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In the Netherlands recirculation of the nutrient solution is statutory required in soilless culture systems. The goal is to achieve a zero liquid discharge, it means no solution with fertilizers, pesticides and/or cleansing products are allowed to be discharged to surface or ground water or the sewage system. It also means that products added to the system should be taken up by the plants or broken down. The objectives of this research were to investigate i) if frequently used cleansing products accumulate in the nutrient solution and may harm growth of the plants, and ii) if the used concentrations of cleansing products were able to eliminate pathogens in the circulating nutrient solution. Gerbera was used as a pilot crop. The research was divided in four steps. As a first step growers and consultants were inquired (1) about the use of cleansing products additional to the traditional disinfection methods. It was followed by laboratory experiments (2) to test a few cleansing products in various concentrations against plant pathogens. A next step was a greenhouse experiment in which gerbera plants were infected with Fusarium oxysporum (3). Finally sampling at commercial farms (4) was performed to investigate if accumulation did really appear. The inquiry showed that nearly all growers were using, additional to UV or heat treatment for disinfection, cleansing products such as hydrogen peroxide, bleach, chlorine dioxide or ECA water. They were mainly used for cleaning of the pipework. From the laboratory experiments it appeared that the concentration to eliminate the pathogen was much higher as the concentration used to clean the pipe work. In the greenhouse experiment two cleansing products (hydrogen peroxide, chlorine dioxide) were added in five concentrations with two replicates and compared with a control. All treatments were infested with F. oxysporum, except for the control. During the short growing cycle there were no symptoms of F. oxysporum at the plants. However, it appeared that the higher the concentration of added cleansing products the worse the state of the plants, decreasing plant growth. Additionally, bleach showed high sodium concentrations, while the iron chelate was broken down by the hydrogen peroxide. Looking to the cleansing products at commercial farms hardly any accumulation could be measured. It was concluded that the low concentrations applied in commercial practice do not accumulate to toxic levels while a side effect of cleansing products against pathogens cannot be expected.

Nederland is een van de grootste producenten van champignons in de wereld. Er zijn echter de laatste decennia slechts weinig nieuwe champignon-gebaseerde producten op de markt gekomen. Dit project beoogt een aanzet te leveren tot de ontwikkeling van champignonrassen die zich onderscheiden in smaak en die zich daarnaast zichtbaar onderscheiden van de huidige commercieel verkrijgbare champignons. Als eerste stap voor dergelijk toekomstig veredelingsonderzoek moeten metabolieten in champignons worden geïdentificeerd die voorspellende waarde hebben voor de smaak. Als dergelijke merker-moleculen betrouwbaar zijn geïdentificeerd, kan in een vervolgproject daadwerkelijk een veredelingstraject worden opgestart. Uit een collectie van ongeveer 250 wildisolaten van de champignons is een selectie gemaakt van 43 isolaten die de gehele genetische variatie van de collectie min of meer omvatten. Deze isolaten zijn opgekweekt in 6 verschillende teeltproeven en aangeboden aan een sensorisch panel dat verschillende aspecten van de smaak heeft beoordeeld. Statistische analyse van de resultaten laat zien dat hoewel voor de meeste isolaten de smaak erg lijkt op de commercieel beschikbare witte champignons, er een aantal isolaten zijn die anders smaken. Dezelfde champignons die zijn aangeboden aan het sensorisch panel zijn daarnaast onderzocht op metaboliet samenstelling. Het is nog niet mogelijk gebleken om de verschillen in smaak te koppelen aan specifieke metaboliet samenstellingen in de champignons. Een van de oorzaken is de grote variatie in beoordeling van smaakaspecten door het sensorisch panel. Daarnaast bleek bij vergelijking van de verschillende batches van controle ras A15, ook batch tot batch variatie op te treden in metabolietgehalten. Vervolgens is geprobeerd om de variatie in beoordeling door het sensorisch smaakpanel te verminderen door: • Veel minder rassen aanbieden aan het sensorisch panel • Rassen met grootst mogelijk verschil in smaak aanbieden • Interne herhalingen aanbieden als extra controle. Helaas bleek ook bij deze opzet het niet mogelijk om de beoordeling van de verschillende aspecten van champignonsmaak te koppelen aan merkermoleculen.

In this project, solutions are developed to minimise leaching of nutrients and pesticides from greenhouses to the environment (esp. surface water), in order to comply with legislation and societal demands. In 2017 the following questions have been addressed: To prevent emission, drain solutions are reused or purified. Other water flows may deviate in compositionand possibilities for reuse or purification. The option for reuse or purification for these water flows has been investigated, and a working methodology for the end of a cultivation (e.g. cleaning) has been developed. Applications of Forward Osmosis in horticulture have been investigated. Water extracted from the discharge flow with Forward Osmosis using the concentrated nutrient solution holds prospects, but extracting irrigation water from brackish groundwater seems less feasible. In a long-term experiment, sodium (Na) standards for sweet pepper have been reinterpreted. It was shown that an increase in the Na standard up to 8-10 mmol/l causes no damage or loss in pepper production. Inaddition, it was shown that the split-root system can be used for uptake of extra Na without growth hampering. Furthermore, applying humate can prevent negative sodium effects at high sodium levels (Chinese cabbage). Finally, insight was gained into the risks associated with the use of chlorinated cleaning products in zero-discharge cultivations. In dit tweejarige project zijn openliggende kennisvragen opgepakt om de laatste stappen naar de gewenste nulemissie bij substraatteelten mogelijk te maken. In 2017 zijn de volgende vragen onderzocht: Voor waterstromen die sterk afwijken van gangbaar lozingswater, is de samenstelling geanalyseerd en zijn mogelijkheden tot hergebruik dan wel zuivering verkend. Tevens is onderzocht hoe bedrijven in de praktijk omgaan met deze waterstromen. Voor waterstromen die bij de teeltwisseling vrijkomen is een werkwijze ontwikkeld; in2018 komen best practices beschikbaar voor de andere waterstromen. De toepassing van Forward Osmosis in de tuinbouw is onderzocht. Voor het indikken van de spuiwaterstroom biedt Forward Osmosis met als trekvloeistof een geconcentreerde nutriëntenoplossing perspectief, voor het onttrekken van gietwater uit brak grondwater minder. In 2018 volgt een pilot proef en optimalisatie van de scenario’s. De Na-normen voor paprika zijn geherinterpreteerd met een duurproef, waarbij bleek dat een verhoging van Na-norm voor paprika tot 8-10 mmol/l veilig kan. Daarnaast is aangetoond dat de restgoot-methode (gescheiden wortelsysteem) gebruikt kan worden om extra Na op te nemen zonder negatieve gevolgen voor groei. In 2018wordt deze methode op semi-praktijkschaal getest. Ook het toedienen van humaat kan de negatieve gevolgen vaneen hoog natrium teniet doen (Chinese kool). Tenslotte is er inzicht verkregen in de risico’s bij het gebruik van chloorhoudende reinigingsmiddelen in emissieloze teelten.

