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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    Food capture, transport and swallowing in white-spotted bamboo sharks (Chiloscyllium plagiosum)
    Meer, N.M.M.E. van; Weller, H.I. ; Manafzadeh, A.R. ; Kaczmarek, E.B. ; Scott, B. ; Gussekloo, S.W.S. ; Wilga, C.D. ; Brainerd, E.L. ; Camp, A.L. - \ 2019
    In: SCIB 2019 Annual Meeting Abstracts. - Tampa : Society for Experimental Biology - p. 414 - 414.
    Intra-oropharyngeal food transport and swallowing in white-spotted bamboo sharks
    Meer, Noraly M.M.E. van; Weller, Hannah I. ; Manafzadeh, Armita R. ; Kaczmarek, Elska B. ; Scott, Bradley ; Gussekloo, Sander W.S. ; Wilga, Cheryl D. ; Brainerd, Elizabeth L. ; Camp, Ariel L. - \ 2019
    Journal of Experimental Biology 2019 (2019)222. - ISSN 0022-0949 - 9 p.

    Despite the importance of intraoral food transport and swallowing, relatively few studies have examined the biomechanics of these behaviors in non-tetrapods, which lack a muscular tongue. Studies show that elasmobranch and teleost fishes generate water currents as a ‘hydrodynamic tongue’ that presumably transports food towards and into the esophagus. However, it remains largely unknown how specific musculoskeletal motions during transport correspond to food motion. Previous studies of white-spotted bamboo sharks (Chiloscyllium plagiosum) hypothesized that motions of the hyoid, branchial arches and pectoral girdle, generate caudal motion of the food through the long oropharynx of modern sharks. To test these hypotheses, we measured food and cartilage motion with XROMM during intra-oropharyngeal transport and swallowing (N=3 individuals, 2–3 trials per individual). After entering the mouth, food does not move smoothly toward the esophagus, but rather moves in distinct steps with relatively little retrograde motion. Caudal food motion coincides with hyoid elevation and a closed mouth, supporting earlier studies showing that hyoid motion contributes to intra-oropharyngeal food transport by creating caudally directed water currents. Little correspondence between pectoral girdle and food motion was found, indicating minimal contribution of pectoral girdle motion. Transport speed was fast as food entered the mouth, slower and step-wise through the pharyngeal region and then fast again as it entered the esophagus. The food's static periods in the step-wise motion and its high velocity during swallowing could not be explained by hyoid or girdle motion, suggesting these sharks may also use the branchial arches for intra-oropharyngeal transport and swallowing
    Genomic Breeding Value Estimation in countries without large-scale genotyping: merging two training populations to increase genomic reliabilities
    Stoop, W.M. ; Calus, M.P.L. ; Schrooten, C. ; Gombacsi, P. ; Weller, J.I. ; Jong, G. de - \ 2018
    In: Proceedings of the 11th World Congress on Genetics Applied to Livestock Production. - WCGALP - 6 p.
    For countries without large-scale genotyping, it is a challenge to implement an effective genomic evaluation system. Breeding company CRV has merged its bull training population with two such countries to build a training population of significance, and provide genomic software. Results show 6-20 times increase in training population adding the CRV bulls. The b-factors of the model(s) improve for most traits for both countries, with an exception for Israeli calving traits. Finally, the added reliability of genomic information, measured as equivalent daughter contributions, is on average four times bigger in the training populations including the CRV bulls, as compared to using only bulls genotyped by the country itself. Validation success may depend on the heritability of the trait, the estimated between-country correlation for the trait, the kinship between the two populations, as well as between the training population and the validation population, and -implicit in that between-country kinship- the past selection criteria as reflected in the similarities in the total merit indices over time.
    Conjectural ‘Landscape Cities’ and the Gap of Imagination
    Abbott, Mick ; Roncken, P.A. ; Lee, Woody ; Pickett, Tenille - \ 2018
    Landscape Review 18 (2018)1. - ISSN 2253-1440 - 11 p.
