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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    Over-expression of Arabidopsis AtCHR23 chromatin remodeling ATPase results in increased variability of growth and gene expression
    Folta, A. ; Severing, E.I. ; Krauskopf, J. ; Geest, H.C. van de; Verver, J. ; Nap, J.P.H. ; Mlynarova, L. - \ 2014
    BMC Plant Biology 14 (2014). - ISSN 1471-2229 - 18 p.
    rna-seq - seed-germination - stress responses - root-growth - thaliana - plant - pickle - noise - identification - consequences
    Background Plants are sessile organisms that deal with their -sometimes adverse- environment in well-regulated ways. Chromatin remodeling involving SWI/SNF2-type ATPases is thought to be an important epigenetic mechanism for the regulation of gene expression in different developmental programs and for integrating these programs with the response to environmental signals. In this study, we report on the role of chromatin remodeling in Arabidopsis with respect to the variability of growth and gene expression in relationship to environmental conditions. Results Already modest (2-fold) over-expression of the AtCHR23 ATPase gene in Arabidopsis results in overall reduced growth compared to the wild-type. Detailed analyses show that in the root, the reduction of growth is due to reduced cell elongation. The reduced-growth phenotype requires sufficient light and is magnified by applying deliberate abiotic (salt, osmotic) stress. In contrast, the knockout mutation of AtCHR23 does not lead to such visible phenotypic effects. In addition, we show that over-expression of AtCHR23 increases the variability of growth in populations of genetically identical plants. These data indicate that accurate and controlled expression of AtCHR23 contributes to the stability or robustness of growth. Detailed RNAseq analyses demonstrate that upon AtCHR23 over-expression also the variation of gene expression is increased in a subset of genes that associate with environmental stress. The larger variation of gene expression is confirmed in individual plants with the help of independent qRT-PCR analysis. Conclusions Over-expression of AtCHR23 gives Arabidopsis a phenotype that is markedly different from the growth arrest phenotype observed upon over-expression of AtCHR12, the paralog of AtCHR23, in response to abiotic stress. This demonstrates functional sub-specialization of highly similar ATPases in Arabidopsis. Over-expression of AtCHR23 increases the variability of growth among genetically identical individuals in a way that is consistent with increased variability of expression of a distinct subset of genes that associate with environmental stress. We propose that ATCHR23-mediated chromatin remodeling is a potential component of a buffer system in plants that protects against environmentally-induced phenotypic and transcriptional variation.
    Tolerance of Four Tropical Tree Species to Heavy Petroleum Contamination
    Perez-Hernandez, I. ; Ochoa-Gaona, S. ; Schroeder, R.H.A. ; Rivera-Cruz, M.C. ; Geissen, V. - \ 2013
    Water Air and Soil Pollution 224 (2013)8. - ISSN 0049-6979
    soil-water relations - oxidative stress - bioremediated soils - seed-germination - end-point - phytoremediation - oil - hydrocarbons - growth - plants
    Four species of trees were selected to evaluate the tolerance to heavy crude oil contamination by means of a tolerance index integrating germination, height, biomass and survival as variables. Fresh seeds to Cedrela odorata (tropical cedar), Haematoxylum campechianum (tinto bush), Swietenia macrophylla (mahogany) and Tabebuia rosea (macuilis) were planted in a Vertisol to which heavy crude petroleum was added at four different treatments (C0, 0; C1, 18,940; C2, 44,000; and C3, 57,000 mg kg(-1)), with the control being uncontaminated soil. The experiment was carried out in a greenhouse during 203 days with a completely random design. The presence of petroleum in soil stimulated and increased germination of S. macrophylla and C. odorata, accelerated the germination of T. rosea and did not affect the germination of H. campechianum. The height and biomass of all species was reduced in the presence of petroleum in the soil. The survival of S. macrophylla and H. campechianum was not affected by petroleum at any concentration studied. On the other hand, C. odorata and T. rosea showed high mortality at all concentrations. The tolerance index showed that S. macrophylla was best at tolerating petroleum in soil and could be employed as a productive alternative for the advantageous use of contaminated sites. The use of tree species could be important because of the great potential of trees for phytoremediation due to their long life, biomass and deep roots that can penetrate and remediate deeper soil layers.
