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Participation has been proposed to improve agricultural extension programmes in developing countries. This paper reports on experience with COCREATE, an approach to agricultural extension programmes that supports agricultural chain actors in self-directed learning in action research with smallholder farmers and local traders in Indonesia. This approach resulted in the changes in relation and task division between farmers and their local traders in the agricultural production and supply and chains, improved their market position and in new institutions.

Background.Revealing tacit knowledge often is seen as very valuable for organizations, although it is usually challenging to enunciate and share this type of knowledge.Methods.This study uses a participatory design and the application of a board gaming simulation as instruments to extract tacit knowledge. To illustrate this application, the gaming simulation is played with entrepreneurs from horticulture. Horticulture represents a complex social system where tacit knowledge plays a major role in the trade process. A participatory design process is used to explore whether the design and play of gaming simulations enable participants to explicate their tacit knowledge. Participants’ participation in designing the gaming simulation explicated that reconstructing reality was a prerequisite for their commitment.Results.The results from playing simulation sessions show that participants were able to: (1) narrow down the anecdotic behaviour to a few factors; (2) to structure these factors; (3) explore how these factors relate to trade barriers and (4) to explain which tactics are applied to foster trade.Conclusion.The educational value of this study is that it helped entrepreneurs in understanding complex real-life situations.

Participation of local actors has shown to be of significant importance to the uptake of new approaches to agricultural initiatives in developing countries. This paper proposes a new approach to empower local chain actors to work together to understand their own and others’ challenges, to pursue common understanding of their situations and challenges, and to then co-create solutions. Reflection on each other’s position is crucial to this process, and is core to the participatory approach designed to this purpose. Agricultural chains are the focus of a case study in Indonesia involving both farmers and wholesalers in the chain. Results show that the approach has led to new forms of collaboration between farmers, and between farmers and wholesalers, increasing market potential.

Sustainable agricultural development (SAD) requires empowerment and engagement of all actors in the agricultural production and supply chain to enable change. This paper proposes a novel framework for Participatory Sustainable Agricultural Development (PSAD) that distinguishes four main classes of factors that influence participation in SAD: environmental, economic, social and governance-related. The factors in each of these classes are analysed in relation to their effect over time, on the basis of 49 SAD programmes reported in the literature. Findings show that the social factors of engagement and empowerment, not often addressed in existing SAD programmes, are of significant influence to effect over time, as are the environmental factors of food safety, and the economic factors of production and capacity development. As such this paper shows that in in addition to the well-acknowledged need for knowledge and skills related to food safety, production and capacity development, SAD programmes also need to address the social factors of engagement and empowerment to enable sustainable change over time for SAD through participation.

It has been shown that the identification of many foods including vegetables based on flavour cues is often difficult. The effect of providing texture cues in addition to flavour cues on the identification of foods and the effect of providing taste cues only on the identification of foods have not been studied. The aim of this study was to assess the role of smell, taste, flavour and texture cues in the identification of ten vegetables commonly consumed in The Netherlands (broccoli, cauliflower, French bean, leek, bell pepper, carrot, cucumber, iceberg lettuce, onion and tomato). Subjects (n = 194) were randomly assigned to one of four test conditions which differed in the sensory cues available for vegetable identification: taste, smell (orthonasal), flavour (taste and smell) and flavour-texture (taste, smell and texture). Blindfolded subjects were asked to identify the vegetable from a list of 24 vegetables. Identification was the highest in the flavour-texture condition (87.5%). Identification was significantly lower in the flavour condition (62.8%). Identification was the lowest when only taste cues (38.3%) or only smell cues (39.4%) were provided. For four raw vegetables (carrot, cucumber, onion and tomato) providing texture cues in addition to flavour cues did not significantly change identification suggesting that flavour cues were sufficient to identify these vegetables. Identification frequency increased for all vegetables when perceived intensity of the smell, taste or flavour cue increased. We conclude that providing flavour cues (taste and smell) increases identification compared to only taste or only smell cues, combined flavour and texture cues are needed for the identification of many vegetables commonly consumed in The Netherlands.

The quantum efficiency of photosynthesis of leaves is wavelength dependent and peaks in red (620–670 nm). However when cucumber plants are raised under pure red light, leaf photosynthesis becomes severely impaired. This “red light syndrome” has been characterized before by a low Fv/Fm, unresponsive stomatal conductance (gs), and a low photosynthetic capacity (Amax). It is not known if the syndrome also occurs in fully developed leaves that are exposed to pure red light after reaching maturity and if initially injured leaves can recover from the syndrome. This study investigates the plasticity leaf photosynthetic apparatus after inducing or releasing the “red light syndrome” in leaves of young cucumber plants. The plants were grown under pure red (R) or mixed red/blue (RB; 70%R) LED light and subsequently exposed to RB (R/RB) and R (RB/R) light (100 μmol PPFD m−2 s−1, 16 h photoperiod) or kept at their initial growth spectrum (R/R) and (RB/RB). Acclimation of fully developed leaves was monitored with gas exchange and chlorophyll fluorescence (CF) over a period of 8–10 days after the shift. After switching to RB, R injured leaves recovered from photodamage within 4 days. Photosynthetic capacity (Amax) and gs partly recovered, but did not restrict the net CO2 assimilation rate at growth irradiance (A100), which increased to the same level as in healthy (RB/RB) leaves. After imposing injurious R to healthy mature leaves, they transiently developed signs of the red light-syndrome: a slightly decreased Fv/Fm and more severely reduced Amax and gs. However, A100 did not significantly decrease. CF quenching analysis revealed an potentially harmful increased quantum yield of non-regulated non-photochemical energy loss in PSII under R, which was higher in leaves that developed under R than in leaves that were exposed to R after reaching maturity. We conclude that exposure to pure red light is harmful to photosynthetic systems in both developing and developed leaves of cucumber, but the effect on CO2 assimilation rate and Fv/Fm is much more severe in developing leaves than in mature leaves at low growth irradiance. Chloroplasts of previously R light injured leaves can recover within a few days after releasing from R light, while stomatal conductance and other (partial) morphologically determined leaf factors do not completely acclimate.

Broccoli combines high levels of vitamins, fibres and glucosinolates (GLS) with a low calorie count. GLS are precursors for the characteristic broccoli flavour and have anti-carcinogenic properties. This study describes the effect of controlled atmo¬sphere (CA) and temperature on GLS concentrations in broccoli. Data on GLS behaviour and gas exchange were gathered for broccoli heads that were stored at three temperatures and subjected to four levels of O2 and three levels of CO2. The GLS behaviour of three GLS (raphanin, GB and neo-GB) was examined that showed exponential decrease over time, possibly representing the GLS interaction with myrosinase. The most striking feature is the large variation in GLS concentrations at harvest. The propagation of the variation in GLS over time is clearly affected by CA and temperature. Variation in GLS concentrations over time at the same gas condi¬tions and temperature was interpreted with the moment of harvest as main cause of random variation. Assuming that this random variation is normally distributed, the exponential function over time can be transformed into a batch model that describes the changes of variation over time (Schouten et al., 2004, Hertog et al. 2004). The effect of the CA was modelled using the standard gas exchange model. This calibrated gas exchange model was then linked via the reaction rate constant to the batch model to create an integrated batch model. This integrated batch model was subsequently calibrated to describe the variation of the GLS as function of O2, CO2, time, tempera¬ture and the batch parameters (average biological age and standard deviation). The percentage variance accounted for was on average 85%. Considering that this modelling effort is based on destructive GLS measurements, this is a rather high value. All GLS species were retained by suitable (low O2, high CO2) gas conditions, but remarkably, raphanin was found to be less affected by temperature, indicating that CA storage and low temperature would both retain this GLS species to the same extent, while low temperature storage is a better option for e.g. neo-GB

