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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    Vision: the hefty price tag on biodiversity loss
    Schouten, Matthijs - \ 2020
    Size development of tomatoes growing in trusses: linking time of fruit set to diameter
    Tijskens, L.M.M. ; Mourik, S. van; Dieleman, J.A. ; Schouten, R.E. - \ 2020
    Journal of the Science of Food and Agriculture 100 (2020)10. - ISSN 0022-5142 - p. 4020 - 4028.
    Background: Size of fruit is an important issue in determining yield at harvest. Even under controlled conditions, variation between fruit and trusses can be considerable. As an easy to measure indication of size, the diameter of tomatoes growing in trusses was assessed in three experiments with different number of tomatoes per truss, as well as cultivars, and also by varying the level of ions in the recirculated drain water.
    Results: By applying the von Bertalanffy growth model, more than 99% of the variation present could be explained by the time of fruit set for all tomatoes growing anywhere in the trusses. A linear relationship between time of fruit set and the biological shift factor, an indication of developmental age, was observed. Integrating this linear relationship in the analysis of the diameter data removed one stochastic variable (biological shift factor), effectively halving the number of parameters to be estimated.
    Conclusion: The results of the present study indicate that the major part of the variation present in the diameter of tomatoes growing in trusses is the result of variation in the time of fruit set of individual fruits. The position within the greenhouse (i.e. local differences in assimilates supply) exerted only a minor effect on diameter development. Accordingly, the time of fruit set largely determines fruit size. Likely, growing conditions before fruit set are crucial for final fruit size. The time of fruit set of each tomato in the truss and the local growing conditions within the greenhouse that affect assimilate supply need to be assessed accurately for a reliable size prediction.
    Effects of exogenous compound sprays on cherry cracking: skin properties and gene expression
    Correia, Sofia ; Santos, Marlene ; Glińska, Sława ; Gapińska, Magdalena ; Matos, Manuela ; Carnide, Valdemar ; Schouten, Rob ; Silva, Ana Paula ; Gonçalves, Berta - \ 2020
    Journal of the Science of Food and Agriculture 100 (2020)7. - ISSN 0022-5142 - p. 2911 - 2921.
    BACKGROUND Cherry fruit cracking is a costly problem for cherry growers. The effect of repeated sprayings (gibberellic acid – GA3; abscisic acid – ABA; salicylic acid – SA; glycine betaine – GB, and Ascophyllum nodosum – AN) combined with CaCl2, on ‘Sweetheart’ cherry fruit‐cracking characteristics was investigated. Cracking was quantified in terms of cracking incidence, crack morphology, confocal scanning laser microscopy, cuticular wax content, cell‐wall modification, and cuticular wax gene expression.RESULTS All spray treatments reduced cracking compared with an untreated control (H2O), with fewer cheek cracks. The least cracking incidence was observed for ABA + CaCl2‐ and GB + CaCl2‐treated fruits, indicating an added benefit compared to spraying with CaCl2 alone. In addition, GB + CaCl2‐treated fruits showed higher fruit diameter. ABA + CaCl2 and GB + CaCl2 sprays showed higher wax content and higher cuticle and epidermal thickness compared with the control, including increased expression of wax synthase (ABA + CaCl2) and expansin 1 (GB + CaCl2). CONCLUSION In general, factors that improve the cuticle thickness appear to be important at the fruit‐coloring stage. At the fruit‐ripening stage, larger cell sizes of the epidermis, hypodermis, and parenchyma cells lower cracking incidence, indicating the importance of flexibility and elasticity of the epidermis. © 2020 Society of Chemical Industry
    Climate conditions and spray treatments induce shifts in health promoting compounds in cherry (Prunus avium L.) fruits
    Correia, Sofia ; Aires, Alfredo ; Queirós, Filipa ; Carvalho, Rosa ; Schouten, Rob ; Silva, Ana Paula ; Gonçalves, Berta - \ 2020
    Scientia Horticulturae 263 (2020). - ISSN 0304-4238
    Ascorbic acid - Calcium - Carotenoids - Growth regulators - Phenolic compounds - Sweet cherry