    CAROTENOID CLEAVAGE DIOXYGENASE 7 modulates plant growth, reproduction, senescence, and determinate nodulation in the model legume Lotus japonicas
    Liu, J. ; Novero, M. ; Charnikhova, T. ; Ferrandino, A. ; Schubert, A. ; Ruyter-Spira, C.P. ; Biofante, P. ; Lovisolo, C. ; Bouwmeester, H.J. - \ 2013
    Journal of Experimental Botany 64 (2013)7. - ISSN 0022-0957 - p. 1967 - 1981.
    strigolactone analog gr24 - f-box protein - leaf senescence - germination stimulants - seed-germination - parasitic plants - key component - am fungi - arabidopsis - rice
    Strigolactones (SLs) are newly identified hormones that regulate multiple aspects of plant development, infection by parasitic weeds, and mutualistic symbiosis in the roots. In this study, the role of SLs was studied for the first time in the model plant Lotus japonicus using transgenic lines silenced for CAROTENOID CLEAVAGE DIOXYGENASE 7 (LjCCD7), the orthologue of Arabidopsis More Axillary Growth 3. Transgenic LjCCD7-silenced plants displayed reduced height due to shorter internodes, and more branched shoots and roots than the controls, and an increase in total plant biomass, while their root:shoot ratio remained unchanged. Moreover, these lines had longer primary roots, delayed senescence, and reduced flower/pod numbers from the third round of flower and pod setting onwards. Only a mild reduction in determinate nodule numbers and hardly any impact on the colonization by arbuscular mycorrhizal fungi were observed. The results show that the impairment of CCD7 activity in L. japonicus leads to a phenotype linked to SL functions, but with specific features possibly due to the peculiar developmental pattern of this plant species. It is believed that the data also link determinate nodulation, plant reproduction, and senescence to CCD7 function for the first time.
    New strigolactone mimics: structure-activity relationship and mode of action as germinating stimulants for parasitic weeds.
    Zwanenburg, B. ; Nayak, S.K. ; Charnikhova, T. ; Bouwmeester, H.J. - \ 2013
    Bioorganic and Medicinal Chemistry Letters 23 (2013)18. - ISSN 0960-894X - p. 5182 - 5186.
    seed-germination - orobanche-minor - plant hormones - am fungi - striga-hermonthica - red-clover - analogs - inhibition - ring - phelipanche
    Strigolactones (SLs) are new plant hormones with varies important bio-functions. This Letter deals with germination of seeds of parasitic weeds. Natural SLs have a too complex structure for synthesis. Therefore, there is an active search for SL analogues and mimics with a simpler structure with retention of activity. SL analogues all contain the D-ring connected with an enone moiety through an enol ether unit. A new mechanism for the hydrolysis SL analogues involving bidentate bound water and an a,ß-hydrolase with a Ser-His-Asp catalytic triad has been proposed. Newly discovered SL mimics only have the D-ring with an appropriate leaving group at C-5. A mode of action for SL mimics was proposed for which now supporting evidence is provided. As predicted an extra methyl group at C-4 of the D-ring blocks the germination of seeds of parasitic weeds.
    Identification of microRNA targets in tomato fruit development using high-throughput sequencing and degradome analysis
    Karlova, R.B. ; Haarst, J.C. van; Maliepaard, C.A. ; Geest, H.C. van de; Bovy, A.G. ; Lammers, M. ; Angenent, G.C. ; Maagd, R.A. de - \ 2013
    Journal of Experimental Botany 64 (2013)7. - ISSN 0022-0957 - p. 1863 - 1878.
    solanum-lycopersicon - small rnas - flower development - parallel analysis - seed-germination - sirna biogenesis - leaf development - mirna targets - arabidopsis - expression
    MicroRNAs (miRNAs) play important roles in plant development through regulation of gene expression by mRNA degradation or translational inhibition. Despite the fact that tomato (Solanum lycopersicum) is the model system for studying fleshy fruit development and ripening, only a few experimentally proven miRNA targets are known, and the role of miRNA action in these processes remains largely unknown. Here, by using parallel analysis of RNA ends (PARE) for global identification of miRNA targets and comparing four different stages of tomato fruit development, a total of 119 target genes of miRNAs were identified. Of these, 106 appeared to be new targets. A large part of the identified targets (56) coded for transcription factors. Auxin response factors, as well as two known ripening regulators, COLORLESS NON-RIPENING (CNR) and APETALA2a (SlAP2a), with developmentally regulated degradation patterns were identified. The levels of the intact messenger of both CNR and AP2a are actively modulated during ripening, by miR156/157 and miR172, respectively. Additionally, two TAS3-mRNA loci were identified as targets of miR390. Other targets such as ARGONAUTE 1 (AGO1), shown to be involved in miRNA biogenesis in other plant species, were identified, which suggests a feedback loop regulation of this process. In this study, it is shown that miRNA-guided cleavage of mRNAs is likely to play an important role in tomato fruit development and ripening
    Post-harvest Proteomics and Food Security
    Pedreschi Plasencia, R.P. ; Lurie, S. ; Hertog, W. ; Nicolai, B. ; Mes, J.J. ; Woltering, E.J. - \ 2013
    Proteomics 13 (2013)12-13. - ISSN 1615-9853 - p. 1772 - 1783.
