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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    Effects of pellet diameter during and after lactation on feed intake of piglets pre- and post weaning
    Brand, H. van den; Warmsteeker, D. ; Oostindjer, M. ; Enckevort, L.C.M. van; Poel, A.F.B. van der; Kemp, B. ; Bolhuis, J.E. - \ 2014
    Journal of Animal Science 92 (2014)9. - ISSN 0021-8812 - p. 4145 - 4153.
    individual variation - diet quality - young-pigs - creep food - performance - behavior - growth - sow - consumption
    Effects of two pellet diameters for piglets pre and post weaning on feed intake, BW, and feed-related behaviour were studied in 3 experiments. In experiment 1, 19 litters were provided with pellets of 2 and 12-mm in diameter in a choice-feeding setup from d 4 of lactation onward. From d 4 to 18, piglets preferred the 12-mm diameter pellet over the 2-mm diameter pellet (519 vs. 168 g/pen; P
    Structure-function analysis of a downstream signalling NB-LRR from tomatio
    Sueldo, D.J. ; Enckevort, E. van; Prins, M. ; Joosten, M.H.A.J. ; Tameling, W.I.L. - \ 2013
    In: Book of Abstracts Keystone Symposia on Molecular and Cellular Biology, Big Sky, Montana, USA, 7-12 April 2013. - - p. 60 - 60.
    Effects of Dextrose Plus Lactose in the Sows Diet on Subsequent Reproductive Performance and within Litter Birth Weigt Variation
    Brand, H. van den; Enckevort, L.C.M. van; Hoeven, E.M. van der; Kemp, B. - \ 2009
    Reproduction in Domestic Animals 44 (2009)6. - ISSN 0936-6768 - p. 884 - 888.
    to-estrus interval - luteinizing-hormone - primiparous sows - preweaning survival - embryo survival - ovulation rate - energy-source - feed-intake - insulin - growth
    Effects of dextrose plus lactose in sow's feed were tested on subsequent reproductive performance and within litter birth weight variation. During the last week of gestation and lactation, sows were either fed a commercial lactation diet (Control: C), or an isocaloric diet containing 25 g/kg dextrose plus 25 g/kg lactose (Treatment: T). In the subsequent weaning-to-oestrus interval (WEI), all sows received the same amount of a commercial feed, but T sows were supplemented with 150 g dextrose plus 150 g lactose per day. Weight and backfat changes were recorded as well as litter characteristics during the treatment period and the subsequent parity. No significant effect of treatment was found on the subsequent reproductive performance, including the number of piglets born, although the number of live born piglets was 0.51 larger (p = 0.31) and weight of the live born piglets was 84 g higher in the T sows (p = 0.07) than in the C sows. When sows were categorized in sows with 12 or less and more than 12 total born piglets in the previous litter, treatment of sows with dextrose plus lactose resulted for the group with 12 or less piglets in a strong increase in subsequent total born piglets (13.97), whereas in the untreated sows the subsequent litter size was 11.89. In the group with more than 12 total born piglets, no effect of treatment was found (interaction between previous litter size and treatment p = 0.03). The within litter variation in birth weight in the subsequent litter was numerically lower in the T sows. We concluded that the use of dextrose and lactose during lactation and WEI seems to enhance litter size in sows with low previous litter size and seems to have the potential to reduce the within litter variation in birth weight.
    Dextrose improves birth weight uniformity
    Brand, H. van den; Enckevort, L.C.M. van - \ 2007
    International Pig Topics 22 (2007)7. - ISSN 0963-5866 - p. 13 - 15.
