Over the last years, energy consumption in greenhouse horticulture has been reduced considerably by using (multiple) screens, controlled dehumidification and more efficient use of assimilation light. All these actions affect greenhouse climate and thereby plant processes. Measuring crop photosynthesis, a process that responds very rapidly to changes in climate, would be suited to monitor whether the climate is set according to the needs of the plant. Two monitoring systems have been developed, the crop photosynthesis monitor and the CropObserver. The crop photosynthesis monitor is a soft sensor that calculates the CO2 uptake of the entire greenhouse, based on the mass balance of a greenhouse for CO2. At known CO2 supply rates, measuring the CO2 concentrations inside and outside the greenhouse, and determining the ventilation loss allows the calculation of the crop photosynthesis. The CropObserver is a fluorescence sensor that provides laser light pulses from above in a surface of 3×3 m. Since the measurements are fast, the sensor provides a good image of the electron transport rate (ETR) of a large crop area in a short period of time. Evaluation of the sensors in a tomato cultivation showed that the data of the crop photosynthesis monitor matched the daily pattern of manual photosynthesis data up-scaled to crop photosynthesis by a crop growth model reasonably well. The CropObserver data were very comparable to local reference fluorescence measurements, and closely followed irradiance patterns over the day. Both systems have attracted the attention of Dutch growers, and will be further evaluated in commercial greenhouses.

Het basisproces voor de groei en productie van een gewas is de fotosynthese. Het meten van de gewasfotosynthese is dus van belang om goed te monitoren hoe het gewas er voor staat en of het kasklimaat is ingesteld naar de behoefte van het gewas. In dit project zijn twee meetsystemen ontwikkeld en getest om de gewasfotosynthese te meten. (1) De gewasfotosynthesemonitor is een soft sensor die de CO2 opname van een hele kas met gewas kan berekenen. Dit doet deze monitor op basis van de balans tussen enerzijds CO2 dosering en anderzijds verlies van CO2 door ventilatie en gewasfotosynthese. Door de CO2 concentratie en de luchtvochtigheid binnen en buiten de kas te meten kan de gewasfotosynthese berekend worden. (2) De nieuwe fluorescentiesensor die ontwikkeld is, de CropObserver, meet de efficientie van de lichtbenutting als maat voor de fotosynthese van een groot oppervlakte gewas (3 x 3 m2). Het gewas wordt belicht met korte laserlichtpulsen bovenin de kas, de sensor meet het terugkomende fluorescentiesignaal. Beide nieuwe sensoren zijn begin 2014 getest in een tomatengewas. De eerste testen waren veelbelovend. De sensoren hebben zonder problemen gefunctioneerd en leverden een dagverloop van de fotosynthese op, dat redelijk tot goed overeen kwam met referentiemetingen.

Some stresses in immature soybean plants, such as nematode infection, can result in premature plant death and produce greenish seeds with low physiological potential. The objective of this study was to evaluate Meloidogyne javanica infection on soybean plants and its relationship to plant growth, green seeds occurrence and their physiological potential. Plants of two soybean cultivars (TMG-115RR and M 7908 RR) were exposed or not to nematodes (0 or 7,000 nematodes per plant) and submitted or not to water stress treatments. The plant characteristics evaluated included phenology, pod and seed production, nematode multiplication in roots, seed moisture content, seed physiological potential (germination test, accelerated ageing, electrical conductivity and seedling emergence in sand), green seeds occurrence (visual method and chlorophyll fluorescence) and cell cycle activity (using flow cytometry). Depending on the cultivar tolerance, the population of 7,000 nematodes reduced the soybean plant cycle due to a shorter senescent stage, thereby causing premature death and the production of more green seeds. Moreover, the infection adversely affected seed production and quality. Meloidogyne javanica on soybean plants roots increased green seeds occurrence and reduceed their physiological potential due to reduction in cell cycle activity which affected aspects of germination and vigour.

