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More biodiversity and genetic diversity in crops, trees, and livestock is considered an important strategy to improve resilience and sustainability of agricultural and forestry production systems that contribute to climate mitigation and adaptation. Plant and animal breeding need to provide well-adapted varieties and breeds that fit into these systems.In this report, we draw visions of five innovative agricultural production and forestry systems and used them in focus groups of scientists, breeders, and pioneer entrepreneurs to discuss the contribution of biodiversity and genetic diversity to the sustainability and resilience of the system, breeding goals, access to genetic material to realize the breeding goals, and the priorities for breeding and research. Although transition pathways can differ between systems, strategic research i should concentrate on the relationship between wider use of genetic resources, increasing beneficial species/breed/variety interactions, and the resilience of production systems.---Meer biodiversiteit en genetische diversiteit in gewassen, bossen en landbouwhuisdieren wordt beschouwd als een belangrijke strategie voor veerkrachtige en duurzame land- en bosbouwsystemen die bijdragen aan klimaatmitigatie en -adaptatie. Veredeling en fokkerij moeten goed aangepaste rassen leveren die passen bij deze systemen. In ditr apport schetsen wij vijf visies van innovatieve land- en bosbouwsystemen en hebben deze gebruikt in focusgroepdiscussies met wetenschappers, fokkers en veredelaars, en pioniers. Met hen hebben we de bijdrage van biodiversiteit en genetische diversiteit aan de duurzaamheid en weerbaarheid van het systeem, de fok- en veredelingsdoelen, de toegang tot genetisch materiaal om die doelen te realiseren, en de prioriteiten voor onderzoek bediscussieerd. Hoewel systemen kunnen verschillen in het transitiepad, is strategisch onderzoek nodig, gericht op de relatie tussen een breder gebruik van genetische bronnen, verbetering van gunstig

Crassulacean acid metabolism (CAM) is a photosynthetic adaption that has evolved in response to water stress and/ or high temperatures. CAM can be found in plants that grow in (semi)-arid habitats, but CAM also appears in plants in the humid tropics, for example, in epiphytes that have no direct access to soil. CAM plants are remarkable at conserving water, because they take up CO2 during the night, which allows them to keep their stomata closed during the hottest part of the day. The aim of this thesis was to increase understanding of CAM physiology by studying the economically important ornamental orchid Phalaenopsis. To reach this objective, Phalaenopsis plants were grown at several combinations of temperature and light. The response to these treatments was determined on different biological scales (from leaf to plant growth) and on different temporal scales (from seconds to the entire period of cultivation).Chapter 1 introduces CAM and describes how the diel cycle of CO2 uptake and CO2 refixation can be captured in four phases. CAM plants are often not considered when looking for future-proof solutions in agriculture, but one option that is being explored is the bio-engineering of CAM into C3 plants, which is also discussed here. The second half of this general introduction focuses on CAM in the orchid Phalaenopsis. The cultivation practice of the economically important Phalaenopsis pot plant is outlined, and the effects of temperature, light and CO2 on Phalaenopsis growth and development are summarized.Chapter 2 introduces a conceptual framework for CAM plants. A literature study revealed that currently no mechanistic models for CAM growth exist. Therefore, a conceptual framework was developed, which consists of three modules, covering 1) CAM photosynthesis, 2) allocation of assimilates among carbon pools, and 3) biomass accumulation among plant organs. The framework covers processes related to CAM physiology on different biological (from leaf to plant) and tem

