Home Posts Tagged "research" (Page 2)


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The range of plant invigorators and water treatments on offer has increased significantly in recent years. Some look set to deliver growth effects in practice.

This has sparked interest in growth tests that highlight differences in plant growth in standard conditions. There are many different growth tests available, ranging from lab tests in Petri dishes to growth tests on a semi-practical scale. We have adapted one of these – the BioTest Phytotoxkit test – into a quick, relatively cheap and broad growth response test.

The test consists of a three-day germination test with three different crops, usually mustard, cress and sorghum. The test can detect minor differences with a high degree of certainty. Other benefits are the reports on both above- and below-ground growth, and the fact that effects due to differences in nutrients, pH and EC are excluded.

The test is too short in duration to test growth effects caused by microorganisms in the root environment, but it is suitable for determining growth inhibition caused by substrate and drain water. Separate growth tests are available for measuring the growth effects of microorganisms in the root environment.

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Certhon is building its own research facility next to its office in Poeldijk: the Certhon Innovation Centre. The Dutch greenhouse designer and builder has been conducting pioneering research on optimising the technology of growing without daylight for the past two years. By the end of 2017, the facility will contain eight growth cells, where continuous research to develop the next generation cultivation system will be carried out.

Certhon started building its Innovation Centre last month. It will be used to further develop Certhon’s PlantyFood cultivation system, which involves growing vegetables, fruits and flowers without daylight. Demand for safe and healthy food, which is sustainable and locally produced, is increasing worldwide.

Daylight-free cultivation

The greenhouse designer and builder is expecting the demand for indoor cultivation solutions to grow rapidly. However, cultivation in a growth cell requires different methods than growing in a traditional greenhouse. The biggest change, compared to traditional growing methods, is that cultivation methods are not determined by the outside climate; instead, state-of-the-art technology is used to create an indoor climate. Research will be conducted in an area of 240 m2, which will be used to establish best practice for large-scale daylight-free cultivation.

Crop tests

Certhon sees great potential in the daylight-free cultivation of tomato, pepper, soft fruit, lettuce, herbs and other crops. These crops will be tested in different climates, with different humidity and lighting programs. Tests will also be conducted with lighting, sensors, and hardware and software. “We are not a research Institute”, says John van der Sande, Head of R&D at Certhon. “We can use the knowledge we acquire in our own research institute to help our clients maximise results in the first couple of years. As well as tools to create an ideal environment, we also offer specific agronomical expertise.”

Source/photo: Certhon.

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How much leaf does a tomato plant need to produce a good yield? That’s the main question behind a research project, The New Crop. The trial at Wageningen UR Greenhouse Horticulture, the Netherlands, produced a surprising result because 'bullying’ the plant by removing extra leaves led to an increase rather than a decrease in yield.

Removing leaves to produce the optimal Leaf Area Index (LAI) is ingrained within tomato growers but how far can you go? Should you primarily remove the old leaves or indeed remove more leaves at a very young stage? A plant with a small leaf surface area will transpire less and that could save energy. In the winter it helps if artificial or natural light is allowed to penetrate deeper into the crop. It certainly seems time to pay more attention to ensuring a good ratio between leaf and fruit.
Wageningen UR Greenhouse Horticulture has been running a project called, Het Nieuwe Gewas’ (‘The New Crop’) as part of the program, Kas als Energiebron (Greenhouse as Energy Supply). Researcher Arie de Gelder gives an update.

Just one leaf between bunches

Commercial nurseries with artificial lighting usually have a LAI of 3 to 4. In this trial the researchers cut it back to a LAI of 2 to 3. This was achieved by removing more leaves at an early stage. This produced a more open crop structure which they hoped would lead to better light utilisation during the winter. The trial in Bleiswijk had three sections that were planted with the variety Brioso in the second week of October. Stem density at the beginning was 2.5 per m2. Extra stems were maintained in week 50 and in week 4 so that the final density was 3.75 stems per m2. The roof covering is diffuse glass with a high haze and high light transmission.
A tomato plant produces three leaves between each bunch. In the control area one leaf was removed (33%) between each bunch so two leaves remained. In the area with the ‘open’ crop one leaf and then two leaves were removed alternatively (44%). In the area with the ‘very open’ crop firstly one leaf was removed and then two leaves were removed twice (55%). Therefore just one leaf was often present between the tomatoes.
From the bottom of the crop leaves were picked at the same bunch height in all three areas. As a result the plants kept 14, 12 and 10 leaves respectively. Brioso is well known as a vegetative variety so it was a good choice for this experiment.