    Accelerating the reconstruction of genome-scale metabolic networks
    Notebaart, Richard A. ; Enckevort, Frank H.J. van; Francke, Christof ; Siezen, Roland J. ; Teusink, Bas - \ 2006
    BMC Bioinformatics 7 (2006). - ISSN 1471-2105

    Background: The genomic information of a species allows for the genome-scale reconstruction of its metabolic capacity. Such a metabolic reconstruction gives support to metabolic engineering, but also to integrative bioinformatics and visualization. Sequence-based automatic reconstructions require extensive manual curation, which can be very time-consuming. Therefore, we present a method to accelerate the time-consuming process of network reconstruction for a query species. The method exploits the availability of well-curated metabolic networks and uses high-resolution predictions of gene, equivalency between species, allowing the transfer of gene-reaction associations from curated networks. Results: We have evaluated the method using Lactococcus lactis IL1403, for which a genome-scale metabolic network was published recently. We recovered most of the gene-reaction associations (i.e. 74 - 85%) which are incorporated in the published network. Moreover, we predicted over 200 additional genes to be associated to reactions, including genes with unknown function, genes for transporters and genes with specific metabolic reactions, which are good candidates for an extension to the previously published network. In a comparison of our developed method with the well-established approach Pathologic, we predicted 186 additional genes to be associated to reactions. We also predicted a relatively high number of complete conserved protein complexes, which are derived from curated metabolic networks, illustrating the potential predictive power of our method for protein complexes. Conclusion: We show that our methodology can be applied to accelerate the reconstruction of genome-scale metabolic networks by taking optimal advantage of existing, manually curated networks. As orthology detection is the first step in the method, only the translated open reading frames (ORFs) of a newly sequenced genome are necessary to reconstruct a metabolic network. When more manually curated metabolic networks will become available in the near future, the usefulness of our method in network prediction is likely to increase.

    Andere maatstaven voor nitraatuitspoeling dan Minas met name lastig voor zandbedrijven
    Dijk, W. van; Enckevort, P.L.A. van; Schoot, J.R. van der - \ 2005 2005 (2005)1 juli.
    bemesting - nitraat - normen - bodemtypen - mineralenboekhouding - akkerbouw - uitspoelen - fertilizer application - nitrate - standards - soil types - nutrient accounting system - arable farming - leaching
    Op de meeste akkerbouwbedrijven zijn de Minasnormen goed haalbaar. Eerdere studies hebben dat uitgewezen. Het is echter de vraag of op droge zandgronden met Minas de EU-nitraatrichtlijn wel wordt gehaald. Met alternatieven, zoals een uitgebreidere N-balans of meting van de hoeveelheid minerale bodem-N na de oogst of in de late herfst, is het een stuk lastiger om te voldoen aan de gestelde streefwaarden. Dit blijkt uit de volgende evaluatie.
    EU-OSTID: A collection of transposon insertional mutants for functional genomics in rice
    Enckevort, L.J.G. van; Droc, G. ; Piffanelli, P. ; Greco, R. ; Gagneur, C. ; Weber, C. ; Gonzalez, V.M. ; Cabot, P. ; Fornara, F. ; Berri, S. ; Miro, B. ; Lan, P. ; Rafel, M. ; Capell, T. ; Puigdomenech, P. ; Ouwerkerk, P.B.F. ; Meijer, A.H. ; Pe', E. ; Colombo, L. ; Christou, P. ; Guiderdoni, E. - \ 2005
    Plant Molecular Biology 59 (2005)1. - ISSN 0167-4412 - p. 99 - 110.
    reverse genetics - homeobox genes - mutagenesis - expression - system - family - annotation - generation - resources - activator
    A collection of 1373 unique flanking sequence tags (FSTs), generated from Ac/Ds and Ac transposon lines for reverse genetics studies, were produced in japonica and indica rice, respectively. The Ds and Ac FSTs together with the original T-DNAs were assigned a position in the rice genome sequence represented as assembled pseudomolecules, and found to be distributed evenly over the entire rice genome with a distinct bias for predicted gene-rich regions. The bias of the Ds and Ac transposon inserts for genes was exemplified by the presence of 59% of the inserts in genes annotated on the rice chromosomes and 41% present in genes transcribed as disclosed by their homology to cDNA clones. In a screen for inserts in a set of 75 well annotated transcription factors, including homeobox-containing genes, we found six Ac/Ds inserts. This high frequency of Ds and Ac inserts in genes suggests that saturated knockout mutagenesis in rice using this strategy will be efficient and possible with a lower number of inserts than expected. These FSTs and the corresponding plant lines are publicly available through OrygenesDB database and from the EU consortium members.
