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Adaptation and acclimation of seed performance
Souza Vidigal, D. De - \ 2015
Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Leonie Bentsink; Henk Hilhorst. - Wageningen University - ISBN 9789462575943 - 156
zaden - zaadkwaliteit - zaadkieming - klimaatverandering - adaptatie - arabidopsis - kiemrust - klimaatadaptatie - seeds - seed quality - seed germination - climatic change - adaptation - arabidopsis - seed dormancy - climate adaptation
Dissecting the seed-to-seedling transition in Arabidopsis thaliana by gene co-expression networks
Silva, A.T. - \ 2015
Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Henk Hilhorst; Wilco Ligterink. - Wageningen : Wageningen University - ISBN 9789462575929 - 177
arabidopsis thaliana - zaden - zaadkieming - zaailingen - genexpressie - uitdrogingstolerantie - arabidopsis thaliana - seeds - seed germination - seedlings - gene expression - desiccation tolerance
One of the most important developmental processes in the life-cycle of higher plants is the transition from a seed to a plant and from a generative to a vegetative developmental program. The major hallmark or end-point of the transition from seed to plant is the onset of photosynthesis and the concomitant shift from a heterotrophic to an autotrophic organism. It is advantageous for a species to keep the period of seedling establishment as short as possible since young seedlings are highly sensitive to biotic and abiotic stresses. This implies that the extreme stress tolerance of seeds to i.e. desiccation is lost upon germination. If the regulatory principles of the seed-to-seedling transition are better understood it may become feasible to maintain the seed’s stress tolerance well into the seedling stage.
Despite the profound impact of seedling performance on crop establishment and yield, the seed-to-seedling transition has hardly been studied at the molecular level. This thesis aims at deciphering and understanding the molecular processes that govern this transition in Arabidopsis thaliana. A high-resolution study of the molecular events that occur during these successive transitional stages may provide clues as to the regulatory principles that drive this transition. It may also yield information about the factors that determine the (in)ability to revert to a developmental mode and which features are critical for the maintenance and loss of desiccation tolerance and other stress responses.
In Chapter 1 important processes such as abscisic acid and their regulation are described and it is discussed in what way the seed-to-seedling transition may have links to a trait such as desiccation tolerance. An overview is presented of the current knowledge of the seed-to-seedling phase transition and the existence of a temporal developmental block that can be manipulated by osmotic treatment, the carbon/nitrogen balance and by abscisic acid which results in the re-establishment of desiccation tolerance.
Chapter 2 focuses on comprehensive gene regulation by a detailed transcriptional analysis across seven developmental stages of the seed-to-seedling transition. It describes the inference of a gene co-expression network and several transcriptional modules. I show that such an approach highlights important molecular processes during seedling development, which would not likely be derived from comparative transcript profiling. Moreover, I show that a putative key regulator in one of the transcriptional modules affects late seedling establishment.
In Chapter 3 it is shown how this phase transition is expressed in the primary metabolite profiles in correlation with gene expression. A metabolite-metabolite correlation analysis suggested two profiles, which point at the metabolic preparation of seed germination and of vigorous seedling establishment. Furthermore, a linear correlation between metabolite contents and transcript abundance (Chapter 2) provides a global view of the transcriptional and metabolic changes during the seed-to-seedling transition. It creates new perspectives of the regulatory complexes underlying the seed-to-seedling transition.
Chapter 4 describes the development of a novel method to re-establish desiccation tolerance during the seed-to-seedling transition without adverse effects such as those caused by an osmotic treatment with polyethylene glycol. By using this method, named ‘Mild Air Drying Treatment’ (MADT), I show that the re-establishment of desiccation tolerance is not linked to a reduced ability to accumulate ABA in the desiccation sensitive seeds (germinated seeds at root hair stage). I also present a genetic interaction study of ABSCISIC ACID INSENSITIVE (ABI) genes in their germination response to ABA, and their response to the re-establishment of desiccation tolerance using the MADT. The interaction between ABI3 and ABI4, and between ABI4 and ABI5 act synergistically in the re-establishment of DT, as well as in the germination response to ABA.
In a more in depth study in Chapter 5 I carried out an extensive transcript analysis to infer possible mechanisms of the re-establishment of desiccation tolerance using the MADT protocol. Possible mechanisms underlying the re-establishment of desiccation tolerance were inferred by employing a time-series comparison of germinated desiccation tolerant and -sensitive seeds. Early-response genes of the re-establishment of desiccation tolerance may play a role in events that promote the initial protection to dehydration stress, whereas the late-response genes may play a role in events that help seed to respond to the changes in water dynamics. Moreover, using a gene co-expression network and transcriptional module I concluded that a crosstalk between ABA-dependent and ABA-independent transcription factors regulate the re-establishment of desiccation tolerance.
In Chapter 6 I discuss how the results presented in this thesis contribute to our knowledge of the molecular basis of the seed-to-seedling transition and the re-establishment of desiccation tolerance during its phase changes. Finally, new possibilities for further research are discussed, as well as the further use of the data sets to delineate the mechanisms underlying the seed-to-seedling transition and desiccation tolerance. Possible applications of the results for crop improvement are addressed. Thus, the generation of genetically modified plants that produce seeds with a stress tolerance that extends well into seedling stage may be feasible.
Functional analyses of AtCHR12 and AtCHR23 : plant growth responses upon over-expression of chromatin remodeling ATPase genes
Folta, A. - \ 2015
Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Ludmila Mlynarova. - Wageningen : Wageningen University - ISBN 9789462575561 - 144
planten - groei - genexpressie - chromatine - atp - arabidopsis - solanum lycopersicum - zaadkieming - groeiregulatoren - plants - growth - gene expression - chromatin - atp - arabidopsis - solanum lycopersicum - seed germination - growth regulators
Living organisms have to deal with changing environmental conditions during their whole life cycle. In contrast to animals, plants are sessile organisms. Therefore they have evolved multiple regulatory mechanisms that help them to cope with changing conditions. One of the first responses to stress conditions is reduction or arrest of growth. Therefore regulation of growth and development is essential to successfully complete their life cycle. To correctly time their development, plants need to integrate various environmental signals with intrinsic developmental programs. In this integration, regulation of gene expression plays a major role.
The genetic information of an organism is stored in DNA sequence. DNA forms a complex with histones and other proteins, which is called chromatin. Chromatin is a highly dynamic complex and modification of the chromatin structure makes DNA more or less accessible to the transcriptional machinery and other regulatory proteins. The modification of chromatin organization is called chromatin remodeling and it involves both covalent modifications of DNA and histone tails, and non-covalent modification of chromatin structure by ATP-dependent chromatin remodeling complexes. ATP-dependent chromatin remodeling complexes comprise multiple protein subunits with SNF2 ATPase as a catalytic subunit. Depending on the subunit composition, the complexes can perform different tasks at various places of chromatin, and can be active at different developmental stages (Chapter 1).