    This report discusses the results and layout of a design research studio focused on applying methods related to speculation and imagination. Three main findings are presented: a review of six methods that can direct designerly speculations; development of 11 'landscape city' scenarios; and a discussion of the role design 'challenges' can play in studio research settings. These outcomes reveal that creative discoveries are not bound to elaborative final outcomes only. Some of the intermediate results, particularly those with explicit habit-breaking effects on the imagination of the designers involved, and the process-driven materials produced, are equally valuable. This report seeks a reconsideration of the presentation and sharing of research results through designing, moving from the familiar focus on high-end, 'glossy' finalisations towards those more revealing of intermediate and abstract products of inquiry. In conclusion, an argument is made as to what can be framed as an 'imagination gap' that suggests possibility operates as a counterpoint to empiricism. L andscape architecture has a speculative role in imagining diverse, innovative and environmentally responsive futures (Waldheim, 2012; Weller, 2009). In its research, the discipline is prone to critique by a scientific community that either disqualifies speculative approaches or does not know how to assess the associative imaginations on which most design processes depend. Such critique is constructive as it urges clarification of what is both unique and systematic about design-directed research.
    Validation of four real-time TaqMan PCRs for the detection of Ralstonia solanacearum and/or Ralstonia pseudosolanacearum and/or Clavibacter michiganensis subsp. sepedonicus in potato tubers using a statistical regression approach
    Vreeburg, R.A.M. ; Zendman, A.J.W. ; Pol, A. ; Verheij, E. ; Nas, M. ; Kooman-Gersmann, M. - \ 2018
    EPPO Bulletin 48 (2018)1. - ISSN 0250-8052 - p. 86 - 96.
    A new DNA extraction method and a new multiplex real-time TaqMan PCR test for detection of Ralstonia solanacearum, Ralstonia pseudosolanacearum and Clavibacter michiganensis subsp. sepedonicus in asymptomatic potato tubers are presented. This new multiplex PCR and three published TaqMan PCRs for detection of R. solanacearum and/or R. pseudosolanacearum and/or R. syzygii spp. and/or C. michiganensis subsp. sepedonicus were validated using linear regression analysis for estimating the Ct values and its variation at 5 × 103 bacteria mL−1. The three published PCRs that have been validated are Massart et al. (2014, detecting R. solanacearum and C. michiganensis subsp. sepedonicus), Weller et al. (1999, detecting R. solanacearum, R. pseudosolanacearum and R. syzygii spp.) and Gudmestad et al. (2009, detecting C. michiganensis subsp. sepedonicus). All tested PCRs were fit for purpose for their target organisms. The PCR tests have different target genes, allowing one of the sets to be used as first screening test and another as second screening test for the detection of R. solanacearum and/or R. pseudosolanacearum and/or C. michiganensis subsp. sepedonicus in asymptomatic potato tubers.
    A metabolic profile is associated with the risk of incident coronary heart disease
    Vaarhorst, A. ; Verhoeven, A. ; Weller, C.M. ; Bohringer, S. ; Brandt, P.A. van den; Greevenbroek, M.M. ; Merry, A.H. ; Verschuren, W.M.M. ; Boer, J.M.A. ; Feskens, E.J.M. ; Heijmans, B.T. ; Slagboom, P.E. - \ 2014
    American Heart Journal 168 (2014)1. - ISSN 0002-8703 - p. 45 - 52.e7.
    artery-disease - cardiovascular events - population - prediction - plasma - phosphatidylcholine - metabonomics - netherlands - mortality - cohort
    Background Metabolomics, defined as the comprehensive identification and quantification of low-molecular-weight metabolites to be found in a biological sample, has been put forward as a potential tool for classifying individuals according to their risk of coronary heart disease (CHD). Here, we investigated whether a single-point blood measurement of the metabolome is associated with and predictive for the risk of CHD.
