinary study reveals the dynamic plant phenotype that is modulated by subtle changes in relative phytohormonal titres and consequences for the dynamic host-plant selection by an herbivore. The longer-term effects on plant–herbivore interactions deserve further investigation.
    Induction of indirect plant defense in the context of multiple herbivory : gene transcription, volatile emission, and predator behavior
    Menzel, T.R. - \ 2014
    Wageningen University. Promotor(en): Marcel Dicke; Joop van Loon. - Wageningen : Wageningen University - ISBN 9789462571297 - 146
    planten - plaagresistentie - geïnduceerde resistentie - verdedigingsmechanismen - multitrofe interacties - phaseolus lunatus - mijten - tetranychus urticae - roofmijten - phytoseiulus persimilis - voedingsgedrag - genen - transcriptie - genexpressie - herbivoor-geinduceerde plantengeuren - plants - pest resistance - induced resistance - defence mechanisms - multitrophic interactions - phaseolus lunatus - mites - tetranychus urticae - predatory mites - phytoseiulus persimilis - feeding behaviour - genes - transcription - gene expression - herbivore induced plant volatiles

    Abstract

    Plants live in complex environments and are under constant threat of being attacked by herbivorous arthropods. Consequently plants possess an arsenal of sophisticated mechanisms in order to defend themselves against their ubiquitous attackers. Induced indirect defenses involve the attraction of natural enemies of herbivores, such as predators and parasitoids. Predators and parasitoids use odors emitted by damaged plants that serve as a “cry for help” to find their respective prey or host herbivore. The aim of this thesis was to use a multidisciplinary approach, with focus on molecular and chemical methods, combined with behavioral investigations, to elucidate the mechanisms of plant responses to multiple herbivory that affect a tritrophic system consisting of a plant, an herbivore and a natural enemy.

    Induced plant defenses are regulated by a network of defense signaling pathways in which phytohormones act as signaling molecules. Accordingly, simulation of herbivory by exogenous application of phytohormones and actual herbivory by the two-spotted spider mite Tetranychus urticae affected transcript levels of a defense gene involved in indirect defense in Lima bean. However, two other genes involved in defense were not affected at the time point investigated. Moreover, application of a low dose of JA followed by minor herbivory by T. urticae spider mites affected gene transcript levels and emissions of plant volatiles commonly associated with herbivory. Only endogenous phytohormone levels of jasmonic acid (JA), but not salicylic acid (SA), were affected by treatments. Nevertheless, the low-dose JA application resulted in a synergistic effect on gene transcription and an increased emission of a volatile compound involved in indirect defense after herbivore infestation.

    Caterpillar feeding as well as application of caterpillar oral secretion on mechanically inflicted wounds are frequently used to induce plant defense against biting-chewing insects, which is JA-related. Feeding damage by two caterpillar species caused mostly identical induction of gene transcription, but combination of mechanical damage and oral secretions of caterpillars caused differential induction of the transcription of defense genes. Nevertheless, gene transcript levels for plants that subsequently experienced an infestation by T. urticae were only different for a gene potentially involved in direct defense of plants that experienced a single event of herbivory by T. urticae. Indirect defense was not affected. Also sequential induction of plant defense by caterpillar oral secretion and an infestation by T. urticae spider mites did not interfere with attraction of the specialist predatory mite P. persimilis in olfactometer assays. The predator did distinguish between plants induced by spider mites and plants induced by the combination of mechanical damage and caterpillar oral secretion but not between plants with single spider mite infestation and plants induced by caterpillar oral secretion prior to spider mite infestation. The composition of the volatile blends emitted by plants induced by spider mites only or by the sequential induction treatment of caterpillar oral secretion followed by spider mite infestation were similar. Consequently, the induction of plant indirect defense as applied in these experiments was not affected by previous treatment with oral secretion of caterpillars. Moreover, herbivory by conspecific T. urticae mites did not affect gene transcript levels or emission of volatiles of plants that experienced two bouts of herbivore attack by conspecific spider mites compared to plants that experienced only one bout of spider mite attack. This suggests that Lima bean plants do no increase defense in response to sequential herbivory by T. urticae.

    In conclusion, using a multidisciplinary approach new insights were obtained in the mechanisms of induction of indirect plant defense and tritrophic interactions in a multiple herbivore context, providing helpful leads for future research on plant responses to multiple stresses.