As of January 1st 2005, a system of reduced checks for phytosanitary inspections of certain plants and plant products imported into the European Union (EU) is in place. Under this system, plants and plant products satisfying special criteria may be inspected with a reduced frequency. These criteria are based on EU-wide data on historical volumes of import and interceptions of harmful organisms in particular products. The objective of this paper is two-fold. Firstly, the paper analyses whether proportions of interceptions of harmful organisms associated with cut flowers imported into the Netherlands ? the largest EU importer of cut flowers ? support the application of reduced checks for certain genera and trades (commodity-exporting country combinations) of cut flowers. Secondly, the paper analyses how effective the reduced checks system is in minimizing the expected costs of introduction of harmful organisms in the EU. For that, a theoretically optimal system for allocating inspection effort to commodities is described. Using an illustrative example and stochastic simulations, the expected costs of introduction of harmful organisms under the theoretically optimal system and the current system of reduced checks are compared. Examination of interceptions of harmful organisms supports application of reduced checks for most genera and trades of cut flowers in the Netherlands. The results of stochastic simulations show that reduced checks may not minimize the expected costs of introduction of harmful organisms into the EU. Accounting for possible economic impacts of harmful organisms in determining the frequencies of reduced checks may help optimize the current system

'Generativity' and 'strength' are elusive concepts. They are in the daily vocabulary of growers, but objective determination and quantification is hard. Therefore they are avoided in science. The incorporation of 'generativity' and 'strength' into the vocabulary of science will increase the understandability of scientific results to growers, and open possibilities for applied research questions. Here we propose a multivariate approach. A tomato crop was monitored with observations that are common in tomato cultivation. The measurements included stem diameter, leaf length, length growth of the stem, harvested fruit weight and brix. A principal component analysis was performed on the plant observations to find out whether the principal components can be linked to the crop attributes 'generativity' and 'strength'. To create a difference in 'generativity' two different irrigation regimes and two different leaf pruning regimes were applied. This article presents a proof of principle. We demonstrate that a multivariate analysis can be used to visualize the crop condition in a way that is recognizable for growers. This opens the possibility for quantification of 'generativity' and 'strength'.

This paper focuses on the critical success factors in entrepreneurial innovation, and the role of cooperation with chain partners, knowledge institutions and colleague firms in the Dutch glasshouse industry. This industry, typified by a large number of family-owned entrepreneurial firms, is generally acknowledged as one of the world leaders in horticultural production and trade. Not only are the auctions of Aalsmeer and Naaldwijk among the most important horticultural auctions in the world, but the knowledge of cultivation techniques is also highly developed in the Netherlands. In order to maintain its leading position and to compete successfully with low-cost countries, Dutch horticulture is constantly reinventing itself. If we take a closer look, however, we see that only a limited number (3%) of the Dutch glasshouse companies actually take the lead in innovation. Using expert advice, we selected the 74 most successful innovative companies to be included in this study, of which 44 companies were willing to participate. In 2004, all the participating companies were visited. In total 139 innovations were analysed, using a combination of half-structured in-depth interviews with the glasshouse entrepreneurs and a structured questionnaire based on 10-point Likert scales. The entrepreneurs were asked to fill out the questionnaire for their most and least successful innovations. As expected, more successful (87) than failed innovations (52) were reported. Our results show that the characteristics demonstrated by the innovative entrepreneurs are essential for success in innovation. The innovative entrepreneur has a strategic vision of how to serve the market and create value. Also, team communication was extremely important. Successful entrepreneurs maintain an open atmosphere and show real commitment to the innovation process. They are in contact with a diverse network of business relations to develop innovations. Intensifying the network relations, e.g. by clustering glasshouse companies, leads to more successful innovation. The more firms in the horticultural production chain were actively involved in the innovation process, the bigger the chances of success. This was especially true for firms downstream toward the market.

With the present developments in CA technology it becomes possible to fine tune the storage conditions to the specific needs of the product. This generates the need to know the exact quality conditions of the product before storage starts. By measuring the initial quality we can determine these conditions optimally. At present the most likely candidates to assess the initial quality with fast and non-destructive measurements are colour, chlorophyll fluorescence, and maybe NIR spectroscopy. Two examples are presented where initial colour measurements on all products in a batch can be shown to be indicative for the keeping quality of that batch. The first example focuses on how initial colour measurements using a 3CCD video camera can be utilised to predict the keeping quality of a batch of cucumbers where colour itself is regarded as the most important quality attribute. The second example focuses on how colour measurements can be used to predict the keeping quality of a batch of strawberries where the ability to suppress a Botrytis cinerea infection is the most important quality attribute. Furthermore, attention is given to the use of modulated chlorophyll fluorescence imaging as a possible initial quality indicator for rose leafy stem cuttings. The level of inhomogeneity in the quantum yield of photochmistry od PSII of leaves of rose cuttings may be an indictor of the capability of the cutting to recover from severance, and to form roots and generate regrowth

Flower size and number of flowers per plant are important external quality aspects in cut chrysanthemum. The present work is conducted in a glasshouse and aims at investigating how these quality aspects can be predicted. To evaluate individual flower size, different levels of supplementary lighting (control and assimilation light), plant density (32, 48 and 64 plants m-2) and lateral flower bud removal (leaving 1 flower, 4 flowers and control) were applied. To analyse the effect of assimilate supply on number of flowers per plant, three light intensities (no shade control, 65␕ight, and 45␕ight) where combined with three plant densities (32, 64, and 80 plants m-2). Individual flower size was negatively influenced by competition for assimilates in the treatments with a fixed number of flowers per plant (1 or 4 flowers). In such treatments, plants grown under no supplementary assimilation light, higher plant density, or with higher number of flowers per plant resulted in significantly lower individual flower dry mass and area. However, when no lateral flower buds were removed (control), higher assimilate supply resulted in more flowers rather than in larger flowers. Number of flowers per plant (including flower buds) showed a positive linear increase with total dry mass per plant. The combination of 32 plants m-2 and no shade resulted in the highest number of flowers per plant (33 flowers) in contrast with 80 plants m-2 and 45␕ight intensity (only 9 flowers).

The influence of manure and diammonium phosphate (DAP) mineral fertilizer on germination, leaf nitrogen content, nitrate accumulation and yield of vegetable amaranth (Amaranthus hypochondriacus) was investigated. Field trials were set up at the University of Nairobi Field Station at the Upper Kabete Campus during the long rains of March–May in 2007 and 2008. Trials were laid out as complete randomized block design with four fertilization treatments: 20, 40, and 60 kg nitrogen (N) ha-1 supplied by DAP (18:46:0), 40 kg N ha-1 supplied by cattle manure and an unfertilized control variant. The vegetables were harvested at three maturity stages at 6, 7, and 8 weeks after planting. Results indicated that there were significant differences between treatments in germination percentage, leaf nitrogen content, nitrate accumulation and vegetable yield. Plants that received manure had a higher germination percentage than those that received the same amount of N supplied by the chemical fertilizer DAP. The yields generally increased from week 6 to week 8. The highest yield was recorded in plots receiving 40 kg N ha-1 from DAP at eight weeks after planting. Plots that were supplied with manure recorded the lowest yield when compared to the fertilizer treated plots at all rates. Leaf nitrogen content increased with increasing rate of N but only when N was supplied by DAP fertilizer. The leaf nitrogen content decreased with increasing age of the plants. The leaf nitrate content increased with increase in DAP application rate. Results indicate that manure application produced quality vegetables in terms of low nitrate levels, but leaf nitrogen and vegetable yields were low. DAP application effected higher yields, but the vegetables had high though acceptable nitrate levels