    Effects of repeated sprayings expected to affect phenolic, anthocyanin, carotenoid and ascorbic acid content in ‘Skeena’ and ‘Sweetheart’ cherries were observed during two years (without addition of calcium (Ca) in 2015, and with Ca in 2016). A shift in phytonutrients, with higher phenolic and carotenoid- and lower ascorbic acid content was observed when comparing Ca and the control (water) treatments in 2016 compared to 2015. Higher radiation, higher temperatures and less precipitation in 2015 compared to 2016 likely contributed to this shift. Gibberellic acid (GA3), abscisic acid (ABA), salicylic acid (SA) and glycine betaine (GB) sprays increased anthocyanin content in 2015 and for ‘Skeena’ cherries in 2016. GA3 and GB induced lower carotenoid content for ‘Skeena’- in 2015 and for ‘Sweetheart’ cherries in 2016 and lowered ascorbic acid content for ‘Sweetheart’ cherries. GA3 sprays induced the largest changes, increasing anthocyanin- (42 %), lowering carotenoid (19 %) and ascorbic acid content (53 %) compared to control. Ascophyllum nodosum, one of the novel spray treatments next to GB, appears to induce an effect opposite to GB, increasing carotenoid and ascorbic acid, but lowering phenolic content. Whether these phytonutrient shifts, due to climate conditions or to spray treatments, are beneficial to consumer health is unclear.

    Far-red light during cultivation induces postharvest cold tolerance in tomato fruit
    Affandi, Fahrizal Y. ; Verdonk, Julian C. ; Ouzounis, Theoharis ; Ji, Yongran ; Woltering, Ernst J. ; Schouten, Rob E. - \ 2020
    Postharvest Biology and Technology 159 (2020). - ISSN 0925-5214
    We investigated the role of far-red LED light during cultivation on postharvest cold tolerance in tomato fruit (Solanum lycopersicum cv Moneymaker). Red and blue top LED light, providing 150 μmol m−2 s-1 photo-synthetically active radiation (PAR) at plant height for 16 h daily, was combined with 0, 30 or 50 μmol m−2 s-1 (non-PAR) far-red LED light. Tomatoes were harvested at the mature green or red stage and subjected to cold storage for 0, 5, 10, and 15 d at 4 °C, followed by 20 d shelf-life at 20 °C.
    Mature green harvested tomatoes, cultivated with additional far-red light, showed reduced weight loss, less pitting, faster red colour development during shelf-life (when prior long cold stored), and less softening (when prior short or non-cold stored). FR lighting during cultivation likely protects the membrane integrity of MG tomatoes and thus allows uninterrupted lycopene synthesis. Red harvested tomatoes cultivated with additional far-red light were firmer at harvest, showed reduced weight loss and less decay during shelf-life. Less red colouration was observed for red harvested fruits at the start of shelf-life when fruits were prior cold stored, indicative of lycopene breakdown during cold storage. The improved cold tolerance of red harvested fruits grown under additional far-red light is likely due to higher firmness at the start of the shelf-life period with lycopene acting as antioxidant during cold storage. In conclusion, additional far-red light during cultivation improved postharvest cold tolerance for tomatoes harvested at both the green and red maturity stage, and might therefore be suitable to prolong the storage potential of tomato at sub-optimal temperatures.
    Partnering capacities for inclusive development in food provisioning
    Vellema, Sietze ; Schouten, Greetje ; Tulder, Rob Van - \ 2019
    Development Policy Review (2019). - ISSN 0950-6764
    business models - deliberation - embeddedness - institutional work - partnerships

    Context: This article focuses on partnerships working on inclusive development and food security in agri-food chains and agribusiness clusters that may feature institutional arrangements reinforcing inequality or inducing exclusion. Research question: The article develops a theory-driven capacity framework for investigating how intervention strategies related to partnering generate developmental outcomes. Methods: Building on action–research and drawing on complementary literature streams, the framework distinguishes four specific capacities that individually and in configuration contribute to processes of inclusive development triggered by partnering processes. The framework is applied to two case examples targeting inclusive development in agri-food chains and agribusiness clusters in domestic food markets in Benin and Nigeria. Results: Four capacities that enable partnerships to contribute to inclusive development are distinguished: deliberative, alignment, transformative and fitting capacity. Processes of inclusive development emerge from mobilizing and combining these complementary capacities. Capacities emerging in evolving joint actions, negotiations and deliberations in partnering processes generate developmental outcomes, which are not self-evident results of partnerships. Presence of the four capacities propels the partnership’s influence on transforming the terms of inclusion for specific groups. Policy implications: The differentiation of specific capacities embedded in partnering processes contrasts with generic partnership formulas focusing on the formalized and organizational features of partnerships and emphasizing sharing of resources and inputs. For partnerships to make a development impact, new capacities need to be developed and mobilized. This underscores the importance of skilful and experienced facilitators.