The SNF2 ATPases are conserved from yeast to plants. In Arabidopsis, 41 SNF2 ATPases have been identified. The focus of this thesis is on two of those ATPases – AtCHR12 and AtCHR23. It has been shown previously that AtCHR12 is involved in growth responses to environmental cues. We have extended these studies to its paralog AtCHR23 (Chapter 2). In contrast to over-expression of AtCHR12, which affects growth only during reproductive stage of development, over-expression of AtCHR23 leads to smaller seedlings and reduced vegetative growth. Upon application of mild abiotic stress, the growth reduction is stronger than in wild-type plants. Moreover, the transgenic plants manifest increased variability of growth. The increased growth variability correlates with increased expression variability of genes associated with stress. The results indicate that accurate and controlled expression of AtCHR23 is required for stability and robustness of growth, as well as gene expression.
Regulation of growth is important not only during vegetative or reproductive stage of development, but also during embryo development. The growth of the embryo is interrupted during the embryo maturation phase and it was suggested that AtCHR12 may be involved in this temporary growth arrest. Here we have shown that both AtCHR12 and AtCHR23 are expressed during embryo development, and that over-expression of AtCHR12 or AtCHR23 affects the embryo maturation phase with consequences on two important developmental transitions in plant life – germination and transition to flowering.
Over-expression of AtCHR12 or AtCHR23 leads to reduced seed germination, which is more pronounced under stress conditions (Chapter 3). The reduced germination of over-expressing lines is associated with increased transcript levels of seed maturation genes and reduced degradation of their mRNAs in germinating seeds. The results indicate that repression of AtCHR12 and AtCHR23 in germinating seeds is required for full germination.
The connection between embryo development and flowering time control was observed in transgenic lines over-expressing AtCHR12 (Chapter 4). Over-expression of AtCHR12 results in early flowering under both long- and short-day conditions. The early flowering phenotype correlates with reduced expression of the main flowering repressor, FLC. The reduced FLC expression correlates with increased levels of repressive histone mark H3K27me3 on the FLC locus. Additionally, FLC expression was affected already during FLC reprogramming, which takes place during embryo development. This leads to reduced FLC expression in mature embryos. The results show that AtCHR12 over-expression affects flowering time by different mechanisms than other Snf2-subfamily ATPases. In contrast to AtCHR12, BRAHMA was shown to regulate flowering time via the photoperiod pathway, while SPLAYED affects flowering time by repressing FT expression.
We have observed that over-expression of AtCHR12 or AtCHR23 affects plant growth in response to stress, and play a role in germination and transition to flowering. These traits are also important for agriculture, and such genes are potentially interesting targets for breeding programs. To test, if such genes have a similar role in crops, we have studied the effect of the tomato ortholog of AtCHR12 and AtCHR23 on tomato growth.
Tomato (Solanum lycopersicum), as well as other crops, have only one ortholog of AtCHR12 and AtCHR23, which was suggested to possess a role of both ATPases. We have successfully cloned the tomato ortholog and over-expressed it in tomato plants (Chapter 5). The transgenic tomato plants have reduced vegetative growth and compacted reproductive structures, resembling the phenotype of AtCHR23 and AtCHR12 over-expression, respectively. However, in contrast to Arabidopsis, the tomato plants responded to abiotic stress similarly as wild-type, and they flowered later than wild-type plants. The results indicate that modification of expression of AtCHR12 and AtCHR23 orthologs could be used to develop novel methods to control plant growth.
Taken together, the research described in this thesis identifies AtCHR12 and AtCHR23 as regulators of plant growth, especially in response to environment, as well as of the seed maturation program with clear effects on seed germination and flowering time, and we show that such genes can be potentially interesting for agriculture and horticulture practice.
Biochemical, physiological and molecular responses of Ricinus communis seeds and seedlings to different temperatures: a multi-omics approach
Ribeiro de Jesus, P.R. - \ 2015
Wageningen University. Promotor(en): Harro Bouwmeester, co-promotor(en): Henk Hilhorst; Wilco Ligterink. - Wageningen : Wageningen University - ISBN 9789462574700 - 203
ricinus communis - zaden - zaailingen - plantenfysiologie - temperatuur - moleculaire biologie - genexpressie - zaadkieming - zaadopkomst - ricinus communis - seeds - seedlings - plant physiology - temperature - molecular biology - gene expression - seed germination - seedling emergence
Biochemical, physiological and molecular responses of Ricinus communis seeds and seedlings to different temperatures: a multi-omics approach
by Paulo Roberto Ribeiro de Jesus
The main objective of this thesis was to provide a detailed analysis of physiological, biochemical and molecular-genetic responses of Ricinus communis to temperature during seed germination and seedling establishment.
In Chapter 2, I describe the assessment of 17 candidate reference genes across a diverse set of samples, including several tissues, various developmental stages and environmental conditions, encompassing seed germination and seedling growth in R. communis. These genes were tested by RT-qPCR and ranked according to the stability of their expression using two different approaches: GeNorm and NormFinder. Both GeNorm and Normfinder indicated that ACT, POB and PP2AA1 represent the optimal combination for normalization of gene expression data in inter-tissue studies. I also describe the optimal combination of reference genes for a subset of samples from root, endosperm and cotyledonary tissues. The selection of reference genes was validated by normalizing the expression levels of three target genes involved in energy metabolism with the identified optimal reference genes. This approach allowed me to identify stably expressed genes, and, thus, reference genes for use in RT-qPCR studies in seeds and seedlings of R. communis.
In Chapter 3, a thermo-sensitive window is identified during seed germination in which high temperatures compromise subsequent seedling development. I assessed the biochemical and molecular requirements of R. communis germination for successful seedling establishment at varying temperatures. For that, I performed metabolite profiling (GC-TOF-MS) and measured transcript levels of key genes involved in several energy-generating pathways such as storage oil mobilization, β-oxidation of fatty acids and gluconeogenesis of seeds germinated at three different temperatures. Transient overexpression of genes encoding for malate synthase (MLS) and glycerol kinase (GK) resulted in higher starch levels in N. benthamiana leaves, which highlights the likely importance of these genes in energy-generating pathways for seedling establishment. Additionally, I showed that γ-aminobutyric acid (GABA), which is a stress-responsive metabolite, accumulated in response to the water content of the seeds during the initial phase of imbibition.