Shorter plants

Before the trial started the researchers and growers thought that such rigorous removal of the leaves (55%) would be risky. However, they were able to apply and sustain this treatment even during the transition from winter to spring. Leaf length, leaf width and plant length were accurately recorded, as were the thickness of the top, plant weight and dry matter.
It soon became apparent that the extreme pruning had a big impact on plant length. By April for example, the difference had risen to a metre. The plants in the very open section were the shortest. The leaves remained likewise shorter. De Gelder: “That isn’t a complete reflection on leaf area because it’s the width, not the length, which determines that.”
In general the tops of the stems were thickest on the plants in the standard area but up until week 12 there were many moments that the open plants were ahead. The top was usually the thinnest in the very open section There was also a large variation in LAI. For example, in the standard treatment this was 2.6 in December while in the very open section in January it was just 1.8.

More drain

Watering and fertilisation were in line with that used in commercial practice, although some growers think that the content of nitrogen in this trial is a bit high. The plants in the very open section took up less water and fertilisers. That’s logical if the plants have significantly fewer leaves. Also, the very open section had more drain.
It is necessary to mention that during the research the leaves were picked from underneath, in all sections at the same time. “It will be interesting in follow-up research to keep the leaf on the plant in the very open section for longer so all sections have approximately the same assimilating area,” says De Gelder.

Steer crop by leaf picking

Of course all eyes are focused on yield. De Gelder expected the best yield to be in the middle treatment, in the open section. After all the very open section was a very extreme treatment. However, it was somewhat different.
At the beginning, yield in the very open section took the lead while the average fruit weight, shelf life and taste were no different from the others. The difference in yield, compared with the standard section, rose to 0.9 kg/m2 early in the spring. In week 17 yield in the standard section was 19.4 kg/m2 compared with 20.3 kg/m2 in the very open section. This result is, in the very least, striking.
“We concluded, even though this is not a practical situation, that by removing leaves we can steer the crop considerably more than we thought. It might be possible to pick an extra kilo in winter,” says de Gelder.

Energy saving

The research began with the aim of saving energy by more efficient light utilisation and less transpiration. If the plants transpire less by removing leaves that should be reflected in energy consumption. The researchers found that differences did occur. When energy consumption was 20 m3/m2 of gas the difference between the standard and very open crop was 1 m3/m2.
Up until the end of April the crop received 1,650 hours of artificial lighting with SON-T lamps. The light intensity is 210 µmol/m2.s. The length of the lighting period is clearly under that used in practise and the light sum is partially compensated for by the intensity. The light was able to penetrate deeper into the crop due to the open nature of the crop.
The interesting results so far are an invitation to do further research into leaf removal. De Gelder already has ideas for a new research project. In addition, he would like to know if these measures also work in a normal crop without lighting. In any case, the first step to better steering the growth and production of tomatoes has been made.


Research into the extreme removal of leaves from tomato plants has yielded surprising results. Not only does it seem possible to bring forward production by removing extra leaves but it also saves energy. The challenge now will be to see if the results achieved in research units at Wageningen UR Greenhouse Horticulture can be reproduced in practise.

Text and images: Pieternel van Velden

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On 13 September, construction work on the Greenport Horti Campus in Naaldwijk started. The new name was also unveiled: World of Westland. In a year’s time, 1,200 students will be able to attend classes, and 80 companies will be able to show their latest developments in the field of horticulture. World of Westland will become the number one global knowledge and innovation centre for the greenhouse industry.

Several hundred leading figures from the horticultural sector watched a three-dimensional presentation yesterday on the new building, which will be built on undeveloped land in front of the flower auction. The striking of the first pile of the building was interrupted by students, who wanted to mark the building envelope themselves. The contours were made visible with red and white ribbon.


The complex combines three functions: teaching, research and presentation. Besides senior secondary vocational education (MBO) students from Albeda College, ROC Mondriaan and Lentiz Education Group, the school will also offer space for higher professional education (HBO) colleges and research institutes. Cooperation between education and business has already started. A course in nutrition and health is planned, with assistance from Koppert Cress among others. Dutch Flower Group and Nature's Pride will be giving input to the Trade and Logistics course. The building will be provided with a mechatronics room, a flower tie room, and a 300-seat auditorium.