    Introduction.
    Schouten, A. - \ 2019
    In: Endophyte biotechnology / Schouten, A., CABI - ISBN 9781786399427 - p. 1 - 5.
    This chapter gives an overview on the current knowledge about endophytic fungi and bacteria, their diversity, their relationships with pests and pathogens, their distribution and activities inside the plant and their (potential) applications in developing more sustainable agricultural practices. Furthermore, the identification of chemical constituents synthesized by endophytes or by the endophyte-host plant association is discussed, as they can be most relevant for identifying novel compounds relevant for medicine, such as antibiotics and anticancer drugs, and for agriculture, such as biologically sound pesticides.
    Wat is de natuur ons waard?
    Soons, M. ; Visseren-Hamakers, I.J. ; Schouten, M.G.C. - \ 2019
    Utrecht University
    De biodiversiteit gaat in rap tempo achteruit. Hoe serieus zijn we over het behoud van de natuur? Wat houdt ons tegen effectieve maatregelen te treffen? Met bioloog prof. dr. Merel Soons (UU), ecoloog en filosoof prof. dr. Matthijs Schouten (WUR/Staatsbosbeheer) en milieukundige prof. dr. Ingrid Visseren-Hamakers (RU).
    Breeding Has Increased the Diversity of Cultivated Tomato in The Netherlands
    Schouten, Henk J. ; Tikunov, Yury ; Verkerke, Wouter ; Finkers, Richard ; Bovy, Arnaud ; Bai, Yuling ; Visser, Richard G.F. - \ 2019
    Frontiers in Plant Science 10 (2019). - ISSN 1664-462X
    breeding - diversity - introgressions - metabolomics - tomato varieties

    It is generally believed that domestication and breeding of plants has led to genetic erosion, including loss of nutritional value and resistances to diseases, especially in tomato. We studied the diversity dynamics of greenhouse tomato varieties in NW Europe, especially The Netherlands, over the last seven decades. According to the used SNP array, the genetic diversity was indeed very low during the 1960s, but is now eight times higher when compared to that dip. The pressure since the 1970s to apply less pesticides led to the introgression of many disease resistances from wild relatives, representing the first boost of genetic diversity. In Europe a second boost ensued, largely driven by German popular media who named poor tasting tomatoes Wasserbomben (water bombs). The subsequent collapse of Dutch tomato exports to Germany fueled breeding for fruit flavor, further increasing diversity since the 1990s. The increased diversity in composition of aroma volatiles observed starting from 1990s may reflect the efforts of breeders to improve fruit quality. Specific groups of aroma compounds showed different quantitative trend over the decades studied. Our study provides compelling evidence that breeding has increased the diversity of tomato varieties considerably since the 1970s.