Semi-closed greenhouses have been developed in which window ventilation is minimized due to active cooling, enabling enhanced CO2 concentrations at high irradiance. Cooled and dehumidified air is blown into the greenhouse from below or above the canopy. Cooling below the canopy may induce vertical temperature gradients along the length of the plants. Our first aim was to analyze the effect of the positioning of the inlet of cooled and dehumidified air on the magnitudes of vertical temperature and VPD gradients in the semi-closed greenhouses. The second aim was to investigate the effects of vertical temperature gradients on assimilate production, partitioning, and fruit growth. Tomato crops were grown year-round in four semi-closed greenhouses with cooled and dehumidified air blown into the greenhouses from below or above the crop. Cooling below the canopy induced vertical temperature and VPD gradients. The temperature at the top of the canopy was over 5°C higher than at the bottom, when outside solar radiation was high (solar radiation >250 J cm-2 h-1). Total dry matter production was not affected by the location of the cooling (4.64 and 4.80 kg m-2 with cooling from above and from below, respectively). Percentage dry matter partitioning to the fruits was 74% in both treatments. Average over the whole growing season the fresh fruit weight of the harvested fruits was not affected by the location of cooling (118 vs 112 g fruit-1). However, during summer period the average fresh fruit weight of the harvested fruits in the greenhouse with cooling from below was higher than in the greenhouse with cooling from above (124 vs 115 g fruit-1)

Western-European consumers have become demanding on product availability in retail outlets and vegetable attributes such as quality, integrity, safety. When (re)designing vegetable supply chain networks one has to take these demands into consideration, next to traditional efficiency and responsiveness requirements. In post¬harvest research, much attention has been paid to quality decay modelling and the development of Time-Temperature Indicators to individually monitor the temperature conditions of vegetables throughout distribution. This paper discusses opportunities to use time-dependent product quality information in supply chain/logistics decision making to improve the design of vegetable supply chain networks. If product quality in each step of the supply chain can be predicted, product flows based on availability predictions can be controlled and better chain designs can be established. A case is presented to illustrate the value of this innovative concept of Quality Controlled Logistics through a Dutch tomato chain.

A (semi-)closed greenhouse is a novel greenhouse with an active cooling system and temporary heat storage in an aquifer. Air is cooled, heated and dehumidified by air treatment units. Climate in (semi-)closed greenhouses differs from that of conventional open greenhouses. The aims of our research were first, to analyze the effect of active cooling on greenhouse climate, in terms of stability, gradient and average levels; second, to determine crop growth and production in closed and semi-closed greenhouses. An experiment with tomato crop was conducted from December 2007 until November 2008 in a closed greenhouse with 700 W m-2 cooling capacity, two semi-closed greenhouses with 350 and 150 W m-2 cooling capacity, respectively, and an open greenhouse. The higher the cooling capacity, the more independent the greenhouse climate was of the outside climate. As the cooling ducts were placed underneath the plants, cooling led to a remarkable vertical temperature gradient. Under sunny conditions temperature could be 5°C higher at the top than at the bottom of the canopy in the closed greenhouse. Cumulative production in the semi-closed greenhouses with 350 and 150 W m-2 cooling capacity were 10% (61 kg m-2) and 6% (59 kg m-2) higher than that in the open greenhouse (55 kg m-2), respectively. Cumulative production in the closed greenhouse was 14% higher than in the open greenhouse in week 29 after planting but at the end of the experiment the cumulative increase was only 4% due to botrytis. Model calculations showed that the production increase in the closed and semi-closed greenhouses was explained by higher CO2 concentration.

Broccoli combines high contents of vitamins, fibres and glucosinolates with a low calorie count and is sometimes referred to as the 'crown jewel of nutrition'. Colour is one of the most important quality attributes of broccoli, and yellowing due to senescence of broccoli florets is the main external quality problem in the broccoli supply chain. Controlled Atmosphere (CA) is a very effective method to maintain broccoli quality but the effects of CA on colour retention have not been studied extensively. The aim of this paper is to characterise the colour behaviour (measured by RGB colour image analysis) of broccoli as affected by CA and temperature. Data on colour behaviour and gas exchange were gathered for broccoli heads that were stored in containers at three temperatures and subjected to four levels of O 2 and three levels of CO 2 . Gas conditions and temperature have a clear effect on the colour change of broccoli especially at low O 2 in combination with high CO 2 . An integrated colour model is proposed that combines a colour model with a standard gas exchange model. The colour model is based on three differential equations describing the formation of (blue/green) chlorophyllide from the colourless precursor, the bidirectional conversion of chlorophyllide into (blue/green) chlorophyll, and the decay of chlorophyllide. During the first step of building the integrated model, gas exchange data were analysed simultaneously using multi response regression analysis. No fermentation was encountered for this batch of broccoli. During the second step it was found that only one of the reactions of the colour model, the decay of chlorophyllide, is affected by the gas conditions. In the final step, a multi-response approach was applied where gas exchange parameters were estimated using the gas exchange model, the colour parameters were estimated using the colour model with both models linked via the reaction rate constant affected by the gas conditions. Such a calibrated, integrated, model could be used as a tool for predicting colour change in the postharvest chain.

Background A substantial number of children with an obstetric brachial plexus lesion (OBPL) will develop internal rotation adduction contractures of the shoulder, posterior humeral head subluxations and glenohumeral deformities. Their active shoulder function is generally limited and a recent study showed that their shoulder muscles were atrophic. This study focuses on the role of shoulder muscles in glenohumeral deformation and function. Methods This is a prospective study on 24 children with unilateral OBPL, who had internal rotation contractures of the shoulder (mean age 3.3 years, range 14.7 months to 7.3 years). Using MR imaging from both shoulders the following parameters were assessed: glenoid form, glenoscapular angle, subluxation of the humeral head, thickness and segmental volume of the subscapularis, infraspinatus and deltoid muscles. Shoulder function was assessed measuring passive external rotation of the shoulder and using the Mallet score for active function. Statistical tests used are t-tests, Spearman's rho, Pearsons r and logistic regression. Results The affected shoulders showed significantly reduced muscle sizes, increased glenoid retroversion and posterior subluxation. Mean muscle size compared to the normal side was: subscapularis 51%, infraspinatus 61% and deltoid 76%. Glenoid form was related to infraspinatus muscle atrophy. Subluxation was related to both infraspinatus and subscapularis atrophy. There was no relation between atrophy of muscles and passive external rotation. Muscle atrophy was not related to the Mallet score or its dimensions. Conclusion Muscle atrophy was more severe in the subscapularis muscle than in infraspinatus and deltoid. As the muscle ratios are not related to passive external rotation nor to active function of the shoulder, there must be other muscle properties influencing shoulder function.

When we look at the ornamental supply chain in the Netherlands as a Value Chain (Porter, 1998) it strikes us that most actors in the chain are obsessed by the product and have no idea how the value of these products is developed throughout the entire production and supply chain. Any value chain starts with the value a group of consumers attributes to the product. So it all starts with finding out what consumers want and then finding the most cost effective way of delivering that product with the desired attributes to these consumers. In the USA the South American producers expected to be able to compete with the local production by offering the product (cut flowers) at a lower price (Reid, 2002). In the first instance this worked very well and the local production virtually disappeared. However the quality of the imported product was a dismal failure and while imports surged, total flower consumption plummeted in the 90s. In the UK the retail chains such as Sainsbury’s and Tesco wanted to improve their ornamental categories. They invented the ‘Vase Life Guarantee’ and improved their quality considerably. This resulted in an increase in market share from 18 to 60% over 15 years, while the total flower consumption in the UK doubled in the past 15 years. A research will be shown on the response of stakeholders in the ornamental industry and consumers on the question whether they would see the ‘Vase Life Guarantee’ as a value addition in the supply chain. This research was done in the UK and the Netherlands (where no vase life guarantee was used explicitly in the retail) at the turn of the millennium. It clearly shows the difference between the judgements of the stakeholders versus the opinions of the consumers. If we want to create Value Added Chains in the ornamental industry it is about time to find out what the consumer really wants!