    cell-wall proteome - peach fruit - chilling injury - botrytis-cinerea - tomato fruit - citrus-fruit - sugar-beet - wide characterization - gel-electrophoresis - seed-germination
    To guarantee sufficient food supply for a growing world population, efforts towards improving crop yield and plant resistance should be complemented with efforts to reduce postharvest losses. Post-harvest losses are substantial and occur at different stages of the food chain in developed and developing countries. In recent years a substantially increasing interest can be seen in the application of proteomics to understand post-harvest events. In the near future post-harvest proteomics will be poised to move from fundamental research to aiding the reduction of food losses. Proteomics research can help in reducing food losses through (i) identification and validation of gene products associated to specific quality traits supporting marker-assisted crop improvement programs, (ii) delivering markers of initial quality that allow optimization of distribution conditions and prediction of remaining shelf life for decision support systems and (iii) delivering early detection tools of physiological or pathogen related post-harvest problems. In this manuscript, recent proteomics studies on post-harvest and stress physiology are reviewed and discussed. Perspectives on future directions of post-harvest proteomics studies aiming to reduce food losses are presented.
    Striga hermonthica parasitism in maize in response to N and P fertilisers
    Jamil, M. ; Kanampiu, F.K. ; Karaya, H. ; Charnikova, T. ; Bouwmeester, H.J. - \ 2012
    Field Crops Research 134 (2012). - ISSN 0378-4290 - p. 1 - 10.
    sorghum-bicolor - soil fertility - phosphorus deficiency - northeast nigeria - seed-germination - root parasites - western kenya - sudan savanna - early growth - sowing date
    Parasitism by the parasitic weed, Striga hermonthica (Striga), constitutes a major biological constraint to maize production in sub-Sahara Africa. Nutrient deficiency is known to aggravate Striga infestation and in a number of plant species it was recently shown that this may be due to increased secretion of Striga germination stimulants into the soil. The present study was designed to observe the connection between soil fertility, secretion of germination stimulants and Striga infection in maize under greenhouse and field conditions. The experiments were conducted during two successive cropping seasons (2008 and 2009). The greenhouse study showed that maize secretes a number of so far unidentified strigolactones that induce Striga seed germination and the amount of these strigolactones increases upon N and P deficiency. The increased secretion of germination stimulants under N and P deficiency resulted in increased Striga infection in pot experiments. The on-station and on-farm field trials in Western Kenya also showed reduction in Striga infestation with the application of mineral nutrients but the results were less consistent than in the greenhouse. Increasing levels of N showed a fair reduction of Striga in the field especially during the first year, whereas P application did not have much effect in contrast to the greenhouse study where both N and P clearly reduced Striga infection. The likely explanation for this discrepancy is that availability of mineral nutrients under field conditions is less predictable than under greenhouse conditions, due to a number of factors such as soil texture and structure, pH, salinity, drought, leaching and runoff. Hence, further studies are needed on the importance of these factors before a fertiliser application strategy can be formulated to improve control of Striga in maize in the field.
    Can the negative plant-soil feedback of Jacobaea vulgaris be explained by autotoxicity?
    Voorde, T.F.J. van de; Putten, W.H. van der; Bezemer, T.M. - \ 2012
    Basic and Applied Ecology 13 (2012)6. - ISSN 1439-1791 - p. 533 - 541.