    Aantal eikenprocessierupsen in jaar tijd verdriedubbeld in Nederland
    Vliet, Arnold van - \ 2019
    Saving resources: the exploitation of endophytes by plants for the biosynthesis of multi-functional defence compounds
    Schouten, A. - \ 2019
    In: Endophyte biotechnology: potential for agriculture and pharmacology / Schouten, A., CABI (CABI Biotechnology Series ) - ISBN 9781786399427 - p. 122 - 144.
    Plants are effective in defending themselves against herbivores, parasites and pathogens. To accomplish this, they employ various strategies, one of them being the synthesis of antimicrobial and antiherbivory compounds. To reduce the amount of energy spent, such compounds can be efficiently synthesized in multi-enzyme complexes and may have multiple roles in plant life. The synthesis can further be economized when the plant exploits associated microorganisms for the synthesis of these 'plant' compounds. Due to the potential multi-functionality of plant compounds, it is often difficult to establish what their roles are in the plant's physiology and ecology, particularly because these various roles can be quite unrelated. The research on endophytes, their synthetic abilities and their role in the ecology of the plant may, however, shed light on this issue. Indeed, it was found that particular compounds produced by endophytes, which are considered phytohormones, have additional activities, being toxic for nematodes.
    Endophytic fungi: definitions, diversity, distribution and their significance in plant life.
    Schouten, A. - \ 2019
    In: Endophyte biotechnology: potential for agriculture and pharmacology / Schouten, A., CABI (CABI Biotechnology Series ) - ISBN 9781786399427 - p. 6 - 31.
    Endophytes are set opposite to pathogens and therefore should colonize plants asymptomatically. However, as will be illustrated, endophytic fungi may behave differently under various biotic and abiotic circumstances, in which the host plant can play a defining role as well. The genetic differences between an endophytic fungus and a phylogenetically related pathogenic fungus may vary significantly. Nevertheless, over the years endophytic fungi have frequently been isolated and never elicit disease symptoms in various host plants. Such true endophytes are considered mutually beneficial; the endophyte, embedded in the stable, protective and resource-rich environment of the host plant, supports the host plant to sustain biotic and abiotic stress conditions. The mechanisms by which endophytic fungi protect the host plant against biotic stress factors are generally diverse because they can directly antagonize pests or pathogens, trigger plant defence mechanisms or do both simultaneously.
    Endophyte Biotechnology : Potential for Agriculture and Pharmacology
    Schouten, A. - \ 2019
    CABI (CABI Biotechnology Series ) - ISBN 9781786399427 - 215 p.
    This book gives an overview on the current knowledge about endophytic fungi and bacteria, their diversity, their relationships with plant pests and pathogens, their distribution and activities inside the plant and their (potential) applications in developing more sustainable agricultural practices. Furthermore, the identification of chemical constituents synthesized by endophytes or by the endophyte-host plant association is discussed, as they can be most relevant for identifying novel compounds significant for medicine, such as antibiotics and anticancer drugs, and for agriculture, such as biologically sound pesticides. It demonstrates that the current research on endophytes is highly technology-based on every level, relying on state-of-the-art molecular, biochemical, microscopical, computational and biological methods.
    Effects of LED lighting recipes on postharvest quality of leafy vegetables grown in a vertical farm
    Nicole, C.C.S. ; Mooren, J. ; Pereira Terra, A.T. ; Larsen, D.H. ; Woltering, E.J. ; Marcelis, L.F.M. ; Verdonk, J. ; Schouten, R. ; Troost, F. - \ 2019
    Acta Horticulturae 1256 (2019). - ISSN 0567-7572 - p. 481 - 488.
    LED lighting - Nitrate - Shelf life - Taste - Vertical farming - Vitamin C - Vitamin K

    Vertical farming is a technology that controls climate, water, nutrients and light to grow food in a closed environment. This allows vegetables to grow pesticide free and without other contaminants. We investigated how to influence the postharvest quality by controlling the preharvest growth conditions while keeping a high production rate. Several standard LED lighting recipes (red/blue or red/white either with or without far red) are in use in commercial farms. For this research we used lettuce, baby leaf spinach, rocket and basil from various cultivars all grown in a vertical farm research facility. We used the standard red white LED light recipe as control, while we changed the spectrum with higher blue and/or higher far-red or apply few days of continuous light stimulation just before the harvest (preharvest). Quality at harvest and quality loss during postharvest storage was monitored. We observed that light quality affects shelf life of baby leaf spinach and rocket by several days. The best light recipe for shelf life had a high blue content (35%) while the worst was with a high far red (25%). In addition, contents of vitamin C, K, nitrate, chlorophyll and flavonols were different under various light quality. Nitrate (in lettuce, rocket and spinach) and vitamin C in rocket were strongly affected by preharvest continuous light, offering a way to reduce the nitrate and improve the antioxidant level. In addition, taste was also found to change as a function of light quality but magnitude of this change is shown to be strongly cultivar dependent.