Demokwekerij Westland (Westland Demo Nursery) will be leaving its current site in Zwethlaan in late 2017, and is building brand new research greenhouses with the latest technology. Manager Peet van Adrichem says, "Continuous and accelerated innovation is vital to maintain the Netherlands’ leading position in the world. We initiate and facilitate cultivation and technology innovation for the national and international horticulture sectors, so we thought it only logical that we should be part of World of Westland."


The third function of World of Westland is as a demonstration and presentation area. 80 companies will be able to show their latest flowers, plants and technology, over an area of almost 10,000 m2. 80% of this space has already been rented out, to the satisfaction of Jaap van Duijn, one of the initiators.
World of Westland will also serve as a focus point for foreign visitors who come to Westland because of the horticultural sector. Mark Zwinkels of Greenport Food & Flower Xperience says, “They often don’t know where to start when they come to Westland. This is a place where they can orientate themselves."

Source: Greenport Horti Campus/AD Westland. Artist impression: Greenport Horti Campus.

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Machiel Reinders is a senior researcher of Marketing & Consumer Behaviour at LEI Wageningen University Research Centre. He is currently focusing on trends in the agrifood market, in which capacity he is also involved in the Fresh ONLINE Pack project. In the previous years, Reinders mapped out the existing situation and the situation that is desirable in the future with respect to the online sale of fresh produce.

This study included a mystery shopping experiment, in which products, packaging and the ordering procedure of various online sellers of fruit and vegetables were tested. ‘The study revealed that there were substantial differences not only with regard to the ordering and delivery processes, but also in respect of the product ranges, delivery frequencies, packaging and the payment methods offered.’

Critical success factors

What requirements would you need to satisfy if you wish to be successful in the online sale of fresh produce? According to Reinders, one of the biggest obstacles is logistics. How can you be sure that your fresh products will be delivered on time and in the desired manner, and in a way that is profitable to you? Door-to-door delivery is expensive, particularly when your customers have individual wishes with regard to delivery and are only willing to pay limited delivery costs.

A study conducted by Deloitte in 2015 reveals that consumers increasingly want to pick up their own groceries.

There are a few ways to keep these costs down, according to the researcher: ‘If you opt for home delivery, you can limit yourself to a specific delivery radius or ‘pick’ your orders in a decentralised manner, like at the local supermarket or greengrocer’s. Another alternative is to use pick-up points at supermarkets or community centres. The study conducted by Deloitte in 2015 reveals that consumers increasingly want to pick up their own groceries. The most important reason for this the ability to pick up your groceries when it’s most convenient to you.’

Speed and convenience

Reinders believes that opportunities abound in an online environment. Groceries can be put together according to individual specifications, or linked to a personal profile, such as a specific diet. An online environment can also offer consumers inspiration, in the form of videos, for example. Platforms like these also enable information to be shared via social media. ‘Online channels offer the ultimate in speed and convenience.’

The researcher also believes that online sales offer opportunities in the field of freshness and quality. ‘Supplying products of a consistently high quality and responding to the demands of target groups could make it easier to achieve higher profit margins. Differentiation in products range and delivery methods are also opportunities that could be explored. Also, differentiation raises efficiency in the chain: food waste can be reduced and chains shortened.’

An online environment offers opportunities for demand-driven innovation and marketing, because it is easier to gain insight into the behaviour and wishes of customers who order their products online.

According to Reinders an online environment also offers opportunities for demand-driven innovation and marketing, because it is easier to gain insight into the behaviour and wishes of customers who order their products online. ‘This will provide an incentive for new products or concepts to be developed based on customers’ prior ordering behaviour.’

The threats facing the online sale of produce lie mainly in the fact that the Dutch fresh produce sector is still highly traditional in its commercial development, says Reinders. ‘The Netherlands is not a front runner in digital technology. Also, the online delivery of a consistent and high quality still constitutes a challenge. Moreover, many consumers believe online purchases to be more expensive. This also forms a serious threat.’

New initiatives

Reinders expects the online market to keep growing unabatedly over the next few years. ‘The ING bank anticipates the online portion of sales achieved by Dutch supermarkets to reach 15 to 20 per cent by 2020. Developments follow one another at a rapid pace; new online initiatives are mushrooming. I think that growers and suppliers responding to these developments can be assured of becoming the preferred business partners of certain sales outlets and retailers. As far as this is concerned, the sector should not let these opportunities slip by!’