    Intra-specific variation in wild Brassica oleracea for aphid-induced plant responses and consequences for caterpillar-parasitoid interactions
    Li, Y. ; Dicke, M. ; Harvey, J.A. ; Gols, R. - \ 2014
    Oecologia 174 (2014)3. - ISSN 0029-8549 - p. 853 - 862.
    phloem-feeding insect - induced resistance - defense responses - interspecific interactions - multitrophic interactions - arabidopsis-thaliana - phytophagous insects - nicotiana-attenuata - jasmonic acid - host plants
    Herbivore-induced plant responses not only influence the initiating attackers, but also other herbivores feeding on the same host plant simultaneously or at a different time. Insects belonging to different feeding guilds are known to induce different responses in the host plant. Changes in a plant's phenotype not only affect its interactions with herbivores but also with organisms higher in the food chain. Previous work has shown that feeding by a phloem-feeding aphid on a cabbage cultivar facilitates the interaction with a chewing herbivore and its endoparasitoid. Here we study genetic variation in a plant's response to aphid feeding using plants originating from three wild Brassica oleracea populations that are known to differ in constitutive and inducible secondary chemistry. We compared the performance of two different chewing herbivore species, Plutella xylostella and M. brassicae, and their larval endoparasitoids Diadegma semiclausum and M. mediator, respectively, on plants that had been infested with aphids (Brevicoryne brassicae) for 1 week. Remarkably, early infestation with B. brassicae enhanced the performance of the specialist P. xylostella and its parasitoid D. semiclausum, but did not affect that of the generalist M. brassicae, nor its parasitoid M. mediator. Performance of the two herbivore-parasitoid interactions also varied among the cabbage populations and the effect of aphid infestation marginally differed among the three populations. Thus, the effect of aphid infestation on the performance of subsequent attackers is species specific, which may have concomitant consequences for the assembly of insect communities that are naturally associated with these plants.
    Induced plant responses to microbes and insects
    Pieterse, C.M.J. ; Poelman, E.H. ; Wees, S.C.M. van; Dicke, M. - \ 2013
    Frontiers in Plant Science 4 (2013). - ISSN 1664-462X - 3 p.
    induced resistance - arabidopsis - volatiles - susceptibility - pathways - immunity - defense - stress - growth - acid
    Plants are members of complex communities and interact both with antagonists and beneficial organisms. An important question in plant defense-signaling research is how plants integrate signals induced by pathogens, insect herbivores and beneficial microbes into the most appropriate adaptive response. Molecular and genomic tools are now being used to uncover the complexity of the induced defense signaling networks that have evolved during the arms races between plants and the other organisms with which they intimately interact. To understand the functioning of the complex defense signaling network in nature, molecular biologists and ecologists have joined forces to place molecular mechanisms of induced plant defenses in an ecological perspective. In this Research Topic, we aim to provide an on-line, open-access snapshot of the current state of the art of the field of induced plant responses to microbes and insects, with a special focus on the translation of molecular mechanisms to ecology and vice versa. We will collect Original Research and Review papers on the topic, but also other article types, such as Methods and Opinions are welcome.
    A test of genotypic variation in specificity of herbivore-induced responses in Solidago altissima L. (Asteraceae)
    Uesugi, A. ; Poelman, E.H. ; Kessler, A. - \ 2013
    Oecologia 173 (2013)4. - ISSN 0029-8549 - p. 1387 - 1396.
    milkweed asclepias-syriaca - induced plant-responses - induced resistance - nicotiana-attenuata - common milkweed - interspecific interactions - specialist herbivores - phytophagous insects - tall goldenrod - defense
    Plant-induced responses to multiple herbivores can mediate ecological interactions among herbivore species, thereby influencing herbivore community composition in nature. Several studies have indicated high specificity of induced responses to different herbivore species. In addition, there may be genetic variation for plant response specificity that can have significant ecological implications, by altering the competitive strength and hierarchical relationships among interacting herbivore species. However, few studies have examined whether plant populations harbor genetic variation for induction specificity. Using three distinct genotypes of Solidago altissima plants, we examined whether specialist herbivore species Dichomeris leuconotella, Microrhopala vittata, and Trirhabda virgata elicit specific induction responses from plants (specificity of elicitation), and whether induction differentially affects these herbivore species (specificity of effect). Results from bioassays and secondary metabolite analyses suggest that there is specificity of both elicitation and effect in the induced responses: D. leuconotella and M. vittata preferred and performed better on leaves damaged by conspecifics than heterospecifics, and induced qualitatively different secondary metabolite profiles. In contrast, T. virgata equally avoided but physiologically tolerated all types of damage. These patterns of specificity suggest that plant-induced responses mediate asymmetric competitive interactions between herbivore species, which potentially intensifies inter-specific relative to intra-specific competition. Plant genotypes widely differed in overall susceptibility to the herbivores and secondary metabolite production, yet we found no genotype-by-treatment interactions in insect performance, preference and plant secondary metabolite production. This lack of genetic variation for induction specificity suggests that competitive interactions between herbivore species on S. altissima are homogeneous across plant genotypes.
