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.

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The fish egg microbiome : diversity and activity against the oomycete pathogen Saprolegnia
Liu, Y. - \ 2016
University. Promotor(en): Francine Govers; Jos Raaijmakers, co-promotor(en): Irene de Bruijn. - Wageningen : Wageningen University - ISBN 9789462577671 - 169 p.
salmon - fish eggs - marine microorganisms - microbial diversity - bioinformatics - genomics - saprolegnia - oomycota - fish diseases - suppression - fungal antagonists - zalm - visseneieren - mariene micro-organismen - microbiële diversiteit - bio-informatica - genomica - oömycota - visziekten - onderdrukking - schimmelantagonisten

Y. Liu

Prof. dr. F. Govers (promotor); Prof. dr. J.M. Raaijmakers (promotor); Dr. I. de Bruijn (co-promotor); Wageningen University, 13 June 2016, 170 pp.

The fish egg microbiome: diversity and activity against the oomycete pathogen Saprolegnia

Emerging oomycete pathogens increasingly threaten biodiversity and food security. This thesis describes the study of the microbiome of Atlantic salmon (Salmo salar L.) eggs and analyses of the effects of infections by the oomycete pathogen Saprolegnia on the microbial architecture. A low incidence of Saprolegniosis was correlated with a relatively high abundance and richness of specific commensal Actinobacteria. Among the bacterial community, the isolates Frondihabitans sp. 762G35 (Microbacteriaceae) and Pseudomonas sp. H6 significantly inhibited hyphal attachment of Saprolegnia diclina to live salmon eggs. Chemical profiling showed that these two isolates produce furancarboxylic acid-derived metabolites and a lipopeptide viscosin-like biosurfactant, respectively, which inhibited hyphal growth of S. diclina in vitro. Among the fungal community, the fungal isolates obtained from salmon eggs were closely related to Microdochium lycopodinum/Microdochium phragmitis and Trichoderma viride. Both a quantitative and qualitative difference in the Trichoderma population between Saprolegnia-infected and healthy salmon eggs was observed, which suggested that mycoparasitic Trichoderma species could play a role in Saprolegnia suppression in aquaculture. This research provides a scientific framework for studying the diversity and dynamics of microbial communities to mitigate emerging diseases. The Frondihabitans, Pseudomonas and Trichoderma isolates, and/or their bioactive metabolites, are proposed as effective candidates to control Saprolegniosis.

Disease suppression in cropping systems
Postma, Joeke - \ 2015
strawberries - small fruits - plant protection - fungus control - phytophthora cactorum - suppression - mycorrhizas - composts - biological control - biochar
Early-season movement dynamics of phytophagous pest and natural enemies across a native vegetation-crop ecotone
Macfadyen, S. ; Hopkinson, J. ; Parry, H. ; Neave, M.J. ; Bianchi, F.J.J.A. ; Zalucki, M.P. ; Schellhorn, N.A. - \ 2015
Agriculture, Ecosystems and Environment 200 (2015). - ISSN 0167-8809 - p. 110 - 118.
managing ecosystem services - agricultural landscape - biological-control - spatial scales - dispersal - colonization - predators - ecology - parasitoids - suppression
There is limited understanding about how insect movement patterns are influenced by landscape features, and how landscapes can be managed to suppress pest phytophage populations in crops. Theory suggests that the relative timing of pest and natural enemy arrival in crops may influence pest suppression. However, there is a lack of data to substantiate this claim. We investigate the movement patterns of insects from native vegetation (NV) and discuss the implications of these patterns for pest control services. Using bi-directional interception traps we quantified the number of insects crossing an NV/crop ecotone relative to a control crop/crop interface in two agricultural regions early in the growing season. We used these data to infer patterns of movement and net flux. At the community-level, insect movement patterns were influenced by ecotone in two out of three years by region combinations. At the functional-group level, pests and parasitoids showed similar movement patterns from NV very soon after crop emergence. However, movement across the control interface increased towards the end of the early-season sampling period. Predators consistently moved more often from NV into crops than vice versa, even after crop emergence. Not all species showed a significant response to ecotone, however when a response was detected, these species showed similar patterns between the two regions. Our results highlight the importance of NV for the recruitment of natural enemies for early season crop immigration that may be potentially important for pest suppression. However, NV was also associated with crop immigration by some pest species. Hence, NV offers both opportunities and risks for pest management. The development of targeted NV management may reduce the risk of crop immigration by pests, but not of natural enemies.