The optimization of heating in greenhouses should be an energy saving target in the cultivation of sweet pepper plants; from both an environmental and economical point of view. It is important to understand the effect of low temperatures on this crop. While the effect of low temperature has been studied in plants exposed to light, there are few studies on the effect of cold in the dark, which is a more realistic situation in greenhouses. The objective of this work was to study the effect of low temperatures during the night in sweet peppers and to assess the physiological consequences during the following day. Therefore, we subjected sweet pepper plants of two cultivars to 5 or 7 cycles of 12/12 h warm light (500 μmol m-2 s-1 PAR, 21°C) and cold dark (6°C). After the treatment, several measurements were performed on leaves (first in the dark and cold, and one hour after light was switched on): chlorophyll fluorescence (spot and imaging) and measurements of biomass. Our results showed a decrease in the efficiency of photochemistry in photosystem II (Y(II)) during the dark, cold period related to a stimulation of photoprotection mechanisms in the photosynthetic apparatus. However, 1 h after rewarming in light conditions, leaves had recovered high values of Y(II). In addition, fully expanded leaves increased their specific leaf area and fresh to dry weight ratio during this period. This may indicate that, during the recovery period, dry weight decreased due to redistribution of assimilates to expanding leaves and/or that leaf water content increased. The fast recovery of this crop after several cold nights opens possibilities for new strategies of energy saving in greenhouses. However, more studies should be carried out within this area.

In de afgelopen jaren is het energiegebruik in de glastuinbouw steeds verder teruggebracht door het gebruik van (meerdere) schermen, verlagen van de buistemperaturen, gecontroleerde ontvochtiging en efficienter belichten. Al deze acties hebben effecten op het kasklimaat. Ze beinvloeden daarmee ook de plantprocessen en uiteindelijk de ontwikkeling, groei en productie van het gewas. Die reacties zijn vaak pas na uren of dagen zichtbaar, terwijl een teler binnen minuten of uren moet sturen. Een methode waarmee dit snel in kaart kan worden gebracht, is daarom gewenst.

The chlorophyll (Chl) fluorescence imaging technique was applied to cashew seedlings inoculated with the fungus Lasiodiplodia theobromae to assess any disturbances in the photosynthetic apparatus of the plants before the onset of visual symptoms. Two-month-old cashew plants were inoculated with mycelium of L. theobromae isolate Lt19 or Lt32. Dark-adapted and light-acclimated whole plants or previously labelled, single, mature leaf from each plant were evaluated weekly for Chl fluorescence parameters. From 21 to 28 days, inoculation with both isolates resulted in the significantly lower maximal photochemical quantum yield of PSII (Fv/Fm) than those for control samples, decreasing from values of 0.78 to 0.62. In contrast, the time response of the measured fluorescence transient curve from dark-acclimated plants increased in both whole plants and single mature leaves in inoculated plants compared with controls. The Fv/Fm images clearly exhibited photosynthetic perturbations 14 days after inoculation before any visual symptoms appeared. Additionally, decays in the effective quantum yield of PSII photochemistry and photochemical quenching coefficient were also observed over time. However, nonphotochemical quenching increased during the evaluation period. We conclude that Fv/Fm images are the effective way of detecting early metabolic perturbations in the photosynthetic apparatus of cashew seedlings caused by gummosis in both whole plants and single leaves and could be potentially employed in larger-scale screening systems.

Xanthomonas fragariae is the causative agent of angular leaf spot disease of strawberry. Greenhouse experiments were conducted using a X. fragariae isolate tagged with a green fluorescent protein (GFP) for detailed population dynamic studies in and on leaves after spray‐inoculation. The GFP‐tagged bacteria were monitored with dilution plating of leaf washings and leaf extracts, and analysis of intact leaves using a non‐invasive monitoring system called PathoScreen, based on laser radiation of fluorescent cells in plant tissues and signal recording with a sensitive camera. PathoScreen was also used to monitor bacteria grown on an agar medium after leaf printing. During the first 3 days after inoculation, bacterial populations washed off leaves rapidly decreased by at least a factor of 1000, after which populations remained stable until 14 days post‐inoculation (dpi), when symptoms first started to appear. Thereafter, populations increased to a level of 1012 colony‐forming units (CFU) g−1 of leaf material or higher. Similarly, densities in leaf extracts were low during the first 3 days after inoculation, at a level of 100–1000 CFU g−1 of leaf tissue. Gradually populations increased to a level of 109–1012 CFU g−1 at 28 dpi. Higher densities of epiphytic populations were found on the abaxial side than on the adaxial leaf side during the first 2 weeks after inoculation. After spray‐inoculation of leaves, bacterial populations released from infected plants remained low until symptoms appeared, after which plants became highly infectious, in particular under high humidity.