Agri-food supply chains are currently being confronted with many requirements regarding the product quality of their products. In recent years, concerns about food quality have risen among consumers as a result of several outbreaks of diseases and various environmental concerns. This has stimulated governments to introduce stricter regulations concerning food quality and safety issues. Besides governmental regulations, retailers also impose food quality requirements and standards on their supply chains. The goal of this paper is therefore to develop a method for analysing the impact of different quality assurance systems (QAS) requirements on the performance of the different stages of the supply chain and of the chain as a whole. Performance in this study includes components of efficiency, flexibility and responsiveness as well as food quality. This study uses perceptions of the Dutch tomato supply chain members in an effort to understand the perceived impact of different QAS requirements on the performance of the tomato supply chain. These perceptions are obtained using an adapted self-explicated method. Results indicate that some QAS requirements are perceived to have a positive impact on some supply chain members' performance, while they are perceived to have a negative impact on other supply chain members' performance. Overall, results reveal that all selected QAS requirements are perceived to have a positive impact on the performance of the supply chain, as a whole, although the total impact is relatively small. The performance measurement model developed in this study allows supply chain members to develop a clear view of the impact of QAS requirements. Also, the model makes it possible to make trade-offs between issues such as production costs and food safety, within the own firm as well as throughout the chain

The world's fresh accessible water situation is deteriorating at a dismal pace. Though the situation is already quite dramatic in Africa, the near future will bring us great problems in Asia as well, considering the pace at which the population is growing and the rise in water use per capita as the economy induces a raised demand. Agricultural consumption of fresh water is one of the main water uses world wide; however, it appears that protected cultivation of horticultural crops can alleviate the problem. Drip irrigation already reduces water use dramatically. However, novel high technological solutions in greenhouse production can lead the way to highly efficient water use production techniques. Adoption of more efficient water use techniques will contribute to sustainability, especially in highly populated urban areas. The novel Dutch technology of closed greenhouses could help develop water efficient production systems

Phytosanitary inspection of imported plants and flowers is a major means for preventing pest invasions through international trade, but in a majority of countries availability of resources prevents inspection of all imports. Prediction of the likelihood of pest infestation in imported shipments could help maximize the efficiency of inspection by targeting inspection on shipments with the highest likelihood of infestation. This paper applies a multinomial logistic (MNL) regression model to data on import inspections of ornamental plant commodities in the Netherlands from 1998 to 2001 to investigate whether it is possible to predict the probability that a shipment will be (i) accepted for import, (ii) rejected for import because of detected pests, or (iii) rejected due to other reasons. Four models were estimated: (i) an all-species model, including all plant imports (136,251 shipments) in the data set, (ii) a four-species model, including records on the four ornamental commodities that accounted for 28.9% of inspected and 49.5% of rejected shipments, and two models for single commodities with large import volumes and percentages of rejections, (iii) Dianthus (16.9% of inspected and 46.3% of rejected shipments), and (iv) Chrysanthemum (6.9 and 8.6%, respectively). All models were highly significant (P < 0.001). The models for Dianthus and Chrysanthemum and for the set of four ornamental commodities showed a better fit to data than the model for all ornamental commodities. Variables that characterized the imported shipment's region of origin, the shipment's size, the company that imported the shipment, and season and year of import, were significant in most of the estimated models. The combined results of this study suggest that the MNL model can be a useful tool for modeling the probability of rejecting imported commodities even with a small set of explanatory variables. The MNL model can be helpful in better targeting of resources for import inspection. The inspecting agencies could enable development of these models by appropriately recording inspection results.

LEDs may be a suitable light source for future use as assimilation lighting in protected greenhouse cultivation. LEDs have properties which offer advantages compared to other light sources, but which also raise specific research questions. The narrow band spectrum of LEDs enables manufacturers to produce LED based lightsources specifically suitable for photosynthesis and other horticulturally relevant plant properties. The low radiated heat also makes LEDs suitable for interlighting (i.e. lighting from within the canopy), for which high pressure sodium lamps are not suitable. However, when using LEDs, crops must be able to acclimate their photosynthetic functioning to narrow band lighting (NBL) to efficiently use this light. Also, daylight-adapted leaves must be able to re-acclimate to NBL if LEDs would be used for interlighting in a high-wire grown crop. If low photosynthesis rates in older, lower leaves of the crop are also due to leaf age, besides low light, interlighting would be less effective. For investigating the intrinsic effect of NBL, we used 9 different arrays comprised of a single LED type (peak wavelengths in the range 460-668 nm) at lightlimited irradiance (50 μmol m s). Spirodela polyrrhiza (Lemnaceae) was cultivated as its leaves can not change in distance or orientation towards the light source. This enabled us to compare the effects of the different light sources on parameters such as growth rate and photosynthetic pigment composition. In order to separate the effect of light intensity and leaf age on photosynthesis, tomato plants were grown horizontally, so that older leaves were not shaded by younger leaves. Re-acclimation of leaves to NBL was investigated by illuminating older leaves (low in the canopy) using different LED arrays in a high-wire grown tomato crop. The light-harvesting apparatus of Spirodela polyrrhiza acclimated to the different NBL regimes within 6 days. Leaf age proved to be an irrelevant factor for photosynthetic capacity (Pmax) of greenhouse grown tomato plants. Pmax of leaves at a low position in a high-wire grown tomato crop, with a low Pmax, did re-acclimate to the higher light intensities supplied by the supplemental NBL by progressively increasing their Pmax. However, as it took 14 days for Pmax to increase from 5.6 to 12.4 μmol CO2 m s, maintaining a continuously higher light level within the canopy would be more effective. INTRODUCTION Recently, light emitting diodes (LEDs) are subject of debate and research with respect to their possible future use for assimilation lighting in protected plant cultivation. At this moment LED lighting systems are too expensive and, more important, not efficient enough in terms of light output per Watt energy use, for large scale replacement of high pressure sodium (HPS) assimilation lamps for commercial greenhouse horticulture. However, the light-output efficiency of LEDs increased dramatically in recent years and production costs of LED systems aimed at the horticulture will decrease Proc. XXVII IHC-S6 High-Qual. Crop Prod. under Protect. Cultiv. Ed.-in-Chief: D.J. Cantliffe Acta Hort. 761, ISHS 2007 184 if demand would be sufficient. So as well as yielding new, fundamental knowledge on plant functioning, research on plant responses to LED lighting is highly relevant for the horticultural industry. Compared to other light sources used for plant production, LEDs have several properties which are potentially useful in relation to horticulture. LEDs emit light in a relatively narrow band spectrum, so they can be manufactured with a wavelength output tailored to the plant responses desired by growers. In order to enhance production, LED arrays with wavelengths favourable for photosynthesis would be desired. However, wavelengths influencing other plant properties such as morphology (blue light enhances compactness of plants) could be desirable for ornamental horticulture. Also, nutritional qualities of food crops may be influenced by the illumination spectrum used (e.g. antioxidant content; see e.g. Oelmuller and Mohr, 1985). At this moment, LEDs produce more heat than HPS lamps per Watt energy input, due to their lower energy/light conversion efficiency. However, the radiated heat of LEDs is very low compared to HPS lamps. This affords the opportunity to cool LED lighting systems and to reuse the (low caloric) heat for e.g. greenhouse heating. The low radiated heat output also makes LEDs suitable for interlighting, i.e. lighting inside the canopy, instead of or in combination with lighting above the canopy. Previous research on interlighting with HPS lamps (Hovi et al., 2004) indicated that interlighting may be more efficient than lighting from above. Interlighting could contribute to a more effective use of light by crops, as inside the canopy light levels are low, whereas above the canopy solar radiation already provides a considerable photosynthetic photon flux (PPF) during daytime. Especially in high-wire cultivated crops (e.g. tomato, cucumber and sweet pepper) with low photosynthesis rates lower in the canopy (see e.g. Xu et al., 1997), interlighting could offer a means to enhance production. The considerable percentage of radiated heat HPS lamps produce makes it impossible to situate HPS lamps close to the leaves of a crop. LEDs, on the other hand, with their low radiated heat output and overall lower temperature, can be in contact with the leaves. Though this may not be good for photosynthesis, the leaf will not be burned. LED light output is proportional to electric current through the device, so light intensity can be controlled in a versatile way. Therefore, the light output of LED lighting systems can be easily, rapidly and efficiently adjusted to match environmental conditions or production requirements within the greenhouse, such as natural light or the stage of the crop in the production cycle. Also if lighting systems would be used comprised of different LED types, emitting light with different spectra, light quality could be adjusted to the needs of the crop. For example, the use of near far red light (690 nm) was found to increase the leaf area of developing leaves (Goins, 2002), which would result in a more effective use of the available light in early stages of the production cycle. A socially relevant issue concerning assimilation lighting, called “light pollution” (public agitation and the disturbance of the natural rhythm of birds etc. due to lighted greenhouses at night) may be reduced by the replacement of HPS lamps by LEDS for assimilation lighting. The human eye is much more sensitive to yellow/orange light (the dominant colour of HPS lamps) than it is to red light (a potentially useful colour for LED lighting systems), so an equal amount of μmols PPF can give a very different perception of light intensity for the (human) eye (Fig. 1). Mammals and birds are also more sensitive to yellow/orange light than to red (Goldsmith, 2006). Furthermore, interlighting would reduce radiation loss from the greenhouse considerably due to increased light interception within the canopy. Nonetheless, several questions need to be addressed, concerning the possible use of LEDs for assimilation lighting. In order to grow crops efficiently using narrow band lighting (NBL), plants have to be able to acclimate their photosynthetic apparatus to NBL. Any imbalance in excitation of the photosystems I and II would lead to a loss of quantum yield for CO2 fixation in a leaf. Also, the dynamics of re-acclimation to NBL of daylightadapted leaves in a crop are essential for the efficiency of interlighting in a canopy. As the production time of a leaf in a high-wire grown crop is relatively short (approximately 8