Tomato yellow leaf curl virus resistance by ty-1 involves increased cytosine methylation of viral genomes and is compromised by cucumber mosaic virus infection
Butterbach, P.B.E. ; Verlaan, M.G. ; Dullemans, A.M. ; Lohuis, H. ; Visser, R.G.F. ; Bai, Y. ; Kormelink, R.J.M. - \ 2014
Proceedings of the National Academy of Sciences of the United States of America 111 (2014)35. - ISSN 0027-8424 - p. 12942 - 12947.
short interfering rna - dna methylation - geminivirus al2 - l2 proteins - adenosine kinase - gene - suppression - arabidopsis - plants - locus
Tomato yellow leaf curl virus (TYLCV) and related begomoviruses are a major threat to tomato production worldwide and, to protect against these viruses, resistance genes from different wild tomato species are introgressed. Recently, the Ty-1 resistance gene was identified, shown to code for an RNA-dependent RNA polymerase and to be allelic with Ty-3. Here we show that upon TYLCV challenging of resistant lines carrying Ty-1 or Ty-3, low virus titers were detected concomitant with the production of relatively high levels of siRNAs whereas, in contrast, susceptible tomato Moneymaker (MM) revealed higher virus titers but lower amounts of siRNAs. Comparative analysis of the spatial genomic siRNA distribution showed a consistent and subtle enrichment for siRNAs derived from the V1 and C3 genes in Ty-1 and Ty-3. In plants containing Ty-2 resistance the virus was hardly detectable, but the siRNA profile resembled the one observed in TYLCV-challenged susceptible tomato (MM). Furthermore, a relative hypermethylation of the TYLCV V1 promoter region was observed in genomic DNA collected from Ty-1 compared with that from (MM). The resistance conferred by Ty-1 was also effective against the bipartite tomato severe rugose begomovirus, where a similar genome hypermethylation of the V1 promoter region was discerned. However, a mixed infection of TYLCV with cucumber mosaic virus compromised the resistance. The results indicate that Ty-1 confers resistance to geminiviruses by increasing cytosine methylation of viral genomes, suggestive of enhanced transcriptional gene silencing. The mechanism of resistance and its durability toward geminiviruses under natural field conditions is discussed.
Nonlinearities Lead to Qualitative Differences in Population Dynamics of Predator-Prey Systems
Ameixa, O. ; Messelink, G.J. ; Kindlmann, P. - \ 2013
PLoS ONE 8 (2013)4. - ISSN 1932-6203
intraguild predation - biological-control - aphid populations - field experiments - interspecific competition - ecological communities - emergent impacts - natural enemies - suppression - consequences
Since typically there are many predators feeding on most herbivores in natural communities, understanding multiple predator effects is critical for both community and applied ecology. Experiments of multiple predator effects on prey populations are extremely demanding, as the number of treatments and the amount of labour associated with these experiments increases exponentially with the number of species in question. Therefore, researchers tend to vary only presence/absence of the species and use only one (supposedly realistic) combination of their numbers in experiments. However, nonlinearities in density dependence, functional responses, interactions between natural enemies etc. are typical for such systems, and nonlinear models of population dynamics generally predict qualitatively different results, if initial absolute densities of the species studied differ, even if their relative densities are maintained. Therefore, testing combinations of natural enemies without varying their densities may not be sufficient. Here we test this prediction experimentally. We show that the population dynamics of a system consisting of 2 natural enemies (aphid predator Adalia bipunctata (L.), and aphid parasitoid, Aphidius colemani Viereck) and their shared prey (peach aphid, Myzus persicae Sulzer) are strongly affected by the absolute initial densities of the species in question. Even if their relative densities are kept constant, the natural enemy species or combination thereof that most effectively suppresses the prey may depend on the absolute initial densities used in the experiment. Future empirical studies of multiple predator – one prey interactions should therefore use a two-dimensional array of initial densities of the studied species. Varying only combinations of natural enemies without varying their densities is not sufficient and can lead to misleading results.
Biological control of aphids in the presence of thrips and their enemies
Messelink, G.J. ; Bloemhard, C.M.J. ; Sabelis, M.W. ; Janssen, A. - \ 2013
BioControl 58 (2013)1. - ISSN 1386-6141 - p. 45 - 55.