Text: Tuinbouwteksten.nl/Ank van Lier. Photo: LEI Wageningen UR.

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Wageningen UR Greenhouse Horticulture and its partners won a design award for its Vegetable Palace in West Flanders: an ambitious building for research and demonstrations in the field of vegetable cultivation. ‘This constitutes an unprecedented development in urban rooftop gardening,’ says Jan Willem de Vries van Wageningen UR. ‘It will be the biggest in Europe, for which we will be happy to make available all our expertise.’

A team of designers from the Greenhouse Horticulture division of Wageningen University Research Centre, Van Bergen Kolpa Architecten, Meta, Smiemans and Tractebel Engineers jointly produced the innovative designs for the Vegetable Palace: a genuine landmark for ‘The Green Hub’ on the Roeselare ring road.  The building will be built on the roof of REO Veiling, Belgian’s fruit and vegetable auction and the food logistics heart of West Flanders. The Vegetable Palace is constructed from glass and steel, an airy greenhouse frame that rests on the concrete pillar of the auction building. The project, with its innovative design, is to be an example for urban food production, the intensive use of space, circular energy and water consumption and sustainability in greenhouse horticulture.


The 9,500 m2 building will house high-tech research facilities for the cultivation of fruit and green leafy vegetables, surrounded by an educational routing for the general public. The cultivation of tomatoes and lettuce, as well as pepper and strawberries can be experienced hands-on in four different climate zones.  The entrance, with an imposing staircase, leads to the Urban Farming Square with visitor facilities at the heart of the building. The ‘Façade Greenhouse’ at the ring road will feature a special greenhouse that will focus on innovation in vertical farming and that will be twice as high as conventional greenhouses. Rainwater will be collected at the foot of this ‘Façade Greenhouse’ with a reed filter for the purification of waste water.

Construction of the greenhouse is scheduled to start in early 2017, and it is expected to open its doors to growers, researchers and the general public at the beginning of 2018.

Source: Wageningen UR Glastuinbouw. Photo: Van Bergen Kolpa Architecten.

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Manufacturers and horticultural suppliers alike have been expressing increasing interest in the development and market for plant strengtheners. A whole series of products based on substances of a natural origin, from micro-bacteria to hormones and from fungal preparations to seaweed and from algae to fatty acids, are lauded for their resilience-boosting capacities. An overview, however temporary, is presented below.

Our planet’s flora and fauna offer a wide range of substances that are beneficial to crop protection. The members of Artemis develop agents and systems that increase plant resilience to such an extent that diseases and pests simply won’t stand a chance. Artemis is the industry organisation and interest group for biological crop protection. The organisation is composed of manufacturers and suppliers of natural enemies, pollinators and plant protection products of natural origin. The substances (i.e. products) impact a wide range of functions in plant physiology.

Defence proteins

According to Alwin Scholten, cultivation advisor and owner of PlantoSys, plant strengtheners can be used in multiple ways. PlantoSys incorporates the plant-based defence protein salicylic acid into its products. Every plant produces this naturally. If the concentration is high enough, the plant starts to produce defence proteins that can block the growth of bacteria, fungi and viruses. ‘Salicylic acid is, in itself, not an antibody. It spurs the plant to produce defence proteins,’ explains Scholten. ‘However, a sufficiently high concentration must be attained in the plant before this will work. This level can be increased by administering salicylic acid to the plant’s leaves (by spraying) or roots. Stimulating the plant’s own immune system through the application of salicylic acid has proved to be highly effective in combating fungus or bacteria-related problems.’ The product appears to be highly effective against biotrophic fungi, such as powdery and downy mildew, Fusarium, rust, fruit rot (Colletotrichum) and Alternaria. It also inhibits the development of spider mites, whiteflies and aphids. Scholten recommends weekly doses as long as problems are anticipated. His product, SalicylPuur, has been approved by the Ctgb as a fertiliser. Other products developed by PlantoSys, with combinations of micro-silver and micro-copper, are marketed likewise. Scholten has noticed a growing interest among horticulturists in plant-strengthening fertilisers. ‘Four years ago the majority of the response I received was predominantly sceptical, but the sector is becoming more open-minded, particularly in the past two years.’

‘Four years ago the majority of the response I received was predominantly sceptical, but the sector is becoming more open-minded, particularly in the past two years.’