Translucency is one of the major problems in fresh-cut fruit. This phenomenon seriously limits the use of fruit by the fresh-cut industries. Techniques for measuring translucency in this kind of product are not readily available. As a consequence, the processes that are important in the development of translucency are little understood, let alone described in detail. Based on techniques used in the industry of paint, paper and textiles, a measuring technique using video image analysis (VIA) involving light reflected from a sample placed in a double white and black background was used to assess the development of translucency and its interference with colour measurement in fresh-cut tomatoes. The effects of stage of maturity at the time of processing as well as the effect of storage temperature were studied in two separate experiments. The data were expressed as the average intensities per pixel of red (R), green (G) and blue (B) for the white and for the black background separately. A model was developed and presented that describes the change in the RGB values of tomatoes after cutting and during storage. In the model, the observed effects were considered to be the result of two processes namely changes in colour due to the production or degradation of pigments and development of translucency (i.e. physical water-soaking). Both processes resulted in changes in each one of the colour aspects R, G and B. Each colour aspect was considered to be built up by a variable part that changes according to a first order reaction mechanism and a fixed part that is invariable under the circumstances under study. The data obtained on both experiments were used to estimate the model parameters by multiple non-linear regression analysis using R, G and B as response variables and time, temperature, stage of maturity and background simultaneously as explaining variables. The change from opacity to translucency in the pericarp was the main change in appearance of tomato slices during refrigerated storage, for all stages of maturity and storage temperatures. Changes in colour were much less pronounced and related to a small increase in redness for all stages. The susceptibility to develop translucency was very much dependent on the maturity stage of the fruit at harvest and rather independent of temperature.

The world is getting smaller and smaller. All participants to this conference are the best example for that: we come from all over the world to discuss themes related to our daily food. Living in a small world has great advantages but also some drawbacks. We like to think we are ready for a major up scaling of our food supplies, but are we really? What do we need to answer to this challenge? How can we manage these large scale operations? Where do we get useful information? How do we discriminate useful information from misinformation?

There is a growing awareness amongst researchers in the field of fruit and vegetable postharvest that quality is generated in the process of plant growth and all well advanced postharvest techniques and technologies can merely retain, as good as possible, the quality that is already present in the produce. Information and knowledge about the evolution of properties and quality attributes, that are so important for understanding postharvest behaviour, is very limited due to the use of completely different frameworks in preharvest and postharvest quality analyses. In this paper, based on theoretical considerations, a number of models and possible behaviour are developed and presented, that could indicate along which lines this exchange of information could be achieved. But the most important message of this paper is just plainly and simply that researchers and practitioners in both preharvest and postharvest areas do need one another desperately in order not to loose the contact with consumers.

Standard colour measurements can pose a serious problem for interpretation. For tomatoes the maturity at harvest does affect the colour that can maximally be obtained during postharvest storage. For more mature fruit up to 2 units (compared to 18 units tops) were found. This effect was ascribed to the level of a precursor produced during growth. More mature fruit also exhibit a more pronounced sensitivity to becoming translucent upon storage. This effect was also ascribed to the stage of development at harvest. Models were derived on plausible mechanisms to account for both effects of maturity at harvest in tomatoes.

Tomato fruit (Lycopersicon esculentum cv. Belissimo) at different stages of maturity were sliced in 7-mm thick transverse slices and stored at 5 °C. In a second experiment, slices obtained from fruit at the light-red stage were stored at temperatures from 5 to 13 °C. Intact control fruit were stored under the same conditions. Digital images were taken immediately after processing, before cooling, and at regular intervals during storage, after placing the slice in a double (half white, half black) background. The data were expressed as the average intensities per pixel of red (R), green (G) and blue (B) separately for the white background and for the black background. Additional indices were obtained by algebraic calculations from the original RGB values and through the conversion of RGB into L*a*b* values. The development of translucency in the pericarp was the main change in appearance of cut tomato. This process was strongly affected by the stage of maturity of the fruit and independent of storage temperature. The more mature the fruit the faster and more intense was the development of translucency. Using video image analysis, an increase in translucency could be assessed by a decrease in the amount of red pixels when the sample was measured against a black background. Changes in colour due to maturation could be measured both by a decrease in the amount of green pixels or by an increase in the proportion of red pixels (R/(R + G + B)), when the sample was placed on a white background. Using the L*a*b* colour space, an increase in translucency corresponded to a decrease in lightness and changes in colour due to maturation resulted in an increase in a*-value.