intraguild predation - generalist predators - alternative prey - apparent competition - suppression - biocontrol - biodiversity - communities - parasitoids - predictions
Generalist predators are often used in biological control programs, although they can be detrimental for pest control through interference with other natural enemies. Here, we assess the effects of generalist natural enemies on the control of two major pest species in sweet pepper: the green peach aphid Myzus persicae (Sulzer) and the western flower thrips Frankliniella occidentalis (Pergande). In greenhouses, two commonly used specialist natural enemies of aphids, the parasitoid Aphidius colemani Viereck and the predatory midge Aphidoletes aphidimyza (Rondani), were released together with either Neoseiulus cucumeris Oudemans, a predator of thrips and a hyperpredator of A. aphidimyza, or Orius majusculus (Reuter), a predator of thrips and aphids and intraguild predator of both specialist natural enemies. The combined use of O. majusculus, predatory midges and parasitoids clearly enhanced the suppression of aphids and consequently decreased the number of honeydew-contaminated fruits. Although intraguild predation by O. majusculus on predatory midges and parasitoids will have affected control of aphids negatively, this was apparently offset by the consumption of aphids by O. majusculus. In contrast, the hyperpredator N. cucumeris does not prey upon aphids, but seemed to release aphids from control by consuming eggs of the midge. Both N. cucumeris and O. majusculus did not affect rates of aphid parasitism by A. colemani. Thrips were also controlled effectively by O. majusculus. A laboratory experiment showed that adult predatory bugs feed on thrips as well as aphids and have no clear preference. Thus, the presence of thrips probably promoted the establishment of the predatory bugs and thereby the control of aphids. Our study shows that intraguild predation, which is potentially negative for biological control, may be more than compensated by positive effects of generalist predators, such as the control of multiple pests, and the establishment of natural enemies prior to pest invasions. Future work on biological control should focus on the impact of species interactions in communities of herbivorous arthropods and their enemies.
Functional analysis of the omega-6 fatty acid desaturase (CaFAD2) gene family of the oil seed crop Crambe abyssinica using RNAi-mediated gene silencing
Cheng, J. ; Zhu, L. ; Salentijn, E.M.J. ; Huang, B. ; Gruber, J. ; Dechesne, A.C. ; Krens, F.A. ; Qi, W. ; Visser, R.G.F. ; Loo, E.N. van - \ 2013
BMC Plant Biology 13 (2013). - ISSN 1471-2229
high oleic-acid - erucic-acid - brassica-napus - fad2 gene - fae1 gene - carrier protein - expression - suppression - metabolism - mutations
Background Crambe abyssinica produces high erucic acid (C22:1, 55-60 %) in the seed oil, which can be further increased by reduction of polyunsaturated fatty acid (PUFA) levels. The omega-6 fatty acid desaturase enzyme (FAD2) is known to be involved in PUFA biosynthesis. In crambe, three CaFAD2 genes, CaFAD2-C1, CaFAD2-C2 and CaFAD2-C3 are expressed. Results The individual effect of each CaFAD2 gene on oil composition was investigated through studying transgenic lines (CaFAD2-RNAi) for differential expression levels in relation to the composition of seed-oil. Six first generation transgenic plants (T1) showed C18:1 increase (by 6% to 10.5 %) and PUFA reduction (by 8.6% to 10.2 %). The silencing effect in these T1-plants ranged from the moderate silencing (40% to 50% reduction) of all three CaFAD2 genes to strong silencing (95% reduction) of CaFAD2-C3 alone. The progeny of two T1-plants (WG4-4 and WG19-6) was further analysed. Four or five transgene insertions are characterized in the progeny (T2) of WG19-6 in contrast to a single insertion in the T2 progeny of WG4-4. For the individual T2-plants of both families (WG19-6 and WG4-4), seed-specific silencing of CaFAD2-C1 and CaFAD2-C2 was observed in several individual T2-plants but, on average in both families, the level of silencing of these genes was not significant. A significant reduction in expression level (P <0.01) in both families was only observed for CaFAD2-C3 together with significantly different C18:1 and PUFA levels in oil. Conclusions CaFAD2-C3 expression is highly correlated to levels of C18:1 (r = -0.78) and PUFA (r = 0.75), which suggests that CaFAD2-C3 is the most important one for changing the oil composition of crambe.
Isolation and characterization of the omega-6 fatty acid desaturase (FAD2) gene family in the allohexaploid oil seed crop Crambe abyssinica Hochst
Cheng, J. ; Salentijn, E.M.J. ; Huang Bangquan, ; Krens, F.A. ; Dechesne, A.C. ; Visser, R.G.F. ; Loo, E.N. van - \ 2013
Molecular Breeding 32 (2013)3. - ISSN 1380-3743 - p. 517 - 531.