    Ontwikkeling van een indicator om te sturen op nitraat; gegevens en regressie-analyse voor het eerste meetseizoen (2000-2001)
    Hack-ten Broeke, M.J.D. ; Burgers, S.L.G.E. ; Berge, H.F.M. ten; Enckevort, P.L.A. van; Gruijter, J.J. de; Hoving, I.E. ; Smit, A. ; Velthof, G.L. - \ 2003
    Wageningen : Alterra (Alterra-rapport 772) - 65
    dierlijke meststoffen - uitspoelen - nitraten - grondwaterverontreiniging - indicatoren - regressieanalyse - nitraat - nederland - mineralenboekhouding - animal manures - leaching - nitrates - groundwater pollution - indicators - regression analysis - nitrate - netherlands - nutrient accounting system
    In het project STuren OP NITraat wordt gezocht naar verbanden tussen zogenaamde kandidaat-indicatoren voor de nitraatbelasting van het grondwater. Na analyse van de gegevens van één meetseizoen (2000/2001) komt in ieder geval de indeling in drie Gt-groepen naar voren als een verklarende factor voor het niveauverschil in de gemeten nitraatconcentraties in het voorjaar van 2001. De hoeveelheid Nmin in oktober-december 2000, gesommeerd over de drie bodemlagen (i.e. 0-90 cm), komt naar voren als het meest geschikt als indicator voor nitraatuitspoeling. Opschaling naar bedrijfsniveau resulteert in een voorspelling op basis van rekenregels van de bedrijfsgemiddelde nitraatconcentratie in het grondwater met een veel lagere voorspelfout dan wanneer op puntniveau voorspellingen worden gedaan. Dit biedt zicht op een praktisch toepasbare indicator op bedrijfsniveau.
    Gegevensverzameling Sturen op nitraat; op zoek naar een indicator
    Smit, A. ; Hack-ten Broeke, M.J.D. ; Berge, H.F.M. ten; Burgers, S.L.G.E. ; Chardon, W.J. ; Enckevort, P.L.A. van; Gruijter, J.J. de; Hoving, I.E. ; Velthof, G.L. - \ 2003
    Wageningen : Alterra (Alterra-rapport 658) - 48
    bodemchemie - grondanalyse - nitraten - bemonsteren - uitspoelen - grondwaterspiegel - soil chemistry - soil analysis - water table - nitrates - sampling - leaching
    In dit rapport worden de onderzoeksopzet en de bemonsteringsmethodieken van het project Sturen op nitraat beschreven. Het monitoringsysteem, de stratificering en de verdeling van proefplekken over de verschillende strata worden statistisch onderbouwd.Verder komen de bemonsterings- en meettechnieken aan bod die op proefplekniveau zijn gehanteerd. Hier worden zowel de metingen in het veld als de analyses in de laboratoria beschreven. In hoofdstuk 4 worden de berekeningsmethoden beschreven die zijn gehanteerd bij het vaststellen van perceels- en bedrijfsoverschotten. Tenslotte wordt in dit rapport ook aandacht besteed aan de manier waarop de gegevens binnen dit project beheerd worden.
    Relatie tussen N-overschot en N-uitspoeling : op gewasniveau voor de akkerbouw en vollegrondsgroenteteelt
    Enckevort, P.L.A. van; Schoot, J.R. van der; Berg, W. van den - \ 2002
    Lelystad : Praktijkonderzoek Plant & Omgeving, Sector AGV - 60
    Voorwaarts met de milieuprestaties van de Nederlandse open-teelt sectoren: een verkenning naar 2020 ten behoeve van 'Telen met toekomst'
    Buck, A. de; Ruijter, F. de; Wijnands, F. ; Enckevort, P. van; Dijk, W. van; Pronk, A. ; Haan, J. de; Booij, R. - \ 2001
    Lelystad : Praktijkonderzoek Plant & Omgeving B.V. (Telen met toekomst nr. 1) - 93
    vollegrondsteelt - akkerbouw - bloembollen - boomteelt - emissiereductie - nutriëntenuitspoeling - pesticiden - milieueffect - duurzaamheid (sustainability) - waterkwaliteit - nederland - outdoor cropping - arable farming - ornamental bulbs - arboriculture - emission reduction - nutrient leaching - pesticides - environmental impact - sustainability - water quality - netherlands
    Dit rapport beschrijft het overheidsbeleid voor landbouw en milieu op het gebied van nutriënten en gewasbeschermingsmiddelen, en de daaruit afgeleide doelen welke voor de bedrijven binnen 'Telen met toekomst' gesteld zullen worden. Verder worden beschreven de huidige milieuprestaties van de vier sectoren en de tekortkomingen ten aanzien van milieudoelstellingen en oplossingsrichtingen om de gestelde doelen te kunnen gaan voldoen
    Andere maatstaven voor nitraatuitspoeling dan Minas met name lastig voor zandbedrijven
    Dijk, W. van; Enckevort, P.L.A. van; Schoot, J.R. van der - \ 2001
    PPO-bulletin akkerbouw 5 (2001)4. - ISSN 1385-5301 - p. 27 - 31.