In Chapter 4 I undertook a genomics approach using microarray analysis to determine transcriptome changes in three distinct developmental stages during seed germination at 20, 25 and 35ºC that could explain the thermo-sensitive window that is described in Chapter 3. Most of the differences in the R. communis transcriptome occurred between 6 hours of imbibition and the commencement of germination, i.e. radicle protrusion. This coincides with the thermo-sensitive window identified during seed germination in which high temperatures compromise seedling development. The transcriptome data was used to identify heat-stress responsive genes that might be involved in thermotolerance of R. communis during germination. Temperature had a major effect on genes involved in energy generating pathways, such as the Calvin-Benson-Bassham cycle, gluconeogenesis, and starch- and triacylglycerol degradation. Transcripts coding for ATP binding proteins, DNA binding proteins, RNA binding proteins, DNA-directed RNA polymerases I, II, and III, heat shock factor proteins, multiprotein-bridging factor proteins, and zinc finger proteins were also affected by temperature suggesting the whole transcriptional regulatory machinery was altered in response to temperature. Among the downregulated transcripts under high temperature, only three were shared by all three stages: an oxidation-related zinc finger 2, an F-box and wd40 domain protein, and a DNA binding protein/MYB-like transcription factor. Among the upregulated transcripts, nine were shared by all three stages: a BET1P/SFT1P-like protein, 14BB, a low-molecular-weight cysteine-rich protein LCR78, a WD-repeat protein, a GAST1 protein, an adenylate kinase 1/P-loop containing nucleoside triphosphate hydrolases superfamily protein, and four conserved hypothetical proteins. These genes constitute good candidates for further characterization of temperature-responsive genes in R. communis.
In Chapter 5, I studied the genetic variation in the effect of temperature on growth of young R. communis seedlings and measured primary and secondary metabolites in roots and cotyledons of three R. communis genotypes, varying in stress tolerance. Seedling biomass was strongly affected by the temperature, with the lowest total biomass observed at 20ºC. The response in terms of biomass production for the genotype MPA11 was clearly different from the other two studied genotypes: genotype MPA11 produced heavier seedlings at all temperatures but the root biomass of this genotype decreased with increasing temperature, reaching the lowest value at 35ºC. In contrast, root biomass of genotypes MPB01 and IAC80 was not affected by temperature, suggesting that the roots of these genotypes are less sensitive to changes in temperature. A shift in carbon-nitrogen metabolism towards the accumulation of nitrogen-containing compounds seems to be the main biochemical response to support growth at higher temperatures. Carbohydrate content was reduced in response to increasing temperature in both roots and cotyledons, whereas amino acids accumulated to higher levels. The results in this chapter show that a specific balance between amino acids, carbohydrates and organic acids in the cotyledons and roots of genotype MPA11 seems to be an important trait for faster and more efficient growth of this genotype at higher temperatures.
In Chapter 6, I decided to focus on the differential ability of genotypes MPA11 and IAC80 to sustain root biomass production at higher temperatures. Biomass allocation was assessed by measuring dry weight of roots, stems, and cotyledons of seedlings grown at three different temperatures. Seedlings grown at 25ºC and 35ºC showed greater biomass than seedlings grown at 20ºC. Cotyledon and stem dry weight increased for both genotypes with increasing temperature, whereas root biomass allocation showed a genotype-dependent behaviour. Genotype MPA11 showed a continuous increase in root dry weight with increasing temperature, while genotype IAC80 was not able to sustain further root growth at higher temperatures. Metabolite and gene expression profiles of genotype MPA11 demonstrated an increase in the levels of osmoprotectant molecules, such as galactinol and transcripts of genes encoding antioxidant enzymes and heat shock proteins, to a higher extent than in genotype IAC80.
In Chapter 7 I raised the question whether carbohydrate accumulation in R. communis leaves, roots, and seeds, grown at low temperatures, as compared to higher temperatures, results from up-regulation of biosynthetic pathways, from down-regulation of catabolic pathways, or both. To answer this question, transcript levels were measured of genes encoding enzymes involved in starch biosynthesis, starch catabolism, and gluconeogenesis in leaves, roots, and seeds grown at 20ºC and 35ºC. Transcript levels of genes involved in starch catabolism were higher in leaves grown at 20ºC than at 35ºC, but up-regulation of genes involved in starch biosynthesis seems to compensate for this and, therefore, is the likely explanation for higher levels of starch in leaves grown at 20ºC. Higher levels of soluble carbohydrates in leaves grown at 20ºC may have been caused by a coordinated up-regulation of starch catabolism and gluconeogenesis pathways. In roots, starch catabolism and gluconeogenesis seem to be enhanced at elevated temperatures. Higher levels of starch in seeds germinated at low temperatures is associated with higher transcript levels of genes involved in starch biosynthesis. Similarly, higher transcript levels of RcPEPCK and RcFBPase are most likely causal for fructose and glucose accumulation in seeds germinated at 20ºC.
This thesis provides important insights in the understanding of the plasticity of R. communis in response to temperature. The knowledge obtained may apply to other species as well. Additionally, based on the transcriptomics data, we selected several candidate genes that are potentially involved in, or required for, proper seed germination and seedling establishment under different temperatures, such as a number of transcription factors, a zinc finger protein, heat-shock proteins, malate synthase and glycerol kinase. Overexpressing Arabidopsis lines transformed with these R. communis genes, as well as Arabidopsis T-DNA lines, in which Arabidopsis homologs of these genes are knocked-out, are being generated for further phenotypical analysis. These overexpression and T-DNA lines should help us to understand the molecular requirements for vigorous seedling growth of R. communis under different environmental conditions.
This work was performed at the Laboratory of Plant Physiology, Wageningen University. This research was financially supported by the Brazilian Government through the National Counsel of Technological and Scientific Development (CNPq grant number 200745/2011-5).
A systems genetics study of seed quality and seedling vigour in Brassica rapa
Basnet, R.K. - \ 2015
Wageningen University. Promotor(en): Richard Visser, co-promotor(en): Guusje Bonnema; Chris Maliepaard. - Wageningen : Wageningen University - ISBN 9789462574250 - 177
brassica campestris - zaadkwaliteit - groeikracht - zaden - zaadontwikkeling - zaadkieming - zaailingen - plantengenetica - genomica - brassica campestris - seed quality - vigour - seeds - seed development - seed germination - seedlings - plant genetics - genomics
Seed is the basic and most critical input for seed propagated agricultural crops: seed quality and seedling vigour determine plant establishment, growth and development in both natural and agricultural ecosystems. Seed quality and seedling vigour are mainly determined by the interactions of the following three components: genetic background, physiological quality and the environmental conditions during seed set, seed ripening, storage, seed germination and early seedling development. In the past, many efforts have been made to improve seed germination and seedling vigour by optimizing physiological and environmental factors (non-genetic factors); however, the paradigm has shifted to investigate genetic factors and to use these to improve crop performance by plant breeding. The aim of this thesis is to unravel the genetics of seed germination and seedling vigour under different conditions in Brassica rapa, using a systems genetics approach. Studies in many crop species have reported that seed germination and seedling vigour traits are governed by many genes and are strongly affected by environmental conditions. As salinity stress is becoming one of the most important abiotic stresses affecting crop growth and yield, we studied the genetics of seed germination and seedling vigour under neutral and salt stress conditions. For a number of crops, it has been established that larger seed size and higher seed weight indicate more reserve food and contribute positively to seedling establishment. Therefore, our hypothesis for this thesis is that transcriptional regulation of genes during seed development determines the composition and content of seed reserves, and that these seed reserves play a major role in seed germination and seedling growth, especially at the heterotrophic stage under optimal and sub-optimal conditions.
