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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Microbiome dynamics of disease suppresive soils
Gómez Expósito, Ruth - \ 2017
University. Promotor(en): Francine Govers; Jos Raaijmakers, co-promotor(en): Joeke Postma; Irene de Bruijn. - Wageningen : Wageningen University - ISBN 9789463431774 - 267
suppressive soils - soil suppressiveness - plant diseases - thanatephorus cucumeris - microbial ecology - soil microbiology - rhizosphere bacteria - soil bacteria - community ecology - soil fungi - transcriptomics - taxonomy - ziektewerende gronden - bodemweerbaarheid - plantenziekten - microbiële ecologie - bodemmicrobiologie - rizosfeerbacteriën - bodembacteriën - gemeenschapsecologie - bodemschimmels - transcriptomica - taxonomie

Disease suppressive soils are soils in which plants do not get diseased from plant pathogens due to the presence (and activities) of the microbes present in the soil. Understanding which microbes contribute to confer suppression and through which mechanisms they can protect plants is crucial for a sustainable control of plant diseases. In the research conducted in this thesis, I first examined the role of Lysobacter species, previously associated with disease suppressive soils, in suppressing damping-off disease caused by the soil-borne fungal pathogen Rhizoctonia solani on sugar beet. The majority of the Lysobacter strains tested revealed a broad metabolic potential in producing a variety of enzymes and secondary metabolites able to suppress R. solani in vitro. However, any of these strains could consistently suppress damping-off disease when applied in soil bioassays. Their ability to promote plant growth was also tested for sugar beet, cauliflower, onion or Arabidopsis thaliana. Results indicated that any of the Lysobacter strains could consistently promote plant growth, neither via direct contact nor via volatile production. Second, I investigated whether the antagonistic activity of Lysobacter species could be triggered when applied as bacterial consortia, together with Pseudomonas and Streptomyces species. Although several bacterial combinations showed an increased antagonistic effect towards R. solani in vitro, no consistent effects were observed when these bacterial consortia were applied in vivo. Third, I investigated the dynamical changes in the bacterial community composition and functions occurring during the process of disease suppressiveness induction by performing whole community analyses using next-generation sequencing techniques. Results indicated that suppressiveness induction was most associated with changes in certain bacterial traits rather than changes in the bacteria community composition itself. Among the functions found as more active in suppressive soils were several ‘classic’ mechanisms of disease suppression, including competition for nutrients, iron and space and production of extracellular enzymes, indol-acetic-acid and hydrogen cyanide. Among the enzymes found in higher abundance in suppressive soil were these ones involved in the degradation of oxalic acid, a pathogenicity factor produced by pathogenic fungi to help infecting the host plant. Hence, I finally studied the role of bacteria able to produce enzymes able to degrade oxalic acid in suppressing R. solani disease. Enrichment of native oxalotrophic bacteria existing in soil, their isolation and further application into soil revealed that they could effectively suppress Rhizoctonia disease. Characterization of these oxalotrophic bacteria revealed that members within the Caulobacter and Nocardioides species could suppress R. solani disease by their own. Furthermore, the research done in this thesis highlights the importance of combining different techniques to unravel the mechanisms underlying disease suppression and the importance of studying function-over-phylogeny. Additionally, it also highlights the importance of organic amendments (such as oxalic acid) directly into soils in order to “engineer” the bacterial functions towards the control of diseases caused by R. solani.