    mineralen - boekhouding - voedingsstoffenbalans - stikstof - nitraat - nitraten - mineraalovermaat - voedingsstoffenovermaat - uitspoelen - verliezen uit de bodem - normen - methodologie - bodem - mineraalgehalte - agrarische bedrijfsvoering - veldgewassen - akkerbouw - teeltsystemen - bedrijfssystemen - plantenvoeding - bemesting - minerals - accounting - nutrient balance - nitrogen - nitrate - nitrates - mineral excess - nutrient excesses - leaching - losses from soil - standards - methodology - soil - mineral content - farm management - field crops - arable farming - cropping systems - farming systems - plant nutrition - fertilizer application
    Door het Minas-beleid probeert de Nederlandse overheid te voldoen aan de EU-nitraatrichtlijn. De vraag is of het Minas-N-overschot in alle gevallen wel de juiste maatstaf is voor de nitraatuitspoeling. In het project 'Sturen op nitraat' worden de Minas-maatstaven vergeleken met mogelijke alternatieve maatstaven: het werkelijke N-overschot (waarin de depositie is meegenomen en niet gerekend is met de forfaitaire maar met de werkelijke N-afvoer), de minerale stikstof in de bodem na de oogst, en de minerale stikstof in de bodem in de late herfst (1 december). Voor een aantal bedrijfstypen op zand en op klei zijn modelberekeningen uitgevoerd om te bepalen in hoeverre bij het hanteren van de diverse maatstaven wordt voldaan aan de streefwaarden voor het N-overschot. De bedrijfstypen verschilden in bouwplansamenstelling (representatief voor Nederlandse akkerbouwregio's) en in bemestingsstrategie (kunstmest of kunstmest plus organische mest)
    Nitraatuitspoeling: geschikte maatstaven en risicovolle gewassen
    Enckevort, P.L.A. ; Schoot, J.R. van der; Schröder, J.J. - \ 2001
    PPO-bulletin akkerbouw 5 (2001)3. - ISSN 1385-5301 - p. 31 - 36.
    mineralen - boekhouding - stikstof - nitraat - uitspoelen - verliezen uit de bodem - normen - mineraalovermaat - voedingsstoffenovermaat - voedingsstoffenbalans - voedingsstoffenbehoeften - veldgewassen - bodem - plantenvoeding - mineralenopname - voedingsstoffenopname (planten) - mineraalgehalte - oogstresten - bemesting - minerals - accounting - nitrogen - nitrate - leaching - losses from soil - standards - mineral excess - nutrient excesses - nutrient balance - nutrient requirements - field crops - soil - plant nutrition - mineral uptake - nutrient uptake - mineral content - crop residues - fertilizer application
    Door het Minas-beleid probeert Nederland te voldoen aan de Europese nitraatrichtlijn. De vraag is echter wat de voorspellende waarde is van de volgens Minas berekende stikstofoverschotten voor de werkelijke uitspoeling van nitraat naar het grondwater. In het kader van het project 'Sturen op nitraat' (Alterra, PPO, PRI, PV en CLM) worden voor een groot aantal teelten en gewassen de Minas-maatstaven vergeleken met mogelijke andere maatstaven voor nitraatuitspoeling: het werkelijke N-overschot (waarin de N-depositie uit de lucht en neerslag is meegenomen, evenals de berekende werkelijke N-afvoer), de minerale stikstof in de bodem na de oogst (risico van nitraatuitspoeling is in de winter het grootst), en de minerale stikstof in de bodem in de late herfst (1 december). De bepalende factoren voor de aan- en afvoer van stikstof, de correlaties tussen de verschillende maatstaven en de voorspellende waarde worden besproken
    Development of Ac and Ds transposon tagging lines for gene isolation in diploid potato
    Enckevort, L.J.G. van; Lasschuit, J. ; Stiekema, W.J. ; Jacobsen, E. ; Pereira, A. - \ 2001
    Molecular Breeding 7 (2001)2. - ISSN 1380-3743 - p. 117 - 129.