    Canopy light cues affect emission of constitutive and methyl jasmonate-induced volatile organic compounds in Arabidopsis thaliana
    Kegge, W. ; Weldegergis, B.T. ; Soler, R. ; Vergeer-van Eijk, M.H. ; Dicke, M. ; Voesenek, L.A.C.J. ; Pierik, R. - \ 2013
    New Phytologist 200 (2013)3. - ISSN 0028-646X - p. 861 - 874.
    salicylic-acid - host-plant - induced resistance - insect herbivores - indirect defenses - chemical ecology - shade avoidance - abiotic factors - bean-plants - ethylene
    The effects of plant competition for light on the emission of plant volatile organic compounds (VOCs) were studied by investigating how different light qualities that occur in dense vegetation affect the emission of constitutive and methyl-jasmonate-induced VOCs. Arabidopsis thaliana Columbia (Col-0) plants and Pieris brassicae caterpillars were used as a biological system to study the effects of light quality manipulations on VOC emissions and attraction of herbivores. VOCs were analysed using gas chromatography-mass spectrometry and the effects of light quality, notably the red : far red light ratio (R : FR), on expression of genes associated with VOC production were studied using reverse transcriptase-quantitative PCR. The emissions of both constitutive and methyl-jasmonate-induced green leaf volatiles and terpenoids were partially suppressed under low R : FR and severe shading conditions. Accordingly, the VOC-based preference of neonates of the specialist lepidopteran herbivore P. brassicae was significantly affected by the R : FR ratio. We conclude that VOC-mediated interactions among plants and between plants and organisms at higher trophic levels probably depend on light alterations caused by nearby vegetation. Studies on plant-plant and plant-insect interactions through VOCs should take into account the light quality within dense stands when extrapolating to natural and agricultural field conditions.
    Dealing with double trouble: consequences of single and double herbivory in Brassica juncea
    Mathur, V. ; Tytgat, T.O.G. ; Graaf, R.M. de; Kalia, V. ; Reddy, A.S. ; Vet, L.E.M. ; Dam, N.M. van - \ 2013
    Chemoecology 23 (2013)2. - ISSN 0937-7409 - p. 71 - 82.
    induced plant-responses - milkweed asclepias-syriaca - plutella-xylostella - specialist herbivores - induced resistance - diamondback moth - wild radish - nicotiana-attenuata - insect resistance - black mustard
    In their natural environment, plants are often attacked simultaneously by many insect species. The specificity of induced plant responses that is reported after single herbivore attacks may be compromised under double herbivory and this may influence later arriving herbivores. The present study focuses on the dynamics of induced plant responses induced by single and double herbivory, and their effects on successive herbivores. Morphological (leaf length, area and trichome density) and chemical changes (leaf alkenyl and indole glucosinolates) in Brassica juncea were evaluated 4, 10, 14 and 20 days after damage by the specialist Plutella xylostella alone, or together with the generalist Spodoptera litura. To assess the biological effect of the plant's responses, the preference and performance of both herbivores on previously induced plants were measured. We found that alkenyl glucosinolates were induced 20 days after damage by P. xylostella alone, whereas their levels were elevated as early as 4 days after double herbivory. Trichome density was increased in both treatments, but was higher after double herbivory. Interestingly, there was an overall decrease in indole glucosinolates and an increase in leaf size due to damage by P. xylostella, which was not observed during double damage. S. litura preferred and performed better on undamaged plants, whereas P. xylostella preferred damaged plants and performed better on plants damaged 14 and 10 days after single and double herbivory, respectively. Our results suggest that temporal studies involving single versus multiple attacker situations are necessary to comprehend the role of induced plant responses in plant-herbivore interactions.
