Resilient Cultivation Systems

A healthy substrate or soil is an important starting point for any healthy horticultural crop. Therefore, sustainable adaptations and cultivation techniques are important to create resilient cultivation systems.

In resilient cultivation systems, more emphasis is put on preventing diseases as opposed to treating outbreaks. To achieve better disease prevention, a multi-disciplinary approach is needed. This requires optimal physical, chemical and biological characteristics in the rhizosphere and rooting environment so that better growth and higher resilience of the plant, as well as the control of pathogens, can be achieved.

Both physical and biological measures are adapted to growing plants on substrates and soils. These adjustments increase stability, drainage and carrying capacity for fungi and bacteria that improve growth and increase resilience of the soil or substrate. Higher biomass and diversity of soil organisms (such as useful microorganisms, nematodes and mites) means there is less niche space available for pests and diseases in the soil or substrate. Applications can range from solutions within existing cultivation systems such as selecting better soil and propagation material, potting mixes, growth substrates (e.g., rock wool, coconut, perlite), organic substrates to new cultivation systems such as those that seek to grow bulbs, vegetables and ornamental plants without soil. 

Viral diseases have an important influence on the cultivation of various greenhouse crops. In both vegetable and ornamental cultivation, viruses can result in loss of yields, even if no symptoms have been detected.

A mechanically transmittable virus can be introduced via infected plant material and seeds. The virus can spread rapidly through mechanical transmission, contact, and crop handling. An example of a mechanically transmissible virus is cucumber green mottle mosaic virus in cucumbers. As well as through mechanical transmission, plant viruses can also be spread by vectors (insects, fungi, nematodes).

Like viruses, viroids can cause symptoms such as malformation, reduced growth, and deviations in colour in their host plants, and the transmission methods are also similar. Many viroids can be transmitted through contact such as crop handling. The business unit Greenhouse Horticulture is carrying out research with the aim of making it possible to take adequate prevention measures at a sufficiently early stage. This research is designed to increase knowledge regarding the behaviour of viruses and viroids and the interaction between the virus, the plant, the plant's environment, the host plant, and the vectors. The research is being carried out for and in collaboration with the professional field.

It is not possible to directly combat viruses, viroids, and bacteria in a plant. Therefore it is necessary to prevent infection from arising in a crop in the first place. It is important to use clean propagation material and to take the appropriate hygiene measures. A hygiene protocol can offer excellent assistance in this regard. The business unit Greenhouse Horticulture has written hygiene protocols for preventing various diseases.

It is recommended that thorough cleaning and disinfection be carried out when crops are rotated. Knowledge about the pathogens present in the crop is essential to ensure the use of the appropriate measures and disinfectants. The business unit Greenhouse Horticulture regularly carries out research into the effectiveness of various disinfectants.

A number of plant pathogens are transmitted via water. It is therefore important that nutrient solution be disinfected before reuse. The business unit Greenhouse Horticulture is working on new disinfectant equipment and methods. Research is being carried out to determine whether the equipment is effective against various pathogens, and in particular which dose is most effective.

Nearly all greenhouse crops are subject to damaging pests. These may be insects such as aphids, mealy bugs, whitefly, or thrips; or mites such as spider mites, thread-footed mites, and russet mites.

Research focuses on new natural enemies, methods to support natural enemies, interactions between natural enemies, biological and chemical agents, side effects of agents on natural enemies, odours for pests and natural enemies, and the development of total concepts for integrated crop protection.

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Greenhouse horticulture is often confronted with yield and production losses caused by fungal  and/ or bacterial plant pathogens. Some of these microorganisms, such as the fungi e.g. Fusarium, Rhizoctonia or oomycetes Pythium and Phytophthora and bacteria e.g. Agrobacterium, Pectobacterium  and Ralstonia, cause damage to the root system, which results in damping-off or wilting of plants. Infection by other plant pathogens manifest itself aboveground e.g. powdery mildew, oomycete Phytophthora infestans or bacteria such as Acidovorax, Xanthomonas and Clavibacter.

Retail and the public are increasingly demanding crops and ornamental plants which are free of  residues from chemical plant protection products. Additionally, the effectiveness of available chemical control agents is under pressure due to the development of resistance in various plant pathogens.

Bacterial diseases are difficult to control because there are currently not many plant protection products available on the market which can be used specifically against bacterial plant diseases. Prevention of infection, application of biological control and priming of plant resistance against these pathogens are therefore the preferred solutions for fungal and bacterial diseases.

To achieve this new cultivation management strategies have to be introduced in greenhouses, in which the resilience of the system have a central position. Research at Wageningen UR Business Unit Greenhouse Horticulture and Flower Bulbs therefore focuses on alternative, sustainable options and applications for plant diseases control which include:  a) prevention (hygiene), b) development of new biological control strategies and agents (BCA), c) (induced) plant resistance, d) climate control (e.g. ventilation) or e) physical solutions, such as application of UV light and different LED spectra.

Plant resilience is the natural potential of plants to defend themselves against pests en diseases. While plant resistance is constitutive, i.e. is its based genetically and is always present, plant resilience is induced, i.e. it is activated the moment the plant is attacked.

Resilience is based on morphological traits such as trichomes, leaf wax layers... etc. Next to these, plants are rich in chemical compounds, especially secondary metabolites, which are used for plant defence against pests and diseases. Especially wild species are rich in chemical compounds. Comparing these traits between susceptible and less susceptible plants within a crop we are able to identify morphological as well as chemical traits related to plant resilience against pests and diseases.

We, subsequently, apply this knowledge in three areas: development of resilience markers, development of green plant protection products and targeted steering of resilience traits by light, microorganisms and elicitors to make susceptible plants less susceptible. In this way we contribute to a sustainable and integrated manner of pest and disease control in protected crops.

Pollination plays a crucial role in the production of vegetables and soft fruit crops. Good pollination ensures higher production and higher fruit quality. Bumblebees are successfully used in tomato cultivation.

Pollination is not yet optimized in soft fruit cultivation. Also bees are used there in addition to bumblebees. Both perform erratically on dark days and at low temperatures in the winter period. With changing cultivation conditions, such as fossil free cultivation, the use of LED lighting, energy screens and colder greenhouse climate, the currently used pollinators are struggling. That is why it is very important to introduce pollinators that are better adapted to changing conditions in greenhouses. By using multiple pollinating insect species that can complement each other, pollination can be optimized.