brassica-napus l. - high oleic-acid - erucic-acid - expression - genome - biosynthesis - suppression - stability - evolution - varieties
Crambe (Crambe abyssinica Hochst ex. R. E. Fries) is an ideal crop for industrial oil production because of its high erucic acid content (C22:1, approx. 60 %) in its seed oil. The value of crambe oil can be improved by increasing C22:1 content or reducing polyunsaturated fatty acids (PUFA). The FAD2 gene plays a critical role in PUFA biosynthesis. To identify targets for breeding, we characterized FAD2 in crambe for copy number and expression profile. Seven copies of FAD2 were detected in allohexaploid crambe. Three genes (CaFAD2-C1, -C2 and -C3) were expressed in multiple tissues, including root, seedling, leaf, flower, bud and developing seeds. In developing seeds, the expression of these genes was upregulated with CaFAD2-C3, being expressed predominantly with a peak at 20 days after pollination. This gene is therefore a promising candidate gene for determining PUFA levels in seed oil. Four other FAD2 genes were considered to be “pseudo-genes” as they harbour internal stop codons and were not expressed. Among the six crambe varieties with consistent variation in oil composition, no nucleotide polymorphisms were found in the CaFAD2-C1, -C2 and -C3 genes. In seeds at 30 days after pollination, statistically significant expression level polymorphisms for only one gene, CaFAD2-C2, was found among the varieties. However, although significantly different, the difference in expression was small and did not explain the variation in oil composition. Given the absence of genetic variation in CaFAD2 genes in crambe breeding lines, breeding for high erucic acid content calls for a molecular breeding approach whereby mutations are chemically induced to increase the genetic variation.
Verkenning van mogelijkheden voor plantweerbaarheid tegen bladluis in paprika
Messelink, G.J. ; Bloemhard, C.M.J. ; Kok, L.W. - \ 2013
Bleiswijk : Wageningen UR Glastuinbouw (Rapporten WUR GTB 1242) - 22
biologische bestrijding - myzus persicae - reductie - paprika's - capsicum annuum - onderdrukking - insectenplagen - populatiegroei - immuniteitsreactie - glastuinbouw - nederland - biological control - reduction - sweet peppers - suppression - insect pests - population growth - immune response - greenhouse horticulture - netherlands
Het doel van dit onderzoek was om maatregelen te vinden waarmee bladluis in paprika via de plant geremd kan worden. Hoewel er in de literatuur duidelijke aanwijzingen zijn dat de plantweerbaarheid verhoogd kan worden, is dit niet naar voren gekomen in dit onderzoek. Een verhoogde kaliumgift, wormenhumus en plantversterkers op basis van huminezuren of salicylzuur konden géén significante remming geven van bladluis. Wel is het omgekeerde gevonden: wanneer veen voor 20 procent werd gemengd met wormenhumus resulteerde dit in 35 procent meer populatiegroei van rode perzikluis ten opzichte van onbehandelde planten op alleen veen. Dit onderzoek heeft verder laten zien dat de reactie van bladluis op de plantbehandeling zelfs binnen een soort kan variëren. Het groene fenotype van perzikluis reageerde anders dan het rode fenotype, waarschijnlijk omdat de positie die deze bladluizen innemen op de plant ook anders is.
Integrated mosquito larval source management reduces larval numbers in two highland villages in western Kenya
Imbahale, S.S. ; Githeko, A. ; Mukabana, W.R. ; Takken, W. - \ 2012
BMC Public Health 12 (2012). - ISSN 1471-2458
insecticide-treated nets - malaria vector control - dar-es-salaam - microbial larvicides - tanzania - transmission - suppression - epidemics - association - temperature
Background: In western Kenya, malaria remains one of the major health problems and its control remains an important public health measure. Malaria control is by either use of drugs to treat patients infected with malaria parasites or by controlling the vectors. Vector control may target the free living adult or aquatic (larval) stages of mosquito. The most commonly applied control strategies target indoor resting mosquitoes. However, because mosquitoes spend a considerable time in water, targeting the aquatic stages can complement well with existing adult control measures. Methods: Larval source management (LSM) of malaria vectors was examined in two villages i.e. Fort Ternan and Lunyerere, with the aim of testing strategies that can easily be accessed by the affected communities. Intervention strategies applied include environmental management through source reduction (drainage of canals, land levelling or by filling ditches with soil), habitat manipulation (by provision of shading from arrow root plant), application of Bacillus thuringiensis var israelensis (Bti) and the use of predatory fish, Gambusia affinis. The abundance of immature stages of Anopheles and Culex within intervention habitats was compared to that within non-intervention habitats. Results: The findings show that in Fort Ternan no significant differences were observed in the abundance of Anopheles early and late instars between intervention and non-intervention habitats. In Lunyerere, the abundance of Anopheles early instars was fifty five times more likely to be present within non-intervention habitats than in habitats under drainage. No differences in early instars abundance were observed between non-intervention and habitats applied with Bti. However, late instars had 89 % and 91 % chance of being sampled from non-intervention rather than habitats under drainage and those applied with Bti respectively. Conclusion: Most of these interventions were applied in habitats that arose due to human activities. Involvement of community members in control programs would be beneficial in the long term once they understand the role they play in malaria transmission. Apart from the need for communities to be educated on their role in malaria transmission, there is a need to develop and test strategies that can easily be accessed and hence be used by the affected communities. The proposed LSM strategies target outdoor immature mosquitoes and hence can complement well with control measures that target indoor resting vectors. Therefore inclusion of LSM in Integrated Vector Management (IVM) program would be beneficial.