    Plant pathogens structure arthropod communities across multiple spatial and temporal scales
    Tack, A.J.M. ; Dicke, M. - \ 2013
    Functional Ecology 27 (2013)3. - ISSN 0269-8463 - p. 633 - 645.
    tobacco mosaic-virus - weed cirsium-arvense - shared host-plant - induced resistance - mediated interactions - phytopathogenic fungus - phytophagous insects - powdery mildew - rust fungus - interspecific interactions
    Plant pathogens and herbivores frequently co-occur on the same host plants. Despite this, little is known about the impact of their interactions on the structure of plant-based ecological communities. Here, we synthesize evidence that indicates that plant pathogens may profoundly impact arthropod performance, preference, population dynamics and community structure across multiple spatial and temporal scales. Intriguingly, the effects of plantpathogenherbivore interactions frequently cascade up and down multiple trophic levels and explain variation in the arthropod community at spatial scales ranging from patterns within single host plants to entire landscapes. This review indicates that knowledge on pathogenherbivore interactions may be crucial for understanding the dynamics of terrestrial communities.
    Beneficial microbes in a changing environment: are they always helping plants to deal with insects?
    Pineda, A. ; Dicke, M. ; Pieterse, C.M.J. ; Pozo, M.J. - \ 2013
    Functional Ecology 27 (2013)3. - ISSN 0269-8463 - p. 574 - 586.
    arbuscular mycorrhizal symbiosis - ultraviolet-b radiation - abscisic-acid - climate-change - induced resistance - defense responses - water-stress - signaling pathways - fungal endophyte - salicylic-acid
    Plants have a complex immune system that defends them against attackers (e.g. herbivores and microbial pathogens) but that also regulates the interactions with mutualistic organisms (e.g. mycorrhizal fungi and plant growth-promoting rhizobacteria). Plants have to respond to multiple environmental challenges, so they need to integrate both signals associated with biotic and abiotic stresses in the most appropriate response to survive. Beneficial microbes such as rhizobacteria and mycorrhizal fungi can help plants to deal' with pathogens and herbivorous insects as well as to tolerate abiotic stress. Therefore, beneficial microbes may play an important role in a changing environment, where abiotic and biotic stresses on plants are expected to increase. The effects of beneficial microbes on herbivores are highly context-dependent, but little is known on what is driving such dependency. Recent evidence shows that abiotic stresses such as changes in soil nutrients, drought and salt stress, as well as ozone can modify the outcome of plantmicrobeinsect interactions. Here, we review how abiotic stress can affect plantmicrobe, plantinsect and plantmicrobeinsect interactions, and the role of the network of plant signal-transduction pathways in regulating such interactions. Most of the studies on the effects of abiotic stress on plantmicrobeinsect interactions show that the effects of microbes on herbivores (positive or negative) are strengthened under stressful conditions. We propose that, at least in part, this is due to the crosstalk of the different plant signalling pathways triggered by each stress individually. By understanding the cross-regulation mechanisms we may be able to predict the possible outcomes of plant-microbeinsect interactions under particular abiotic stress conditions. We also propose that microbes can help plants to deal with insects mainly under conditions that compromise efficient activation of plant defences. In the context of global change, it is crucial to understand how abiotic stresses will affect species interactions, especially those interactions that are beneficial for plants. The final aim of this review is to stimulate studies unravelling when these beneficial' microbes really benefit a plant.
    Citrus phenylpropanoids and defence against pathogens. Part I: Metabolic profiling in elicited fruits
    Ballester, A.R. ; Lafuente, M.T. ; Vos, R.C.H. de; Bovy, A.G. ; González-Candelas, L. - \ 2013
    Food Chemistry 136 (2013)1. - ISSN 0308-8146 - p. 178 - 185.
    penicillium-digitatum sacc - induced resistance - phytophthora-citrophthora - scoparone accumulation - flavonoid composition - postharvest decay - mass-spectrometry - lemon fruit - grapefruit - induction
    Penicillium spp. are among the major postharvest pathogens of citrus fruit. Induction of natural resistance in fruits constitutes one of the alternatives to chemical fungicides. Here, we investigated the involvement of the phenylpropanoid pathway in the induction of resistance in Navelate oranges by examining changes in the metabolic profile of upon eliciting citrus fruits. By using both HPLC-PDA-FD and HPLC-PDA-QTOF–MS allowed the identification of several compounds that seem to be relevant for induced resistance. In elicited fruits, a greater diversity of phenolic compounds was observed in the flavedo (outer coloured part of the peel) when compared to the albedo (inner white part). Moreover, only small changes were detected in the most abundant citrus flavonoids. The coumarin scoparone was among the compounds with the highest induction upon elicitation. Two other highly induced compounds were identified as citrusnin A and drupanin aldehyde. All three compounds are known to exert antimicrobial activity. Our results suggest that phenylpropanoids and their derivatives play an important role in the induction of resistance in citrus fruit/
    Rhizobacteria modify plant–aphid interactions: a case of induced systemic susceptibility
    Pineda, A. ; Zheng, S.J. ; Loon, J.J.A. van; Dicke, M. - \ 2012
    Plant Biology 14 (2012)Suppl. s1. - ISSN 1435-8603 - p. 83 - 90.