In greenhouse horticulture, efficiency of climate control and plant protection can be improved by having an accurate impression of plant status, such as photosynthesis or chemical composition. Recent advances in remote sensing technologies have brought about a range of innovations in precision agriculture, with the potential for adaptation to greenhouses. Simple, traditionally used indices employ only one or two spectral bands, in which the contributions of various pigments and leaf or canopy structure can highly overlap. Consequently, such indices may be insufficient for applications. State-of-the-art models have been developed that can better interpret hyper- and multispectral leaf and canopy imagery by employing the biochemical and radiative transfer properties of vegetation. An example is the soil-canopy observation of photosynthesis and energy balance (SCOPE) model, which was developed specifically for crop canopies. Here we present one of the pillars of SCOPE, the leaf radiative transfer (RT) model Fluspect. Fluspect simulates leaf chlorophyll fluorescence, reflectance and transmittance spectra. The model can be inverted to obtain estimates of leaf chlorophylls, carotenoids, anthocyanins, xanthophyll epoxidation, water and dry matter content. Moreover, it can be linked to a model for leaf photosynthesis and when inverted, provide a method to estimate photosynthesis directly from leaf spectral information. We test the model against a tomato data set, with measured hyperspectral images, chlorophyll, sugar, acid, starch, dry matter content and nutrients. The first study of the data set, using partial least square regression, showed that hyperspectral images have a high correlation with important fruit and leaf compounds. We compared these results to Fluspect retrievals and conventional vegetation indices. In the paper, we discuss the potential added value of using RT models in greenhouse horticulture.

Over the last decade, LED lighting has gained considerable interest as an energy efficient light source in greenhouse horticulture. Much work on LED lighting is done under controlled conditions in the absence of sun light, whereas the primary application lies in supplementation of low light conditions in winter. A frequently forgotten aspect herein is that spectral composition may also affect the biology of pests and their natural enemies, both directly and indirectly through an impact on induced plant resistance. In this paper, we present results of trials with chrysanthemum and alstroemeria cut flowers which were exposed to lighting regimes with varying contributions of blue, green, red and far-red light. These trials were done under low levels of natural light, mimicking winter conditions. In chrysanthemum, spectra where blue or green were added did not affect stem length, plant dry weight and number of flowers when the percentage of red light remained over 75%. Replacing part of the photosynthetically active radiation (PAR) light by far-red light considerably increased stem length and (in some species) plant dry weight, at the expense of flowering. In alstroemeria, the number of flowers harvested, their length and fresh weight was largest in the treatment with equal shares of blue, green, red and far-red light. In chrysanthemum, the beneficial insect Orius laevigatus was introduced and its egg-laying activity and population development under different lighting strategies was monitored. The number of eggs laid by the first Orius generation was affected by the percentage red light in the spectrum, with the lowest egg number found in plants grown under 95% red. The results for egg-laying by the second Orius generation differed among chrysanthemum cultivars. The implications of this work on lighting strategies for greenhouse horticulture are discussed, both in spectral composition and in timing during the day and the season.

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.

Next to its intensity, the spectral composition of light is one of the most important factors affecting plant growth and morphology. The introduction of light emitting diodes (LEDs) offers perspectives to design optimal light spectra for plant production systems. However, knowledge on the effects of light quality on physiological plant processes is still limited. The aim of this study is to determine the effects of six light qualities on growth and plant architecture of young tomato plants, and to upscale these effects to the crop level using a multispectral, functional-structural plant model. Young tomato plants were grown under 210 μmol m-2 s-1 blue, green, amber, red, white or red/blue (92%/8%) LED light with a low intensity of sunlight as background. Plants grown under blue light were shorter and developed smaller leaves which were obliquely oriented upward. Leaves grown under blue light contained the highest levels of light harvesting pigments, but when exposed to blue light only, they had the lowest rate of leaf photosynthesis. However, when exposed to white light these leaves had the highest rate of photosynthesis. Under green light, tomato plants were taller and leaves were nearly horizontally oriented, with a high specific leaf area. The open plant structure combined with a high light transmission and reflection at the leaf level allowed green light to penetrate deeper into the canopy. Plants grown under red, amber and white light were comparable with respect to height, leaf area and biomass production. The 3D model simulations indicated that the observed changes in plant architecture had a significant impact on light absorbance at the leaf and crop level. The combination of plant architecture and spectrum dependent photosynthesis was found to result in the highest rate of crop photosynthesis under red light in plants initially grown under green light. These results suggest that dynamic light spectra may offer perspectives to increa