    For the development of an efficient transposon tagging strategy it is important to generate populations of plants containing unique independent transposon insertions that will mutate genes of interest. To develop such a transposon system in diploid potato the behavior of the autonomous maize transposable element Ac and the mobile Ds element was studied. A GBSS (Waxy) excision assay developed for Ac was used to monitor excision in somatic starch-forming tissue like tubers and pollen. Excision of Ac results in production of amylose starch that stains blue with iodine. The frequency and patterns of blue staining starch granules on tuber slices enabled the identification of transformants with different Ac activity. After excision the GBSS complementation was usually not complete, probably due to the segment of DNA flanking Ac that is left behind in the GBSS gene. Molecular and phenotypic analyses of 40 primary transformants classified into 4 phenotypic classes revealed reproducible patterns. A very high percentage (32.5€of the primary transformants clearly showed early excision in the first transformed cell as displayed both by the analysis of the GBSS excision marker gene as well as DNA blot analyses. Genotypes useful for tagging strategies were used for crosses and the frequency of independent germinal transpositions was assessed. In crosses to Ds genotypes, excision of Ds was revealed that correlated to the activity of the Ac genotype. A line displaying Ac amplification to multiple copies conferred a high frequency of independent Ds transpositions. The genotypes described here are useful in somatic insertion mutagenesis aimed at the isolation of tagged mutations in diploid potato.
    Induction of recessive mutations in potato using tissue culture techniques
    Enckevort, L.J.G. van; Hoogkamp, T.J.H. ; Bergervoet-van Deelen, J.E.M. ; Visser, R.G.F. ; Jacobsen, E. ; Stiekema, W.J. ; Pereira, A. - \ 2001
    In: Joint FAO/IAEA Division of Nucelar Techniques in Food and Agriculture : In vitro techniques for selection of radiation induced mutations adapted to adverse environmental conditions, Shanghai, China, 1998 / International Atomic Energy Agency Wenen : IAEA - p. 15 - 25.
    Minas, lastiger voor de vollegrondsgroenteteelt dan voor de akkerbouw
    Enckevort, P.L.A. van - \ 2000
    PAV-bulletin. Vollegrondsgroenteteelt / Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt 4 (2000)4. - ISSN 1385-5298 - p. 8 - 10.
    plantenvoeding - veldgewassen - groenteteelt - mineralen - stikstof - dierlijke meststoffen - zandgronden - zware kleigronden - boekhouding - agrarisch recht - agrarische bedrijfsvoering - nederland - vollegrondsteelt - plant nutrition - field crops - vegetable growing - minerals - nitrogen - animal manures - sandy soils - clay soils - accounting - agricultural law - farm management - netherlands - outdoor cropping
    Gegevens in bijgaande tabellen: 1) Voorgestelde Minas-eindnormen in 2003 voor akkerbouw- en vollegrondsgroentebedrijven; 2) Enkele voorbeelden van berekende Minas N-overschotten en e.o.s. aanvoer op akkerbouwbedrijven met wissellend aandeel vollegrondsgroenten in het bouwplan op zand- en kleigronden. In de berekeningen is uitgegaan van bemesting volgens goede landbouwpraktijk met gebruik van dunne vleesvarkensmest en de inzet van groenbemesters waar mogelijk; 3) Engele voorbeelden van berekende Minas N-overschotten en e.o.s. aanvoer op gespecialiseerde vollegrondsgroentebedrijven op zand- en kleigronden. Gegevens in bijgaande figuur: N-inzet voor enkele veel voorkomende akkerbouwgewassen en vollegrondsgroenten op zand en klei bij een bemesting volgens goede landbouwpraktijk en het effect van voorjaarstoediening van dunne varkensmest. De inzet is vergeleken met de maximale inzet volgens de Minas-eindnormen voor droge zandgronden en overige gronden
    Voorwaarts met de milieuprestaties van de Nederlandse open-teelt sectoren: een verkenning naar 2020
    Buck, A.J. de; Ruijter, F.J. de; Wijnands, F.G. ; Enckevort, P.L.A. van; Dijk, W. van; Pronk, A.A. ; Haan, J.J. de; Booij, R. - \ 2000
    Wageningen : Plant Research International (Rapport / Plant Research International 6) - 138
    tuinbouw - groenteteelt - landbouw bedrijven - akkerbouw - bloembollen - houtachtige planten als sierplanten - milieueffect - mineralen - pesticiden - monitoring - duurzaamheid (sustainability) - bedrijfssystemen - proefbedrijven - nederland - toekomst - vollegrondsteelt - horticulture - vegetable growing - farming - arable farming - ornamental bulbs - ornamental woody plants - environmental impact - minerals - pesticides - monitoring - sustainability - farming systems - pilot farms - netherlands - future - outdoor cropping
    Potato Biotechnology: A global scenario
    Jacobsen, E. ; Bachem, C.W.B. ; Enckevort, E. van; Pereira, A. ; Stiekema, W.J. ; Hoogkamp, T. ; Bakker, J. ; Visser, R.G.F. ; Eck, H.J. van - \ 2000
    In: Potato, Global Research & Development / Paul Khurana, S.M., Shekhawat, G.S., Singh, B.P., Pandey, S.K., Shimla : Indian Potato Association - p. 173 - 184.
