E. Davelaar

University of Nottingham, Nottingham, ENG, United Kingdom

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Publications (26)39.27 Total impact

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    ABSTRACT: 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
    Biological Control 03/2009; · 1.92 Impact Factor
  • 01/2009;
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    ABSTRACT: The present invention relates to a composition comprising a soluble combination comprising lignosulfonate, a metal salt, and a phosphorus compound selected from the group consisting of phosphorus acid and spontaneously soluble salts thereof, and mixtures thereof. The present invention also relates to the use of such compositions as pesticide
    01/2009;
  • 01/2009;
  • Gewasbescherming 39 (2008) Special. 01/2008;
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    ABSTRACT: Cauliflower (Brassica oleracea var. botrytis) was transformed, using Agrobacterium tumefaciens, with an autoregulated isopentenyl transferase (ipt) gene under the control of a senescence-associated gene promoter, pSAG12, isolated from Arabidopsis thaliana. The effect of introducing this chimeric construct on cytokinin (CK) content, chlorophyll retention, and plant morphology and development were investigated. A range of CK and chlorophyll contents was found among the individual primary transformants. Progeny were studied from one of the primary transformed lines that did not have elevated cytokinin content and was phenotypically similar to the parent line but displayed delayed leaf senescence. The pSAG12:ipt gene was inherited in a Mendelian manner, and the effect of this gene on senescence-related parameters was observed in a number of the progeny. While the pSAG12:ipt progeny did exhibit delayed leaf senescence, it was accompanied by undesirable agronomic traits, including less synchronous curd initiation, smaller curd size, and greater susceptibility to fungal infection.
    International Journal of Plant Sciences 169 (2008) 3. 01/2008;
  • C. R. Vonk, E. Davelaar
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    ABSTRACT: Transport and metabolism of 8-14 C-zeatin, applied to an attached de-tipped one-year-old mature leaf of a Yucca plant bearing a bleeding inflorescent stalk, has been studied. Radioactive zeatin ribotide was found in the exudate of the bleeding inflorescence, which was collected over a period of 5 days. Radioactive zeatin ribotide was mainly extracted from the fed leaf. Minor conversion products in this leaf were zeatin ribotide, zeatin-o-β-glucoside and zeatinriboside o-β-glucoside.In not zeatin fed plants, zeatin-o-β-glucoside was tentatively identified as the main endogenous cytokinin in one-year-old mature leaves. In the bleeding sap of not treated plants no free bases of zeatin or zeatin ribosides were found. After alkaline phosphatase treatment zeatin-riboside was detected by combined gas chromatography-mass spectrometry, indicating the presence of zeatin ribotide in the bleeding sap. High β-glucosidase activity was found in the stern.Results suggest that stared cytokinin glucosides from Yucca leaves are, converted by β-glucosidase in leaves and stem, transported through the inflorescent stalk as zeatin nucleotides.
    Physiologia Plantarum 04/2006; 52(1):101 - 107. · 3.66 Impact Factor
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    ABSTRACT: The present invention relates to a composition comprising a metal compound, a lignosulfonate and phosphorous acid and/or a salt and/or a hydrate and/or an ester thereof and its use as fungicide, bactericide or fertilizer and its use in preventing the formation of a metal phosphite precipitate in an aqueous composition. The composition is preferably an aqueous composition comprising 0.1 wt.% to 40 wt.% of dry matter, calculated on the total weight of the aqueous composition. The present invention also relatesto a process for preparing the aqueous composition
    Biosystems Engineering - BIOSYST ENG. 01/2006;
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    ABSTRACT: An ipt gene under control of the senescence-specific SAG12 promoter from Arabidopsis (P(SAG12)-IPT) significantly delayed developmental and postharvest leaf senescence in mature heads of transgenic lettuce (Lactuca sativa L. cv Evola) homozygous for the transgene. Apart from retardation of leaf senescence, mature, 60-d-old plants exhibited normal morphology with no significant differences in head diameter or fresh weight of leaves and roots. Induction of senescence by nitrogen starvation rapidly reduced total nitrogen, nitrate, and growth of transgenic and azygous (control) plants, but chlorophyll was retained in the lower (outer) leaves of transgenic plants. Harvested P(SAG12)-IPT heads also retained chlorophyll in their lower leaves. During later development (bolting and preflowering) of transgenic plants, the decrease in chlorophyll, total protein, and Rubisco content in leaves was abolished, resulting in a uniform distribution of these components throughout the plants. Homozygous P(SAG12)-IPT lettuce plants showed a slight delay in bolting (4-6 d), a severe delay in flowering (4-8 weeks), and premature senescence of their upper leaves. These changes correlated with significantly elevated concentrations of cytokinin and hexoses in the upper leaves of transgenic plants during later stages of development, implicating a relationship between cytokinin and hexose concentrations in senescence.
