Understanding the mechanisms involved in host plant resistance opens the way for improved resistance breeding programs by using the traits involved as markers. Pest management is a major problem in cultivation of ornamentals. Gladiolus... more
Understanding the mechanisms involved in host plant resistance opens the way for improved resistance breeding programs by using the traits involved as markers. Pest management is a major problem in cultivation of ornamentals. Gladiolus (Gladiolus hybridus L.) is an economically important ornamental in the Netherlands. Gladiolus is especially sensitive to attack by western flower thrips (Frankliniella occidentalis (Pergande) (Thysanoptera:Thripidae)). The objective of this study was, therefore, to investigate morphological and chemical markers for resistance breeding to western flower thrips in Gladiolus varieties. We measured thrips damage of 14 Gladiolus varieties in a whole-plant thrips bioassay and related this to morphological traits with a focus on papillae density. Moreover, we studied chemical host plant resistance to using an eco-metabolomic approach comparing the 1H NMR profiles of thrips resistant and susceptible varieties representing a broad range of papillae densities. ...
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The applicability of traditional models of life-history evolution is restricted because models assume constant environments without density-dependence. In these models the geometric growth rate (?) of a lineage is the natural choice for... more
The applicability of traditional models of life-history evolution is restricted because models assume constant environments without density-dependence. In these models the geometric growth rate (?) of a lineage is the natural choice for the fitness criterion. Because in growing populations ? is very sensitive to changes in generation time, biennials appear at a disadvantage when compared to species with annual
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A longstanding question in ecology is how species interactions are structured within communities. Although evolutionary theory predicts close size matching between floral nectar tube depth and pollinator proboscis length of interacting... more
A longstanding question in ecology is how species interactions are structured within communities. Although evolutionary theory predicts close size matching between floral nectar tube depth and pollinator proboscis length of interacting species, such size matching has seldom been shown and explained in multispecies assemblages. Here, we investigated the degree of size matching among Asteraceae and their pollinators and its relationship with foraging efficiency. The majority of pollinators, especially Hymenoptera, choose plant species on which they had high foraging efficiencies. When proboscides were shorter than nectar tubes, foraging efficiency rapidly decreased because of increased handling time. When proboscides were longer than nectar tubes, a decreased nectar reward rather than an increased handling time made shallow flowers more inefficient to visit. Altogether, this led to close size matching. Overall, our results show the importance of nectar reward and handling time as drivers of plant – pollinator network structure
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Hybridization is known to be involved in a number of evolutionary processes, including species formation, and the generation of novel defense characteristics in plants. The genus Senecio of the Asteraceae family is highly speciose and has... more
Hybridization is known to be involved in a number of evolutionary processes, including species formation, and the generation of novel defense characteristics in plants. The genus Senecio of the Asteraceae family is highly speciose and has historically demon-strated significant levels of inter-specific hybridization. The evolu-tion of novel chemical defense characteristics may have con-tributed to the success of Senecio hybrids. Chemical defense against pathogens and herbivores has been studied extensively in the model species Senecio jacobaea, which is thought to hybridize in nature with Senecio aquaticus. Here, we use AFLPs and pyrrolizidine alkaloid (PA) composition to confirm that natural hybridization occurs between S. jacobaea and closely related species S. aquaticus, and we use AFLPs to estimate ancestry of hybrids. We also demonstrate that even highly backcrossed hybrids can possess a unique mixture of defense chemicals specif-ic to each of the parental species. This hybrid s...
Among other consequences in plants, hybridization may influence the expression and evolution of resistance to natural enemies. Plant resistance to parasites, including both microbial pathogens and herbivores, is often mediated by the... more
Among other consequences in plants, hybridization may influence the expression and evolution of resistance to natural enemies. Plant resistance to parasites, including both microbial pathogens and herbivores, is often mediated by the composition of second-ary metabolites expressed by the plant. Here, we focus on pyrrolizidine alkaloids (PAs), a class of secondary metabolites that exhibits high structural diversity among species within the plant genus Senecio. We examine PA composition in Senecio jacobaea, S. aquaticus, artificially generated F1 hybrids, and also later gener-ation natural hybrids between these two species. We test the hypothesis that hybridization may contribute to PA diversity with-in plants, by comparing PA expression in hybrids to that in parents across a range of water and nutrient treatments. We report that hybrids produce a putatively novel PA, and that this PA is con-served in natural hybrids, which are highly backcrossed to S. jacobaea. Also, the range of PA ...