Het klimaat in een kas wordt ingesteld om een optimale gewasfotosynthese, assimilatenverdeling en plantvorm te realiseren. Om momentaan het kasklimaat aan te kunnen passen aan de behoeftes van de plant is het van groot belang inzicht te hebben in de directe gevolgen van aanpassingen in het klimaat op de plant prestaties, in het bijzonder op de fotosynthese. Dit is te doen met de volgende methodes: 1. Gasuitwisseling van bladeren: nauwkeurige metingen van de fotosynthese van een stukje blad, met draagbare meetapparatuur. 2. Plantivity: een commercieel verkrijgbare meter die de fluorescentie van een stukje blad meet. 3. Kas-in-kas: een niet-geklimatiseerde meetkamer waarin CO 2 opname van een aantal planten gemeten kan worden. 4. Fluorescentie-imaging: fluorescentie metingen op afstand aan een groter oppervlakte gewas. 5. Fotosynthese-monitor: soft-sensor waarmee de CO 2 opname van een kas berekend wordt op basis van ventilatievoud en metingen van de CO 2 concentratie binnen en buiten de kas. Uit twee workshops met telers bleek dat zij fotosynthese als een belangrijk proces beschouwen in de teelt van hun gewas, en dat zij de fotosynthese van hun gewas graag momentaan online zouden willen meten. Het is daarom wenselijk door te gaan met de ontwikkeling van een robuust en betrouwbaar meetsysteem voor de gewasfotosynthese

Het klimaat in een kas wordt ingesteld om een optimale gewasfotosynthese, assimilatenverdeling en plantvorm te realiseren. Om momentaan het kasklimaat aan te kunnen passen aan de behoeftes van de plant is het van groot belang inzicht te hebben in de directe gevolgen van aanpassingen in het klimaat op de plant prestaties, in het bijzonder op de fotosynthese. Dit is te doen met de volgende methodes: 1. Gasuitwisseling van bladeren: nauwkeurige metingen van de fotosynthese van een stukje blad, met draagbare meetapparatuur. 2. Plantivity: een commercieel verkrijgbare meter die de fluorescentie van een stukje blad meet. 3. Kas-in-kas: een niet-geklimatiseerde meetkamer waarin CO 2 opname van een aantal planten gemeten kan worden. 4. Fluorescentie-imaging: fluorescentie metingen op afstand aan een groter oppervlakte gewas. 5. Fotosynthese-monitor: soft-sensor waarmee de CO 2 opname van een kas berekend wordt op basis van ventilatievoud en metingen van de CO 2 concentratie binnen en buiten de kas. Uit twee workshops met telers bleek dat zij fotosynthese als een belangrijk proces beschouwen in de teelt van hun gewas, en dat zij de fotosynthese van hun gewas graag momentaan online zouden willen meten. Het is daarom wenselijk door te gaan met de ontwikkeling van een robuust en betrouwbaar meetsysteem voor de gewasfotosynthese

Geassisteerd door glastuinbouw-onderzoekers Henk Jalink en Rob van der Schoor bedacht ontwerper Tiddo Bakker In Vena Verbum.