    Plant physiology 11/2001; 127(2):505-16. · 6.56 Impact Factor
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    ABSTRACT: Microcolumn liquid chromatography (microLC) combined with electrospray tandem mass spectrometry is used for the determination of intact glycosylated cytokinins and the corresponding aglycons at picomole and sub-picomole levels in plant tissue. Routine analysis was done on C8-bonded silica using a methanol-water gradient. Data acquisition was performed by multiple reaction monitoring. Quantification was carried out by using isotopically labelled analogues and applying linear regression to the response factor versus concentration data. For routine analysis a calibration range from 0.5 to 10 pmole injected on-column was used. The limits of detection ranged from 50 to 100 fmole injected on-column. The microLC procedure was used to analyse plant tissue extracts from transgenic homozygote and hemizygote as well as wild-type Nicotiana tabacum species, and cauliflower samples. The data were compared with results obtained by conventional immunoassay and a satisfactory correlation was found. Validation data are presented.
    Journal of Chromatography A 10/2001; 929(1-2):31-42. · 4.61 Impact Factor
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    ABSTRACT: Using cDNA-AFLP RNA fingerprinting throughout potato tuber development, we have isolated a transcript-derived fragment (TDF511) with strong homology to plant steroid dehydrogenases. During in vitro tuberization, the abundance profile of the TDF shows close correlation to the process of tuber formation. However, when tuberization is inhibited by the addition of gibberellins (GAs) to the growth medium, the appearance of TDF511 in the fingerprint is delayed, then steadily increases in intensity during later stages of development. TDF511 was used to isolate the corresponding cDNA (CB12). The DNA and deduced amino-acid sequences of the cDNA show high homology to a fruit-ripening gene from tomato, a series of steroid dehydrogenases, and the maize Ts2 gene. A section of the cDNA was cloned in antisense orientation behind a 35S CaMV promoter and transformed into potato. Transgenic plants expressing the antisense gene showed significantly earlier emergence, an increase in height, and longer tuber shape. In vitro tuberization experiments reveal extended stolon lengths in comparison to the controls. The analysis of endogenous GA levels showed that the transgenic antisense plants have elevated levels of biologically active GAs and their respective precursors. We propose that this gene plays a role in the metabolism of plant-growth substances important for tuber life cycle and plant development.
    The Plant Journal 02/2001; 25(6):595 - 604. · 6.58 Impact Factor
  • J. of Chrom. A, 929, p. 31-42. 01/2001;
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    ABSTRACT: ABSTRACT We studied the impact of delayed leaf senescence on the functioning of plants growing under conditions of nitrogen remobilization. Interactions between cytokinin metabolism, Rubisco and protein levels, photosynthesis and plant nitrogen partitioning were studied in transgenic tobacco (Nicotiana tabacum L.) plants showing delayed leaf senescence through a novel type of enhanced cytokinin syn-thesis, i.e. targeted to senescing leaves and negatively auto-regulated (PSAG12–IPT), thus preventing developmental abnormalities. Plants were grown with growth-limiting nitrogen supply. Compared to the wild-type, endogenous levels of free zeatin (Z)- and Z riboside (ZR)-type cytokinins were increased up to 15-fold (total ZR up to 100-fold) in senescing leaves, and twofold in younger leaves of PSAG12–IPT. In these plants, the senescence-associated declines in N, protein and Rubisco levels and photosynthesis rates were delayed. Senescing leaves accumulated more (15N-labelled) N than younger leaves, associated with reduced shoot N accumulation (–60%) and a partially inverted canopy N profile in PSAG12–IPT plants. While root N accumulation was not affected, N translocation to non-senescing leaves was progressively reduced. We discuss potential consequences of these modified sink–source relations, associated with delayed leaf senescence, for plant productivity and the efficiency of utilization of light and minerals.