    Selection of independent Ds transposon insertions in somatic tissue of potato by protoplast regeneration
    Enckevort, L.J.G. van; Bergervoet-van Deelen, J.E.M. ; Stiekema, W.J. ; Pereira, A. ; Jacobsen, E. - \ 2000
    Theoretical and Applied Genetics 101 (2000). - ISSN 0040-5752 - p. 503 - 510.
    Potato is an autotetraploid crop plant that is not very amenable to the deployment of transposon tagging for gene cloning and gene identification. After diploidisation it is possible to get potato genotypes that grow well, but they are self-incompatible. This prevents the production of selfed progeny that are normally used in gene tagging approaches to select for parental lines with the target gene to be tagged in a homozygous stage. We describe here an alternative selection method for directed transposon tagging for a gene of interest in a heterozygous background. Diploid potato plants with a Ds transposon linked to the desired gene of interest (the Phytophthora infestans R1 resistance locus) in a heterozygous stage were used for the development of this directed transposon tagging strategy. After crossing to a diploid Ac transposon-containing genotype, 22 ’interesting' seedlings (R1Ds/r-; Ac/-) were selected that showed active Ds transposition as displayed by DNA blot hybridisation, empty donor site PCR and sequencing. Protoplast isolation and the use of the hygromycin gene as a cell-specific selection marker of Ds excision enabled the direct selection of Ds excision sectors in these highly chimaeric seedlings. This somatic selection of Ds transpositions and the regeneration through protoplasts resulted in the development of a large population of almost 2000 hygromycin-resistant plants. Southern blot analysis confirmed the insertion of Ds at independent positions in the genome. Every selected plant displayed independent Ds excisions and re-insertions due to the expression of the Ac transposase throughout development. This population, which is developed from seedlings with the desired R1 gene in a heterozygous stage, is directly useful for searching for transposon-tagged R1 mutants. In general, this approach for selecting for somatic transpositions is particularly suitable for the molecular isolation of genes in a heterozygous crop like potato.
    Identification of potato genes involved in Phytophthora infestans resistance by transposon mutagenesis
    Enckevort, L.J.G. van - \ 2000
    Agricultural University. Promotor(en): E. Jacobsen; A. Pereira. - S.l. : S.n. - ISBN 9789058083432 - 144
    aardappelen - solanum tuberosum - phytophthora infestans - plantenziekteverwekkende schimmels - ziekteresistentie - transposons - merken van genen - selectie - plantenveredeling - transpositie - mutagenese - potatoes - solanum tuberosum - phytophthora infestans - plant pathogenic fungi - disease resistance - transposable elements - transposition - mutagenesis - gene tagging - selection - plant breeding

    The late blight disease, caused by the oomycete Phytophthora infestans (Mont.) de Bary, is a serious threat to the potato crop every growing season. This has, for example, led to the disastrous Irish famine in the middle of the 19 th century, and continued in the 20 th century to remain a serious problem for potato growers. Since the early 1980s P. infestans populations changed more rapidly and epidemics even increased in their severity. Resistance breeding stimulated the introduction of resistance genes ( R genes) from wild Solanum species into cultivated potato, Solanum tuberosum , but newly occurring virulent races of P. infestans circumvented these R gene mediated resistances and no cultivars with durable resistance were obtained. At the moment, methods using fungicides supervised by spraying control via decision support systems are the only available control measures.