    Partnering for inclusive business in food provisioning
    Schouten, Greetje ; Vellema, Sietze - \ 2019
    Current Opinion in Environmental Sustainability 41 (2019). - ISSN 1877-3435 - p. 38 - 42.

    This review aims to unravel how partnering processes relate to processes of inclusion in the context of food provisioning. In food provisioning, inclusion has two key dimensions: the inclusion of (low-income) consumers to increase levels of food security, and the inclusion of smallholder producers to promote inclusive economic growth. This review discusses both dimensions and shows that the tandem of inclusive businesses and partnering processes reconfiguring the terms under which social groups at both sides of the agri-food chain are included is largely uncharted terrain. The paper ends with three promising areas for further research, which require a further integration of different literatures and perspectives.

    Inkomenseffecten van de GLB-aanpassingen per 2020 : een quick scan
    Berkhout, Petra ; Jager, Jacob ; Smit, Bert - \ 2019
    Wageningen : Wageningen Economic Research (Wageningen Economic Research rapport 2019-114) - ISBN 9789463951944 - 41
    Minister Schouten heeft in mei 2019 vier scenario’s geschetst voor de nationale invulling van het Gemeenschappelijke Landbouwbeleid (GLB) na 2020. Kamerlid Bisschop heeft gevraagd om een vijfde scenario op te stellen, en de gevolgen van de verschillende scenario’s voor het inkomen uit bedrijf en de economische vitaliteit van landbouwbedrijven in kaart te laten brengen. Dit rapport geeft een doorrekening op hoofdlijnen van de scenario’s voor het inkomen uit bedrijf en een analyse van de gevolgen voor de economische vitaliteit van landbouwbedrijven. De laatste is mede gebaseerd op een analyse van de wijze waarop bedrijven in de huidige implementatieperiode van het GLB (2014-2020) zijn omgegaan met veranderingen in de toeslagen.
    Poor vitamin d status in active pulmonary tuberculosis patients and its correlation with leptin and tnf-α
    Wang, Qiuzhen ; Ma, Aiguo ; Gao, Tianlin ; Liu, Yufeng ; Ren, Lisheng ; Han, Lei ; Wei, Boyang ; Liu, Qian ; Dong, Chunjiang ; Mu, Yuze ; Li, Duo ; Kok, Frans J. ; Schouten, Evert G. - \ 2019
    Journal of Nutritional Science and Vitaminology 65 (2019)5. - ISSN 0301-4800 - p. 390 - 398.
    Co-morbidity - Diabetes - Immune activity - Inflammatory markers - Leptin - Serum 25(OH)D - TNF-α - Tuberculosis

    Summary Vitamin D deficiency (VDD) is common in tuberculosis (TB) and may be implicated in the etiology of the disease and in its clinical course. The aim of this study was to investigate the association between leptin, inflammatory markers and VD status in TB patients, stratified for presence or absence of diabetes mellitus (DM). Two hundred ninety-nine TB patients were recruited from October 2015 to August 2016. Also, 91 normal controls were included. The information including socio-demographics, dietary intake and living habits was obtained by face-to-face interview. Serum concentrations of leptin and TNF-α, CRP and IL-6 were compared between TB patients with and without severe VDD (SVDD). Pearson’s correlation was used to analyze the association between TNF-α, leptin and 25-hydroxyvitamin D (25(OH)D). A significantly higher prevalence of VDD and SVDD was observed in TB patients compared with normal controls (93.0% vs 70.3%, 65.9% vs 3.3% respectively). Concentration of leptin was significantly lower, while TNF-α higher in TB patients with SVDD compared to those without (p<0.05). After adjustment for con-founders, leptin was positively associated with 25(OH)D (r=0.210, p=0.002) with similar correlation in TB patients with DM (r=0.240, p=0.020). A negative association between TNF-α and 25(OH)D was observed (r=-0.197, p=0.003), which was significant only in the subgroup without DM (r=-0.304, p=0.001). Our findings indicate that a higher VD status in TB patients may be related to higher immune activity and less serious tissue damage, and that this relation is different according to presence or absence of DM co-morbidity.