Root system

Plant strengtheners are commonly applied to the soil (the substrate) or administered as a fertiliser when watering the plant. The interest expressed by professional growers for soil and crop stimulation agents is growing, but Aly Loes Vellema of ECOstyle bv in Appelscha still has the impression that as long as chemical alternatives are still widely available, the majority prefers to stick to these. Researchers at WUR are also of the opinion that plant strengtheners are not ready to replace crop protection agents, but are a good supplement. ECOstyle focuses on ecologically responsible fertilisers, soil improvers and crop protection agents. Vellema is the supplier of the bio-stimulating soil improver Exsol P, a composite of various types of bacteria. The Bacillus combination has the capacity to free organically bound phosphates and phosphates bound to minerals from the soil, which allows the root system to develop better and the plant to better absorb water and nutrients, thus boosting overall plant resilience. ECOstyle is currently engaged in the development of plant strengthening substances, about which Vellema is not yet ready to share the details.


There are also plant strengtheners on the market that work at photosynthesis level. Pentakeep is a liquid nitrogen fertiliser that is blended with 5-aminolevulinic acid. Administration of this fertiliser causes photosynthesis to be prolonged, and as a result, the production of sugars and dry matter. Cor den Hartog of Pentagrow, importer and distributor of this originally Japanese product, has had over fifteen years of experience with the application of this product in greenhouse horticulture. Tests and studies have demonstrated that Pentakeep enhances vigour and resilience in crops. ‘Research conducted in practice has shown that crops treated with Pentakeep are less susceptible to mildew,’ den Hartog explains. ‘When applied properly, you will have a success rate of 100%.’

5-aminolevulinic acid (5-ALA) occurs naturally in plants, but its production rate depends on the speed of the plant’s metabolism. This metabolism can be accelerated by giving the plant an extra dose of Pentakeep. Plants need 5-aminolevulinic acid to produce chlorophyll. In addition to this, 5-aminolevulinic acid will increase the production of sugars and accelerate the absorption of fertilisers. The result is improved overall growth, higher production rates and stronger plants. Den Hertog confirms that Pentakeep is an NPK fertiliser and regrets that it is not yet 100% biological. The firm aims to bring a biological variant of Pentakeep to the market in the near future.

Soil resilience

On the list of the most important disciplines, Koppert Biological Systems occupies the top position with ‘resilient cultivation with NatuGro’. The international market leader of biological crop protection products has placed its resilience activities with EBIC, an international platform for enterprises engaged in the promotion of the bio-stimulants industry in an endeavour to encourage sustainable agriculture and horticulture.

Koppert is convinced that soil resilience is the key to healthy and vigorous plants.

Koppert is convinced that soil resilience is the key to healthy and vigorous plants. With a system that is composed of a diversity of products, soil analyses and expert advice, Koppert offers an all-encompassing approach under the name NatuGro. The products that are included in the NatuGro system are not stand-alone, but form part of an integrated approach: a system that enhances the biodiversity of the cultivation medium and increases the plant’s resistance to disease. A healthy and well-balanced soil life is crucial to this. Pathogenic fungi and bacteria will be inhibited because they are challenged or attacked by various groups of useful organisms in the root environment. One of Koppert’s best-known products is Trianum, a biological plant strengthener containing Trichoderma harzianum T-22 spores. While having a strengthening effect, it also enhances plant resilience in general against a variety of soil fungi. Other products included in the NatuGro system are used in the propagation stage, to stimulate root development and enhance root quality, or to improve photosynthesis.

Other multinationals such as Syngenta, BASF, Bayer and Monsanto are also manifesting themselves on the market of resilience-boosting products. Syngenta is now marketing the biostimulant Hicure and BASF has taken over Becker Underwood, specialised in biological seed treatment. Bayer has submitted an application for the approval of its ‘green’ line of Serenade fungicides and Monsanto is developing various products through its subsidiary BioDirect.

Plant strengtheners

Biobest, established in Lier and a subsidiary of Biobest NV in Belgium, has also developed activities on the market for plant strengthening products. Biobest recently expanded its product range with several items that have a plant-strengthening effect. One of these is Greenstim, about which Biobest claims that it accelerates the transport of specific nutrients. According to this supplier of horticultural products, this has a positive effect on the quality of fruit and perishability. Prestop and PreFeRal are two products that have been introduced into the Biobest range of biological products. Prestop is a biofungicide that combats Botrytis in various crops. Bart Sosef, Director of Biobest Nederland, expects the company’s range of biological products to be expanded in the near future. In relation to this, he has mentioned the fungus Trichoderma, which has a destructive effect on roots.