Worldwide increase of water shortage and competition for fresh water is raising the awareness that an increase in water use efficiency in horticulture is a necessity. At the same time, environmental awareness and legislation (e.g. the EU Water Framework Directive 2000/60/EC) restricts the emissions of nutrients and plant protection products (PPPs). In the Netherlands in soilless growing systems much effort is put into measures to enable maximal recycling of nutrient solutions, thereby decreasing the required amount of fresh water needed and the emission of nutrients and PPPs. Recycling of water fluxes also implicates that the drain water has to be disinfected to prevent rapid dispersal of pathogens. Heat treatment, filtration, Ozone and UV treatment are commonly used disinfection technologies. Some of these technologies (Ozone and UV) are known for their ability to break down PPPs and therefore their joint application (disinfection and end-of-pipe purification of discharged drain water) have been studied. In this paper we present the results of the integration and optimisation of ozone technology in a cucumber and a sweet pepper soilless cultivation. An Agrozone ozone unit that alternately treated the recycled nutrient solution for the elimination of pathogens and removed PPPs from discharge water was investigated. The ozone unit eliminates pathogens and PPPs by direct oxidation of organic material batchwise. It was shown that both disinfection of the recirculating nutrient solution and removal of PPPs from discharge water are possible with the same ozone equipment, if installed correctly. Preliminary tests with Tomato Mosaic Virus have shown that this technology can completely disinfect (from 402 to 0 lesions per plant), and remove up to 98% of PPPs from standardised greenhouse discharge water. For disinfection purposes shorter treatment times and lower ozone doses can be applied.

In this manuscript we provide evidence for the seed transmission of Pepino mosaic virus (PepMV) in tomato. Fruit was harvested from a tomato crop artificially infected with both European and CH2 genotypes of PepMV and more than 100,000 seeds were extracted and cleaned using an enzymatic treatment without disinfection. Infection assays using indicator plants confirmed the presence of viable virus on the seeds. Seeds were distributed to ten different laboratories in three separate batches, where they were germinated and the young plants tested by ELISA. In total over 87,000 plants were tested and 23 positives detected, indicating an overall transmission rate of 0.026%. However, the observed seed transmission rates varied from 0.005% to 0.057%, depending on the seed batch used. Results clearly showed that PepMV can be transmitted from seeds contaminated with virus to seedlings, highlighting the risk of using seeds from PepMV-infected plants and the potential for seed transmission to contribute to the further spread of PepMV.

Pepino mosaic virus (PepMV) has recently emerged as a highly infectious viral pathogen in tomato crops. Greenhouse trials were conducted under conditions similar to commercial tomato production. These trials examined whether tomato plants can be protected against PepMV by a preceding infection with an attenuated isolate of this virus. Two potential attenuated isolates that displayed mild leaf symptoms were selected from field isolates. Two PepMV isolates that displayed severe leaf symptoms were also selected from field isolates to challenge the attenuated isolates. The isolates with aggressive symptoms were found to reduce bulk yields by 8 and 24% in single infections, respectively. Yield losses were reduced to a 0–3% loss in plants that were treated with either one of the attenuated isolates, while no effects were observed on the quality of the fruits. After the challenge infection, virus accumulation levels and symptom severity of the isolates with aggressive symptoms were also reduced by cross-protection. Infection with the attenuated isolates alone did neither affect bulk yield, nor quality of the harvested tomato fruits.

At the beginning of 1999, a new virus disease occurred in protected tomato crops in The Netherlands. Initial diagnostic tests revealed the presence of a potexvirus but serological tests ruled out the presence of Potato X potexvirus (PVX). Tests for other potexviruses reported from solanaceous crops provisionally identified the virus as Pepino mosaic potexvirus (PepMV). The virus was purified, and an antiserum was produced, which showed strong reactions with both the type isolate of PepMV from pepino and two other isolates from tomato. Host range and symptomatology of the pepino and tomato isolates of PepMV revealed clear differences from PVX. However, differences were also observed between the pepino and tomato isolates of PepMV. Sequence alignment of DNA fragments of 584 bp derived from the RNA polymerase cistron showed almost 95% identity with the pepino isolate, whereas the identity with PVX appeared to be < 60%. Together, these results identified PepMV as the causal agent of the new virus disease in tomato. Based on the differences from the type isolate from pepino (Solanum muricatum), the isolates from tomato should be considered as a distinct strain of PepMV for which the name tomato strain is proposed.