Accurate mass screening of pharmaceuticals and fungicides in water by U-HPLC-Exactive Orbitrap MS
Chitescu, C.L. ; Oosterink, E. ; Jong, J. de; Stolker, A.A.M. - \ 2012
Analytical and Bioanalytical Chemistry 403 (2012)10. - ISSN 1618-2642 - p. 2997 - 3011.
liquid-chromatography - antifungal agents - surface-water - spectrometry - antibiotics - groundwater - suppression - resistance - residues - time
The use of pharmaceuticals in livestock production is a potential source of surface water, groundwater and soil contamination. Possible impacts of antibiotics on the environment include toxicity and the emergence of antibiotic resistance. Monitoring programs are required to record the presence of these substances in the environment. A rapid, versatile and selective multi-method was developed and validated for screening 43 pharmaceutical and fungicides compounds, in surface and groundwater, in one single full-scan MS method, using benchtop U-HPLC-Exactive Orbitrap MS at 50,000 (FWHM) resolution. Detection was based on calculated exact masses and on retention time. Sample volume, pH conditions and solid-phase extraction (SPE) sample clean-up conditions were optimized. In the final method, 74 % of the compounds had recoveries higher than 80 %, 15 % of the compounds had recoveries between 60 % and 80 %, and 7 % of the compounds had recoveries between 40 % and 50 %. One of the compounds (itraconazole) had a recovery lower than 10 % and nystatin was not detected. The level of detection was 10 ng L-1 for 61 % of the compounds, 50 ng L-1 for 32 % and 100 ng L-1 for 5%. In-house validation, based on EU guidelines, proves that the detection capability CC beta is lower than 10 ng L-1 (for beta error 5 %) for 37 % of the compounds, lower than 50 ng L-1 for 35 % of the compounds and lower than 100 ng L-1 for 14 % of compounds. This study demonstrates that the ultra-high resolution and reliable mass accuracy of Exactive Orbitrap MS permits the detection of pharmaceutical residues in a concentration range of 10-100 ng L-1, applying a post target screening approach, in the multi-method conditions.
Diameter Growth of Juvenile Trees after Gap Formation in a Bolivian Rain Forest: Responses are Strongly Species-specific and Size-dependent.
Soliz-Gamboa, C.C. ; Sandbrink, A. ; Zuidema, P.A. - \ 2012
Biotropica 44 (2012)3. - ISSN 0006-3606 - p. 312 - 320.
tropical forest - ring analysis - canopy - increment - dynamics - patterns - release - rates - suppression - disturbance
We evaluated growth responses to gap formation for juvenile individuals of three canopy rain forest species: Peltogyne cf. heterophylla, Clarisia racemosa and Cedrelinga catenaeformis. Gaps were formed during selective logging operations 7 yr before sampling in a Bolivian rain forest. We collected wood samples for tree-ring analyses at different distances to the stump (40 m) and from trees with different diameters (5–30 cm diameter at breast height [dbh]). Tree-rings width was measured in at least two radii and converted to average diameter growth. Changes in 7-yr median diameter growth before and after selective logging were analyzed. Diameter growth rates significantly increased by 0.7–0.8 mm/yr after gap formation for P. heterophylla and C. catenaeformis, but not for C. racemosa. We applied a multiple regression analysis to explain variation in growth responses of P. heterophylla and C. catenaeformis by distance to logging gap and tree size. For P. heterophylla we found that growth increase occurring close to logging gaps was strongest for large juvenile trees (20–25 cm dbh) and almost absent in small juveniles. For C. catenaeformis, variation in growth responses was not related to tree size or distance to gaps. Our results show that growth responses to gap formation strongly differ across species and tree sizes. This finding calls for caution in the interpretation of growth releases in tree-ring series, as gap formation does not necessarily invoke growth responses and if such growth responses occur, their strength is species- and size specific.