Biobest is evolving from a manufacturer and supplier of exclusively microbial products into a company that is also active in ‘macrobials’: useful insects and pollinators. Microbials focus more on fungicides that have a direct effect on pests, and in relation to which Sosef has mentioned the biological insecticide PreFeRal. Biobest is seeking collaboration with various partners for the further development of these products, while the marketing emphasis will be placed on guidance and advice. ‘Biobest aims to bring only products to the market that can guarantee the effectiveness they claim,’ explains Sosef.

Text: Tuinbouwteksten.nl/Suzan Crooijmans. Photos: Fotostudio GJ Vlekke, GAPS Photography.

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Resilient crops and robust cultivation systems are in the spotlight these days. We want plants that are tough enough to withstand disease from mere contact with a fungus, virus or bacterium. Researchers and the corporate community have joined forces in the quest for increased crop resilience.

Increasing consumer demand for environmentally-friendly grown and residue-free produce is putting the use of chemical crop protection agents under pressure. At the same time - or in connection with this - an increasing number of crop protection agents are no longer available. The horticulture industry is therefore hard at work searching for alternative ways to protect crops from pests and diseases.

What does resilient mean?

Resilience is a modern name for a natural way of being that has almost been forgotten. For many years, the necessity of crop resilience was relegated to the background with the advent of chemical agents, while the intensification of horticultural crop production was placing a more strenuous burden on crop health at the same time. Cultivation methods, the speed at which crops are produced, the larger number of plants being grown, the greenhouse climate, varietal selection and the use of chemical crop protection agents have all been instrumental in the extent to which plants are resilient and susceptible to disease and damage.

Now that sustainable cultivation has become a market criterion, plant resilience is quickly gaining in importance. Additionally, due to the increasingly narrower package of chemical agents available today, treating your crops with chemical agents no longer as self-evident as it was a few years ago. As a result, plant resilience is becoming an increasingly urgent point on the agenda. At the same time, there is a large group of growers who don’t find the problem to be as pressing: ‘We still have chemistry, don’t we? There must be some adjustments that can be made.’

The number of activities and studies currently focusing on ways to increase plant resilience - and therefore reducing plants’ susceptibility to pests and diseases - is astounding. The numerous studies are being regarded with great interest. They are receiving financial support from governmental institutions and applauded by environmental and social organisations. If we are successful in increasing plant resilience, our faith in healthy cultivation without any need for chemicals will surely increase.

Plant resilience is, however, very difficult to measure. Methods used for this include scouring for symptoms of disease, measuring spore impact or conducting tests for disease on flower and plant materials (bio-testing). A proposal was submitted at the ‘Topsector Tuinbouw en Uitgangsmaterialen’ summit for horticulture and plant materials held in September 2015 for in-depth research into the measurability of plant resistance.

Influence of light and substrate

Parameters are being sought on a diversity of fields to influence plant resilience. A connection has been discovered, for example, between plant resilience and light. Red light, far-red light and UV light all have an effect in the immune system. Studies into plant resilience in relation to light have been conducted at the initiative of Philips and Wageningen University and Research Centre (WUR). One of the conclusions is as follows: ‘We know from literature that light is not necessary for assimilation alone; those parts of a plant that are exposed to sufficient light are less susceptible to mildew, for example.’

Several studies are investigating the effect of substrates on plant resilience. A perfect example is injection with rhizobacteria. This natural enrichment of substrates, called Induced Systematic Resistance (IRS), has been noted as highly promising by the WUR research staff. Additionally, endophytes – micro-organisms – are also being investigated as an alternative for boosting resilience. Another factor to take into consideration involves plant strengtheners, such as seaweed, mineral oil, fatty acids, garlic and fungus spores.

The end of 2014 saw numerous proposals for fundamental research being submitted to the Netherlands Organisation for Scientific Research (NWO Green) within the framework of the ‘Topsector Tuinbouw en Uitgangsmaterialen’ summit. One of the studies given a green light was a project investigating plant resilience in chrysanthemum cultivation. The study focuses on how the inoculation of sterilized soil media with soil micro-organisms affected the sensitivity of above-ground pests. The research objective was to develop soil inoculants that could be used to promote resilience in cut flower varieties against diseases and pests in the soil as well as above the ground.