The last decade has seen an increasing interest in indicators of supply-chain performance. A large number of various performance indicators have been used to characterize supply chains, ranging from highly qualitative indicators like customer or employee satisfaction to quantitative indicators like return on investments. This large number of different performance indicators, and the lack of consensus on what determines performance of supply chains, complicates the selection of performance measures. Furthermore, combining these indicators into one measurement system proves to be difficult. Efforts as well as progress have been made in this area but supply-chain performance measurement received little or no attention in the field of food and agribusiness. This paper provides a literature review on existing performance indicators and models, and discusses their usefulness in agri-food supply chains. Furthermore, based on this overview, a conceptual framework is developed for further research in this area.

Tomato fruit (Lycopersicon esculentum cv. Belissimo) were harvested at three different stages of ripening, sliced and stored at five different temperatures. Red-green-blue (RGB) images of the slices were taken regularly during storage, using a image processing system. For constructing a model, each of these colour aspects was considered to be built up by a variable part that changes according to a first order reaction mechanism and a fixed part that is invariable under the circumstances under study. All three colour aspects of the tomato slices (R, G and B) decreased exponentially during storage. The parameters of the model were estimated using multiple-response multiple-variate non-linear regression analysis using R, G and B simultaneously as response variables and time, temperature and ripening stage of the fruit at harvest simultaneously as explaining variables. To combine the information on the behaviour of the colour aspects during the preharvest and the postharvest period at different temperatures, it was assumed that the process of change during ripening was the same whether the fruit ripened on the plant or off-vine. So, the initial value for all three colour aspects (Col0,R, Col0,G and Col0,B) during the postharvest experiments depended on the time the tomatoes were allowed to ripen on the plant. By using this fundamental approach to build the model and using all available data and information it became possible to describe and simulate the behaviour of the colour aspects of tomato slices as a function of the ripening stage and the applied storage temperature. Although the variance between replicates was high, the statistical analysis on the mean values of colour aspects over the replicates provided a percentage variance accounted for of 95%. The same model was validated with data of another experiment with another tomato cultivar (Durinta) over a larger range of maturity stages

Individuals differ in development stage or biological age. This difference can be taken into account when modelling the quality behaviour of various fruits and vegetables. Even on a batch level, the same principle can be applied, provided the variation within a batch is not too large. By applying the biological shift factor, i.e. a shift in calendar time, the effects of different growing and harvesting condition can be included in modelling quality behaviour, which widely opens alleys for producing models applicable in the entire globalised food chain. The variation in biological shift factor over individuals in a batch and over several batches seems to exhibit a normal distribution pattern.

A batch model is presented for the interpretation of batch behaviour in terms of current maturity, biological variation and maximal maturity towards keeping quality of cucumbers. The batch model describes the influence of one source of biological variation, here assumed to be variation in light conditions during the pre-harvest period, on the variation of precursor concentrations. The batch model consists of a kinetic part, describing the behaviour of the precursor for individuals, and a stochastic part, describing the precursor variation. The stochastic part is generic, but the kinetic part depends on the processes that determine keeping quality. The batch model is tested and validated using colour data of two sets of cucumber batches. Applying a previously developed cucumber colour model [Postharvest Biol. Technol. 26 (2002) 209], the precursor concentration determining the keeping quality at harvest was estimated. The amount of colour precursor at maximal maturity could be estimated in common for batches of the same cultivar and was defined as cultivar keeping quality. The batch model enables estimation of cultivar-specific information. It thereby takes advantage of the biological variation present in all biological batches, instead of treating it as a nuisance. © 2004 Elsevier B.V. All rights reserved.

Over the years a Dutch vegetable chain with preferred suppliers has improved its efficiency in tuning demand with supply. Because of working with fresh produce, waste product occurs in the different links. The wholesaler estimates that 5 to 10% of the total production, never reaches the end customer. Reduction of the amount of waste product would improve the profit as well as the environment. In this research the supply chain has been studied to establish where and how waste product occurs. Furthermore a study has been carried out for finding solutions for 1. reducing the amount of waste product, and 2. for value improvement of waste product. The bottlenecks are at the entrance and outlet of the chain. Improving the value of waste at the outlet makes is not easy. At the entrance of the chain the occurrence of waste downstream the supply chain is unpredictable, which makes it hard to find customers for the waste product. At the outlet high costs would have to be made for poor quality waste. So, the first priority would be minimising the flow of waste product. This can be achieved by an earlier and more precise prediction of harvested amounts by the growers and of the demanded amount of product by the retailer. For these purposes existing instruments should be applied and adjusted for this chain. Working in this way, it will give the wholesaler more time to match demand with supply and to find customers for processing the waste product.

The DIF concept states that equal internode length can be achieved with the same difference between day and night temperature irrespective of the mean 24 h temperature. However, the physiological background of the DIF concept is unclear. An attempt to model internode elongation is presented based on three plausible processes, namely (1) the accumulation of elongation requirements during the day, (2) elongation during the night using elongation requirements and (3) the limitation of internode length due to low turgor pressure unable to counter cell wall elasticity. Each reaction rate constant, one per process, depends on temperature according to Arrhenius' Law. The resulting process-based model describes internode elongation in time and was calibrated on a chrysanthemum data set. Chrysanthemum plants were grown in growth chambers with rigorously defined day and night temperatures. In total, 16 temperature treatments were applied, resulting from the combination of four day and four night temperatures (16, 20, 24 and 28 degrees C). Internode elongation was measured for the tenth internode in ten plants per treatment. The percentage variance accounted for, R2adj, was almost 91%. Transferability of model parameters was shown to exist by cross validation. Simulation of the internode length in time as function of mean 24 h temperature and DIF showed that the DIF concept is not apparent after a growing period of 10 d, but is visible after 20 d. This model structure for describing internode elongation might also be applicable for other plants that show the DIF concept.

The above-ground parts of two years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed to filtered air, NH3, NO2+, SO2 (66, 96 and 95 μg m−3, respectively), to a mixture of NO2+NH3 (55 + 82 μg m−3) or SO2+NO2 (128 + 129 μg m−3), for 8 months in fumigation chambers. Both chlorophyll fluorescence and gas exchange measurements were carried out on shoots which had sprouted at the beginning of the exposure period. The chlorophyll fluorescence measurements were performed after 3 and 5 months of exposure (average shoot age 70 and 140 days, respectively). Light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. In addition, light response curves of net CO2 assimilation were determined after 5 months of exposure. After 3 months of exposure (average shoot age 70 days) all exposure treatments showed a lower maximum electron transport rate (Jmax) as compared to the control shoots (filtered air). A large reduction (45%) was observed for shoots exposed to SO2+NO2. During the exposure period between 3 and 5 months (average shoot age 70 and 140 days, respectively) a decrease of Jmax was observed for all treatments. Jmax had further declined some time after termination of the exposure, when average shoot age was 310 days. Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum net CO2 assimilation (Pmax) as compared to the control shoots. However, shoots exposed to NO2 showed no reduction and even a higher Pmax was observed for shoots exposed to NH3 or NO2+NH3. Needles of these treatments also showed a higher chlorophyll content which might explain the contradictory results obtained for these treatments: the increased amount of photosynthetic units counteracts the reduction in Jmax and consequently no reduction in Pmax is measured. Shoots exposed to SO2 and SO2+NO2 also showed a reduction in maximum stomatal conductance (gs). However, the stomatal opening was larger than could be expected on basis of their (maximum) CO2 assimilation rate. Consequently, water use efficiency of these shoots was lower than that of the control shoots. Also shoots exposed to NO2 had a lower water use efficiency due to a significantly higher maximum gs. Shoots exposed to NH3 showed a high transpiration rate in the dark, indicating imperfect stomatal closure.