    gene-expression - arabidopsis-thaliana - brevicoryne-brassicae - signaling pathways - induced resistance - insect herbivores - abscisic-acid - disease resistance - defense responses - myzus-persicae
    Beneficial microbes, such as plant growth-promoting rhizobacteria and mycorrhizal fungi, may have a plant-mediated effect on insects aboveground. The plant growth-promoting rhizobacterium Pseudomonas fluorescens can induce systemic resistance in Arabidopsis thaliana against several microbial pathogens and chewing insects. However, the plant-mediated effect of these beneficial microbes on phloem-feeding insects is not well understood. Using Arabidopsis as a model, we here report that P. fluorescens has a positive effect on the performance (weight gain and intrinsic rate of increase) of the generalist aphid Myzus persicae, while no effect was recorded on the crucifer specialist aphid Brevicoryne brassicae. Additionally, transcriptional analyses of selected marker genes revealed that in the plant–microbe interaction with M. persicae, rhizobacteria (i) prime the plant for enhanced expression of LOX2, a gene involved in the jasmonic acid (JA)-regulated defence pathway, and (ii) suppress the expression of ABA1, a gene involved in the abscisic acid (ABA) signalling pathway, at several time points. In contrast, almost no effect of the plant–microbe interaction with B. brassicae was found at the transcriptional level. This study presents the first data on rhizobacteria-induced systemic susceptibility to an herbivorous insect, supporting the pattern proposed for other belowground beneficial microbes and aboveground phloem feeders. Moreover, we provide further evidence that at the transcript level, soil-borne microbes modify plant–aphid interactions.
    Indirect plant-mediated interactions among parasitoid larvae
    Poelman, E.H. ; Gols, R. ; Snoeren, T.A.L. ; Muru, D. ; Smid, H.M. ; Dicke, M. - \ 2011
    Ecology Letters 14 (2011)7. - ISSN 1461-023X - p. 670 - 676.
    interspecific interactions - phytophagous insects - induced resistance - cotesia-rubecula - interaction webs - pieris-rapae - herbivore - host - responses - defense
    Communities are riddled with indirect species interactions and these interactions can be modified by organisms that are parasitic or symbiotic with one of the indirectly interacting species. By inducing plant responses, herbivores are well known to alter the plant quality for subsequent feeders. The reduced performance of herbivores on induced plants cascades into effects on the performance of higher trophic level organisms such as parasitoids that develop inside herbivores. Parasitoids themselves may also, indirectly, interact with the host plant by affecting the behaviour and physiology of their herbivorous host. Here, we show that, through their herbivorous host, larvae of two parasitoid species differentially affect plant phenotypes leading to asymmetric interactions among parasitoid larvae developing in different hosts that feed on the same plant. Our results show that temporally separated parasitoid larvae are involved in indirect plant-mediated interactions by a network of trophic and non-trophic relationships
    Transcriptional responses of Brassica nigra to feeding by specialist insects of different feeding guilds
    Broekgaarden, C. ; Voorrips, R.E. ; Dicke, M. ; Vosman, B. - \ 2011
    Insect Science 18 (2011)3. - ISSN 1672-9609 - p. 259 - 272.
    aphid brevicoryne-brassicae - indirect plant defense - nicotiana-attenuata - arabidopsis-thaliana - gene-expression - pieris-rapae - microarray analysis - induced resistance - glucosinolate profiles - secondary metabolites
    Plants show phenotypic changes when challenged with herbivorous insects. The mechanisms underlying these changes include the activation of transcriptional responses, which are dependent on the attacking insect. Most transcriptomic studies on crucifer–insect interactions have focused on the model plant Arabidopsis thaliana, a species that faces low herbivore pressure in nature. Here, we study the transcriptional responses of plants from a wild black mustard (Brassica nigra) population to herbivores of different feeding guilds using an A. thaliana-based whole-genome microarray that has previously been shown to be suitable for transcriptomic analyses in Brassica. Transcriptional responses of B. nigra after infestation with either Pieris rapae caterpillars or Brevicoryne brassicae aphids are analyzed and compared. Additionally, the insect-induced expression changes of some individual genes are analyzed through quantitative real-time polymerase chain reaction. The results show that feeding by both insect species results in the accumulation of transcripts encoding proteins involved in the detoxification of reactive oxygen species, defensive proteins and glucosinolates and this is correlated with experimental evidence in the literature on such biochemical effects. Although genes encoding proteins involved in similar processes are regulated by both insects, there was little overlap in the induction or repression of individual genes. Furthermore, P. rapae and B. brassicae seem to affect different phytohormone signaling pathways. In conclusion, our results indicate that B. nigra activates several defense-related genes in response to P. rapae or B. brassicae feeding, but that the response is dependent on the attacking insect species.