Fusarium is toenemend probleem in teelt van amaryllis : drie ziekteverwekkers en doorelkaar lopende symptomen
Kromwijk, Arca - \ 2016
fusarium - plant diseases - plant disease control - plant pathogens - plant protection - greenhouse horticulture - amaryllis - biological control
Inventarisatie van de uitbreiding van de bloedingsziekte in paardenkastanjebomen in Den Haag
Kuik, A.J. van - \ 2016
Wageningen Plant Research, Bloembollen, Boomkwekerij & Fruit (Rapport Wageningen Plant Research 2017-02) - 17 p.
aesculus hippocastanum - plantenziekten - pseudomonas syringae - steden - zuid-holland - plant diseases - towns
Sinds 2004 wordt door Wageningen Plant Research in opdracht van de gemeente Den Haag het paardenkastanje bestand beoordeeld op het voorkomen van de bloedingsziekte. Bomen die zijn aangetast door de bloedingsziekte, veroorzaakt door de bacterie Pseudomonas syringae pv aesculi blijken in de praktijk snel te kunnen aftakelen. Door de kastanjebomen regelmatig te beoordelen op de mate van aantasting en toezicht op het verloop van de aftakeling kunnen voor de omgeving gevaarlijke bomen tijdig worden gesignaleerd zodat actie kan worden ondernomen. Hiermee worden ongelukken door uitvallende takken zoveel mogelijk voorkomen. Naast de schadelijke aantasting door de bacterie zelf vormen de scheuren die zijn ontstaan door de bloedingsziekte een geschikte invalspoort voor boomverzwakkende schimmels, zoals de bundelzwam, paarse korstzwam, honingzwam en de oesterzwam. Bijna alle bomen die tot dusverre een kapadvies hebben gekregen waren ook aangetast door genoemde parasitaire boomschimmels.
Plant growth promotion by Pseudomonas fluorescens : mechanisms, genes and regulation
Cheng, X. - \ 2016
University. Promotor(en): Francine Govers; J.M. Raaijmakers, co-promotor(en): M. van der Voort. - Wageningen : Wageningen University - ISBN 9789462578753 - 192 p.
soil bacteria - pseudomonas fluorescens - plants - growth stimulators - soil suppressiveness - plant diseases - induced resistance - biochemistry - biosynthesis - plant-microbe interactions - transcriptomics - bodembacteriën - planten - groeistimulatoren - bodemweerbaarheid - plantenziekten - geïnduceerde resistentie - biochemie - biosynthese - plant-microbe interacties - transcriptomica

Pseudomonas fluorescens is a Gram-negative rod shaped bacterium that has a versatile metabolism and is widely spread in soil and water. P. fluorescens strain SBW25 (Pf.SBW25) is a well-known model strain to study bacterial evolution, plant colonization and biocontrol of plant diseases. It produces the biosurfactant viscosin, a lipopeptide that plays a key role in motility, biofilm formation and activity against zoospores of Phytophthora infestans and other oomycete pathogens. In addition to viscosin, Pf.SBW25 produces other metabolites with activity against plant pathogens. The production of these yet unknown metabolites appeared to be regulated by the GacS/GacA two-component regulatory system (the Gac-system). The second P. fluorescens strain SS101 (Pf.SS101) studied in this thesis is known for its plant growth-promoting activities but the underlying mechanisms and genes are largely unknown. Therefore, in this study, we aimed to identify novel metabolites and biosynthetic genes in Pf.SBW25 and Pf.SS101, and to investigate their role in plant growth promotion and biocontrol. To this end, a multidisciplinary approach involving bioinformatic analysis of the genome sequences of strains Pf.SBW25 and Pf.SS101, microarray-based expression profiling, screening of genomic libraries, bioactivity assays, mass spectrometric image analysis (MALDI-IMS) and GC/MSMS analysis was adopted. In conclusion, we showed that the GacS/GacA two-component system as a global regulator of the expression of genes play important roles in antagonism of Pseudomonas fluorescens toward plant pathogenic microbes as well as in plant growth promotion and ISR. Growth promotion by P. fluorescens is associated with alterations in auxin biosynthesis and transport, steroid biosynthesis, carbohydrate metabolism and sulfur assimilation. Moreover, advanced chemical profiling allowed us to compare the metabolite profiles of free-living P. fluorescens and P. fluorescens living in association with plant roots. A better understanding of yet unknown mechanisms exploited by the various Pseudomonas fluorescens strains will lead to new opportunities for the discovery and application of natural bioactive compounds for both industrial and agricultural purposes.