Stepwise screening of microorganisms for commercial use in biological control of plant pathogenic fungi and bacteria. Biological Control
Köhl, J. ; Postma, J. ; Nicot, P. ; Ruocco, M. - \ 2011
Biological Control 57 (2011)1. - ISSN 1049-9644 - p. 1 - 12.
biocontrol agents - coniothyrium-minitans - botrytis-cinerea - new-zealand - selection - antagonists - soil - rhizosphere - suppression - diseases
The development of new biocontrol products against plant diseases requires screening of high numbers of candidate antagonists. Antagonists for commercial use have to fulfill many different requirements. Besides being active against the specific targeted plant pathogens they must be safe and cost-effective. Important criteria besides pathogenic efficacy are market size, ecological characteristics, production costs, safety, environmental risks, and possibilities for intellectual property protection. A stepwise screening program considering these very different aspects is proposed. Research highlights ¿ Stepwise screening of microorganisms for commercial use in biocontrol. ¿ Multi-disciplinary approach considering many aspects besides control efficacy. ¿ Examples for protocols for use in screening programmes illustrating this approach. Article Outline 1. Introduction 2. Screening steps 2.1. Step 1: Assessment of targeted crop, disease and markets 2.2. Step 2: Origin and isolation of candidate antagonists 2.3. Step 3: Preliminary assessments in rapid-throughput screening systems 2.4. Step 4: Identification of candidate antagonists and database mining 2.5. Step 5: Efficacy testing against pathogens on plants 2.6. Step 6: Preliminary tests on mass production 2.7. Step 7: Development and testing of a pilot formulation and estimation of registration costs 2.8. Step 8: Field testing and upscaling mass production 2.9. Step 9: Integration into cropping systems Discussion
BNYVV-derived dsRNA confers resistance to rhizomania disease of sugar beet as evidenced by a novel transgenic hairy root approach
Pavli, R. ; Panopoulos, N.J. ; Goldbach, R.W. ; Skaracis, G.N. - \ 2010
Transgenic Research 19 (2010)5. - ISSN 0962-8819 - p. 915 - 922.
double-stranded-rna - yellow-vein-virus - beta-vulgaris l - gene-expression - mediated resistance - antisense rna - interference - plants - suppression - transformation
Agrobacterium rhizogenes-transformed sugar beet hairy roots, expressing dsRNA from the Beet necrotic yellow vein virus replicase gene, were used as a novel approach to assess the efficacy of three intron-hairpin constructs at conferring resistance to rhizomania disease. Genetically engineered roots were similar in morphology to wild type roots but were characterized by a profound abundancy, rapid growth rate and, in some cases, plagiotropic development. Upon challenge inoculation, seedlings showed a considerable delay in symptom development compared to untransformed or vector-transformed seedlings, expressing dsRNA from an unrelated source. The transgenic root system of almost all seedlings contained no or very low virus titer while the non-transformed aerial parts of the same plants were found infected, leading to the conclusion that the hairy roots studied were effectively protected against the virus. This readily applicable novel method forms a plausible approach to preliminarily evaluate transgenic rhizomania resistance before proceeding in transformation and whole plant regeneration of sugar beet, a tedious and time consuming process for such a recalcitrant crop species
Spatially optimal habitat management for enhancing natural control of an invasive agricultural pest: soybean aphid
Zhang, W. ; Werf, W. van der; Swinton, S.M. - \ 2010
Resource and Energy Economics 32 (2010)4. - ISSN 0928-7655 - p. 551 - 565.
land-use - biological-control - landscape - predators - glycines - optimization - suppression - diversity - wildlife - density
By their direct effects on private profitability, invasive agricultural pests create special incentives for management that set them apart from other categories of invasive species. One attractive nonchemical management approach for agricultural pests relies upon biological control by natural enemies. By improving the habitat of natural enemies of invasive agricultural pests, biological pest control can become privately attractive. This study develops a spatial optimization model to explore economically optimal spatial configuration of natural enemy habitat in agricultural landscapes. The model is applied to the management of soybean aphid (Aphis glycines), a recent invasive pest species of soybean production systems in the North Central region of the United States. Results indicate that non-crop habitat management can be a promising pest management option for organic cropping systems. Under current prices, however, habitat management tends to reduce net returns for conventional farms. Both area and configuration of non-crop habitats affect economic performance, with the greatest value coming from small, scattered areas of habitat
Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome
Baxter, L. ; Tripathy, S. ; Ishaque, N. ; Boot, N. ; Cabral, A. ; Kemen, E. ; Thines, M. ; Ah-Fong, A. ; Anderson, R. ; Badejoko, W. ; Bittner-Eddy, P. ; Boore, J.L. ; Chibucos, M.C. ; Coates, M. ; Dehal, P. ; Delehaunty, K. ; Dong, S. ; Downton, P. ; Dumas, B. ; Fabro, G. ; Fronick, C. ; Fuerstenberg, S.I. ; Fulton, L. ; Gaulin, E. ; Govers, F. ; Hughes, L. ; Humphray, S. ; Jiang, R.H.Y. ; Judelson, H. ; Kamoun, S. ; Kyung, K. ; Meijer, H.J.G. ; Minx, P. ; Morris, P. ; Nelson, J. ; Phuntumart, V. ; Qutob, D. ; Rehmany, A. ; Rougon-Cardoso, A. ; Ryden, P. ; Torto-Alalibo, T. ; Studholme, D. ; Wang, Y. ; Win, J. ; Wood, J. ; Clifton, S.W. ; Rogers, J. ; Ackerveken, G. van den; Jones, J.D.G. ; McDowell, J.M. ; Beynon, J. ; Tyler, B.M. - \ 2010
Science 330 (2010)6010. - ISSN 0036-8075 - p. 1549 - 1551.