    Comparative genomics of plant-asssociated Pseudomonas spp.: Insights into diversity and inheritance of traits involved in multitrophic interactions
    Loper, J.E. ; Hassan, K.A. ; Mavrodi, D.V. ; Davis II, E.W. ; Lim, C.K. ; Shaffer, B.T. ; Elbourne, L.D.H. ; Stockwell, V.O. ; Hartney, S.L. ; Breakwell, K. ; Henkels, M.D. ; Tetu, S.G. ; Rangel, L.I. ; Kidarsa, T.A. ; Wilson, N.L. ; Mortel, J.E. van de; Song, C. ; Blumhagen, R. ; Radune, D. ; Hostetler, J.B. ; Brinkac, L.M. ; Durkin, A.C. ; Kluepfel, D.A. ; Wechter, W.P. ; Anderson, A.J. ; Kim, Y.C. ; Pierson III, L.S. ; Pierson, E.A. ; Lindow, S.E. ; Kobayashi, D.Y. ; Raaijmakers, J. ; Weller, D.M. ; Thomashow, L.S. ; Allen, A.E. ; Paulsen, I.T. - \ 2012
    Plos Genetics 8 (2012)7. - ISSN 1553-7404
    iii secretion system - syringae pv. syringae - gamma-aminobutyric-acid - biological-control - fluorescens pf-5 - biocontrol strain - antibiotic production - secondary metabolite - phenylacetic acid - chlororaphis o6
    We provide here a comparative genome analysis of ten strains within the Pseudomonas fluorescens group including seven new genomic sequences. These strains exhibit a diverse spectrum of traits involved in biological control and other multitrophic interactions with plants, microbes, and insects. Multilocus sequence analysis placed the strains in three sub-clades, which was reinforced by high levels of synteny, size of core genomes, and relatedness of orthologous genes between strains within a sub-clade. The heterogeneity of the P. fluorescens group was reflected in the large size of its pan-genome, which makes up approximately 54% of the pan-genome of the genus as a whole, and a core genome representing only 45–52% of the genome of any individual strain. We discovered genes for traits that were not known previously in the strains, including genes for the biosynthesis of the siderophores achromobactin and pseudomonine and the antibiotic 2-hexyl-5-propyl-alkylresorcinol; novel bacteriocins; type II, III, and VI secretion systems; and insect toxins. Certain gene clusters, such as those for two type III secretion systems, are present only in specific sub-clades, suggesting vertical inheritance. Almost all of the genes associated with multitrophic interactions map to genomic regions present in only a subset of the strains or unique to a specific strain. To explore the evolutionary origin of these genes, we mapped their distributions relative to the locations of mobile genetic elements and repetitive extragenic palindromic (REP) elements in each genome. The mobile genetic elements and many strain-specific genes fall into regions devoid of REP elements (i.e., REP deserts) and regions displaying atypical tri-nucleotide composition, possibly indicating relatively recent acquisition of these loci. Collectively, the results of this study highlight the enormous heterogeneity of the P. fluorescens group and the importance of the variable genome in tailoring individual strains to their specific lifestyles and functional repertoire
    Diversity and Evolution of the Phenazine Biosynthesis Pathway
    Mavrodi, D.V. ; Peever, T.L. ; Mavrodi, O.V. ; Parejko, J.A. ; Raaijmakers, J.M. ; Lemanceau, P. ; Mazurier, S. ; Heide, L. ; Blankenfeldt, W. ; Weller, D.M. ; Thomashow, L.S. - \ 2010
    Applied and Environmental Microbiology 76 (2010)3. - ISSN 0099-2240 - p. 866 - 879.