    Herbivore-induced volatiles of cabbage (Brassica oleracea) prime defence responses in neighbouring intact plants
    Peng, J. ; Loon, J.J.A. van; Zheng, S.J. ; Dicke, M. - \ 2011
    Plant Biology 13 (2011)2. - ISSN 1435-8603 - p. 276 - 284.
    octadecanoid-signaling pathway - lima-bean leaves - induced resistance - wild tobacco - carnivore attractants - proteinase-inhibitors - arabidopsis-thaliana - wound induction - predatory mites - tomato leaves
    When attacked by herbivores, plants release herbivore-induced plant volatiles (HIPV) that may function in direct defence by repelling herbivores or reducing their growth. Emission of HIPV may also contribute to indirect defence by attracting natural enemies of the herbivore. Here, cabbage (Brassica oleracea L.) plants (receiver plants) previously exposed to HIPV and subsequently induced through feeding by five Pieris brassicae L. caterpillars attracted more Cotesia glomerata L. parasitoids than control plants. HIPVs to which receiver plants had been exposed were emitted by B. oleracea infested with 50 P. brassicae caterpillars. Control plants had been exposed to volatiles from undamaged plants. In contrast, there were no differences in the attraction of wasps to receiver plants induced through feeding of one or ten larvae of P. brassicae compared to control plants. In addition, RT-PCR demonstrated higher levels of LIPOXYGENASE (BoLOX) transcripts in HIPV-exposed receiver plants. Exposure to HIPV from emitter plants significantly inhibited the growth rate of both P. brassicae and Mamestra brassicae caterpillars compared to growth rates of caterpillars feeding on control receiver plants. Our results demonstrate plant–plant signalling leading to priming of both indirect and direct defence in HIPV-exposed B. oleracea plants.
    Combined effects of patch size and plant nutritional quality on local densities of insect herbivores
    Bukovinszky, T. ; Gols, R. ; Kamp, A. ; Oliveira-Domingues, F. de; Hamback, P.A. ; Jongema, Y. ; Bezemer, T.M. ; Dicke, M. ; Dam, N. ; Harvey, J.A. - \ 2010
    Basic and Applied Ecology 11 (2010)5. - ISSN 1439-1791 - p. 396 - 405.
    flea beetles - allyl isothiocyanate - induced resistance - phyllotreta - cabbage - responses - scale - field - chrysomelidae - consequences
    Plant–insect interactions occur in spatially heterogeneous habitats. Understanding how such interactions shape density distributions of herbivores requires knowledge on how variation in plant traits (e.g. nutritional quality) affects herbivore abundance through, for example, affecting movement rates and aggregation behaviour. We studied the effects of plant patch size and herbivore-induced differences in plant nutritional quality on local densities of insect herbivores for two Brassica oleracea cultivars, i.e. white cabbage and Brussels sprouts. Early season herbivory as a treatment resulted in measurable differences in glucosinolate concentrations in both cultivars throughout the season. Herbivore induction and patch size both influenced community composition of herbivores in both cultivars, but the effects differed between species. Flea beetles (Phyllotreta spp.) were more abundant in large than in small patches, and this patch response was more pronounced on white cabbage than on Brussels sprouts. Herbivore-induction increased densities in all patches. Thrips tabaci was also more abundant in large patches and densities of this species were higher on Brussels sprouts than on white cabbage. Thrips densities were lower on induced than on control plants of both cultivars and this negative effect of induction tended to be more pronounced in large than in small patches. Densities of the cabbage moth (Mamestra brassicae) were lower on Brussels sprouts than on white cabbage and lower on herbivore-induced than on uninduced plants, with no effect of patch size. No clear effects of patch size and induction were found for aphids. This study shows that constitutive and herbivore-induced differences in plant traits interact with patch responses of insect herbivores.
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