    senecio-jacobaea - pyrrolizidine alkaloids - seed-germination - invasive plants - phenolic-acids - allelopathy - growth - succession - field - grassland
    Field and bioassay studies with Jacobaeavulgaris (ragwort) have shown that plants grow poorly in soil originating from the rhizosphere of this species and that this can influence the dynamics of ragwort populations during secondary succession. In the present study we examined whether the negative effect of ragwort on conspecifics may be due to autotoxicity. First, we experimentally established that ragwort exerts negativeplant–soilfeedback. We subsequently examined the inhibitory effects on germination and seedling performance of different strengths of aqueous extracts made from shoot and root tissues of ragwort, and from soil in which ragwort had been growing. The effects of the extracts were tested for seedlings growing in sterilised soil or in glass beads with water. Finally, the inhibitory effect of entire root fragments on seedling performance was tested. We observed that performance of seedlings growing in glass beads was significantly reduced by the high and medium strength root and shoot extracts. Extracts made from soil did not differ significantly from the control, and seedlings growing in sterilised soil were also not affected by ragwort extracts. Seed germination was significantly reduced by the high strength shoot extract only. The root length of seedlings growing in water with root fragments was reduced significantly. We conclude that under laboratory conditions ragwort can be autotoxic and discuss the role that autotoxicity may play in influencing the dynamics of ragwort populations during secondary succession.
    Quantification of the relationship between strigolactones and Striga hermonthica infection in rice under varying levels of nirtrogen and phosphorus
    Jamil, M. ; Charnikhova, T. ; Cardoso, C. ; Jamil, T. ; Ueno, K. ; Verstappen, F.W.A. ; Asami, T. ; Bouwmeester, H.J. - \ 2011
    Weed Research 51 (2011)4. - ISSN 0043-1737 - p. 373 - 385.
    arbuscular mycorrhizal fungi - asiatica l kuntze - germination stimulants - upland rice - seed-germination - parasitic weeds - root parasites - soil fertility - oryza-sativa - sorghum
    Strigolactone exudation, as well as Striga hermonthica germination and attachment, was studied under different levels of nitrogen (N) and phosphorus (P) in two cultivars of rice (IAC 165 and TN 1). Exudation of strigolactones by rice was the highest under mineral-deficient conditions, whereas increasing N and P dose reduced the amount of strigolactones in the exudates. Deficiency of P led to the highest strigolactone exudation, when compared with N or NP deficiency. Production of strigolactones differed strongly between the two cultivars. IAC 165 produced about 100-fold higher amounts than TN 1 of 2'-epi-5-deoxystrigol, orobanchol and three new strigolactones. Across all N and P treatments, a positive relationship was found between the amount of strigolactones in the exudates of both cultivars and in vitro S. hermonthica germination. These results show that the positive effect of fertiliser application in S. hermonthica control is, at least partly, because of the suppression of strigolactone production and hence of S. hermonthica germination and subsequent attachment. This warrants further research into practical application. Maintaining suitable N and P nutrient status of soil through fertiliser use might be a promising strategy to reduce damage in cereals by this notorious weed.
    Residues of bioenergy production chains as soil amendments: Immediate and temporal phytotoxicity
    Gell, K. ; Groenigen, J.W. van; Cayuela, M.L. - \ 2011
    Journal of Hazardous Materials 186 (2011)2-3. - ISSN 0304-3894 - p. 2017 - 2025.
    seed-germination - risk-assessment - rapeseed meal - sewage-sludge - by-products - paper-mill - bio-oil - biochar - growth - pyrolysis
    The current shift towards bioenergy production increases streams of bioenergy rest-products (RPs), which are likely to end-up as soil amendments. However, their impact on soil remains unclear. In this study we evaluated crop phytotoxicity of 15 RPs from common bioenergy chains (biogas, biodiesel, bioethanol and pyrolysis). The RPs were mixed into a sandy soil and the seedling root and shoot elongation of lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), and wheat (Triticum aestivum L.) were measured. Immediate phytotoxic effects were observed with biodiesel and bioethanol RPs (root elongation reduced to 14-60% for the three crops; P
    Strigolactones are transported through the xylem and play a key role in shoot architectural response to phosphate deficiency in nonarbuscular mycorrhizal host Arabidopsis
    Kohlen, W. ; Charnikhova, T. ; Qing, L. ; Bours, R.M.E.H. ; Domagalska, M. ; Beguerie, S. ; Verstappen, F.W.A. ; Leyser, O. ; Bouwmeester, H.J. ; Ruyter-Spira, C.P. - \ 2011
    Plant Physiology 155 (2011)2. - ISSN 0032-0889 - p. 974 - 987.