    Plant Cell and Environment 01/2000; · 5.91 Impact Factor
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    ABSTRACT: The Agrobacterium T- cyt gene was transferred into lettuce, Latuca sativa ‘Saladin’ using a genotype-independent transformation procedure employing a supervirulent Agrobacterium tumefaciens strain carrying the binary vector pMOG23. Kanamycin-resistant shoots were initiated from inoculated explants only when sites were deleted within the T- cyt promoter. In culture, kanamycin-resistant shoots exhibited several phenotypes, including gall production, reduced internode length (dwarfism) and vitrification together with differences in rooting. Rooted, neomycin phosphotransferase (NPTII)-positive plants recovered from their abnormal phenotype and self pollinated to produce viable seed, following transfer to the glasshouse. Kanamycin-resistant lettuce plants exhibited increased cytokinin and chlorophyll contents compared to non-transformed plants, physiological features which could benefit long-term storage of this leafy vegetable. Copyright 1999 Annals of Botany Company
    05/1999;
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    Annals of Botany 83: 559-567. 01/1999;
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    ABSTRACT: Partially purified blackspot pigments from potato tubers (Solanum tuberosum L.) of two commercial cultivars were subjected to a microassay for melanin, which consisted of specific chemical degradation and subsequent HPLC analysis. Permanganate oxidation yielded pyrrole-2,3,5-tricarboxylic acid, whereas hydrolysis in hydriodic acid liberated aminohydroxyphenylalanine isomers. These results indicate that the polymeric pigments, which have previously been found to contain a protein matrix, carry crosslinked 5,6-dihydroxyindole-2-carboxylic acid and benzothiazine units. This leads to the conclusion that free tyrosine and free cysteine are incorporated in the proteinaceous pigments via the polyphenol oxidase catalysed pathway of melanogenesis in the process of blackspot formation. The findings are in accordance with the hypothesis that the process of blackspot formation is a non-regulated cascade of reactions in disintegrated tuber cells, rather than a finely tuned biosynthesis.
    Phytochemistry 01/1998; · 3.35 Impact Factor
  • Nota 122, AB-DLO, Wageningen, 38 pp. + bijlagen. 01/1998;
  • L.H. Stevens, E. Davelaar
    Journal of Agricultural Food Chemistry 45: 4221-4226. 01/1997;
  • L.H. Stevens, E. Davelaar
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    ABSTRACT: Blackspot related pigments were partially purified from bruised tubers of two commercial potato cultivars (cv. Bildtstar and cv. Lady Rosetta). Chemical characterization showed that these pigments consisted of protein and a relatively small amount of covalently bound constituents. These polymeric structures absorbed light throughout the visible spectrum without any maximum. They did not contain eumelanin. Quinic acid was detectable in hydrolysates of the pigments from Bildtstar, but not in those of Lady Rosetta, which indicated that chlorogenic acid may take part in blackspot formation, but is not essential for the discoloration. The results support the hypothesis that blackspot pigments are products of non-regulated reactions between nucleophilic amino acid residues in proteins, and quinones, which are derived from endogenous substrates of polyphenol oxidase. This means that blackspot formation most probably takes place in disintegrated cells.
    Phytochemistry 01/1996; · 3.35 Impact Factor
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    ABSTRACT: It is shown that in bulbous Iris zeatin originates from a nucleotide. This nucleotide is probably zeatin-allylic-phosphate, in which a phosphate group is attached to the isoprenoid side-chain of zeatin. The formation of zeatin-allylic-phosphate from t-zeatin and 8-[14C]-zeatin by the microsomal fractions of Iris bulb disks and Helianthus tubers was demonstrated. The responsible enzyme was partially purified. 5-AMP was found to be a phosphate group delivering substrate. Adenosine and adenine inhibited the enzyme reaction. The significance of the results is discussed in relation to cytokinin biosynthesis and the occurrence of bud blast in Iris.
    Plant Growth Regulation 08/1989; 8(3):263-276. · 1.67 Impact Factor