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Natural hybridization is increasingly recognized as an important process for the ecology and evolution of natural plant populations and species. There is a great need to initiate more studies based on natural populations in order to... more
Natural hybridization is increasingly recognized as an important process for the ecology and evolution of natural plant populations and species. There is a great need to initiate more studies based on natural populations in order to elucidate the possible role of hybrids in nature. The reproductive success of early generation hybrids can make or break hybrid lineages and may determine the genetic structure of hybrid swarms or the potential for gene flow through future generations, but studies of hybrid reproductive success are lacking. Here we measured components of male and female reproductive success in Senecio jacobaea and S. aquaticus (Asteraceae) species and F 1 hybrids between these species under laboratory conditions, and we measured reproductive output from crosses producin F 1, F 2, and backcross (BC) generation hybrids. F 1 hybrids were readily produced, and on average, the success of crosses producing subsequent generations (F 2, BC) decreased (though remained substantial...
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Secondary metabolites play a crucial role in plant defence. The metabolic profile of plants is determined by a complex set of interacting factors. It has been suggested that soil-borne microorganisms may trigger the plant’s defence system... more
Secondary metabolites play a crucial role in plant defence. The metabolic profile of plants is determined by a complex set of interacting factors. It has been suggested that soil-borne microorganisms may trigger the plant’s defence system thereby influencing aboveground defence against herbivores. We studied (1) the effects of belowground soil-borne microorganisms on pyrrolizidine alkaloids (PAs) in the shoots of different Jacobaea vulgaris genotypes and consequently, (2) the effect on aboveground herbivory by thrips. We used clonal plant individuals, propagated by tissue culture, of five genotypes originating from different West European populations; these genotypes included three Jacobineand two Erucifoline-chemotypes. Plants were grown on sterilized soil from Meijendel, a dune area near The Hague (the Netherlands). Plants were subjected to three different soil treatments: sterilized soil, sterilized soil inoculated with 5% of nonsterilized dune soil from Meijendel and sterilized ...
Goal: To provide an alternative to the usual bet-hedging explanation for delayed germination, one that takes account of known facts about germination in stable, fine-grained environments. Context: Small patches with local environmental... more
Goal: To provide an alternative to the usual bet-hedging explanation for delayed germination, one that takes account of known facts about germination in stable, fine-grained environments. Context: Small patches with local environmental conditions (microhabitats) such that seedlings can establish themselves are customarily called safe sites. Key Assumptions: We focus on a single species. Its safe sites become available randomly. Seeds that germinate outside safe sites all die as seedlings. All seeds are equal, i.e. their probability of dying over the year and probabilities to germinate when the right season is there do not depend on their age or any other aspect of their individual history. Moreover, we make the standard assumption of ESS theory that the population is genetically homogeneous but for the occasional mutant 'testing the ESS'. There is a trade-off between the germination probability in safe sites and the probability not to germinate outside safe sites. For germin...
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Background and aimsMany plant species grow better in sterilized than in live soil. Foliar application of SA mitigates this negative effect of live soil on the growth of the plant Jacobaea vulgaris. To examine what causes the positive... more
Background and aimsMany plant species grow better in sterilized than in live soil. Foliar application of SA mitigates this negative effect of live soil on the growth of the plant Jacobaea vulgaris. To examine what causes the positive effect of SA application on plant growth in live soils, we analyzed the effects of SA application on the composition of active rhizosphere bacteria in the live soil. Methods We studied this over four consecutive plant cycles (generations), using mRNA sequencing of the microbial communities in the rhizosphere of J. vulgaris. ResultsOur study shows that the composition of the rhizosphere bacterial communities of J. vulgaris greatly differed among generations. Application of SA resulted in both increases and decreases in a number of active bacterial genera in the rhizosphere soil, but the genera that were affected by the treatment differed among generations. In the first generation, there were no genera that were significantly affected by the SA treatment,...