Alleen systematische aanpak kan overmatige wortelgroei beperken : Bacterie valt pas aan als er een leger is gevormd
Streminska, Marta ; Stijger, Ineke - \ 2016
horticulture - greenhouse horticulture - vegetables - plant diseases - bacterial diseases - rhizobium rhizogenes - disease prevention - microorganisms - agricultural research

Marta Streminska en Ineke Stijger van Wageningen UR Glastuinbouw: "We zijn niet op zoek naar een antibioticum tegen overmatige wortelgroei, maar we bestuderen het hele systeem."

Bottleneck robotisering zit bij financiering, niet bij technologie : aan de vooravond van de doorbraak
Pekkeriet, Erik - \ 2016
horticulture - greenhouse horticulture - robots - harvesting date - maturity - plant diseases - illumination - financing - agricultural research

In de kas komen veel lastig te automatiseren handelingen voor, zoals oogsten, gewasinspectie en -verzorging. Kunstmatige intelligentie, visiontechnieken en communicatiesnelheid ontwikkelen zich echter zo snel, dat robotisering dichtbij is. Bij verwerking en verpakking is dat al meer gemeengoed, maar het kan allemaal veel doordachter en efficiënter.

Supplementary data: Combined biotic and abiotic stress resistance in tomato
Kissoudis, C. ; Chowdhury, Rawnaq ; Heusden, A.W. van; Wiel, C.C.M. van de; Finkers, H.J. ; Visser, R.G.F. ; Bai, Y. ; Linden, C.G. van der - \ 2016
solanum lycopersicum - tomatoes - disease resistance - stress tolerance - defence mechanisms - plant diseases - abiotic injuries - stress response - phenotypic variation - genetic analysisplant breeding - salt tolerance
Abiotic and biotic stress factors are the major constrains for the realization of crop yield potential. As climate change progresses, the spread and intensity of abiotic as well as biotic stressors is expected to increase, with increased probability of crops being exposed to both types of stress. Shielding crops from combinatorial stress requires a better understanding of the plant’s response and its genetic architecture. In this study, we evaluated resistance to salt stress, powdery mildew and to both stresses combined in tomato, using the S. habrochaites LYC4 introgression line (IL) population. The IL population segregated for both salt stress tolerance and powdery mildew resistance. Using SNP array marker data, QTLs were identified for salt tolerance as well as Na+ and Cl- accumulation. Salt stress increased the susceptibility of the population to powdery mildew in an additive manner. Phenotypic variation for disease resistance was reduced under combined stress as indicated by the coefficient of variation (CV). No correlation was found between disease resistance and Na+ and Cl- accumulation under combined stress Most genetic loci were specific for either salt stress tolerance or powdery mildew resistance. These findings increase our understanding of the genetic regulation of responses to abiotic and biotic stress combinations and can provide leads to more efficiently breeding for tomatoes and other crops with a high level of disease resistance while maintaining their performance in combination with abiotic stress.
Supplementary data: Responses to combined abiotic and biotic stress in tomato are governed by stress intensity and mechanism of resistance
Kissoudis, C. ; Sri Sunarti, Sri ; Wiel, C.C.M. van de; Visser, R.G.F. ; Linden, C.G. van der; Bai, Y. - \ 2016
solanum lycopersicum - tomatoes - disease resistance - stress tolerance - defence mechanisms - plant diseases - abiotic injuries - stress response - phenotypic variation - genetic analysisplant breeding - salt tolerance
Stress conditions in agricultural ecosystems can occur in variable intensities. Different resistance mechanisms to abiotic stress and pathogens are deployed by plants. Thus, it is important to examine plant responses to stress combinations under different scenarios. Here, we evaluated the effect of different levels of salt stress ranging from mild to severe (50, 100 and 150mM NaCl) on powdery mildew (PM) resistance and overall performance of tomato introgression lines with contrasting levels of partial resistance, as well as isogenic lines carrying the PM resistance genes Ol-1 (associated with slow Hypersensitivity Response; HR), ol-2 (a mlo mutant associated with papilla formation) and Ol-4 (a R gene associated with fast HR). PM resistance was affected by salt stress in a genotype and stress intensity dependent manner. In