sojae-effector avr1b - downy mildew - phytophthora - plant - thaliana - cells - suppression - parasites - proteins - delivery
Many oomycete and fungal plant pathogens are obligate biotrophs, which extract nutrients only from living plant tissue and cannot grow apart from their hosts. Although these pathogens cause substantial crop losses, little is known about the molecular basis or evolution of obligate biotrophy. Here, we report the genome sequence of the oomycete Hyaloperonospora arabidopsidis (Hpa), an obligate biotroph and natural pathogen of Arabidopsis thaliana. In comparison with genomes of related, hemibiotrophic Phytophthora species, the Hpa genome exhibits dramatic reductions in genes encoding (i) RXLR effectors and other secreted pathogenicity proteins, (ii) enzymes for assimilation of inorganic nitrogen and sulfur, and (iii) proteins associated with zoospore formation and motility. These attributes comprise a genomic signature of evolution toward obligate biotrophy
Effects of compost amendment and the biocontrol agent Clonostachys rosea on the development of charcoal rot (Macrophomina phaseolina) on cowpea
Ndiaye, M. ; Termorshuizen, A.J. ; Bruggen, A.H.C. van - \ 2010
Journal of plant pathology - Formerly Rivista di patologia vegetale 92 (2010)1. - ISSN 1125-4653 - p. 173 - 180.
soil microbial communities - organic amendments - biological-control - root-rot - sclerotia - survival - solarization - suppression - management - pathogens
Macrophomina phaseolina is a destructive pathogen causing charcoal rot of cowpea and other crops in the semi- arid areas of the Sahel (north-west Africa). Chemical management is not feasible in conditions of subsistence farming, and the plurivorous nature of the fungus limits the effectiveness of some cultural methods. This study aimed at identifying the effects of composting on the survival of M. phaseolina and of soil application of compost alone or in combination with the biocontrol agent Clonostachys rosea on inoculum density of M. phaseolina and on cowpea production. Inside the compost heap with diseased cowpea residues, the temperature reached 52 to 60°C and completely destroyed M. phaseolina microsclerotia. Addition of compost to planting holes significantly suppressed charcoal rot disease. Among the doses tested 6 tonnes of compost alone or supplemented with 50 kg NPK ha-1 resulted in 28-45% lower Area-Under- the-Disease-Progress-Curves (AUDPC) and 43-66% higher cowpea production. The addition of compost combined with C. rosea in the planting holes reduced the AUDPC up to 4-fold and increased the grain yield 2-5- fold. The best treatment was a mixture of two C. rosea isolates and the compost.
Effects of different soil amendments on bacterial wilt caused by Ralstonia solanacearum (Smith) Yabuuchi and on the yield of tomato (Lycopersicon esculentum Mill)
Yadessa, G.B. ; Bruggen, A.H.C. van; Ocho, F.L. - \ 2010
Journal of plant pathology - Formerly Rivista di patologia vegetale 92 (2010). - ISSN 1125-4653 - p. 439 - 450.
potato brown-rot - pseudomonas-solanacearum - biological-control - race-3 biovar-2 - suppression - severity - survival - strains - rhizobacteria - management
Ralstonia solanacearum race 3 biovar 2 (phylotype II) is the causal agent of bacterial wilt of tomato, the most destructive bacterial disease of this crop in Ethiopia for which no effective control measures are available. In this study, the effects of amending topsoil with three different levels (1, 5 and 10%) of cocopeat, farmyard manure (FYM) compost and green compost, and two levels of bacterial inoculations were tested on infection of tomato by R. solanacearum compared to non-inoculated treatments. Non-amended topsoil with and without R. solanacearum were included as control treatments. Survival of and infection by R. solanacearum and yield-associated agronomic responses were used for evaluation along with physico-chemical and biological characteristics of amended soils. Amendments resulted in changes in physico-chemical properties (such as electrical conductivity, organic matter content, total carbon, dissolved organic carbon, NH(4)(+), NO(3)(-)) and microbial activity of the amended soil and the effects were found to be higher at the higher rate of application. Effects on disease suppression and survival of the pathogen in the soil differed depending on amendment type and application rate. Higher disease severity was recorded in soil amended with 10% green compost compared to the control treatment. Complete suppression of R. solanacearum was observed in pots amended with 5 and 10% farm yard manure (FYM), 1% green compost and 10% cocopeat. Absence of disease at the highest rate of FYM was supported by a lower number of culturable R. solanacearum bacteria recovered from rhizosphere soil two months post-inoculation in soil amended with 10% FYM. Soil amended with 10% FYM gave higher root and above-ground dry weight. Moreover, FYM added to topsoil at 5 and 10% gave significantly higher above-ground fresh weight. This study indicated that amending topsoil with different types and rates of amendment can suppress bacterial wilt severity and pathogen survival in the soil. Amendments also enhanced tomato yield, the higher rates of amendments being the most effective except green compost at 10% which gave a 27% lower yield compared with the higher rate of FYM. Among the amendments tested, FYM at 5 or 10% would be an interesting option to manage R. solanacearum in the major tomato-growing regions of Ethiopia. However, the mechanisms of disease suppression at higher rates of FYM need to be investigated.