    root-system architecture - germination stimulants - seed-germination - parasitic plants - indole-3-acetic-acid levels - phosphorus deficiency - auxin transport - orobanche spp. - rms1 mutant - am fungi
    The biosynthesis of the recently identified novel class of plant hormones, strigolactones, is up-regulated upon phosphate deficiency in many plant species. It is generally accepted that the evolutionary origin of strigolactone up-regulation is their function as a rhizosphere signal that stimulates hyphal branching of arbuscular mycorrhizal fungi. In this work, we demonstrate that this induction is conserved in Arabidopsis (Arabidopsis thaliana), although Arabidopsis is not a host for arbuscular mycorrhizal fungi. We demonstrate that the increase in strigolactone production contributes to the changes in shoot architecture observed in response to phosphate deficiency. Using high-performance liquid chromatography, column chromatography, and multiple reaction monitoring-liquid chromatography-tandem mass spectrometry analysis, we identified two strigolactones (orobanchol and orobanchyl acetate) in Arabidopsis and have evidence of the presence of a third (5-deoxystrigol). We show that at least one of them (orobanchol) is strongly reduced in the putative strigolactone biosynthetic mutants more axillary growth1 (max1) and max4 but not in the signal transduction mutant max2. Orobanchol was also detected in xylem sap and up-regulated under phosphate deficiency, which is consistent with the idea that root-derived strigolactones are transported to the shoot, where they regulate branching. Moreover, two additional putative strigolactone-like compounds were detected in xylem sap, one of which was not detected in root exudates. Together, these results show that xylem-transported strigolactones contribute to the regulation of shoot architectural response to phosphate-limiting conditions.
    Strigolactone and root infestation by parasitic plants.
    Cardoso, C. ; Ruyter-Spira, C.P. ; Bouwmeester, H.J. - \ 2011
    Plant Science 180 (2011)3. - ISSN 0168-9452 - p. 414 - 420.
    arbuscular mycorrhizal fungi - f-box protein - germination stimulants - seed-germination - phosphorus deficiency - hermonthica - sorghum - host - resistance - witchweed
    Strigolactones are signaling molecules that play a role in host recognition by parasitic plants of the Striga, Orobanche and Phelipanche genera which are among the most detrimental weeds in agriculture. The same class of molecules is also involved in the establishment of the symbiosis of plants with arbuscular mycorrhizal (AM) fungi. In addition, the strigolactones are being shown to be involved in an increasing number of physiological processes in plants, such as the regulation of plant architecture and the response to abiotic factors such as nutrient availability and light. These new findings suggest that biosynthesis and perception of strigolactones are conserved throughout the plant kingdom. The structural variation in the strigolactones discovered so far and its possible role in host recognition by the parasites and AM fungi as well as the evolution of strigolactone-dependent-germination in parasitic plants will be discussed. Finally, due to the recent advance in strigolactone research, new insights are emerging on the relation between parasitic and host plants which may result in new strategies to control parasitic plant infestation that will be discussed in this review.
    Large-scale Gene Ontology analysis of plant transcriptome-derived sequences retrieved by AFLP technology
    Botton, A. ; Galla, G. ; Conesa, A. ; Bachem, C.W.B. ; Ramina, A. ; Barcaccia, G. - \ 2008
    BMC Genomics 9 (2008). - ISSN 1471-2164 - 19 p.
    genome-wide expression - pseudo-testcross strategy - poa-pratensis l - cdna-aflp - candidate genes - seed-germination - cell-division - linkage map - identification - markers
    Background: After 10-year-use of AFLP (Amplified Fragment Length Polymorphism) technology for DNA fingerprinting and mRNA profiling, large repertories of genome- and transcriptome-derived sequences are available in public databases for model, crop and tree species. AFLP marker systems have been and are being extensively exploited for genome scanning and gene mapping, as well as cDNA-AFLP for transcriptome profiling and differentially expressed gene cloning. The evaluation, annotation and classification of genomic markers and expressed transcripts would be of great utility for both functional genomics and systems biology research in plants. This may be achieved by means of the Gene Ontology (GO), consisting in three structured vocabularies (i.e. ontologies) describing genes, transcripts and proteins of any organism in terms of their associated cellular component, biological process and molecular function in a species-independent manner. In this paper, the functional annotation of about 8,000 AFLP-derived ESTs retrieved in the NCBI databases was carried out by using GO terminology. Results: Descriptive statistics on the type, size and nature of gene sequences obtained by means of AFLP technology were calculated. The gene products associated with mRNA transcripts were then classified according to the three main GO vocabularies. A comparison of the functional content of cDNA-AFLP records was also performed by splitting the sequence dataset into monocots and dicots and by comparing them to all annotated ESTs of Arabidopsis and rice, respectively. On the whole, the statistical parameters adopted for the in silico AFLP-derived transcriptome-anchored sequence analysis proved to be critical for obtaining reliable GO results. Such an exhaustive annotation may offer a suitable platform for functional genomics, particularly useful in non-model species. Conclusion: Reliable GO annotations of AFLP-derived sequences can be gathered through the optimization of the experimental steps and the statistical parameters adopted. The Blast2GO software was shown to represent a comprehensive bioinformatics solution for an annotation-based functional analysis. According to the whole set of GO annotations, the AFLP technology generates thorough information for angiosperm gene products and shares common features across angiosperm species and families. The utility of this technology for structural and functional genomics in plants can be implemented by serial annotation analyses of genome- anchored fragments and organ/tissue-specific repertories of transcriptome-derived fragments.