susceptible and partial resistant lines, increased susceptibility was observed under mild salt stress (50mM) which was accompanied with accelerated cell death-like senescence. On the contrary, severe salt stress (150mM) reduced disease symptoms. Na+ and Cl- accumulation in the leaves was linearly related to the decreased pathogen growth under severe stress, suggesting a more direct role for the salt in suppressing PM growth. In contrast, complete resistance mediated by ol-2 and Ol-4 was unaffected under all treatment combinations, and was associated with a decreased growth penalty. Increased susceptibility and senescence under combined stress of the variety Moneymaker (MM) and the NIL Ol-1 was associated with the induction of ethylene and jasmonic acid pathway genes as well as of the cell wall invertase gene LIN6. These results highlight the significance of stress severity and resistance type on the plant’s performance under abiotic and biotic stress combination.
Supplementary data: Hormone signalling regulation of tomato response to combined biotic and abiotic stress
Kissoudis, C. ; Sri Sunarti, Sri ; Wiel, C.C.M. van de; Visser, R.G.F. ; Linden, C.G. van der; Bai, Y. - \ 2016
solanum lycopersicum - tomatoes - disease resistance - stress tolerance - defence mechanisms - plant diseases - abiotic injuries - stress response - phenotypic variation - genetic analysisplant breeding - salt tolerance
Plant hormones are paramount to plant adaptation to changing environmental conditions and interactions with microorganisms. There is currently limited knowledge on their significance in the response to stress combination. Using near isogenic lines (NILs) that carry the Ol-1, ol-2 and Ol-4 gene for resistance to tomato powdery mildew caused by Oidium neolycopersici, this study focused on the responses of these NILs to powdery mildew and salt stress combination. In these NILs, marker genes for monitoring hormonal pathways showed differential expression pattern upon powdery mildew infection. Further by crossing these NILs with tomato mutants notabilis (ABA-deficient), defenseless1 (JA-deficient) and epinastic (ET overproducer) the cross-talk among hormonal pathways was further investigated. Among the mutants, epinastic resulted in increased susceptibility of NIL-Ol-1 and breakdown of NIL-ol-2 resistance, accompanied by reduced callose deposition, effects that were more pronounced under combination with salt stress. On the other hand notabilis, resulting in H2O2 overproduction greatly reduced susceptibility of NIL-Ol-1 under combined stress accompanied however by heightened sensitivity to salt stress. Callose deposition reduction led to partial resistance breakdown in NIL-ol-2 which was reversed under combined stress. NIL-Ol-4 resistance remained robust across all mutant and treatment combinations. We discuss the critical role that hormone signalling appears to have for the outcome of combined stress and powdery mildew in terms of resistance and plant fitness integrating observations from physiological, histochemical and gene expression analyses. These significant insights obtained extend our understanding of hormonal regulation of combined stress responses and can aid in narrowing down targets for improving crop performance under stress combinations.
Supplementary data: Roles and contribution of tomato WRKY genes to salt stress and powdery mildew resistance
Kissoudis, C. ; Gao, D. ; Pramanik, Dewi ; Birhanu, Mengistu ; Wiel, C.C.M. van de; Visser, R.G.F. ; Bai, Y. ; Linden, C.G. van der - \ 2016
solanum lycopersicum - tomatoes - disease resistance - stress tolerance - defence mechanisms - plant diseases - abiotic injuries - stress response - phenotypic variation - genetic analysisplant breeding - salt tolerance
WRKY is a transcription factor family unique to plants with diverse functions in defense pathways, abiotic stress tolerance and developmental programs. Family members are characterized by the conserved WRKY domain and significant sequence variation in the remainder of the protein, which is translated into distinct functions even for closely related genes. We utilized the extensive functional characterization of the Arabidopsis thaliana WRKY family to identify tomato homologues of Arabidopsis WRKY genes that are involved in defense responses (AtWRKY 11, 29, 48, 70 and 72). In total 13 tomato WRKY homologues were identified for these genes, of which 9 were successfully