B. rapa is an extremely diverse Brassica species which includes, besides many diverse leafy vegetable types and turnips, also oilseed crops. Brassica seeds are of high economic importance for several reasons. They are the starting point of the life cycle of the crop, but also they are directly used as sources of vegetable oil or condiments. At present, B. napus is the most important source of vegetable oil worldwide, but B. rapa is often used for introgression breeding to broaden its narrow genetic base resulting in genetic improvements. Therefore, the acquired knowledge is also useful for the scientific community and plant breeders working in B. napus and other Brassica species.
In Chapter 2 we evaluated the genetic diversity of a B. rapa core collection of 168 accessions representing different crop types and geographic origins. Using the Bayesian cluster analysis software STRUCTURE, we identified four subpopulations: subpopulation 1 with accessions of Indian origin, spring oil, yellow sarson and rapid cycling; subpopulation 2 consisting of several types from Asian origins: pak choi, winter oil, mizuna, mibuna, komasuna, turnip green, oil rape and Asian turnip; subpopulation 3, which included mainly accessions of Chinese cabbage and subpopulation 4 with mostly vegetable turnip, fodder turnip and brocoletto accessions from European origin. The geographical distribution of the accessions was very much congruent with genetic, metabolic and morphological diversity. This initial study was followed by association studies for secondary metabolites from the tocopherol and carotenoids pathways, using the population structure of these four subpopulations as a correction term to control for spurious marker-trait associations (Chapter 2). Additionally, we used a machine learning approach, Random Forest (RF) regression, to find marker-trait associations. We chose the RF approach as it can handle large numbers of variables (markers, metabolites, transcript abundance) in combination with relatively small sample sets of accessions, to show its perspectives for application to the increasing amounts of data available through the different ~omics technologies. In our analysis, the markers showing significant association with metabolites identified by the RF approach overlapped with markers obtained from association mapping. Those markers could potentially be used for marker-assisted selection (MAS) in breeding for these secondary metabolites in different morphotypes or sub-populations. Knowledge of genetic distance as evaluated in this chapter allowed the choice of parents to create a segregating population for QTL analyses by maximizing genetic variation between the parents.
In Chapter 4, a doubled haploid (DH) population from a cross of genetically diverse morphotypes of B. rapa, an oil-type yellow sarson (YS143) and a vegetable pak choi (PC175) (Chapter 2), was used to evaluate the genetic basis of seed germination and seedling vigour traits under both non-stress and salt stress conditions. The yellow sarson parent had larger seed size and higher thousand-seed weight than the pak choi parent, and displayed earlier onset, higher uniformity in germination, faster germination and maximum germination, and higher root- and shoot- lengths and biomass under both non-stress and salt stress conditions. Positive correlations of thousand-seed weight with earliness, speed and uniformity of germination and maximum germination percentage, supports that larger seeds germinate earlier, faster, more uniformly and to a higher maximum germination percentage than smaller seeds. Thus, we conclude that yellow sarson had higher seed quality and seedling vigour than pak choi. However yellow sarson also contributed negative alleles to seed germination, as illustrated by its allele of the QTL at A05 which decreases the uniformity of seed germination. In addition we also observed that yellow sarson seedling growth was more affected by salt stress than pak choi. All traits were scored over the DH population, and this clearly showed transgressive variation for most traits. Eight QTL hotspots were identified for seed weight, seed germination, and root and shoot lengths. A QTL hotspot for seed germination on A02 co-located with a homologue of the FLOWERING LOCUS C (BrFLC2) genes and its cis-acting expression QTL (cis-eQTL). FLC2 (BrFLC2 in B. rapa) is an important repressor of flowering time in both A. thaliana and B. rapa and recently, FLC2 was reported for its pleiotropic effect on seed germination in A. thaliana. A QTL hotspot on A05 with salt stress specific QTL co-located with the FATTY ACID DESATURASE 2 (BrFAD2) gene and its cis-eQTL. Besides the role of FAD2 in fatty acid desaturation, the up-regulation of this gene was associated with enhanced seed germination and hypocotyl elongation under salinity in B. napus (BnFAD2) and A. thaliana (FAD2). We observed epistatic interactions between the QTL hotspots at the BrFLC2 and BrFAD2 loci, and between other QTL hotspots.
Seed development is regulated by many dynamic metabolic processes controlled by complex networks of spatially and temporally expressed genes. Therefore, morphological characteristics and the transcriptional signatures of developing seeds from yellow- and brown/black-seeded genotypes were studied to get to know the timing of key metabolic processes, to explore the major transcriptional differences and to identify the optimum stage for a genetical genomics study for B. rapa seed traits (Chapter 3). This is the first study of genome-wide profiling of transcript abundance during seed development in B. rapa. Most transcriptional changes occurred between 25 and 35 days after pollination (between the bent-cotyledon stage and the stage when the embryo fully fills the seed), which is later than in the related species B. napus. A weighted gene co-expression network analysis (WGCNA) identified 47 gene modules with different co-expression patterns, of which 17 showed a genotype effect, 4 modules a time effect during seed development and 6 modules both genotype and time effects. Based on the number of genes in gene modules, the predominant variation in gene expression was according to developmental stages rather than morphotype differences. We identified 17 putative cis-regulatory elements (motifs) for four co-regulated gene clusters of genes related to lipid metabolism. The identification of key physiological events, major expression patterns, and putative cis-regulatory elements provides useful information to construct gene regulatory networks in B. rapa developing seeds and provides a starting point for a genetical genomics study of fatty acid composition and additional seed traits in Chapter 5.