    Strigolactone inhibition of shoot branching
    Gomez-Roldan, M.V. ; Fermas, S. ; Brewer, P.B. ; Puech-Pages, V. ; Dun, E.A. ; Pillot, J.P. ; Letisse, F. ; Matusova, R. ; Danoun, S. ; Portais, J.C. ; Bouwmeester, H.J. ; Becard, G. ; Beveridge, C.A. ; Rameau, C. ; Rochange, S.F. - \ 2008
    Nature 455 (2008). - ISSN 0028-0836 - p. 189 - 195.
    arbuscular-mycorrhizal fungi - root parasitic plants - germination stimulants - phosphorus deficiency - seed-germination - apical dominance - rms1 mutant - arabidopsis - pea - signal
    A carotenoid-derived hormonal signal that inhibits shoot branching in plants has long escaped identification. Strigolactones are compounds thought to be derived from carotenoids and are known to trigger the germination of parasitic plant seeds and stimulate symbiotic fungi. Here we present evidence that carotenoid cleavage dioxygenase 8 shoot branching mutants of pea are strigolactone deficient and that strigolactone application restores the wild-type branching phenotype to ccd8 mutants. Moreover, we show that other branching mutants previously characterized as lacking a response to the branching inhibition signal also lack strigolactone response, and are not deficient in strigolactones. These responses are conserved in Arabidopsis. In agreement with the expected properties of the hormonal signal, exogenous strigolactone can be transported in shoots and act at low concentrations. We suggest that endogenous strigolactones or related compounds inhibit shoot branching in plants. Furthermore, ccd8 mutants demonstrate the diverse effects of strigolactones in shoot branching, mycorrhizal symbiosis and parasitic weed interaction.
    Ecological weed management by cover cropping : effects on weed growth in autumn and weed establishment in spring
    Kruidhof, H.M. ; Bastiaans, L. ; Kropff, M.J. - \ 2008
    Weed Research 48 (2008)6. - ISSN 0043-1737 - p. 492 - 502.
    seed-germination - green manure - alkaloid concentration - secale-cereale - aerobic rice - soil - competitiveness - allelochemicals - suppression - allelopathy
    Cover crops grown in the period between two main crops have potential as an important component of a system-oriented ecological weed management strategy. In late summer and autumn, the cover crop can suppress growth and seed production of weeds, whereas the incorporation of cover crop residues in spring may reduce or retard weed emergence. Based on these two criteria, six cover crop species were evaluated for their weed suppressive potential in 2 years of experimentation in the Netherlands. Fodder radish, winter oilseed rape and winter rye had the strongest competitive ability in autumn; the competitive strength of Italian ryegrass was intermediate and white lupin and lucerne were poor competitors. Competitiveness was strongly correlated to early light interception. Surprisingly, doubling the recommended sowing density did not increase weed suppressive ability. Although a poor competitor in the fall, after incorporation in spring, lucerne had the strongest inhibitory effect on seedling establishment, followed by winter oilseed rape and white lupin. Winter rye and fodder radish did not affect seedling establishment, whereas Italian ryegrass was not evaluated because of re-growth after incorporation. Competition in autumn and subsequent residue-mediated suppression of weed establishment in spring varied among the cover crop species, with winter oilseed rape offering relatively strong effects during both periods.