over-expressed, and 12 stably silenced via RNAi in transgenic tomato lines. The transgenic lines were evaluated for their response to salt stress, powdery mildew resistance and the combination of these stresses. Lines overexpressing SlWRKY11 and SlWRKY23, and RNAi lines of SlWRKY7 and SlWRKY9 showed both increased biomass and improved salt tolerance. For SlWRKY11 and SlWRKY23 overexpression (OE) lines, this was accompanied by a moderate increase in oxidative stress tolerance. The SlWRKY6-OE line showed strongly improved salt stress tolerance, but a growth penalty under control conditions. Exceptional phenotypes were observed for the SlWRKY10-OE line (stunted growth) and the RNAi line SlWRKY23-RNAi (necrotic symptoms), but these phenotypes were partly restored to normal under salt stress. Both these lines exhibited increased resistance to powdery mildew, but this was compromised when the plants were put under salt-stress as well. Important functions for tomato WRKY genes were revealed in both the abiotic and biotic stress response and several genes should be further explored to elucidate their downstream regulatory functions that lead to increased stress tolerance.
Potential food hazards from organic greenhouse horticulture
Alsanius, B.W. ; Dorais, M. ; Doyle, O. ; Oancea, F. ; Spadaro, D. ; Meijer, R.J.M. - \ 2016
BioGreenhouse (Fact sheet BioGreenhouse ) - 3 p.
organic farming - horticulture - greenhouse horticulture - plant protection - plant diseases - food safety - agricultural research - biologische landbouw - tuinbouw - glastuinbouw - gewasbescherming - plantenziekten - voedselveiligheid - landbouwkundig onderzoek
This factsheet describes the critical hazards in organic greenhouse horticulture (OGH) crop production and identifies the crucial knowledge gaps.
Sierteelt in de Biobased Economy : “de plant als producent van groene gewasbeschermingsmiddelen”
Poot, E.H. ; Vos, C.H. de; Smits, J. ; Maghnouji, Rachid ; Korthout, H. ; Staaij, M. van der - \ 2016
Wageningen : Wageningen UR Glastuinbouw - 1 p.
tuinbouw - gewasbescherming - siergewassen - plantenziekten - plantextracten - biobased economy - glastuinbouw - horticulture - plant protection - ornamental crops - plant diseases - plant extracts - greenhouse horticulture
Het consortium Royal FloraHolland, Kenniscentrum Plantenstoffen, Wageningen UR Glastuinbouw en PRI onderzoekt de mogelijkheid om “groene” gewasbeschermingsmiddelen te winnen uit sierteeltgewassen. Dit is van groot belang omdat het pakket aan chemische middelen voor de tuinbouw en in het bijzonder voor de sierteelt, onder druk staat. Poster van het PlantgezondheidEvent 2016.
Bedrijfshygiëne - Opslag en levering van het product : Kennisclip Bogo-project e-learning
Dam, M.F.N. van - \ 2016
Groen Kennisnet
bedrijfshygiëne - fytosanitaire maatregelen - fytosanitaire certificering - exportbeperkingen - plantenziekten - gewasbescherming - glastuinbouw - lesmaterialen - industrial hygiene - phytosanitary measures - phytosanitary certification - export controls - plant diseases - plant protection - greenhouse horticulture - teaching materials
Deze kennisclip maakt onderdeel uit van de lesmodule Internationale handel en plantgezondheid van het CIV T&U.
Bedrijfshygiëne - Waarom bedrijfshygiëne? : Kennisclip Bogo-project e-learning
Dam, M.F.N. van - \ 2016
Groen Kennisnet
bedrijfshygiëne - ziektepreventie - plantenziekten - gewasbescherming - glastuinbouw - lesmaterialen - agrarische bedrijfsvoering - industrial hygiene - disease prevention - plant diseases - plant protection - greenhouse horticulture - teaching materials - farm management
Deze kennisclip maakt onderdeel uit van de lesmodule Internationale handel en plantgezondheid van het CIV T&U.
Genetics and regulation of combined abiotic and biotic stress tolerance in tomato
Kissoudis, C. - \ 2016
University. Promotor(en): Richard Visser, co-promotor(en): Gerard van der Linden; Yuling Bai. - Wageningen : Wageningen University - ISBN 9789462576568 - 212 p.
solanum lycopersicum - tomatoes - disease resistance - stress tolerance - defence mechanisms - plant diseases - abiotic injuries - stress response - phenotypic variation - genetic analysis - plant breeding - salt tolerance - tomaten - ziekteresistentie - stresstolerantie - verdedigingsmechanismen - plantenziekten - abiotische beschadigingen - stressreactie - fenotypische variatie - genetische analyse - plantenveredeling - zouttolerantie