Since Brassica seeds are sources of vegetable oil, genetic studies of the gene regulatory mechanisms underlying lipid metabolism is of high importance, not only in relation to seed and seedling vigour, but also for Brassica oilseed breeding. In Chapter 5, an integrative approach of QTL mapping for fatty acids composition and for transcript abundance (eQTL) of genes related to lipid metabolism, together with gene co-expression networks was used to unravel the genetic regulation of seed fatty acid composition in the DH population of B. rapa. In this study, a confounding effect of flowering time variation was observed on fatty acid QTLs (metabolite level) at linkage group A02 and of seed colour variation on eQTLs (transcript level) at linkage group A09. At A02, fatty acid QTLs from 2009 seeds co-locate with the genetic position of a gene-targeted marker for BrFLC2, its cis-QTL, and a major flowering time QTL. Flowering time variation is very obvious in this DH population and the BrFLC2 gene at A02 (16.7 cM) is the major regulator of flowering time, with a non-functional allele in the yellow sarson parent. When QTL analysis was performed on seeds from 2011, from DH lines that flowered synchronously due to staggered sowing, this fatty acid QTL hotspot disappeared. The 2011 seed lot was used for further analysis combining fatty acid QTLs with eQTLs in this study. On A09, a large trans-eQTL hotspot was co-localized with a major seed colour QTL, in the region where the causal gene, the bHLH transcription factor BrTT8, was cloned. The role of this gene in seed colour development was functionally proven in B. rapa. As the yellow sarson and pak choi parents of this population have contrasting seed coat colour (Chapter 3) the DH lines segregated for seed colour. When seed colour variation was used as a co-variate in our statistical model, we could exclude its confounding effect on eQTL mapping. We compared the fatty acid QTL and eQTL results from the analyses before and after seed colour correction and later discuss the results from the analysis after correction. The distribution of major QTLs for fatty acids showed a relationship with the types of fatty acids: linkage group A03 contained major QTLs for monounsaturated fatty acids (MUFAs), A04 for saturated fatty acids (SFAs) and A05 for polyunsaturated fatty acids (PUFAs). Using a genetical genomics approach, eQTL hotspots were found at major fatty acid QTLs on A03, A04 and A05 and on A09. Finally, an eQTL-guided gene co-expression network of lipid metabolism related genes showed major hubs at the genes BrPLA2-ALPHA, BrWD-40, a number of seed storage protein genes and a transcription factor BrMD-2, suggesting essential roles of these genes in lipid metabolism. Several genes, such as BrFAE1, BrTAG1, BrFAD2, BrFAD5, BrFAD7, which were reported as important genes for fatty acid composition in seeds in other studies of related species, had relatively lower degrees of connection in the networks. However their cis-eQTLs co-localized with specific fatty acid QTLs, making them candidate genes for the observed variation. We hypothesize that these play a role in modifying fatty acid content or composition across genotypes, rather than playing essential roles in the pathway itself. These results suggest the need of a global study of lipid metabolism rather than a strict focus on the fatty acid biosynthesis pathway per se. This study gives a starting point for understanding the genetic regulation of lipid metabolism, by identification of a number of key regulatory genes, identified as major hub genes, and candidate genes for fatty acid QTLs.
In the final chapter (Chapter 6) we summarize and critically discuss the relationships among phenotypic traits, metabolites and expression variation as well as the co-localization of QTLs from these different levels. In this thesis, we developed methodology to integrate transcriptomics and metabolomics data sets and to construct gene regulatory networks related to major fatty acids, and found a set of (possible) candidate genes involved in lipid metabolism. In the future, we recommend to integrate the genome-wide transcriptome data set with all major seed metabolites and phenotypic data on seed and seedling vigour to directly link all three components: transcriptome, metabolome and phenotypic traits, and ultimately expand the knowledge on the genetic regulation of seed metabolites, seed quality and seedling vigour in B. rapa to other Brassica species.
Environmental regulation of seed performance
He, H. - \ 2014
Wageningen University. Promotor(en): Harro Bouwmeester; J.C.M. Smeekens, co-promotor(en): Henk Hilhorst; Leonie Bentsink. - Wageningen University : Wageningen University - ISBN 9789462570337 - 185
arabidopsis - zaden - kiemrust - zaadkieming - milieueffect - genetica - genotypen - temperatuur - arabidopsis - seeds - seed dormancy - seed germination - environmental impact - genetics - genotypes - temperature
The seed stage is an essential episode in the life cycle of higher plants. The environmental cues that seeds experience during their development are important components of their life history. The parental environment, from pre-fertilization until seed dispersal affects performance of the dry mature seed and, therefore, affects the life cycle of the next generation. The evolutionary response to environmental perturbations has resulted in genetic changes in order to increase the fitness of the population, which is called ‘adaptation’. The aims of this study were to increase our understanding of how environments regulate seed performance, both on the long term, i.e. through adaptation of seed performance traits to local conditions and on the short term, i.e. by acclimation of plants to different seed maturation environments.
Seed germination methods for native Caribbean trees and shrubs : with emphasis on species relevant for Bonaire
Burg, W.J. van der; Freitas, J. ; Debrot, A.O. - \ 2014
Wageningen : Plant Research International, Business Unit Agrosystems Research (Report / Plant Research International 551) - 60
zaadkieming - bomen - struiken - zaden - opslag van zaden - zaad verzamelen - kiemrust - bonaire - caribisch gebied - seed germination - trees - shrubs - seeds - seed storage - seed collection - seed dormancy - caribbean
This paper is intended as a basis for nature restoration activities using seeds of trees and (larger) shrubs native to Bonaire with the aim of reforestation. It describes the main seed biology issues relevant for species from this region, to facilitate decisions on time and stage of harvesting, safe storage, breaking dormancy and germinating seeds and planting the young trees in the field. The paper also emphasises that natural process of seedling establishment and succession must be observed in order to be successful. The choice of species and method of protection once planted in nature will prove essential. The paper ends with stressing that such a reforestation activity needs to be planned far ahead: seeds must be collected from tree species taking care of genetic diversity and their storage potential. Recalcitrant seeds (see paper) must be treated carefully and in a different way.
Seed quality in informal seed systems
Biemond, P.C. - \ 2013
Wageningen University. Promotor(en): Paul Struik, co-promotor(en): Tjeerd-Jan Stomph. - S.l. : s.n. - ISBN 9789461736420 - 120
zaadkwaliteit - zaadfysiologie - vigna unguiculata - vignabonen - zaadkieming - zaadpathologie - mycotoxinen - zea mays - nigeria - seed quality - seed physiology - vigna unguiculata - cowpeas - seed germination - seed pathology - mycotoxins - zea mays - nigeria
Keywords: informal seed systems, seed recycling, seed quality, germination, seed pathology, seed health, seed-borne diseases, mycotoxigenic fungi, Fusarium verticillioides, mycotoxins, Vigna unguiculata, Zea mays, Nigeria.
Seed is a crucial input for agricultural production. Approximately 80% of the smallholder farmers in Africa depend for their seed on the informal seed system, consisting of farmers involved in selection, production and dissemination of seed. The lack of overhead, distribution and seed testing costs enables seed-producing farmers to offer seed for low prices, but seed quality is not always good. Seed-producing farmers multiply their seed on-farm without frequent seed renewal, referred to as seed recycling, which may lead to low seed quality. This research analysed the effect of seed recycling on physiological quality and seed health of cowpea and maize, and compared seed quality of the formal and informal seed system.