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SummaryHerbivore population dynamics are strongly influenced by the interactions established through their shared host. Such plant-mediated interactions can occur between different herbivore species and between different life... more
SummaryHerbivore population dynamics are strongly influenced by the interactions established through their shared host. Such plant-mediated interactions can occur between different herbivore species and between different life developmental stages of the same herbivore. Yet, whether these interactions occur between leaf-feeding herbivores and their soil-dwelling pupae is unknown.We studied whether tomato (Solanum lycopersicum) leaf-herbivory by the American serpentine leafminer Lyriomiza trifolii affects the performance of conspecific pupae in the soil adjacent to the plant. To gain mechanistic insights, we performed insect bioassays with the jasmonate-deficient tomato mutant def-1 and its wild type, along with the analysis of phytohormones, gene expression and root volatiles.Leafminer metamorphosis in the soil was accelerated when wild type plants were attacked aboveground by conspecifics, but the opposite was observed in def-1. Changes in pupal developmental rate were mediated by b...
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Variation in the induction of plant defenses along the plant canopy can determine distribution and colonization of arthropod herbivores within the plant. In tomato, type VI glandular trichomes, which are epidermal defensive structures,... more
Variation in the induction of plant defenses along the plant canopy can determine distribution and colonization of arthropod herbivores within the plant. In tomato, type VI glandular trichomes, which are epidermal defensive structures, and their derived volatiles are induced by the phytohormone jasmonic acid (JA). How JA-mediated induction of these trichome-associated chemical defenses depends on the leaf developmental stage and correlates with resistance against herbivory is unknown. We showed that application of JA reduced thrips-associated damage, however the amplitude of this response was reduced in the fully developed leaves compared to those still developing. Although JA increased type-VI trichome densities in all leaf developmental stages, as well as JA-inducible defensive proteins, these increases were stronger in developing leaves. Remarkably, the concentration of trichome-derived volatiles was induced by JA to a larger degree in developing leaves than in fully developed le...
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In cultivated tomato (Solanum lycopersicum), increases in photosynthetically active radiation (PAR) induces type VI leaf glandular trichomes, which are important defensive structures against arthropod herbivores. Yet, how PAR affects the... more
In cultivated tomato (Solanum lycopersicum), increases in photosynthetically active radiation (PAR) induces type VI leaf glandular trichomes, which are important defensive structures against arthropod herbivores. Yet, how PAR affects the type VI trichome-associated leaf chemistry and its biological significance with respect to other photomorphogenic responses in this agronomically important plant species is unknown. We used the type VI trichome deficient tomato mutant odorless-2 (od-2) and its wild-type to investigate the influence of PAR on trichome-associated chemical defenses against thrips (Frankliniella occidentalis). High PAR increased thrips resistance in wild-type plants, but not in od-2. Furthermore, under high PAR thrips preferred od-2 over the wild-type. Both genotypes increased type VI trichome densities under high PAR. Wild-type plants, however, produced more trichome-associated allelochemicals, i.e. terpenes and phenolics, these being undetectable or barely altered in ...
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Ultraviolet (UV) radiation modulates plant defenses against herbivorous arthropods. We investigated how different UV exposure times and irradiance intensities affected tomato (Solanum lycopersicum) resistance against thrips (Frankliniella... more
Ultraviolet (UV) radiation modulates plant defenses against herbivorous arthropods. We investigated how different UV exposure times and irradiance intensities affected tomato (Solanum lycopersicum) resistance against thrips (Frankliniella occidentalis). We assessed UV effects on thrips-associated damage and host-selection, selected metabolites and phytohormone content, expression of defense-related genes, and trichome density and chemistry, the latter having a dual role in defense and UV protection. Short UV daily exposure times increased thrips resistance in the tomato cultivar 'Moneymaker'. This UV-mediated induction of tomato defenses against thrips was not explained by changes in the content of selected leaf polyphenols or terpenes, nor trichome-associated defenses. UV irradiance intensity also affected tomato resistance against thrips. Further analysis using the tomato mutants def-1, impaired in jasmonic acid (JA) biosynthesis, od-2, defective in the production of funct...
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Western flower thrips (WFT) (Pergande) is a key agricultural pest of cultivated tomatoes. Induced host plant resistance by activating jasmonic acid (JA) signaling pathway constitutes a promising method for WFT control. The phytotoxin... more
Western flower thrips (WFT) (Pergande) is a key agricultural pest of cultivated tomatoes. Induced host plant resistance by activating jasmonic acid (JA) signaling pathway constitutes a promising method for WFT control. The phytotoxin coronatine (COR), produced by pv. tomato DC3000 (), mimics the plant hormone JA-Isoleucine and can promote resistance against herbivorous arthropods. Here we determined the effect of and COR on tomato resistance against WFT, induction of JA and salicylic acid (SA) associated defenses, and plant chemistry. Additionally, we investigated the presence of other components in -derived and filtered culture medium, and their interactive effect with COR on tomato resistance to WFT. Our results showed that infiltration of COR or reduced WFT feeding damage in tomato plants. COR and induced the expression of JA-associated gene and protein marker. COR also induced expression of a SA-related responsive gene, although at much less magnitude. Activation of JA defenses ...
