For more than ten years the application of Trichoderma fungi has been common practise in horticulture. They help cultivated crops grow better and become more resistance to diseases. How this symbiosis works is a complex area of research. Nevertheless the developments keep coming. This year a new strain is being launched on the market.
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It has been known for more than 80 years that Trichoderma species can control plant diseases but it was only in the 1990s that they were commercially applied on a large scale in agriculture and horticulture. Several companies supply products that are based on Trichoderma. For example, Koppert Biological Systems, of the Netherlands, has been supplying Trianum for many years.
Biobest introduced the substance Asperello T34 Biocontrol at the end of 2016. The supplier expects this new product to show a number of improved features. It’s a good opportunity therefore to exchange thoughts with Sarah van Beneden, product manager microbials of Biobest and Roger Boer, product manager of Koppert Biological Systems. How exactly does the symbiosis between plant roots and fungi work?
The Trichoderma family is large and includes many species and strains. It includes fungi that cause a lot of damage, for example in tulip and mushroom production, while other family members form allies. Research into this is taking place in universities and laboratories over the whole world.
One such important source is Cornell University in the USA where many different strains of Trichoderma harzianum are researched and isolated. By combining a heat-loving and cold-loving strain they were able to develop the unique strain T-22 which has good disease resistance characteristics. This ‘hybrid’ forms the basis for Trianum.
The University of Barcelona isolated the heat loving Trichoderma asperellum T34 from a compost mix that turned out to suppress disease-causing Fusarium. The company Biocontrol Technologies, a spin-off from the university, undertook its further development. After careful assessment Biobest started a partnership with the company and launched this strain on the Dutch market under the product name Asperello T34 Biocontrol. The product was also launched at the end of 2015 on the American market to control root diseases in ornamentals. The product received a very positive reception. Growers are, for example, very satisfied with its good solubility and strong activity against Fusarium.
Symbiosis between plant and fungus
Production of resilient plants is a concept that is catching on. Fungal preparations fit within this philosophy. They can make plants stronger and some research has shown that they help plants to develop resistance to pathogens. This is particularly useful because it helps to limit the use of crop protection products.
Trichoderma is a soil fungus that can occur in almost all types of soils and substrates. However the symbiosis between plant roots and fungi is complex. Different mechanisms are in motion. The cooperation begins as the fungus colonises the young plant roots. The hyphae, in other words the mycelium of the fungus, grow like a net over the plant’s roots. This soil fungus also lives on the plant’s waste products and faces no competition. Conversely the plant’s roots, due to the presence of Trichoderma better absorb nutrients. In addition the fungus emits hormones that stimulate root growth.
In this way pathogenic fungi such as Fusarium, Pythium, Rhizoctonia and Phytophthora, don’t get the opportunity to reach the root but Trichoderma does even more. The fungus makes enzymes that dissolve the cell walls of pathogenic bacteria and then it feeds on the contents. Some strains can even break down sclerotin (survival structures). There is therefore talk of them being parasites acting on pathogens.
The fungi control these pathogens by direct competition in the root environment but there are also indications that they change the plant physiology. The colonies around the roots influence the genes and proteins in the plant that are responsible for resistance. This strengthens the plant even further.
Must be preventative
Sarah van Beneden is visibly enthusiastic when she describes the launch of Asperello T34 Biocontrol. “Besides the root diseases mentioned we also see opportunities to control leaf diseases such as Botrytis. This new strain has also performed well in research compared with a number of other Trichoderma harzianum strains,” she says. The product also seems to have potential in combatting Fusarium internal rot in sweet peppers. This is currently being researched further. “You also need to realise that it has to be used as a preventative measure so it should be introduced at the beginning of the cultivation or even earlier when at the propagator.”
The company has started demonstration trials at nurseries in the Netherlands and Belgium. A big advantage of this development is that fewer chemical crop protection products are needed. This substance doesn’t leave any chemical residue and, due to the complex collaboration in the root environment, there is no risk of resistance developing.
Extra attention at start
Roger Boer already has a lot of experience with Trichoderma. Trianum is one of the substances within the NatuGro system, a total approach designed for achieving a healthy plant, but it can also be used very well separately. “Many vegetable growers already use this product. Also many phalaenopsis growers are achieving good results with this system so it’s a already a success in ornamental production.” Growers say that they have a stronger crop that is less sensitive to diseases.
Applying the fungus remains a careful process. Extra attention is required at the start of the cultivation because then the colonies need to build up. This occurs much more easily for example, in organic substrates such as cocopeat than in new rockwool. Among other things it also has to do with the method of application. Therefore, in addition to soluble granules, clay-based granules are available that are dosed into the planting hole. This is to encourage their establishment in rockwool as much as possible. “Once the fungi is on the root then it works well,” he explains.
Permit as crop protection product
For years Trianum was registered in the Netherlands as a plant strengthener with an N-number. Because the substance was registered at a later stage on the European Annex 1 as a fungicide, during the re-registration it also had to be registered as a fungicide in the Netherlands. Since November 2015 it has the legal status of a crop protection product. This was a reason for Koppert to slightly change the formulation of the product switching from a powder to a Water-dispersible Granulate (WG). This formulation is very soluble (except for the spores which float in the solution). As well as having a broad application in vegetable and ornamental production it is now also permissible in strawberry production.
Asperello T34 Biocontrol has been used as a crop protection product since it was first launched on the market. The substance is available in powder form and can already be widely used in some countries. In the Netherlands permission has been given for its use in carnation production and fruit vegetables of the Solanum genus (which includes tomato, sweet pepper and aubergine). Cucumber and strawberry, for example, are not included. Biobest is working on a broader application, especially for ornamental production.
Products based on the soil fungus Trichoderma have outgrown their status of plant strengthener and in the meantime are known as crop protection products. The cooperation between roots and fungus provides impetus for resilient cultivation. In addition to the existing products a new promising strain was introduced recently.
Text and image: Pieternel van Velden, Biobest and Koppert.