    Pfcyp51 exclusively determines reduced sensitivity to 14α-demethylase inhibitor fungicides in the banana black Sigatoka pathogen Pseudocercospora fijiensis
    Chong, Pablo ; Vichou, Aikaterini Eleni ; Schouten, Henk J. ; Meijer, Harold J.G. ; Arango Isaza, Rafael E. ; Kema, Gert H.J. - \ 2019
    PLoS ONE 14 (2019)10. - ISSN 1932-6203

    The haploid fungus Pseudocercospora fijiensis causes black Sigatoka in banana and is chiefly controlled by extensive fungicide applications, threatening occupational health and the environment. The 14α-Demethylase Inhibitors (DMIs) are important disease control fungicides, but they lose sensitivity in a rather gradual fashion, suggesting an underlying polygenic genetic mechanism. In spite of this, evidence found thus far suggests that P. fijiensis cyp51 gene mutations are the main responsible factor for sensitivity loss in the field. To better understand the mechanisms involved in DMI resistance, in this study we constructed a genetic map using DArTseq markers on two F1 populations generated by crossing two different DMI resistant strains with a sensitive strain. Analysis of the inheritance of DMI resistance in the F1 populations revealed two major and discrete DMI-sensitivity groups. This is an indicative of a single major responsible gene. Using the DMI-sensitivity scorings of both F1 populations and the generation of genetic linkage maps, the sensitivity causal factor was located in a single genetic region. Full agreement was found for genetic markers in either population, underlining the robustness of the approach. The two maps indicated a similar genetic region where the Pfcyp51 gene is found. Sequence analyses of the Pfcyp51 gene of the F1 populations also revealed a matching bimodal distribution with the DMI resistant. Amino acid substitutions in P. fijiensis CYP51 enzyme of the resistant progeny were previously correlated with the loss of DMI sensitivity. In addition, the resistant progeny inherited a Pfcyp51 gene promoter insertion, composed of a repeat element with a palindromic core, also previously correlated with increased gene expression. This genetic approach confirms that Pfcyp51 is the single explanatory gene for reduced sensitivity to DMI fungicides in the analysed P. fijiensis strains. Our study is the first genetic analysis to map the underlying genetic factors for reduced DMI efficacy.

    Cucumber mildew resistance: identification of cucumber genes involved in susceptibility and resistance to powdery and downy mildew
    Berg, Jeroen A. - \ 2019
    Wageningen University. Promotor(en): Y. Bai; R.G.F. Visser, co-promotor(en): H.J. Schouten. - Wageningen : Wageningen University - ISBN 9789463950572 - 255

    Two of the most limiting diseases in cucumber production are downy mildew (DM), caused by the oomycete Pseudoperonospora cubensis, and powdery mildew (PM), caused by the fungi Podosphaera xanthii and Golovinomyces orontii. Whereas the pathogens causing DM and PM are not related, they share a similar obligate biotrophic lifestyle.

    In my PhD thesis we aimed at identifying genes involved in susceptibility and resistance to these diseases, in order to better understand the interactions between cucumber and mildew pathogens, and contribute to breeding disease resistant cucumbers. One focus point in my research was the concept of susceptibility (S) genes. Loss-of-function of S-genes lead to resistance, which is more durable than classical race-specific resistance (R) genes. A second pillar of my PhD research was to identify causal genes for QTL contributing to disease resistance, which are frequently used in cucumber breeding. Regarding PM, the most important source of resistance is “hypocotyl resistance”, which causes partial resistance characterized by PM-free hypocotyls and stems, and can lead to full resistance when combined with other sources of resistance. One of the most famous examples of an S gene is MLO, loss-of-function alleles of which provide durable PM resistance in barley already for several decades. After the cloning of the causal gene it was found that MLO genes occur in all sequenced plant genomes to date, and that in several plant species MLO homologues in phylogenetic clades IV and V were found to be S genes for PM. In the first two chapters of my thesis I investigated MLO genes in cucumber, leading to the identification and functional characterization of a loss-of-function allele of the clade V CsaMLO8 gene as causal for hypocotyl resistance in cucumber (Chapter 2). Furthermore, we functionally characterized the other clade V MLO genes in cucumber, CsaMLO1 and CsaMLO11, and found that both are functional S-genes too, although they are rather weakly expressed in leaves, presumably leading to a minor role regarding PM susceptibility (Chapter 3).