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Western flower thrips, Frankliniella occidentalis (Pergande), performance on intact chrysanthemums, Dendranthema grandiflora Tzvelev, was compared with that on the sap of squeezed chrysanthemums to examine the importance of plant chemical... more
Western flower thrips, Frankliniella occidentalis (Pergande), performance on intact chrysanthemums, Dendranthema grandiflora Tzvelev, was compared with that on the sap of squeezed chrysanthemums to examine the importance of plant chemical characteristics. Seventy-six percent of the variation in resistance of intact chrysanthemum cultivars could be explained by the variation in resistance of leaf sap. Thus, the chemical composition of chrysanthemum leaves was a significant factor in resistance to F. occidentalis . Because similarities in resistance were found between Rower sap, leaf sap, and intact, nonflowering chrysanthemums, we suggest there is a chemical resemblance among Rowers and leaves causing thrips resistance in chrysanthemum. Grafts were made between a resistant and susceptible cultivar (cultivars 2 and 15, respectively). A resistance factor was transported from the resistant scion to the susceptible stock, further indicating that chemical compounds play a major role in chrysanthemum resistance to thrips. Relative growth and survival of F. occidentalis larvae was correlated with larval longevity and the resulting feeding damage on intact chrysanthemum cultivars. Thus, growth and survival during the 1st few days can be used as a quick measure of thrips resistance in chrysanthemum.
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It has previously been demonstrated by others that acetone extracts of Senecio jacobaea (syn. Jacobaea vulgaris, common or tansy ragwort) test positive in the Salmonella/microsome mutagenicity test (Ames test). Pyrrolizidine alkaloids... more
It has previously been demonstrated by others that acetone extracts of Senecio jacobaea (syn. Jacobaea vulgaris, common or tansy ragwort) test positive in the Salmonella/microsome mutagenicity test (Ames test). Pyrrolizidine alkaloids (PAs) are thought to be responsible for these mutagenic effects. However, it was also observed that the major PA present in common ragwort, jacobine, produced a negative response (with and without the addition of rat liver S9) in Salmonella test strains TA98, TA100, TA1535 and TA1537. To investigate which compounds in the plant extracts were responsible for the positive outcome, the present study investigated the contents and mutagenic effects of methanol and acetone extracts prepared from dried ground S. jacobaea and Senecio inaequidens (narrow-leafed ragwort). Subsequently, a fractionation approach was set up in combination with LC-MS/MS analysis of the fractions. It was shown that the positive Ames test outcomes of S. jacobaea extracts are unlikely ...
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It is hard to assess experimentally the importance of microbial diversity in soil for the functioning of terrestrial ecosystems. An approach that is often used to make such assessment is the so-called dilution method. This method is based... more
It is hard to assess experimentally the importance of microbial diversity in soil for the functioning of terrestrial ecosystems. An approach that is often used to make such assessment is the so-called dilution method. This method is based on the assumption that the biodiversity of the microbial community is reduced after dilution of a soil suspension and that the reduced diversity persists after incubation of more or less diluted inocula in soil. However, little is known about how the communities develop in soil after inoculation. In this study, serial dilutions of a soil suspension were made and reinoculated into the original soil previously sterilized by gamma irradiation. We determined the structure of the microbial communities in the suspensions and in the inoculated soils using 454-pyrosequencing of 16S rRNA genes. Upon dilution, several diversity indices showed that, indeed, the diversity of the bacterial communities in the suspensions decreased dramatically, with Proteobacter...