We tested the physical and physiological quality of cowpea seeds produced by the formal and informal seed system. Five out of six foundation seed samples, 79 out of 81 samples of farmers’ seed, and six out of six seed company samples failed to meet standards for foundation and certified seeds of the National Agriculture Seed Council (NASC), the seed industry regulatory agency in Nigeria. No evidence was found for a negative effect of seed recycling on physiological quality of cowpea seeds. We analysed 45,500 cowpea seeds for seed-borne bacteria and fungi to compare the performance of formal and informal seed systems. All samples were heavily infected with seed-borne pathogens, including Fusarium oxysporum (69% of the samples) and Macrophomina phaseolina (76%). No evidence was found that seed recycling in the informal seed system did lead to increased levels of seed-borne pathogens. We also analysed seed quality of farmer-produced maize seed to compare it with the formal seed system. The seed company samples had significantly higher germination (99.3%) than farmer-produced seed (97.7%), but not a single sample passed the requirements for certified seed of the NASC. Twelve seed-borne pathogens were identified including Bipolaris maydis (found in 45% of the farmer-produced samples), Botryodiplodia theobromae (97%) and Fusarium verticillioides (100%). Seed recycling had no negative effect on the physiological quality or seed health of maize seed. We analysed formal and informal seed systems to assess the opportunities to prevent mycotoxigenic fungi infection in maize seeds. A range of control methods to avoid fungal infection and mycotoxin production is discussed in relation to three criteria for sustainable implementation in developing countries. An integrated approach is recommended, with special attention towards the local seed system. As an overall conclusion of the work it can be stated that the informal seed system did not underperform compared to the formal seed system for cowpea, but did underperform in relation to seed company samples of maize. There was no evidence that seed recycling reduces seed quality of cowpea and maize seed samples, so frequent seed renewal will not improve seed quality of the informal seed system. We recommend a new quality assurance system for the informal seed system based on seed quality testing by farmers themselves, without interference by government or external laboratories. Farmers publish their seed testing results on the bag, while buyers can retest the seed to verify the quality. Further research is required to develop and implement this system in different countries, agro-ecologies and crops, and to develop methods that enable farmers to test seed health quality themselves.
Imaging genetics of seed performance
Joosen, R.V.L. - \ 2013
Wageningen University. Promotor(en): Linus van der Plas, co-promotor(en): Henk Hilhorst; Wilco Ligterink. - S.l. : s.n. - ISBN 9789461734976 - 196
zaden - zaadkieming - kiemkracht - genetica - kiemrust - genomica - arabidopsis thaliana - moleculaire genetica - moleculaire biologie - loci voor kwantitatief kenmerk - seeds - seed germination - germinability - genetics - seed dormancy - genomics - arabidopsis thaliana - molecular genetics - molecular biology - quantitative trait loci
The Netherlands has a long history of plant breeding which has resulted in a leading position in the world with respect to the sales of vegetable seeds. Nowadays high-tech methods are used for crop-production which demands high standards for the quality of the starting materials. While breeding has mainly focused on crop yield and disease resistance in the past, it now becomes equally important to create seeds that rapidly and uniformly germinate under a wide range of production environments. A better understanding of the molecular processes that are underlying seed quality is a crucial first step to enable targeted breeding. In this thesis we describe the results of new methods that were used to map the genetics of seed germination.
For this research we have used the leading plant science model species Arabidopsis thaliana which has a short generation time and a fully sequenced genome. Further, the large scientific community working on this model species is providing a wealth of resources ranging from large collections of worldwide accessions, genetic mapping populations, mutants and knowledge about gene, protein and metabolite action. A disadvantage of using Arabidopsis is the small size of the seeds, which requires evaluation of the germination of individual seeds with the use of magnifying glasses. This problem has been solved by using image analysis to create an automated procedure to obtain detailed information for parameters such as rate, uniformity and maximum germination. This procedure, called ‘the Germinator’, is described in Chapter 2 and has been enthusiastically adopted by the seed community.
Plants cannot walk away from the environment at which the seed is dispersed. To survive and to enable reproduction, plants adapt to the prevailing environment which results in considerable genetic variation. This ‘natural variation’ is a great resource to study the mechanisms of adaptation. In Chapter 3 we have used two distinct Arabidopsis accessions, one originating from Germany (Bayreuth) and the other from high altitude in the Pamiro-Alay Mountains in Tadjikistan (Shahdara). In contrast to the Bayreuth accession, the Shahdara accession is well adapted to survive harsh conditions and is known to be stress tolerant to a range of environments. A genetic mapping (recombinant inbred line; RIL) population, consisting of 165 lines, that was derived from these two accessions is therefore particularly suitable to locate the genomic regions with genetic differences that influence seed germination. Such genomic regions are commonly referred to as quantitative trait loci (QTL). With help of the Germinator system we were able to evaluate germination of this RIL population under many different conditions. This resulted in a description of the ‘genetic landscape of seed performance’ in which we identified many QTLs for Arabidopsis seed germination.
QTL regions are often large and identification of the causal gene requires intensive follow up research. We therefore aimed for a high throughput analysis using modern ‘omics’ techniques to analyze differences in metabolite levels and gene expression between the lines. A method to classify and visualize the vast amount of data derived from such an approach is described in Chapter 4. The so called genetical ‘omics’ experiments are expensive and therefore often force researchers to limit their study to a single developmental stage or environment only. A novel generalized setup overcomes this limitation and was tested for metabolite level changes in Chapter 5. This setup offers a unique reduction of experimental load with minimal effect on statistical power and is of great potential in the field of system genetics. Four different developmental stages of seed germination were tested in the RIL population. This approach resulted in a large dataset for which efficient analytical procedures were lacking. Thus, Chapter 5 also includes a description of a newly developed statistical procedure to analyze this type of data. The same approach and material were used in Chapter 6 to evaluate the genetics of genome wide gene expression.
Another approach to zoom in on the molecular mechanisms underlying seed performance is described in Chapter 7. Here, the genetic diversity was maximized by using 360 different Arabidopsis accessions which had been subjected to ultra-high density genotyping. In potential, such a genome wide association (GWA) study can provide high resolution mapping of genetic variation resulting in only a few candidate genes per association for the phenotype under study. Although we were able to replicate experiments over two years with a high level of heritability, no significant associations were found. This emphasizes the need to critically review the power of such an approach for traits that are expected to be determined by many small effect loci.
Finally, closing in on the molecular mechanisms underlying the seed traits that we studied might be possible by a full integration of the datasets that were described in the different chapters. Two examples that show the potential and the complexity of such integration are described in the General Discussion (Chapter 8). Research focused on seed quality does not end here but has gained an impulse by the described new methods and hypotheses to continue on both the fundamental and applied level in the coming years.
Kieming van zilte schijnspurrie onder invloed van verschillende zoutconcentraties
Blom-Zandstra, G. ; Visser, W. de; Rigter, T. - \ 2012
Wageningen : Plant Research International (Rapport / Plant Research International 478) - 18
onkruidbestrijding - spergularia - zoutwaterlandbouw - salicornia herbacea - zout water - zaadkieming - vollegrondsgroenten - vollegrondsteelt - weed control - saline agriculture - saline water - seed germination - field vegetables - outdoor cropping
Bij de teelt van zeekraal is bestrijding van het onkruid zilte schijnspurrie (Spergularia marina) een probleem. Zaden van dit onkruid kiemen, net als die van de zeekraal, in het voorjaar na een regenbui. De kieming van zilte schijnspurrie wordt weliswaar geremd door zout water, maar zodra de zaden opnieuw in contact komen met zoet water start de kieming weer. In deze studie is onderzocht of deze kieming opnieuw kan worden geremd door toevoeging van zout water en zo ja, wat de tijdsmarge daarvoor is. De resultaten tonen aan dat de stimulerende en remmende effecten van respectievelijk zoet en zout water reversibel zijn. Na de start van de kieming kan het proces opnieuw worden geremd als binnen 1,5 dag zout water wordt gegeven.