    burkholderia-cepacia complex - pseudomonas-chlororaphis pcl1391 - erwinia-herbicola eh1087 - phenazine-1-carboxylic acid - fluorescent pseudomonas - biological-control - virulence factors - genome sequence - aeruginosa pao1 - gene-cluster
    Phenazines are versatile secondary metabolites of bacterial origin that function in biological control of plant pathogens and contribute to the ecological fitness and pathogenicity of the producing strains. In this study, we employed a collection of 94 strains of various geographic, environmental and clinical origins to study the distribution and evolution of phenazine genes in members of Pseudomonas, Burkholderia, Pectobacterium, Brevibacterium and Streptomyces genera. Our results confirmed the diversity of phenazine producers and revealed that most of them appear to be soil-dwelling and/or plant-associated species. Genome analyses and comparisons of phylogenies inferred from sequences of the key phenazine biosynthesis phzF and housekeeping genes (rrs, recA, rpoB, atpD, and gyrB) revealed that the evolution and dispersal of phenazine genes is driven by mechanisms ranging from conservation in Pseudomonas spp. to horizontal gene transfer in Burkholderia spp. and Pectobacterium spp. DNA extracted from cereal crop rhizospheres and screened for the presence of phzF contained sequences consistent with a diverse population of phenazine-producers in commercial farm fields located in central Washington State, thus providing the first evidence of U.S. soils enriched in indigenous phenazine-producing bacteria
    European Survey for Hidden Allergens in Food: A Case Study with Peanut and Hazelnut
    Baumgertner, S. ; Furtler-Leitzenberger, L. ; Molinelli, E. ; Krska, R. ; Immer, U. ; Schmitt, K. ; Bremer, M. ; Haasnoot, W. ; Danks, C. ; Romkies, V. ; Reece, P. ; Wilson, P. ; Kiening, M. ; Weller, M. ; Niessner, R. ; Corsini, E. ; Mendonca, S. - \ 2008
    In: Food Contaminants : Mycotoxins and Food Allergens / Siantar, D.P., Trucksess, M.W., Scott, P.M., Herman, E.M., Washington, DC, USA : American Chemical Society (ACS SYMPOSIUM SERIES 1001) - ISBN 9780841269545 - p. 370 - 381.
    During the EU-funded project Allergentest (QLK1-CT-2001-01151) a survey for the presence of hidden proteins of hazelnut and peanut in suspected pre-packed foodstuffs within EC member states was carried out to check the usefulness of the developed rapid test-kits. There were 11 participating countries in this study: Belgium, Portugal, Italy, Spain, France, United Kingdom, Slovenia, Greece, Norway, Czech Republic, and Austria. Each country submitted between 35-40 food samples. All foodstuffs were tested using the two test kits developed within the EC-project. The results presented were quantitative for the ELISA and qualitative for the LFD method (meaning positive or negative results - presence or absence) for peanut and hazelnut. The results were compared with the information given on the labels. Although at the time of the survey the new European Labelling directive (2003/89/EC) for allergens was not in force, the comparison showed whether the labelling was sufficient or not and where problems occured
    Development of tools needed for an impact analysis for groundwater quality due to changing of agricultural soil use
    Mioduszewski, W. ; Fic, M. ; Slesicka, A. ; Zdanowicz, A. ; Walther, W. ; Paetsch, M. ; Reinstorf, F. ; Weller, D. ; Diankov, S. ; Velovsky, G. ; Radoslavov, S. ; Marinov, W. ; Nicheva, O. ; Querner, E.P. ; Roelsma, J. - \ 2005
    In: Nitrates in groundwater. - Leiden [etc.] : Balkema - ISBN 9789058096647 - p. 123 - 128.
    The role of cryptochrome 2 in flowering in Arabidopsis
    El-Assal, S.E.D. ; Alonso-Blanco, C. ; Peeters, A.J.M. ; Wagemaker, C. ; Weller, J.L. ; Koornneef, M. - \ 2003
    Plant Physiology 133 (2003)4. - ISSN 0032-0889 - p. 1504 - 1516.