L-ascorbate (ASC) is essential for human health. Therefore, there is interest in increasing the ASC content of crops like tomato. High irradiance induces accumulation of ASC in green tomato fruits. The D-mannose/L-galactose biosynthetic pathway accounts for the most ASC in plants. The myo-inositol and galacturonate pathways have been proposed to exist but never identified in plants. The D-mannose/L-galactose starts from D-glucose. In a series of experiments, we tested the hypothesis that ASC levels depend on soluble carbohydrate content when tomato fruits ripen under irradiances that stimulate ASC biosynthesis. We show that ASC levels considerably increased when fruits ripened under light, but carbohydrate levels did not show a parallel increase. When carbohydrate levels in fruits were altered by flower pruning, no effects onASC levels were observed at harvest or after ripening under irradiances that induce ASC accumulation. Artificial feeding of trusses with sucrose increased carbohydrate levels, but did not affect the light-induced ASC levels. We conclude that light-induced accumulation of ASC is independent of the carbohydrate content in tomato fruits. In tomato fruit treated with light, the increase in ASC was preceded by a concomitant increase in myo-inositol.

Selecting rootstocks for high nitrogen acquisition ability may allow decreased N fertilizer application without reducing tomato yields, minimizing environmental nitrate pollution. A commercial hybrid tomato variety was grafted on a genotyped population of 130 recombinant inbred lines (RILs) derived from Solanum pimpinellifolium, and compared with self- and non-grafted controls under contrasting nitrate availabilities (13.8 vs 1.0 mM) in the nutrient solution. Grafting itself altered xylem sap composition under N-sufficient conditions, particularly Na+ (8.75-fold increase) concentration. N deprivation decreased shoot dry weight by 72.7% across the grafted RIL population, and one RIL rootstock allowed higher total leaf N content than the best of controls, suggesting more effective N uptake. Sixty-two significant QTLs were detected by multiple QTL mapping procedure for leaf N concentration (LNC), vegetative growth, and the xylem sap concentrations of Mn and four phytohormone groups (cytokinins, gibberellins, salicylic acid and jasmonic acid). Only three LNC QTLs could be common between nitrogen treatments. Clustering of rootstock QTLs controlling LNC, leaf dry weight and xylem sap salicylic acid concentration in chromosome 9 suggests a genetic relationship between this rootstock phytohormone and N uptake efficiency. Some functional candidate genes found within 2 Mbp intervals of LNC and hormone QTLs are discussed.

(Semi-)closed greenhouses have been developed over the last decades to conserve energy. In a closed greenhouse, window ventilation is fully replaced by mechanical cooling while solar heat is temporarily stored in an aquifer. A semi-closed greenhouse has a smaller cooling capacity than a closed greenhouse and, in which mechanical cooling is combined with window ventilation. (Semi-)closed greenhouses create new climate conditions: high CO2 concentrations irrespective of the outdoor climate, and vertical gradients in temperature and vapour pressure deficit throughout the canopy. This thesis focuses on the crop physiology in (semi-)closed greenhouses, and investigates the effects of the new climate conditions on crop growth, development and underlying processes. Cumulative production in (semi) closed greenhouses increased by 6-14% compared to the open greenhouse, depending on the cooling capacity. The production increase in the (semi-)closed greenhouses was explained by the higher CO2 concentrations. In many species, feedback inhibition of photosynthesis occurs when plants are grown at high CO2. The results, however, suggest that high CO2 concentrations do not cause feedback inhibition in high producing crops, because the plants have sufficient sink organs (fruits) to utilise all assimilates. Pruning experiments showed that photosynthetic acclimation to elevated CO2 concentration only occurred when the number of fruits was considerably reduced. Cooling below the canopy induced vertical temperature and vapour pressure deficit gradients. These gradients correlated with outside radiation and outside temperature. Despite the occurrence of vertical temperature gradients, plant growth and fruit yield were mostly unaffected. Leaf and truss initiation rates did not differ in the presence or absence of a vertical temperature gradients, since air temperatures at the top of the canopy were kept comparable. The only observed response of plants to the vertical temperature gradient w