Soil life

An in-depth research report recently published by a team of WUR researchers, ‘Resilient substrate’, discusses the prospects of resilient cultivation. According to this report, the viability of resilient cultivation is not only confirmed by facts derived from scientific literature, but also by the practical experiences of growers. Increasing plant resilience via the substrate is anticipated to become an increasingly important aspect to take into consideration in combating above-ground pests and diseases. Nutrients in the soil have a direct as well as indirect influence on the resilience of a crop against a diversity of pathogens. The quality and amount of organic substances are key factors in determining the composition of microbial soil life and, as such, crop resilience. Soil life is influenced by organic additives in the form of compost. The type of substrate also plays an important part in this. Coco is rich in bacteria, fungus and protozoans, for example, while rockwool contains mainly bacteria. It is highly probable that not all substrates have the same potential for resilience. Case studies have confirmed this. Cucumber plants grown on champost substrate mats (a residual product from the mushroom sector), for example, are less susceptible to Pythium and mildew. Crops grown on this substrate, which has a hight organic substance content and contains numerous active micro-organisms, will therefore be more resilient.

Researchers have noted that the number of studies demonstrating the impact of the substrate on above-ground pests and diseases is still limited. Apart from that, the effects are not yet conclusive enough to enable this method to serve as an alternative for chemical crop protection. ‘But that’s not what we are aiming for,’ says WUR researcher Jantineke Hofland. ‘We are more inclined to consider this a step towards the full-scale adjustment of the entire cultivation system. Not just one change, but multiple changes at the same time. The entire system needs to be thoroughly reviewed. Now that several studies have shown that plant resilience can be controlled, our research is ready for a next step: the integration of plant resilience into a comprehensive system.’

Two routes

Resilience in plants runs through two different routes: the jasmonic acid route and the salicylic acid route. These routes are named for the alarm substances produced in a plant following a predator attack. Jasmonic acid is produced when plants are exposed to phloem-sap sucking insects and fungi that kill plant tissue and live on dying plant materials, such as Botrytes and Phytophthora. Salicylic acid is formed following an attack by micro-organisms on living plant material. Examples are downy mildew, powdery mildew, rust and scabies

Plant strengtheners are agents that are used preventively and work much in the same way as does a vaccine. Just as pathogens, they stimulate plants to create proteins that increase resistance to disease. Plant strengtheners are not crop protection agents. They increase resistance, but cannot offer a guarantee that plants will not be damaged.

The plant strengtheners used in practice generally focus on boosting resistance via the salicylic route. The Greenhouse Horticulture division of WUR in Bleiswijk is currently researching plant strengtheners. A study conducted on cucumbers tested eight different plant strengtheners, which were administered preventively by spraying them onto the leaves or pouring them onto the roots. The crops were then injected with mildew. Despite the fact that all the plants were, in the end, damaged by the mildew, it took longer for them be infected.

Green crop protection agents

As soon as a product is developed that successfully combats pests or diseases in plants, an application must be submitted for its authorisation. All crop protection agents must be approved by the Board for the Authorisation of Plant Protection Products and Biocides (College voor de Toelating van Gewasbeschermingsmiddelen en Biociden, Ctgb) before they can be marketed. The procedure for ‘green’ crop protection agents is, however, difficult and slow. This is because European regulations for the authorisation of biological crop protection agents have not yet been described. To force an accelerated assessment procedure, the Netherlands has launched the Green Deal ‘Green Crop Protection Agents’ project. Green crop protection agents are substances of a natural origin such as plants micro-organisms and minerals. Plant strengtheners with a nutrient component can be granted authorisation as a fertiliser. The Nutrients Management Institute (Nutriënten Management Instituut, NMI) is the agency that determines this. In practice it makes no difference whether a product has been approved as a fertiliser or a crop protection agent.


In early 2015 a grant application was submitted to the Netherlands Enterprise Agency (Rijksdienst voor Ondernemend Nederland, RVO) for a device that would boost plant resilience in greenhouse horticulture. The device is intended to ‘increase the resilience of greenhouse-grown plants against diseases in a biological manner and in which no chemical substances or metals are applied and the use of crop protection agents is reduced’. The device is ‘a system for increasing plant resilience, excluding water storage facilities and irrigation systems’.

Text: Tuinbouwteksten.nl/Suzan Crooijmans. Photos: Fotostudio GJ Vlekke, GAPS Photography.

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