Projections on the impact of climate change on agricultural productivity foresee prolonged and/or increased stress intensities and enlargement of a significant number of pathogens habitats. This significantly raises the occurrence probability of (new) abiotic and biotic stress combinations. With stress tolerance research being mostly focused on responses to individual stresses, our understanding of plants’ ability to adapt to combined stresses is limited.

In an attempt to bridge this knowledge gap, we hierarchized in chapter 1 existing information on individual abiotic or biotic stress adaptation mechanisms taking into consideration different anatomical, physiological and molecular layers of plant stress tolerance and defense. We identified potentially crucial regulatory intersections between abiotic and biotic stress signalling pathways following the pathogenesis timeline, and emphasized the importance of subcellular to whole plant level interactions by successfully dissecting the phenotypic response to combined stress. We considered both explicit and shared adaptive responses to abiotic and biotic stress, which included amongst others R-gene and systemic acquired resistance as well as reactive oxygen species (ROS), redox and hormone signalling, and proposed breeding targets and strategies.

In chapter 3 we focused on salt stress and powdery mildew combination in tomato, a vegetable crop with a wealth of genetic resources, and started with a genetic study. S. habrochaites LYC4 was found to exhibit resistance to both salt stress and powdery mildew. A LYC4 introgression line (IL) population segregated for both salt stress tolerance and powdery mildew resistance. Introgressions contributing to salt tolerance, including Na+ and Cl- accumulation, and powdery mildew resistance were precisely pinpointed with the aid of SNP marker genotyping. Salt stress (100mM NaCl) combined with powdery mildew infection increased the susceptibility of the population to powdery mildew in an additive manner, while decreasing the phenotypic variation for this trait. Only a few overlapping QTLs for disease resistance and salt stress tolerance were identified (one on a short region at the top of Chromosome 9 where numerous receptor-like kinases reside). Most genetic loci were specific for either salt stress tolerance or powdery mildew resistance indicating distinct genetic architectures. This enables genetic pyramiding approaches to build up combined stress tolerance.

Considering that abiotic stress in nature can be of variable intensities, we evaluated selected ILs under combined stress with salinity ranging from mild to severe (50, 100 and 150mM NaCl) in chapter 4. Mild salt stress (50mM) increased powdery mildew susceptibility and was accompanied by accelerated cell death-like senescence. On the contrary, severe salt stress (150mM) reduced the disease symptoms and this correlated with leaf Na+ and Cl- content in the leaves. The effects of salt stress on powdery mildew resistance may be dependent on resistance type and mechanisms. Near Isogenic Lines (NILs) that carry different PM resistance genes (Ol-1 (associated with slow hypersensitivity response, HR), ol-2 (an mlo mutant associated with papilla formation) and Ol-4 (an R gene associated with fast HR) indeed exhibited differential responses to combined stress. NIL-Ol-1 resembled the LYC4 ILs response, while NIL-ol-2 and NIL-Ol-4 maintained robust resistance and exhibited no senescence symptoms across all combinations, despite the observed reduction in callose deposition in NIL-ol-2. Increased susceptibility, senescence and fitness cost of NIL-Ol-1 under combined stress coincided with high induction of ethylene and jasmonate biosynthesis and response pathways, highly induced expression of cell wall invertase LsLIN6, and a reduction in the expression of genes encoding for antioxidant enzymes. These observations underlined the significance of stress intensity and mechanism of resistance to the outcome of salt stress and powdery mildew combination, underscoring the involvement of ethylene signalling to the susceptibility response under combined stress.