Vervolgstudie naar de kieming van schijnspurrie onder invloed van verschillende zoutconcentraties : afhankelijkheid van het temperatuur regime
Blom-Zandstra, G. ; Visser, W. de - \ 2012
Wageningen : Plant Research International (Rapport / Plant Research International 477) - 12
onkruidbestrijding - zoutwaterlandbouw - nachttemperatuur - temperatuur - spergularia - zaadkieming - vollegrondsgroenten - vollegrondsteelt - weed control - saline agriculture - night temperature - temperature - seed germination - field vegetables - outdoor cropping
Kieming van zilte schijnspurrie (Spergularia marina) in zoet water kan worden geremd door zout water. De tijdsmarge waarin zout water de kieming na de start nog effectief kan remmen is echter in de orde van dagen. In deze studie is onderzocht of verschillende da/nacht temperaturen effect hebben op deze tijdsmarge. De resultaten tonen aan dat het dag/nacht temperatuur regime geen effect heeft op de tijdsmarge tussen de start van de kieming en effectieve remming door zout water. Wel zijn kiempercentages hoger bij hogere dag/nacht temperaturen.
Effecten van enkele additieven op de opkomst van Rosa corymbifera 'Laxa' zaad
Derkx, M.P.M. - \ 2012
Lisse : Praktijkonderzoek Plant & Omgeving BBF - 13
rosa corymbifera - zaden - zaadkieming - zaadbehandeling - plantmateriaal - groeistimulatoren - houtachtige planten als sierplanten - landbouwkundig onderzoek - nederland - seeds - seed germination - seed treatment - planting stock - growth stimulators - ornamental woody plants - agricultural research - netherlands
In een aantal landbouwgewassen is gevonden dat een zaadcoating met additieven een positief effect kan hebben op de kieming, de wortelontwikkeling en de groei. Een zaadcoating is een dun laagje dragermateriaal dat op het zaad wordt aangebracht. Additieven is de verzamelnaam van een groep producten die aan zaden toegevoegd worden vóór uitzaai. Het kunnen gewasbeschermingsmiddelen zijn, maar ook groeistimulatoren en micro-organismen. Om te kijken of additieven ook meerwaarde kunnen hebben voor boomkwekerijgewassen, is een eerste oriënterende proef uitgevoerd met gestratificeerd zaad van Rosa corymbifera ‘Laxa’. Drie verschillende additieven zijn getest. Het ging hierbij om natuurlijke stoffen, o.a. uit humuszuren en uit organisch materiaal. Vanwege het beperkte budget is alleen gekeken naar effecten op de opkomst en is niet gekeken of de additieven een positief effect hebben op de groei en ontwikkeling van bovengrondse en ondergrondse delen. De geteste additieven gaven geen verbetering van de opkomst. De opkomst van alle behandelingen lag tussen 48 en 57%. Ook waren geen effecten op de opkomstsnelheid zichtbaar. Mogelijk hebben de additieven wel invloed op de wortelontwikkeling en de bovengrondse groei. Dit kan in vervolgonderzoek nagegaan worden.
On seed physiology, biomechanics and plant phenology in Eragrostis tef
Delden, S.H. van - \ 2011
Wageningen University. Promotor(en): Paul Struik; Tjeerd-Jan Stomph, co-promotor(en): Jan Vos. - S.l. : s.n. - ISBN 9789085859444 - 185
eragrostis - eragrostis tef - teelt - plantenfysiologie - biomechanica - zaadkieming - legering - oogsten - eragrostis - eragrostis tef - cultivation - plant physiology - biomechanics - seed germination - lodging - harvesting
• Key words: Teff (Eragrostis tef (Zuccagni) Trotter), germination, temperature, model, leaf appearance, phyllochron, development rate, lodging, biomechanics, safety factor, flowering, heading, day length, photoperiod.
• Background Teff (Eragrostis tef (Zuccagni) Trotter) is a C4 annual grass species (Poaceae) originating from Ethiopia. Teff cultivation in the Netherlands is thought to be economically feasible because teff grains and flour do not contain gluten and are rich in iron. These two characteristics make teff a desirable ingredient in health products, particularly for celiac disease patients. At the start of this project Dutch teff yields were modest (1.0 - 1.5 Mg•ha-1). The sowing and harvest dates were (too) late in the season and the crop was sensitive to lodging. Here, lodging is defined as the permanent displacement of shoots from their vertical due to root or shoot failure.
• The objective of this research is to detail some processes that underlie the sensitivity to lodging and the late harvest. Therefore we studied seed germination, lodging resistance, day length response, pace of leaf appearance.
• Germination of teff can be described by assuming a normally distributed rate of germination within the seed population. Minimal and maximal temperatures required for germination depend on water availability (water potential). Conversely, the minimal required water potential for germination depends on temperature.
• Lodging was inevitable for teff grown on a Dutch sandy soil. We identified that not only the shoots of teff are prone to lodging, but that the roots are also a major factor in the lodging process. Furthermore, water adhering to the shoots alone, without wind action, could induce lodging in the studied cultivars.
• Flowering in teff is significantly delayed by exposure to long days. Teff is therefore a short day plant; not only panicle initiation, but also development and outgrowth of the panicle were influenced by photoperiod.
• Phyllochron, defined as the time required between the appearance of two successive teff leaves, increased abruptly for the last few leaves on the main stem of teff. After re-evaluation of literature data this abrupt increase in phyllochron seemed to be also present in both wheat and rice. The delay is most likely independent of temperature, but might be related to the moment of panicle initiation.
• In conclusion, the study on teff identified clear targets for breeding towards a high-yielding cultivar in the Netherlands.
Beoordeling van Zaadkwaliteit met behulp van Chlorofyl Fluorescentie Beelden
Jalink, H. - \ 2010
zaadkieming - chlorofyl - embryo's - fluorescentie - zaden - technieken - capsicum - glastuinbouw - seed germination - chlorophyll - embryos - fluorescence - seeds - techniques - greenhouse horticulture
Tijdens het kiemingsproces van zaden wordt o.a. chlorofyl gevormd. Dit chlorofyl wordt aangemaakt door het embryo. Het is gebleken dat de toename van chlorofyl een maat is voor het verloop van het kiemingsproces. Dit chlorofyl kan gevoelig worden gemeten met een fluorescentietechniek.
Kwaliteit van zaaizaad kool verbeteren
Groot, S.P.C. - \ 2008
BioKennis bericht Akkerbouw & vollegrondsgroenten 12 (2008).
biologische landbouw - akkerbouw - vermeerderingsmateriaal - zaadproductie - koolsoorten - oogsttijdstip - rijpheid - ziektebestrijding - plantenpigmenten - zaadkieming - fusarium - alternaria - vollegrondsteelt - biologische zaden - organic farming - arable farming - propagation materials - seed production - cabbages - harvesting date - maturity - disease control - plant pigments - seed germination - outdoor cropping - organic seeds
Kwalitatief goed biologisch zaaizaad voor koolsoorten is moeilijk te produceren. Oorzaken zijn de ongelijkmatige bloei en afrijping van het zaad. Daarnaast kunnen schimmels en bacteriën via het zaad de plant besmetten. In dit biokennis bericht informatie over onderzoek aan apparatuur die het optimale oogsttijdstip bepaalt of de zieke zaden eruit selecteert.