    Germination rates of Solanum sisymbriifolium: temperature response models, effects of temperature fluctuations and soil water potential
    Timmermans, B.G.H. ; Vos, J. ; Nieuwburg, J.G.W. van; Stomph, T.J. ; Putten, P.E.L. van der - \ 2007
    Seed Science Research 17 (2007)3. - ISSN 0960-2585 - p. 221 - 231.
    potato cyst nematodes - hydrothermal time model - seed-germination - trap crop - alternating temperatures - field performance - growth - sisymbriifolium - emergence - constant
    Four temperature response models were compared describing the emergence rate of Solanum sisymbriifolium (L.) over a broad range of suboptimal temperatures and at different soil water potentials. In the laboratory, the effects were tested on germination rates at constant (9.1-21.8 degrees C) and diurnally fluctuating temperatures at different soil water potentials. Linear, 010, expolinear and quadratic models were fitted to the data on rate of emergence against temperature. For model validation, field emergence was monitored in 11 sowings conducted in 2001-2004. Emergence rate increased with temperature and was relatively high at soil water potentials in the range of -0.21 MPa to -2.6 x 10(-3) MPa, but was almost zero at -0.96 MPa and -1.8 X 10(-3) MPa. Diurnal temperature fluctuations did not have a differing influence on germination rates or final germination percentages compared with constant temperatures. The expolinear and the quadratic models were most accurate in explaining variation of laboratory data, especially at temperatures close to the minimum germination temperature of S. sisymbriffolium. These two models had root mean square errors for predicting field emergence rates (5.9 to 38.4d) of 0.81 and 0.87d, respectively, and were considered more appropriate to predict the time to 50% germination for crops grown in conditions near their 'base temperature' than the widely used linear temperature (thermal time) models. The Gompertz function was fitted to percentage germination versus the time-accumulated germination rate (using the expolinear function to describe the rate-temperature relation). This combined model adequately predicted the temporal pattern of emergence in the field.
    Rhizosphere communication of plants, parasitic plants and AM fungi
    Bouwmeester, H.J. ; Roux, Chr. ; Lopez Raez, J.A. ; Bécard, G. - \ 2007
    Trends in Plant Science 12 (2007)5. - ISSN 1360-1385 - p. 224 - 230.
    arbuscular mycorrhizal fungi - germination stimulants - seed-germination - root exudate - orobanche - striga - arabidopsis - strigolactones - metabolism - phosphate
    Plants use an array of secondary metabolites to defend themselves against harmful organisms and to attract others that are beneficial. However, the attraction of beneficial organisms could also lead to abuse by malevolent organisms. An exciting example of such abuse is the relationship between plants, beneficial mutualistic arbuscular mycorrhizal fungi and harmful parasitic plants. Signalling molecules called strigolactones, which are secreted by plant roots in low concentrations, induce the growth of both obligate biotrophs. Here, we review the importance of strigolactones for these two interactions and discuss possible developments that should further clarify the role of these signalling molecules in rhizosphere processes.
    Long-term management of the parasitic weed Striga hermonthica : strategy evaluation with a population model
    Westerman, P.R. ; Ast, A. van; Stomph, T.J. ; Werf, W. van der - \ 2007
    Crop Protection 26 (2007)3. - ISSN 0261-2194 - p. 219 - 227.
    seed-germination - crop-rotation - sorghum - scrophulariaceae - infestation - dynamics - mali
    To increase sorghum yields in areas in Africa that are heavily infested with the root parasite Striga hermonthica, crop varieties are being bred whose roots emit fewer exudates that stimulate S. hermonthica seeds to germinate. Because S. hermonthica has a persistent seedbank, it is important to anticipate the long-term effects of such breeding efforts on the seedbank dynamics. This study reports the results of analyses conducted with a population model for S. hermonthica based on existing and earlier published models and data. The essential innovation is an explicit modelling of density-dependent feedback, which was included at different points in the life cycle. Sensitivity analyses showed that density-dependence reduced the impact on the equilibrium seedbank density of life cycle parameters at stages preceding the density-dependent process. The implication is that intervention early in the parasite life cycle through, for instance, breeding for low exudate emission of the cereal host, carries the risks of maintaining or increasing S. hermonthica seedbanks, and selection for S. hermonthica populations responsive to the new varieties. Only crop varieties with very low production of germination-stimulant will be effective in the long run. The best breeding strategy is to select for crop varieties that inhibit S. hermonthica development or growth at stages later in the life cycle or that affect the parasite at multiple stages simultaneously. The most effective management strategy is to use control measures that cause a reduction in seed production, viability of newly produced seed, or seed survival in the soil, or to use a combination of measures that affect the parasites at multiple stages. Despite considerable knowledge gaps regarding the basic demography of S. hermonthica, the model proved useful in identifying points in the S. hermonthica life cycle that are of particular interest for designing intervention strategies. In-depth studies on the demography of S. hermonthica and on the location(s) of density-dependence in the parasite's life cycle are needed.