Insect oviposition behavior affects the evolution of adaptation to Bt crops: consequences for refuge policies
Jongsma, M.A. ; Gould, F. ; Legros, M. ; Yang, L. ; Loon, J.J.A. van; Dicke, M. - \ 2010
Evolutionary Ecology 24 (2010)5. - ISSN 0269-7653 - p. 1017 - 1030.
armigera hubner lepidoptera - helicoverpa-zea lepidoptera - transgenic cotton - diamondback moth - pink-bollworm - resistance - noctuidae - field - suppression - management
The major lepidopteran insect pests of cotton and maize harbor intra-specific variation for behavior determining the selection of host plants for oviposition. Yet, the consequences of behavioral adaptation for fitness have neither been modeled nor monitored for Bt cotton and maize crops, the most widely grown transgenic herbivore-resistant plants. Here, we present a general two-locus heuristic model to examine potential outcomes of natural selection when pest populations initially have low frequencies of alleles for both physiological and behavioral adaptation to Bt crops. We demonstrate that certain ecological conditions allow for the evolution of behavioral choices favoring alternative oviposition hosts that limit the increase in resistance alleles, even when they are phenotypically dominant. These results have implications for current refuge policies, which should be adapted to promote the evolution of certain behavioral choices for alternative oviposition hosts in addition to dilution of physiological resistance alleles. Collection of data on oviposition host preference as a component of monitoring schemes will provide important insights into mechanisms underlying the durability of Bt-transgenic host-plant resistance
Biological control of Pythium aphanidermatum in cucumber with a combined application of Lysobacter enzymogenes strain 3.1T8 and chitosan
Postma, J. ; Stevens, L.H. ; Wiegers, G.L. ; Davelaar, E. ; Nijhuis, E.H. - \ 2009
Biological Control 48 (2009)3. - ISSN 1049-9644 - p. 301 - 309.
growth-promoting rhizobacteria - damping-off disease - root-rot - bacteria - plants - rhizosphere - suppression - biocontrol - rockwool - pepper
Pythium aphanidermatum (Edson) Fitzp., causing root and crown rot in cucumber, was successfully managed by Lysobacter enzymogenes strain 3.1T8. Greenhouse experiments were performed with cucumber plants grown in rockwool blocks up to 5 weeks with a recirculated nutrient solution. Application of L. enzymogenes 3.1T8 in combination with chitosan (the deacetylated derivative of chitin) reduced the number of diseased plants by 50–100% in four independent experiments relative to the Pythium control. Application of chitosan or the bacterial inoculant alone was not effective. Washed bacterial cells plus chitosan inhibited Pythium-induced disease, but the supernatant without bacterial cells combined with chitosan was not effective. The most effective and convenient type of commercially available chitosan was selected. Chitosan disappeared from the hydroponic system within 24 h after application, which we attribute to enzyme expression of L. enzymogenes 3.1T8 induced by the exposure to chitosan. Plate counts of the nutrient solution on a general bacterial medium showed the dominance of the inoculated strain, and an increased bacterial population growing on chitin and chitosan as single carbon source. The population density of L. enzymogenes 3.1T8 on the cucumber roots was investigated with a strain specific real-time TaqMan PCR. Highest chitosan concentrations applied (0.1 and 0.03 g/plant) resulted in the highest numbers of L. enzymogenes 3.1T8 present on roots; i.e. 108–109 cells/g root. Substantially higher numbers of bacterial cells were observed by scanning electron microscopy after application of chitosan; no morphological or other qualitative differences were found. The results indicate that addition of chitosan enhanced the biocontrol efficacy of L. enzymogenes 3.1T8; either chitosan serves as C- and N-source for the antagonist, induces antagonistic gene expression, or both. Keywords: Biological control; Lysobacter enzymogenes; Chitosan; Synergistic effect; Quantitative PCR; Root colonization
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