Seed quality in genetic resources conservation : a case study at the Centre for Genetic Resources, the Netherlands
Groot, S.P.C. ; Groot, E.C. de - \ 2008
Wageningen : Centre for genetic resources (CGN) (Report / Centre for Genetic Resources 2008/11) - 47
zaden - kiemrust - zaadlevensduur - zaadkieming - zaadkwaliteit - zaadveroudering - zaadleeftijd - genenbanken - gewassen - zaad verzamelen - aardappelen - uien - spinazie - slasoorten - erwten - vicia faba - bonen - meloenen - komkommers - tomaten - vlas - graansoorten - akkerbouw - zaadproductie - ex-situ conservering - opslag van zaden - seeds - seed dormancy - seed longevity - seed germination - seed quality - seed aging - seed age - gene banks - crops - seed collection - potatoes - onions - spinach - lettuces - peas - beans - melons - cucumbers - tomatoes - flax - cereals - arable farming - seed production - ex situ conservation - seed storage
This report describes an analysis of the impact of workflow and storage conditions at the Centre for Genetic Resources the Netherlands (CGN) on the quality of seed samples in their genebank collection which is maintained under low temperature and low relative humidity conditions. Emphasis is placed on seed longevity and health.
Het opwaarderen van boomzaden door middel van vloeistofscheiden
Derkx, M.P.M. - \ 2007
Lisse : PPO Bloembollen en Bomen - 37
zaadbehandeling - bomen - acer pseudoplatanus - carpinus betulus - crataegus monogyna - prunus avium - larix kaempferi - zaadkieming - seed treatment - trees - seed germination
Voor groente- en bloemzaden is ruim 10 jaar geleden een schoningstechniek ontwikkeld (vloeistofscheiding), waarbij zaden gesorteerd worden op basis van hun dichtheid. Bij deze techniek worden de zaden kort in vloeistoffen met verschillende dichtheden gebracht en dit resulteert in zaadfracties met verschillende dichtheden. De dichtheid van het zaad correleert met het kiemgedrag. De afgelopen jaren is onderzocht of deze techniek ook perspectief biedt voor boomzaden. Gekozen is voor soorten die met de huidige sorteertechnieken onvoldoende te verbeteren zijn, t.w. Acer pseudoplatanus, Carpinus betulus, Crataegus monogyna, Prunus avium en Larix kaempferi. In twee opeenvolgende jaren zijn 2-3 herkomsten van elke soort gesorteerd door middel van vloeistofscheiden. Dit resulteerde in zaadfracties met verschillende dichtheden. Vaak was de kieming van een fractie beter naarmate de dichtheid van het zaad hoger was. Zaadfracties met de laagste dichtheid kiemden soms helemaal niet of zeer beperkt. Op basis van de kiemcijfers van de verschillende fracties kan dan besloten worden welke fracties uitgezaaid worden. Eventueel kunnen slechter kiemende fracties ook uitgezaaid worden, maar dan dichter of eventueel voor een andere toepassing.
|Effect van zaad primen en vroeg zaaien op de opbrengst van cichorei
Brink, L. van den - \ 2007
Kennisakker.nl 2007 (2007)15 jan.
cichorei - cichorium - voorkieming - zaaien - zaden - zaadkieming - rassen (planten) - akkerbouw - chicory - pregermination - sowing - seeds - seed germination - varieties - arable farming
Uit onderzoek naar de mogelijkheden om de veldopkomst van cichorei te verbeteren kwam naar voren dat het primen (voorkiemen) van zaaizaad een snellere veldopkomst en daarnaast mogelijk ook een hogere opbrengst kan geven. In 2004 en 2005 is het effect van het gebruik van geprimed zaaizaad nader onderzocht, waarbij tegelijk ook het effect van zeer vroeg zaaien is meegenomen. De ervaringen waren namelijk dat geprimed zaad vooral een snellere opkomst geeft onder koude omstandigheden. In beide jaren kon bevestigd worden dat geprimed zaad een snellere veldopkomst geeft. Bij alle drie gebruikte rassen leverde geprimed zaad in combinatie met vroeg zaaien meestal een opbrengstverhoging op, variërend van enkele procenten tot maximaal 7,5%. Één ras gaf bij zeer vroege zaai te veel schieters.
Kieming van zaad: een nogal ingewikkeld proces, hormonen belangrijk bij ontstaan en doorbreken van kiemrust
Kierkels, T. ; Heuvelink, E. - \ 2006
Onder Glas 3 (2006)12. - p. 48 - 49.
zaadkieming - kiemrust - plantenfysiologie - temperatuur - klimaatfactoren - glastuinbouw - seed germination - seed dormancy - plant physiology - temperature - climatic factors - greenhouse horticulture
Beschrijving van kiemprocessen van groentegewassen (kiemrust, kiemrustdoorbreking, hormonen en kiemrust, fasen van het kiemproces)
Diversity, users' perception and food processing of sorghum: implications for dietary iron and zinc supply
Kayodé, A.P.P. - \ 2006
Wageningen University. Promotor(en): Tiny van Boekel, co-promotor(en): Rob Nout; Anita Linnemann. - Wageningen : - ISBN 9085044421 - 152
sorghum - voedselverwerking - ijzer - zink - fytinezuur - fytaten - antinutritionele factoren - zaadkieming - fermentatie - rassen (planten) - benin - sorghum - food processing - iron - zinc - phytic acid - phytates - antinutritional factors - seed germination - fermentation - varieties - benin
This thesis focuses on the diversity of sorghum and its post-harvest processing into food. We studied the contribution that sorghum can make to Fe and Zn intake by poor people in Africa, using the situation in Benin as a study context. The culinary and sensory characteristics of sorghum crops and their derived foods in northern Benin were surveyed. Three food categories were identified: pastes, porridges, and beverages. We distinguished more than 100 farmers’ varieties. A genome fingerprinting technique (AFLP) was used to cluster these farmers’ varieties into 45 distinct genotypes which were analyzed for their phytate content and Fe and Zn concentration and in vitro solubility. Seven of the identified genotypes contain adequate in vitro soluble Fe to meet consumers’ requirements. The impact of the local sorghum processing technologies on phytate, phenolics and Fe and Zn in vitro solubility was evaluated. Wet cleaning of sorghum grain, germination and fermentation are the most effective process operations to degrade phytate and phenolics and to increase the solubility of Fe and Zn. A mathematical model used to study the effect of processing variables on Fe and Zn solubility suggests that maximum mineral in vitro solubility in sorghum can be achieved, by processing the grains with combined germination and fermentation. Such combinations would enable the preparation of infant cereal porridges with improved nutrient contents.