Shoots of poplar (Populus euramericana L. cv. Flevo) were exposed to filtered air, SO2, NH3 or a mixture of SO2 and NH3 for 7 weeks in fumigation chambers. After this exposure gas exchange measurements were carried out using a leaf chamber. As compared to leaves exposed to filtered air, leaves pretreated with 112-mu-g m-3 SO2 showed a small reduction in maximum CO2 assimilation rate (P(max)) and stomatal conductance (g(s)). They also showed a slightly higher quantum yield and dark respiration. In addition, the fluorescence measurements indicated that the Calvin cycle of the leaves pretreated with 112-mu-g m-3 SO2 was more rapidly activated after transition from dark to light. An exposure to 64-mu-g m-3 NH3 had a positive effect on P(max), stomatal conductance and NH3 uptake of the leaves. This positive effect was counteracted by an SO2 concentration of 45-mu-g m-3. The exposure treatments appeared to have no effect on the relationship between net CO2-assimilation and g(s). Also, no injury of the leaf cuticle or of epidermal cells was observed. Resistance analysis showed that NH3 transfer into the leaf can be estimated from data on the boundary layer and stomatal resistance for H2O transfer and NH3 concentration at the leaf surface, irrespective of whether the leaves are exposed for a short or long time to NH3 or to a mixture of NH3 and SO2. In contrast SO2 uptake into the leaves was only partly correlated to the stomatal resistance. The results suggest a large additional uptake of this gas by the leaves. The possibility of a difference in path length between SO2 and H2O molecules is proposed.

During recent years there has been remarkable progress in the understanding and practical use of chlorophyll fluorescence in plant science. This 'renaissance' of chlorophyll fluorescence was induced by the urgent need of applied research (like plant stress physiology, ecophysiology, phytopathology etc.) for quantitative, non-invasive, rapid methods to assess photosynthesis in intact leaves. Recent developments of suitable instrumentation and methodology have substantially increased these possibilities. Actually, a vast amount of knowledge on chlorophyll fluorescence had already accumulated over more than 50 years, since the discovery of the Kautsky effect in 1931 (Kautsky and Hirsch 1931) (for reviews, see e.g., Lavorel and Etienne 1977, Briantais et al. 1986, Renger and Schreiber 1986). On the one hand this knowledge was mechanistic, resulting from biophysically oriented basic research. On the other hand it was phenomenological, originating from applied plant physiological research. Until recently the phenomenology of whole leaf chlorophyll fluorescence appeared far too complex to find serious attention of biophysicists. Thus, for a long time, there was a gap between applied and basic research in chlorophyll fluorescence. Developments in instrumentation (Ogren and Baker 1985, Schreiber 1986, Schreiber et al. 1986) and methodology (Bradbury and Baker 1981, Krause et al. 1982, Quick and Horton 1984, Dietz et al. 1985, Demmig et al. 1987, Weis and Berry 1987, Bilger et al. 1989, Genty et al. 1989) has succeeded in closing this gap and bringing these two disciplines into sufficiently close contact and in mutually stimulating interaction. Consequently the present "renaissance" of chlorophyll fluorescence may be the product of a fruitful dynamic interaction between three different research disciplines, i.e., basic and applied research linked to new developments in instrumentation and methodology (see scheme in Fig. 1). As a result, measuring chlorophyll fluorescence has become a very attractive means of obtaining rapid, semiquantitative information on photosynthesis, used by an increasing number of researchers not only in the laboratory but also in the field. The wide range of possible applications is reflected by the broad spectrum of contributions to this issue of Photosynthesis Research. The progress made in chlorophyll fluorescence instrumentation and methodology has also induced new developments in the adjacent fields of absorbance spectroscopy (e.g., Klughammer et al. or Harbinson et al. in this issue), photoacoustic spectroscopy (e.g., Canaani, Dau and Hansen, Kolbowski et al. or Snel et al. in this issue) and chlorophyll luminescence (delayed fluorescence) (Bilger and Schreiber in this issue). These new developments are expected to play a role in

Two year old douglas firs were exposed to moderate concentrations of SO2, NO2, NH3 or combinations of these gases. The effect on photosynthesis of young needles (age between 20 and 135 days, which had sprouted during the fumigation treatment) was determined with Pulse Amplitude Modulated chlorophyll fluorescence (1). The electron transport rate was inferred from the fluorescence measurements by a method described by Genty et al. (2), which was found to be more appropriate for 4cpglas fir than the method described by Weis and Berry (3). The light response curves were fitted to a formula described by Leverenz (4) from which the maximal electron transport rate, the quantum yield and a measure of the convexity of the light response curve can be deduced. All treatments resulted in a reduced rate of electron transport at saturating illumination as compared to the control (exposed to filtered air). But the most severe reduction (>50%) was observed in the plants exposed to a combination of SO2 and NO2. Firs exposed to NO2 alone revealed an enhanced chlorophyll content, which was concluded from a significant decrease in the convexity of the light response curve. The plants exposed to SO2 revealed a slightly enhanced quantum yield, similarly as has been observed before in poplar shoots (5). The reduced maximal electron transport rate in fir needles fumigated with NH3 was in marked contrast to previous measurements in poplar shoots and broad beans (6–8).

Poplar shoots (Populus euramericana L.) obtained from cuttings were exposed for 6 or 8 weeks to NH3 concentrations of 50 and 100 μgm−3 or filtered air in fumigation chambers. After this exposure the rates of NH3 uptake, transpiration, CO2 assimilation and respiration of leaves were measured using a leaf chamber. During the long-term exposure also modulated chlorophyll fluorescence measurements were carried out to obtain information about the photosynthetic performance of individual leaves. Both fluorescence and leaf chamber measurements showed a higher photosynthetic activity of leaves exposed to 100 μg NH3 m−3. These leaves showed also a larger leaf conductance and a larger uptake rate of NH3 than leaves exposed to 50 μg m−3 NH3 or filtered air. The long-term NH3 exposure did not induce an internal resistance against NH3 transport in the leaf, nor did it affect the leaf cuticle. So, not only at a short time exposure, but also at a long-term exposure NH3 uptake into leaves can be calculated from data on the boundary layer and stomatal resistance for H2O and ambient NH3-concentration. Furthermore, the NH3 exposure had no effect on the relation between CO2-assimilation and stomatal conductance, indicating that NH3 in concentrations up to 100 μg m−3 has no direct effect on stomatal behaviour; for example, by affecting the guard or contiguous cells of the stomata.

The effect of uncouplers of photophosphorylation on the kinetics of the flash-induced P515 electrochromic bandshift was investigated in dark-adapted chloroplasts. It was found that the presence of low concentrations of carbonyl cyanide p -trifluoromethoxyphenylhydrazone (FCCP) and carbonyl cyanide m -chloro-phenylhydrazone (CCCP) resulted in the selective suppression of the slow P515 absorbance change (reaction 2), whereas the fast change (reaction 1) was not influenced. In contrast, high concentrations of NH 4 Cl did not alter the P515 response with respect to reactions 1 and 2. These results indicate that reaction 2 is specifically sensitive towards uncouplers which exert their function as a proton carrier in the lipophilic phase of the membrane.