Members of Botryosphaeriaceae family are associated with serious diseases in different plants across the world. In cashew nut plants (Anacardium occidentale), the fungus Lasiodiplodia theobromae causes a severe group of symptoms related to gummosis that results in decreased nut production. The aim of this work was to develop an indirect enzyme-linked immunosorbent assay (ELISA) with sufficient sensitivity and specificity to detect the fungus both in vitro and in planta (artificially and naturally infected) and to increase the detection specificity within the fungi group using primers specific for the internal transcribed spacer (ITS) sequences. A collection of L. theobromae isolates was obtained, and antisera against the fungus were raised in rabbits. Cross-reactivity against Neofusicoccum sp., Colletotrichum gloeosporioides, Phomopsis anacardii and Pestalotiopsis guepinii was examined. Naturally and artificially infected vegetal material were employed in the ELISAs. The fungi ITS sequences were determined, and single nucleotide polymorphisms were identified and used for primer design. For the naturally infected plants, there was an approximately fourfold variation in the absorbance values. Some positive readings for asymptomatic samples were detected. For the artificially infected samples, an ELISA-based weekly time-course analysis was conducted, and the values for samples from 0 and 7 days were lower than the threshold value. Beginning on day 14, the infection could be detected, with rates varying from 40% on day 14 to 80% on day 21 and 100% by the end of the experiment. The ITS sequencing revealed few polymorphisms among the L. theobromae isolates, but for C. gloeosporioides, P. anacardii, P. guepinii and Neofusicoccum sp., the sequences were sufficient to permit reliable discrimination. The feasibility of ELISA as an early detection technique to assist in gummosis management was demonstrated. PCR amplification based on ITS regions increases and complements serological specificity.

We have developed LED (light emitting diode) induced fluorescence transient imaging instrumentation to image the plant health/stress status by calculation of two images: Fv/Fm (variable fluorescence over saturation level of fluorescence) and the time response, tTR, of the fluorescence time curve. Within a short time interval (˜580 ms) multiple images (typically 20) are captured using the LEDs in the pulsed mode. For each pixel of the fluorescence image Fv/Fm and tTR are calculated and presented as images that correlate with the quantum yield of PSII photochemistry and the time response of this process, respectively. The advantage of the technology lies in the imaging of photosynthetic parameters within a short time interval, remotely and under light conditions. This was accomplished by the development of a high intensity pulsed LED light source (total 5 kW electrical power) and using the LEDs in the pulsed mode with a pulse width of 15 ms and time between sequential pulses of 14 ms. Using this instrumentation we investigated the effect of herbicide treatment, Sencor, on black nightshade (Solanum nigrum L.) plants. Effects of the herbicide on the first fluorescence images could be detected. At the saturation level of the fluorescence this effect disappeared. The effect of the herbicide was visualized on the Fv/Fm image and the time response tTR image. Healthy and herbicide treated parts of the plant yielded average values of Fv/Fm=0.81±0.03 and 0.06±0.02, respectively. Furthermore, the effect of drought stress was investigated on saintpaulia (Saintpaulia ionantha) plants. Under dark conditions no differences in the image of Fv/Fm and tTR could be detected between the control and the plant with drought stress. Under actinic light of 90 µmol m-2 s-1 differences were observed in images of (Fm’-F’)/Fm’ and tTR’. We conclude that for the first time images of a time response of the photosynthesis of leaves are presented. Furthermore, the proposed instrumentation can be used for high throughput screening, as a sensor in sorting machines and has potential greenhouse applications.

Fluorescence can be used to measure and visualize the activity of herbicides that inhibit the photosynthesis. Gyphosate, although not acting primarily on the pholosystems, appears to increase fluorescence of plants. We investigated whether fluorescence technology is a useful tool to both quantify and image of the performance of different adjuvants for glyphosate. A red laser beam providing equipment is used to scan black nightshade plants at a low and high light intensity. A cooled, integrating 16 bit CCD camera is used to record the fluorescence during the low level (F-o) and high level scan (F-m). The relative increase of fluorescence expressed as [(F-m-F-o)]F-m] 100% is calculated and color images are produced. Glyphosate was applied at two suboptimal application rates of 16.9 and 33.8 g ae/ha at 200 L/ha. Both the influence of glyphosate rate and the influence of added adjuvants were obvious. The fluorescence data 30 h after treatment demonstrated that the adjuvants HM9121-A and HM9110 performed better than AMS, HM9541-A, HM9910, or HM2005-B. This observation was consistent over the next three observations (54, 78, and 102 h). The fluorescence data after 72 h correlated (R-2=0.82; logarithmic regression) with the fresh weight reduction caused by the glyphosate treatments. The adjuvants HM9121-A and HM9110 performed the best and the adjuvant HM9541-A had little effect on glyphosate performance. Both imaging and fresh weight data indicate that HM9121-A performs somewhat better than HM9110.