    landsberg erecta - phytochrome-a - circadian clock - locus-c - genetic-control - time - thaliana - mutants - encodes - phenotype
    We have investigated the genetic interactions between cry2 and the various flowering pathways in relation to the regulation of flowering by photoperiod and vernalization. For this, we combined three alleles of CRY2, the wild-type CRY2-Landsberg erecta (Ler), a cry2 loss-of-function null allele, and the gain-of-function CRY2-Cape Verde Islands (Cvi), with mutants representing the various photoreceptors and flowering pathways. The analysis of CRY2 alleles combined with photoreceptor mutants showed that CRY2-Cvi could compensate the loss of phyA and cry1, also indicating that cry2 does not require functional phyA or cry1. The analysis of mutants of the photoperiod pathway showed epistasis of co and gi to the CRY2 alleles, indicating that cry2 needs the product of CO and GI genes to promote flowering. All double mutants of this pathway showed a photoperiod response very much reduced compared with Ler. In contrast, mutations in the autonomous pathway genes were additive to the CRY2 alleles, partially overcoming the effects of CRY2-Cvi and restoring day length responsiveness. The three CRY2 alleles were day length sensitive when combined with FRI-Sf2 and/or FLC-Sf2 genes, which could be reverted when the delay of flowering caused by FRI-Sf2 and FLC-Sf2 alleles was removed by vernalization. In addition, we looked at the expression of FLC and CRY2 genes and showed that CRY2 is negatively regulated by FLC. These results indicate an interaction between the photoperiod and the FLC-dependent pathways upstream to the common downstream targets of both pathways, SOC1 and FT.
    Kendrick, R.E. ; Weller, J.L. - \ 2003
    In: Encyclopedia of Applied Plant Sciences / Thomas, B., Murphy, D.J., Murray, B.G., Elsevier/Academic Press - ISBN 9780122270505 - p. 1069 - 1076.
    fotoperiodiciteit - fototropie - fotoreceptoren - lichtregiem - fytochroom - zaadkieming - photoperiodism - phototropism - photoreceptors - light regime - phytochrome - seed germination
    Phytochrome and other photoreceptors
    Kendrick, R.E. ; Weller, J.L. - \ 2003
    In: Encyclopedia of Applied Plant Sciences / Thomas, B., Murphy, D.J., Murray, B.G., Elsevier/Academic Press - ISBN 9780122270505 - p. 1063 - 1069.
    Frequency, diversity and activity of 2,4-diacetylphloroglucinol-producing Pseudomonas spp. in Dutch take-all decline soils
    Souza, J.T. ; Weller, D.M. ; Raaijmakers, J.M. - \ 2003
    Phytopathology 93 (2003)1. - ISSN 0031-949X - p. 54 - 63.
    graminis var tritici - gaeumannomyces-graminis - metabolite 2,4-diacetylphloroglucinol - antibiotic biosynthesis - ecological fitness - biological-control - suppressive soils - wheat roots - rhizosphere - fungus
    Natural suppressiveness of soils to take-all disease of wheat, referred to as take-all decline (TAD), occurs worldwide, It has been postulated that different microbial genera and mechanisms are responsible for TAD in soils from different geographical regions. In growth chamber experiments,,we demonstrated that fluorescent Pseudomonas spp. that produce the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) play a key role in the natural suppressiveness of two Dutch TAD soils. First, 2,4-DAPG-producing fluorescent Pseudomonas spp. were present on roots of wheat grown in both of the TAD soils at densities at or above the threshold density required to control take-all of wheat; in a complementary take-all conducive soil, population densities of 2,4-DAPG-producing Pseudomonas spp. were below this threshold level. Second, introduction of 2,4-DAPG-producing strain SSB17, a representative of the dominant geriotypic group found in the Dutch TAD soils, into the take-all conducive soil at population densities similar to the densities, of indigenous 2,4-DAPG producers found in TAD soils provided control of take-all similar to that observed in the TAD soil, Third, a mutant of strain SSB17 deficient in 2,4-DAPG production was not able to control take-all of wheat, indicating that 2,4-DAPG is a key determinant in take-all suppression, These results show that in addition to the physicochemically different TAD soils from Washington State, 2,4-DAPG-producing fluorescent Pseudomonas spp. are also a key component of the natural suppressiveness found in Dutch TAD soils. Furthermore, it is the first time since the initial studies of Gerlagh (1968) that at least part of the mechanisms and microorganisms that operate in Dutch TAD soils are identified. Although quantitatively similar, the genotypic composition of 2,4-DAPG-producing Pseudomonas spp. varied between the Dutch TAD soils and the TAD soils from Washington State.