    In the second half of my thesis the focus is on identification of genes involved in DM resistance. Currently, the most often used source of DM resistance in cucumber is the Indian semi-wild accession PI 197088, the resistance in which inherits as a polygenic trait. We introgressed one major QTL from this resistant accession in a uniform susceptible background, in order to fine-map it. We found that this QTL consists of several subQTL, each explaining a different aspect of the resistance conferred by the full QTL. Through a combination of transcriptomics and whole genome sequencing, we identified likely candidate genes for two of these subQTL. For subQTL DM4.1.2, which had a dominant effect on sporulation, we found a novel RLK gene (CsLRK10L2) which was strongly upregulated by the pathogen. This gene has homology to LRK10 genes, which were originally found as candidate genes for leaf rust resistance in wheat. This LRK10-like gene had a 551 bp deletion in DM susceptible genotypes compared to resistant genotypes. The cucumber reference genome also shows this deletion. The presence of a predicted oligogalacturonan-binding domain in the CsLRK10L2 protein suggested that this receptor might be involved in sensing cell-wall damage, triggering a defence response (Chapter 4). For subQTL DM4.1.3, which had an effect on both chlorosis and sporulation, we identified a mutation in the Amino Acid Permease 2A (CsAAP2A) gene, encoding a transporter for amino acids. Homologs of this gene were previously found to be S-genes for several obligate parasitic nematode species, as they heavily rely on their host to provide them with amino acid nutrients. We found that cucumber plants with the loss-of-function allele of CsAAP2A contained lower levels of amino acids after inoculation compared to WT plants, indicating that the mutation might decrease amino acid transport to infected leaves. As such, this gene is a novel S-gene for oomycetes (Chapter 5).

    Combined, the results described in this thesis increase our knowledge about the interactions between cucumber and two of its most notorious pathogens, and will facilitate cucumber resistance breeding.

    Far-red radiation increases dry mass partitioning to fruits but reduces Botrytis cinerea resistance in tomato
    Ji, Yongran ; Ouzounis, Theoharis ; Courbier, Sarah ; Kaiser, Elias ; Nguyen, Phuong T. ; Schouten, Henk J. ; Visser, Richard G.F. ; Pierik, Ronald ; Marcelis, Leo F.M. ; Heuvelink, Ep - \ 2019
    Environmental and Experimental Botany 168 (2019). - ISSN 0098-8472
    Botrytis cinerea - Dry mass partitioning - Far red - Growth component analysis - LED lighting - Solanum lycopersicum

    The addition of far-red (FR, 700–800 nm) radiation to standard growth light triggers a set of photomorphogenic responses collectively termed shade avoidance syndrome. Recent research showed that additional FR increased fruit yield in greenhouse tomato production. However, the mechanism behind this increase is not clear; nor is it known whether there is a trade-off between growth and defense against plant diseases in tomato under additional FR. The aims of this study were 1) to quantify the effect of additional FR on tomato fruit growth, 2) to explain this effect based on underlying growth components and 3) to examine the FR effect on resistance against the necrotrophic fungus Botrytis cinerea. Tomato (Solanum lycopersicum ‘Moneymaker’) plants were grown for four months with 30 or 50 μmol m−2 s−1 of FR added to 150 μmol m−2 s−1 red + blue or white background LED lighting. Growth and development parameters were recorded, and a growth component analysis was conducted. Bioassays for resistance against B. cinerea were conducted on leaf samples collected from each light treatment. Additional FR increased total fruit dry mass per plant by 26–45%. FR affected multiple growth components, among which the fraction of dry mass partitioned to fruits was the most prominent with a 15–35% increase. Truss appearance rate was increased 11–14% by FR while instantaneous net photosynthesis rate was not affected. FR also resulted in more severe disease symptoms upon infection with B. cinerea. In conclusion, additional FR increases tomato fruit production mainly by increasing dry mass partitioning to fruits, rather than improving photosynthesis or increasing total plant biomass. However, FR also reduces resistance of tomato leaves against B. cinerea.

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