To examine the significance of hormone signalling in combined stress responses we evaluated crosses of tomato hormone mutants notabilis (ABA-deficient), defenseless1 (JA-deficient) and epinastic (ET overproducer) with NIL-Ol-1, NIL-ol-2 and NIL-Ol-4 in chapter 5. The highly pleiotropic epinastic mutant increased susceptibility of NIL-Ol-1, but decreased the senescence response under combined stress, and resulted in partial breakdown of NIL-ol-2 resistance, accompanied by reduced callose deposition. The effects of ET overproduction on susceptibility were more pronounced under combined stress. ABA deficiency in notabilis on the other hand greatly reduced susceptibility of NIL-Ol-1under combined stress at the expense of stronger growth reduction, and induced ROS overproduction. Partial resistance breakdown in the ol-2xnotabilis mutant accompanied by reduced callose deposition was observed, and this was restored under combined stress. Jasmonic acid deficiency phenotypic effects in defenseless mutants were subtle with modest increase in susceptibility for NIL-Ol-1 and NIL-ol-2. For NIL-ol-2 this increased susceptibility was reverted under combined stress. NIL-Ol-4 resistance remained robust across all mutant and treatment combinations. These results highlight the catalytic role of ET and ABA signalling on susceptibility and senescence under combined stress, accentuating concomitantly the importance of signalling fine tuning to minimize pleiotropic effects.

The potential of exploiting transcription factors to enhance tolerance to multiple stress factors and their combination was investigated in chapter 6 through the identification and functional characterization of tomato homologues of AtWRKYs 11, 29, 48, 70 and 72. Thirteen tomato WRKY homologues were identified, of which 9 were overexpressed (using transformation with A. tumefaciens) and 12 stably silenced via RNAi in tomato cultivar Money Maker (MM). SlWRKY11-OE and SlWRKY23-OE overexpressors and RNAi lines of SlWRKY7 and SlWRKY9 showed both increased biomass and relative salt tolerance. SlWRKY6-OE exhibited the highest relative salt stress tolerance, but had strongly decreased growth under control conditions. Exceptional phenotypes under control conditions were observed for SlWRKY10-OE (stunted growth) and SlWRKY23-RNAi (necrotic symptoms). These phenotypes were significantly restored under salt stress, and accompanied by decreased ROS production. Both lines exhibited increased resistance to powdery mildew, but this resistance was compromised under salt stress combination, indicating that these genes have important functions at the intersection of abiotic and biotic stress adaptation. SlWRKY23 appears to have a key regulatory role in the control of abiotic stress/defense and cell death control.

Experimental observations are critically discussed in the General Discussion with emphasis on potential distinctive responses in different pathosystems and abiotic and biotic stress resistance mechanisms as well as genetic manipulations for effectively achieving combined stress tolerance. This includes deployment of individual common regulators as well as pyramiding of non-(negatively) interacting components such as R-genes with abiotic stress resistance genes, and their translation potential for other abiotic and biotic stress combinations. Understanding and improving plant tolerance to stress combinations can greatly contribute to accelerating crop improvement towards sustained or even increased productivity under stress.