    Photomorphogenesis and photoperiodism in plants in photobiology : The science of light and life
    Weller, J.L. - \ 2002
    In: The science of light and life Dordrecht : Kluwer Academic Publishers - ISBN 9781402008429 - p. 299 - 334.
    Microbial populations responsible for specific soil suppressiveness to plant pathogens
    Weller, D.M. ; Raaijmakers, J.M. ; McSpadden Gardener, B.B. ; Thomashow, L.S. - \ 2002
    Annual Review of Phytopathology 40 (2002). - ISSN 0066-4286 - p. 309 - 348.
    Agricultural soils suppressive to soilborne plant pathogens occur worldwide, and for several of these soils the biological basis of suppressiveness has been described. Two classical types of suppressiveness are known. General suppression owes its activity to the total microbial biomass in soil and is not transferable between soils. Specific suppression owes its activity to the effects of individual or select groups of microorganisms and is transferable. The microbial basis of specific suppression to four diseases, Fusarium wilts, potato scab, apple replant disease, and take-all, is discussed. One of the best-described examples occurs in take-all decline soils. In Washington State, take-all decline results from the buildup of fluorescent Pseudomonas spp. that produce the antifungal metabolite 2,4-diacetylphloroglucinol. Producers of this metabolite may have a broader role in disease-suppressive soils worldwide. By coupling molecular technologies with traditional approaches used in plant pathology and microbiology, it is possible to dissect the microbial composition and complex interactions in suppressive soils.
    Differential ability of genotypes of 2,4-Diacetylphloroglucinol-producing Pseudomonas fluorescens strains to colonize the roots of pea plants
    Landa, B.B. ; Mavrodi, O.V. ; Raaijmakers, J.M. ; McSpadden Gardener, B.B. ; Thomashow, L.S. ; Weller, D.M. - \ 2002
    Applied and Environmental Microbiology 68 (2002)7. - ISSN 0099-2240 - p. 3226 - 3237.
    Indigenous populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing fluorescent Pseudomonas spp. that occur naturally in suppressive soils are an enormous resource for improving biological control of plant diseases. Over 300 isolates of 2,4-DAPG-producing fluorescent Pseudomonas spp. were isolated from the rhizosphere of pea plants grown in soils that had undergone pea or wheat monoculture and were suppressive to Fusarium wilt or take-all, respectively. Representatives of seven genotypes, A, D, E, L, O, P, and Q, were isolated from both soils and identified by whole-cell repetitive sequence-based PCR (rep-PCR) with the BOXA1R primer, increasing by three (O, P, and Q) the number of genotypes identified previously among a worldwide collection of 2,4-DAPG producers. Fourteen isolates representing eight different genotypes were tested for their ability to colonize the rhizosphere of pea plants. Population densities of strains belonging to genotypes D and P were significantly greater than the densities of other genotypes and remained above log 6.0 CFU (g of root)-1 over the entire 15-week experiment. Genetic profiles generated by rep-PCR or restriction fragment length polymorphism analysis of the 2,4-DAPG biosynthetic gene phlD were predictive of the rhizosphere competence of the introduced 2,4-DAPG-producing strains.
    Biocontrol Agents for Take-all
    Raaijmakers, J.M. ; Weller, D.M. ; Thomashow, L.S. ; Cook, R.J. - \ 2002
    Octrooinummer: US6447770, gepubliceerd: 2002-09-10.
    Fluorescent Pseudomonas spp. are described which are effective for the control of diseases caused by the soil-borne fungus, Gaeumannomyces graminis (Gg), such as take-all, in small grain crops or turf grass. The subject biocontrol strains have a unique genotype as shown by a characteristic banding pattern, and exhibit root-colonizing ability which is characterized by both higher population density on roots and extended colonizing activity compared to known Gg-suppressive strains. A further property is the ability of a strain to duplicate the level of biocontrol obtained naturally in a take-all decline soil. Methods for isolation and identification of the strains and their use to control diseases caused by Gg are provided. In particular, strains of P. fluorescens NRRL B-21806 and NRRL B-21807.