The use of organic propagation material is obligatory according to the current EU regulations for organic production. However, frequently difficulties are en-countered regarding the availability, the costs or the quality. In the Netherlands a national research program aims at developing solutions, needed for improving the production of high quality organic propagation material. The main emphasis in the pro-gram is on the model crops cabbage, onion, wheat and potato. Individual projects within the program include epidemiological studies of seed borne dis-eases to develop disease prevention strategies, meth-ods to improve resistance of seeds and seedlings towards pathogens and methods to control silver scurf in seed potatoes, development of multi-spectral analysis and sorting techniques and methods for analysis and improvement of seed vigour. Active involvement of producers and users of the seeds or seed potatoes ensures that the results will be imple-mented in practice. The program also aims at strengthening the international collaboration, amongst others through involvement in international research projects.

Production of high quality organic vegetable seeds encounters several challenges. Research is performed to support seed companies in producing vigorous and healthy organic vegetable seeds. Examples are provided with respect to research on seed vigour, determining critical control points to avoid disease transmission to the seeds, seed treatments with natu-ral compounds, new seed sorting techniques and enhancement of the natural plant defence. It is noticed that the restrictions in EU regulation 2092/91 on organic production are at present blocking the use of promising natural and sustainable components for seed treatments.

Brassica napus seed is composed of low density oil (0.92 g.cm(-3)) and higher density solids (1.3-1.45 g.cm(-3)). Seed buoyant density may potentially be used to determine seed oil content and to separate seeds with different oil contents, however, we have found that seeds with the lowest buoyant density had lower than expected oil contents. It is proposed that the low oil content observed in the lowest density seed is a function of air gaps or pockets within the seed coat with sufficient volume to disrupt the linear relationship between oil content and density. The air gaps make density-based selection of seeds for oil content more difficult. Seed solid and liquid components are essentially incompressible with increased hydrostatic pressure but air gaps in seeds may be compressed or filled if density sorting is conducted in a pressurised apparatus. Experimental evidence shows that compression of air pockets with hydrostatic pressure or filling of air pockets with solvent simplifies the relationship between seed density and oil Content. In spite of applied pressure it was observed that pressure was not sufficient to eliminate the buoyancy of all seeds with air pockets.Seeds containing air pockets may have been immature or improperly filled during maturation. Interrupted maturation, premature maturation or desiccation may potentially interrupt storage compound accumulation and lead to morphological changes. Chlorophyll fluorescence was used in this study as an indicator of seed maturity. An inverse relationship between chlorophyll content and oil content was observed, but was not observed for chlorophyll content and density. This relationship between oil content, chlorophyll content and density suggests that the lowest and highest density seed groups were enriched in immature seed.

Physical sanitation methods are used by the seed industry to prevent transmission of seed-borne diseases, but sensitivity varies between seed lots. The effect of seed maturity on the sensitivity to hot water, aerated steam and electron treatments was studied. Two Brassica oleracea L. and two Daucus carota L. seed lots from commercial production were selected for containing relatively large amounts of less mature seeds. Each seed lot was sorted into three maturity fractions based on the levels of chlorophyll fluorescence of individual seeds. Less mature B. oleracea and D. carota seeds were more susceptible to hot water treatments and less mature B. oleracea seeds to the aerated steam treatment. Seed maturity did not influence the sensitivity to the applied electron seed treatments. Seed lots were not selected for infections with seed-borne pathogens, however the less mature seeds were observed to be more frequently infected. It would be advisable to harvest seeds as mature as possible and to remove less mature seeds during seed processing. Sorting seeds by their level of chlorophyll fluorescence provides a useful method of sorting B. oleracea and D. carota seed lots. This would result in more efficient physical sanitation of seed lots