Screening of the COGEM lists of non-pathogenic bacteria and fungi for postharvest diseases and plant pathogens
Vlugt, R.A.A. van der; Verbeek, M. ; Molhoek, W. ; Stevens, L. - \ 2015
Wageningen : Wageningen UR, Business Unit Biointeractions and Plant Heath (CGM onderzoeksrapport 2016-06) - 109
plantenziekteverwekkers - plantenziekten - bederf na de oogst - plantenziekteverwekkende bacteriën - plantenziekteverwekkende schimmels - screenen - plant pathogens - plant diseases - postharvest decay - plant pathogenic bacteria - plant pathogenic fungi - screening
Ziekteproblemen verhinderen succesvolle bloementeelt : derde seizoen recirculatie amaryllis
Kromwijk, Arca - \ 2015
horticulture - greenhouse horticulture - agricultural research - ornamental bulbs - amaryllis - water reuse - plant diseases - plant protection - steneotarsonemus laticeps - pseudococcidae - haematonectria haematococca - biological control - chemical control - pesticides
Snelle toets tegen agressief snot in hyacint
Vreeburg, P.J.M. ; Leeuwen, P.J. van; Pham, K.T.K. ; Wichers, J.H. - \ 2015
BloembollenVisie 325 (2015). - ISSN 1571-5558 - p. 26 - 26.
bloembollen - hyacinthus - plantenziekten - dickeya - tests - detectors - snelle methoden - ornamental bulbs - plant diseases - rapid methods
PPO heeft een nieuwe toets beschikbaar die binnen een uur aangeeft of Dickeya (agressief snot) de oorzaak is van een snotbol. Telers en handelaren kunnen door deze versnelde diagnose eerder de juiste maatregelen nemen om schade door agressief snot te beperken.
We zien de verbanden, nu nog de keiharde onderbouwing : Stuurgroep Interne Vruchtkwaliteit Paprika weer stap verder
Velden, P. van; Hofland-Zijlstra, J.D. - \ 2015
Onder Glas 12 (2015)2. - p. 12 - 13.
glastuinbouw - groenten - paprika's - capsicum - fusarium - vruchtrot - plantenziekten - samenwerking - landbouwkundig onderzoek - plantgezondheid - gewaskwaliteit - greenhouse horticulture - vegetables - sweet peppers - fruit rots - plant diseases - cooperation - agricultural research - plant health - crop quality
Als er de afgelopen twee jaar één ding duidelijk is geworden dan is het dat er heel veel factoren zijn die hun bijdrage leveren aan het ontwikkelen van Fusarium lactis in de vruchten van paprika’s. Ofwel: alles hangt met alles samen. De sleutel voor succes ligt in zorgvuldig en zorgzaam telen. Het consequent bemonsteren van geoogst product en de daaraan gekoppelde sancties hebben er wel toe bijgedragen dat iedere teler alert is geworden.
Praktijk past onderzoeksresultaten Green challenge meeldauw gretig toe : onderzoek meeldauwbeheersing wegens succes verbreed
Staalduinen, J. van; Hofland-Zijlstra, J.D. - \ 2015
Onder Glas 12 (2015)4. - p. 36 - 37.
glastuinbouw - meeldauw - plantenziekten - ziektebestrijdende teeltmaatregelen - infectie - controle - systemische werking - vermeerderingsmateriaal - potplanten - resistentieveredeling - landbouwkundig onderzoek - greenhouse horticulture - mildews - plant diseases - cultural control - infection - control - systemic action - propagation materials - pot plants - resistance breeding - agricultural research
Onder de noemer Green Challenge Meeldauw startte vorig jaar een door het Productschap Tuinbouw en bedrijfsleven gefinancierd en door LTO Glaskracht Nederland begeleid masterplan, dat meer inzicht en oplossingen moet bieden bij het voorkomen en bestrijden van echte meeldauw. De aanvankelijke focus op siergewassen is inmiddels verbreed met vruchtgroenten. Onderzoekster Jantineke Hofland-Zijlstra van Wageningen UR Glastuinbouw doet verslag van de voorlopige resultaten.
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