Chlorosis in maize (Zea mays L.) is a common phenomenon in the 12 to 17°C temperature range. A newly developed chlorophyll-fluorescence technique was used to elucidate the underlying subcellular processes of resistance to chlorosis. Four populations were used that were developed by divergent mass selection for contrasting resistance to chlorosis in a cold-tolerant dent and a cold-tolerant flint population. Young plants from the four populations were kept for six days at 17/10, 15/10 and 13/10°C (day/night). After 1, 3 and 6 days various chlorophyll-fluorescence parameters were determined. The measurements were done on leaf 4. Differences were not uniform for all fluorescence properties. The resistant and susceptible populations of the two sets differed for the Q-quenching which is related to the electron transport rate in the chloroplast. For the E-quenching which is related to the Calvin cycle activity, the resistant dent differed significantly from the other three populations. The ratio Fm/Fo (related to the transfer of absorbed light-energy from antennae pigments to reaction centers in the chloroplast) was higher for the resistant dent population than for the susceptible one. The flint types did not differ for this property.Apparently, divergent mass selection for chlorosis resistance resulted in various changes at the subcellular level that are not necessarily comparable for flint and dent types.When after 6 days the temperature was raised from 13°C to 17°C, the fluorescence signals led to the conclusion that there was a full recovery of various processes after two days, except for the metabolic activity of the susceptible flint.

A brief review is given of literature on remote sensing of chlorophyll fluorescence. The objective of the project ‘Laser Induced Fluorescence of Trees’ (LIFT) is to investigate the possible use of this technique to observe and monitor vegetation stress by air pollution. The instrumentation and set up is briefly described and measuring results are presented. Relative highs in air pollution appear to be associated with anomalies in fluorescence, implying a stress situation to the plant. Particularly the effect of rather low concentrations ozone (20–30 ppb), possibly in combination with SO2, is very strong.

Vegetable consumption is below recommended intakes in many countries, while the consumption of an adequate amount of vegetables is essential for health. Taste, especially bitter taste, is often suggested as the main cause of low vegetable acceptance. In her dissertation, Vera van Stokkom showed that the intensity of sweetness, sourness, saltiness, bitterness and umami of commonly consumed vegetables is low and that taste plays only a minor role in the identification of vegetables. Enhancing sweetness increased acceptance in both children and adults and combining vegetables compared to individual vegetables can increase acceptance as well. However, vegetable acceptance was still not very high. Mainly sweetness and bitterness were involved in vegetable acceptance, thus taste is important even though intensities are low. The results highlight the difficulty of increasing acceptance of vegetables.

The endogenous neurotoxin 5-S-cysteinyl-dopamine (CysDA) has been linked to the degeneration of dopaminergic neurons in the Substantia nigra. Sulforaphane (SFN) is an isothiocyanate derived from cruciferous vegetables that has been proposed as a potential chemopreventive agent, although its effects on other cells are less clear. This study was undertaken to investigate the protective effects of SFN against CysDA-induced injury in primary cortical neurons. The results indicate that SFN protects primary cortical neurons against CysDA-induced injury by a mechanism involving the increased nuclear translocation of Nrf2 and the increased activity of phase II enzymes such as glutathione-S-transferase, glutathione reductase, and thioredoxine reductase. Moreover, the protection exerted by SFN appears to be mediated by the activation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) and Akt/protein kinase B (PKB) pathways.

Cut flowers show a wide variance of keepability. The market demands more and more a guaranteed quality. Therefore, methods must be developed to predict vase life of cut flowers. Chrysanthemum ( Dendranthema x grandiflorum Tzvelev) and some other cut flowers suffer from unpredicted early leaf wilting during vase life. Researchers from Wageningen University and from the Research Station for Floriculture and Glasshouse Vegetables started a joint project to investigate the problem of early leaf wilting and to come to a better prediction of vase life of cut flowers. Preliminary experiments pointed out that early leaf wilting is caused by a decrease of the water uptake due to embolisms that are induced at the cut surface. This thesis reflects a part of the project on early leaf wilting and is focussed on the anatomical aspects of the stem water transport system.Chrysanthemums are propagated by stem cuttings, which grow in about 12 weeks to commercial maturity. Flowering is induced by a short day treatment. Cut chrysanthemums have an erect stem and the leaves are helically arranged along the stem. The primary vessel bundle network was elucidated, revealing that leaves have their direct water supply from different vascular bundles, which are positioned around nearly half of the circumference of the stem (2.1). The xylem water transport system consists of primary xylem and secondary xylem. The older the stem part (i.e. the lower in the stem) the higher the relative amount of secondary tissue.Digital image analysis procedures were constructed to enable the quantification of large amounts of anatomical data. Xylem vessel characteristics along the chrysanthemum stems were thus quantified and a mathematical description of the vessel characteristics was developed (2.2). Hydraulic conductivity, amount of vessels, average diameter of vessels, and vessel length all showed a gradual exponential decrease from the base to higher up the stem. The hydraulic resistivity calculated from vessel lumina was 30% lower than the experimentally measured resistivity, irrespective of the position in the stem. The remaining 30% is at least partly caused by the resistance of the intervessel pits.A new theory was developed to explain the regulation of vessel lengths in plants (2.3). Vessel length depends on the amount of fused tracheary elements. The only assumption in the theory is that each element has the same chance to be the end of the vessel during vessel formation. This results in an exponential vessel length distribution, which indeed is always found in our chrysanthemum stems. The plant can thus determine its vessel length distribution by just steering the chance factor. This theory provides the most simple mechanism that enables plants to regulate the length of xylem vessels. Stochastic regulation of biological processes might be widely present in nature.We reviewed and refined a method to obtain flat planes in all desired directions through frozen hydrated (biological) specimens (Chapter 3). A combination of proper sample preparation, trimming with a circular diamond saw, tight mounting using indium, and planing with a diamond knife proved to be a useful method to prepare stem xylem tissue for observation in a cryo-scanning electron microscope (cryo-SEM). This planing method is useful for a wide range of other applications of cryo-scanning electron microscopy.We used cryo-SEM to study the dynamics of emboli in stem xylem vessels (Chapter 4). In accordance with our theoretical assumptions, wide vessels that were cut open at the cut surface appeared to embolise at a lower hydraulic tension than narrower vessels (4.1). The tension needed to embolise all vessels is easily reached in cut flowers, and it therefore can be assumed that under normal postharvest conditions all cut open vessels embolise. Our cryo-SEM results agree with the hypothesis that refilling of embolised vessels is needed to restore the fresh weight of cut chrysanthemums on vase after a dehydration treatment (4.2). Under normal post-harvest conditions air only enters cut open xylem vessels (4.3). The blockage of the xylem water flow due to emboli in cut chrysanthemums is therefore located in the base of the stem in the cut open vessels.We developed a physical explanation of the mechanisms of induction and removal of emboli in cut open vessels of cut flowers (5.1). The refilling of embolised vessels after dehydration takes place in two phases:initial rise of vase water into the vessels, resulting in redistribution and compression of the thus entrapped air, anddissolution of the entrapped air into the surroundings.It was concluded that the anatomy of the xylem vessels plays an important role in rehydration capability of cut flowers after air aspiration. A compact vessel system (narrow, short and well connected vessels) restores better from emboli than a vessel system consisting of wide, long and loosely connected vessels.Knowing that the stem anatomy is important with respect to embolism repair, we tried to find an accurate, but easy method to test the stem anatomy on its sensitivity to early leaf wilting (5.2). Within our experiments we found that plants with wider vessels were more sensitive to early leaf wilting, but no absolute thresholds were found at comparing over different experiments. It was confirmed that the anatomy of the stem water transport system is important with respect to vase life quality. However, the combination with several other factors ultimately determines the vase life quality. Xylem thickness and some other stem tissue dimensions seem to be good indicators of the quality of the xylem vessel system and its sensitivity to embolism. A more extensive study is needed to prove the practical value of the use of these indicators. Breeders and growers may use our findings and optimise genotype and growing conditions to obtain chrysanthemums with narrower and shorter vessels at the cut surface in order to prevent the problem of early leaf wilting.