    Fighting Fe deficiency malnutrition in West Africa : an interdisciplinary programme on a food chain approach
    Slingerland, M.A. ; Traore, K. ; Kayodé, A.P.P. ; Mitchikpe, C.E.S. - \ 2006
    NJAS Wageningen Journal of Life Sciences 53 (2006)3-4. - ISSN 1573-5214 - p. 253 - 279.
    voedingsstoornissen - gebreksziekten - ijzer - ijzergebrekanemie - voedselketens - interdisciplinair onderzoek - benin - burkina faso - west-afrika - nutritional disorders - deficiency diseases - iron - iron deficiency anaemia - food chains - interdisciplinary research - benin - burkina faso - west africa - burkina-faso - micronutrient density - nutritional quality - iron availability - edible portions - seed-germination - tannin content - sorghum grain - amino-acids - phosphorus
    About 2 billion people, mainly women and young children, suffer from iron deficiency. The supply of iron (Fe) falls short when consumed foods have a low Fe content or when absorption of Fe is inhibited by the presence of phytic acid and polyphenols in the diet. Current interventions are dietary diversification, supplementation, fortification and biofortification. In West Africa these interventions have only moderate chances of success due to low purchasing power of households, lack of elementary logistics, lack of central processing of food and the high heterogeneity in production and consumption conditions. A staple food chain approach, integrating parts of current interventions was proposed as an alternative. The research was carried out in several villages in Benin and Burkina Faso to take ecological, cultural and socio-economic diversity into account. The interdisciplinary approach aimed at elaborating interventions in soil fertility management, improvement and choice of sorghum varieties and food processing, to increase Fe and decrease the phytic acid-Fe molar ratio in sorghum-based foods. The phytic acid-Fe molar ratio was used as a proxy for Fe bioavailability in food. Synergy and trade-offs resulting from the integrated approach showed its added value. P fertilization and soil organic amendments applied to increase yield were found to also increase phytic acid content of the grain and thus to decrease its nutritional value. Amounts of Fe and phytic acid and their ratio in the grain differed among sorghum varieties, illustrating the presence of genetic variation for Fe bioavailability. The current local food preparation method for one of the main sorghum-based foods (dibou) in northern Benin did not include processing steps that remove or de-activate anti-nutritional factors reducing Fe bioavailability. The preliminary results suggest that a feasible chain solution consists of breeding for high Fe and moderate phytic acid contents and using soil organic amendments and P fertilization to increase yields but that this needs to be followed by improved food processing to remove phytic acid. Further research on timing of application of phosphate, Fe fertilizer and soil organic amendments is needed to improve phytic acid-Fe molar ratios in the grain. Research on the exact distribution of Fe, phosphate, phytic acid and tannins within the sorghum grain is needed to enable the development of more effective combinations of food processing methods aiming for more favourable phytic acid-Fe molar ratios in sorghum-based food.
    The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway
    Matusova, R. ; Rani, K. ; Verstappen, F.W.A. ; Franssen, M.C.R. ; Beale, M. ; Bouwmeester, H.J. - \ 2005
    Plant Physiology 139 (2005)2. - ISSN 0032-0889 - p. 920 - 934.
    abscisic-acid biosynthesis - arbuscular mycorrhizal fungi - isoprenoid biosynthesis - arabidopsis-thaliana - phytoene desaturase - seed-germination - flowering plants - sorghum-bicolor - maize - gene
    The seeds of parasitic plants of the genera Striga and Orobanche will only germinate after induction by a chemical signal exuded from the roots of their host. Up to now, several of these germination stimulants have been isolated and identified in the root exudates of a series of host plants of both Orobanche and Striga spp. In most cases, the compounds were shown to be isoprenoid and belong to one chemical class, collectively called the strigolactones, and suggested by many authors to be sesquiterpene lactones. However, this classification was never proven; hence, the biosynthetic pathways of the germination stimulants are unknown. We have used carotenoid mutants of maize (Zea mays) and inhibitors of isoprenoid pathways on maize, cowpea (Vigna unguiculata), and sorghum (Sorghum bicolor) and assessed the effects on the root exudate-induced germination of Striga hermonthica and Orobanche crenata. Here, we show that for these three host and two parasitic plant species, the strigolactone germination stimulants are derived from the carotenoid pathway. Furthermore, we hypothesize how the germination stimulants are formed. We also discuss this finding as an explanation for some phenomena that have been observed for the host-parasitic plant interaction, such as the effect of mycorrhiza on S. hermonthica infestation
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