    Characteristic for R gene type mediated resistance reactions is the hypersensitive response (HR) leading to local cell death causing necrotic spots at the site of attempted infection. Genetic analysis of HR mediated resistances showed that activation of HR is highly specific and induced upon recognition between a specific R gene in the plant and a corresponding avirulence gene ( Avr gene) in the pathogen. Insights in the molecular mechanisms underlying this HR resistance reaction in Solanum species might facilitate the development of potato cultivars that are more durable in maintaining a resistance phenotype.

    A two component Ac-Ds transposon tagging strategy in diploidised potato was developed to identify and isolate genes involved in the R1 gene mediated resistance response to P. infestans . Transposable elements are molecular genetic tools to mutate and identify genes. The transposable elements Ac and Ds were first characterised in maize and their molecular isolation led to the identification of maize genes that were tagged by these elements. The autonomous Ac element is able to transpose by itself and also to induce transposition of the non-autonomous Ds element that is transposase defective. Introduction of these elements in heterologous species demonstrated their utility for isolating genes in self-fertilising plant species. Also in the highly heterozygous and tetraploid potato, the Ac and Ds transposable elements were shown to be functional. A cell autonomous visual marker gene for potato, the granule bound starch synthase gene ( GBSS gene), enabled a refined characterisation of Ac transposition in potato. Further molecular characterisation showed high levels of Ac-Ds transposition both somatically and germinally, so that suitable populations could be generated for tagging purposes.

    The production of clones homozygous for the gene of interest that are normally required for efficient tagging strategies, turned out to be time consuming in potato due to self-incompatibility at the diploid level. Therefore, an alternative method based on somatic transposition was developed for the direct selection of transposition events instead of recovering germinally transmitted transpositions. Highly chimaeric Ac-Ds seedlings with active Ds transposition linked to the R1 resistance gene on chromosome 5 of potato were selected. Protoplasts were isolated from actively transposing seedlings and using the hygromycin excision selection marker, regenerants could be selected with new independent Ds insertions. The resulting R1 resistant transposon mutagenised population of almost 2000 hygromycin resistant regenerants formed an ideal start for the identification of an R1 tagged mutant, or other Ds insertional mutants with an altered R1 resistance response.

    The somatically regenerated tagging population was analysed for the P. infestansR1 type HR resistance response, using a detached leaf assay for P.infestans inoculation. In a primary screening, 33 potential R1 resistance variants showing partial susceptibility to P. infestans race 0 were identified. These results were further quantified using stringent inoculation conditions on replicate samples leading to the identification of four putative mutants with a distinctly altered R1 resistance response. In these putative mutants less than 50% of the inoculated leaves showed the R1 type HR response and clear colonisation with sporulation of P. infestans was observed. The flanking sequences of the Ds insertion sites in these putative R1 mutants were analysed and in two cases a potential biological correlation between the insertion sequences and the phenotype was evident. One putative mutant contained a Ds insertion in a region with auxin and abscisic acid response cis-elements homologous to a specific region (TAPIR) of the tomato defence related genes TAPG2 and TAP1 .

    The second P. infestansR1 resistance mutant, mutant 1000 with a striking susceptible phenotype was characterised in more detail. Two Ds insertions were identified and the insertion site flanking sequences both showed high homology to serine/threonine protein kinases. The Ds insertion sites turned out to be homologous but not identical, indicating two independent Ds insertions in homologous but not identical genes. Both sequences showed protein identity to all the conserved regions of serine/threonine protein kinases and they contained a conserved intron position. The closest homology was to the serine/threonine protein kinase domain of the Xanthomonas resistance gene Xa21 , which is involved in the induction of a HR resistance response in rice. This indicates that the isolated Solanum tuberosum protein kinase (StPK) homologs are candidate genes involved in resistance gene activity in potato. Further specific molecular analyses identified at least 11 homologs by sequence, which probably belong to a large family of serine/threonine protein kinases in potato. Both homologs in which the Ds transposons are inserted were present in susceptible parental potato clones. Therefore, it is unlikely that the isolated sequences represent the R1 gene itself. The mutated StPKs were designated rpr1 and rpr2 , r equired for P hytophthora infestansr esistance gene 1 and 2. Studying these mutants and the StPKs involved might help in understanding the pathway leading to HR resistance in potato.

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