Research Interests: Environmental Science, Biology, Biodiversity, Medicine, Multidisciplinary, and 12 moreMicrobial Population Biology, Applied Environmental Microbiology, Bacteria, Pyrosequencing, Species Richness, Soil Microbiology, Ribosomal DNA, Soil Water, Proteobacteria, Serial Dilution, Dilution, and bacteroidetes
Research Interests: Molecular Evolution, Biology, Medicine, Genetic Diversity, Biological Sciences, and 12 moreHigh Throughput Sequencing, Domestication, Introgression, Plant Roots, Genotype, Single Nucleotide Polymorphism, Subspecies, Genetic Markers, Daucus Carota, Gene expression profiling, Gene pool, and Medical and Health Sciences
Question: How can protandry of hermaphrodite flowers be an adaptive strategy? Does this differ for plant species with vertical (Digitalis purpurea) and non-vertical (Echium vulgare) inflorescences? Mathematical methods: We develop a... more
Question: How can protandry of hermaphrodite flowers be an adaptive strategy? Does this differ for plant species with vertical (Digitalis purpurea) and non-vertical (Echium vulgare) inflorescences? Mathematical methods: We develop a measure for quantifying rank order of visitation to flowers in the male and female stage. Key assumptions: Protandry is adaptive when it leads to female flowers being visited before
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Summary Some seeds of dioecious plants develop into male plants and others become females. Brothers and sisters can grow close together in the seed shadow of the maternal plant, which promotes sib-mating, and classical sex-allocation... more
Summary Some seeds of dioecious plants develop into male plants and others become females. Brothers and sisters can grow close together in the seed shadow of the maternal plant, which promotes sib-mating, and classical sex-allocation theory predicts a slight female bias among the seeds produced. We describe different ways of examining seed sex ratios and some of the pitfalls involved. The available direct (seed sex ratio) and indirect (proportions of male and female plants in the field) evidence suggests that the seed sex ratio is often close to 0.5, despite the fact that there is genetic variation in the seed sex ratio in some cases. The combination of significant sib-mating and an unbiased seed sex ratio is at odds with classical sex-allocation theory. Genetic conflict theory might provide new insights and should be a central theme in future research. The adult sex ratio can also become male or female biased due to sexually differential mortality, but this does not influence the seed sex ratio. Das Zahlenverhaltnis [0.5] kann aber nur dann rein herauskommen, wenn eine ganze Reihe von Bedingungen erfullt sind. The ratio [0.5] can, however, only emerge, when a whole range of conditions is satisfied. (Correns 1928) Introduction Like most animals, but unlike the great majority of plant species, dioecious plants have separate male and female individuals. Both male and female organs develop in each of their flowers, in separate floral whorls, but the development of one type is halted before maturity (Grant et al. 1994), with the timing of the arrest differing between species.
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Research Interests: Natural Products Chemistry, Chemical Ecology, Biology, Medicine, Biological Sciences, and 13 moreCell line, Environmental Sciences, Animals, Bioassay, Herbivory, CHEMICAL SCIENCES, Larva, Oxides, Plant Insect Interactions, Structure activity Relationship, Biological Assay, Pyrrolizidine Alkaloids, and Spodoptera litura
Plants produce a diversity of secondary metabolites (SMs) to protect them from generalist herbivores. On the other hand, specialist herbivores use SMs for host plant recognition, feeding and oviposition cues, and even sequester SMs for... more
Plants produce a diversity of secondary metabolites (SMs) to protect them from generalist herbivores. On the other hand, specialist herbivores use SMs for host plant recognition, feeding and oviposition cues, and even sequester SMs for their own defense. Therefore, plants are assumed to face an evolutionary dilemma stemming from the contrasting effects of generalist and specialist herbivores on SMs. To test this hypothesis, bioassays were performed with F2 hybrids from Jacobaea species segregating for their pyrrolizidine alkaloids (PAs), using a specialist flea beetle (Longitarsus jacobaeae) and a generalist slug (Deroceras invadens). Our study demonstrated that while slug feeding damage was negatively correlated with the concentration of total PAs and that of senecionine-like PAs, flea beetle feeding damage was not affected by PAs. It was positively correlated though, with leaf fresh weight. The generalist slug was deterred by senecionine-like PAs but the specialist flea beetle was...
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A coupling of above-ground plant diversity and below-ground microbial diversity has been implied in studies dedicated to assessing the role of macrophyte diversity on the stability, resilience, and functioning of ecosystems. Indeed,... more
A coupling of above-ground plant diversity and below-ground microbial diversity has been implied in studies dedicated to assessing the role of macrophyte diversity on the stability, resilience, and functioning of ecosystems. Indeed, above-ground plant communities have long been assumed to drive below-ground microbial diversity, but to date very little is known as to how plant species composition and diversity influence