    Genetic dissection of blue-light sensing in tomato using mutants deficient in cryptochrome 1 and phytochromes A, B1 and B2
    Weller, J.L. ; Perrotta, G. ; Schreuder, M.E.L. ; Tuinen, A. van; Koornneef, M. ; Giuliano, G. ; Kendrick, R.E. - \ 2001
    The Plant Journal 25 (2001). - ISSN 0960-7412 - p. 427 - 440.
    Several novel allelic groups of tomato ( Solanum lycopersicum L.) mutants with impaired photomorphogenesis have been identified after -ray mutagenesis of phyA phyB1 double-mutant seed. Recessive mutants in one allelic group are characterized by retarded hook opening, increased hypocotyl elongation and reduced hypocotyl chlorophyll content under white light (WL). These mutants showed a specific impairment in response to blue light (BL) resulting from lesions in the gene encoding the BL receptor cryptochrome 1 (cry1). Phytochrome A and cry1 are identified as the major photoreceptors mediating BL-induced de-etiolation in tomato, and act under low and high irradiances, respectively. Phytochromes B1 and B2 also contribute to BL sensing, and the relative contribution of each of these four photoreceptors differs according to the light conditions and the specific process examined. Development of the phyA phyB1 phyB2 cry1 quadruple mutant under WL is severely impaired, and seedlings die before flowering. The quadruple mutant is essentially blind to BL, but experiments employing simultaneous irradiation with BL and red light suggest that an additional non-phytochrome photoreceptor may be active under short daily BL exposures. In addition to effects on de-etiolation, cry1 is active in older, WL-grown plants, and influences stem elongation, apical dominance, and the chlorophyll content of leaves and fruit. These results provide the first mutant-based characterization of cry1 in a plant species other than Arabidopsis.
    Exploiting genotypic diversity of 2,4-Diacetylphloroglucinol-producing Pseudomonas spp.: characterization of superior root-colonizing P. fluorescens strain Q8r1-96
    Raaijmakers, J.M. ; Weller, D.M. - \ 2001
    Applied and Environmental Microbiology 67 (2001)6. - ISSN 0099-2240 - p. 2545 - 2554.
    The genotypic diversity that occurs in natural populations of antagonistic microorganisms provides an enormous resource for improving biological control of plant diseases. In this study, we determined the diversity of indigenous 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. occurring on roots of wheat grown in a soil naturally suppressive to take-all disease of wheat. Among 101 isolates, 16 different groups were identified by random amplified polymorphic DNA (RAPD) analysis. One RAPD group made up 50% of the total population of DAPG-producing Pseudomonas spp. Both short- and long-term studies indicated that this dominant genotype, exemplified by P. fluorescens Q8r1-96, is highly adapted to the wheat rhizosphere. Q8r1-96 requires a much lower dose (only 10 to 100 CFU seed-1 or soil-1) to establish high rhizosphere population densities (107 CFU g of root-1) than Q2-87 and 1M1-96, two genotypically different, DAPG-producing P. fluorescent strains. Q8r1-96 maintained a rhizosphere population density of approximately 105 CFU g of root-1 after eight successive growth cycles of wheat in three different, raw virgin soils, whereas populations of Q2-87 and 1M1-96 dropped relatively quickly after five cycles and were not detectable after seven cycles. In short-term studies, strains Q8r1-96, Q2-87, and 1M1-96 did not differ in their ability to suppress take-all. After eight successive growth cycles, however, Q8r1-96 still provided control of take-all to the same level as obtained in the take-all suppressive soil, whereas Q2-87 and 1M1-96 gave no control anymore. Biochemical analyses indicated that the superior rhizosphere competence of Q8r1-96 is not related to in situ DAPG production levels. We postulate that certain rhizobacterial genotypes have evolved a preference for colonization of specific crops. By exploiting diversity of antagonistic rhizobacteria that share a common trait, biological control can be improved significantly.
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