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DIONYSOS: towards an effective biocontrol solution for mildew

Innovation Article published on 24 March 2023 , Updated on 24 March 2023

The DIONYSOS project, which started in the Nanoscience and Innovation for Materials, Biomedicine and Energy laboratory (NIMBE - Univ. Paris-Saclay, CEA, CNRS), is seeking to develop an alternative solution to the use of phytosanitary products, adopting a more favourable environmental profile to combat fungal diseases that affect crops, such as downy mildew in grapes.

Lurking in the ground in winter, it bides its time. With the return of mild temperatures and rainfall in spring and early autumn, it becomes a nightmare for vinegrowers, market gardeners and home gardeners. Its name? Plasmopara viticola and Phytophtora infestans, microscopic fungi responsible for one of the most common fungal (or cryptogamic) diseases in vineyards and vegetable gardens: downy mildew. These fungi manifest their presence by the appearance of spots - translucent, yellow or brown depending on the fungus and the plant affected - on the outside and a white down on the inside of the leaves of the contaminated plant. The inflorescences wither and the fruits turn white or brown and become unfit for consumption. If nothing is done, the fungus destroys the entire crop. 


Phytosanitary products: allies we wish we didn't have

To fight against these parasites, farmers use phytosanitary products, including the well-tested ones composed of copper, which is the only authorised solution in organic agriculture. Copper disrupts the respiratory, enzymatic and membrane activities of the fungus, which then dies. The best known fungicide is Bordeaux mixture - a mixture of water, lime and copper sulfate - invented in the late 19th century.

However, the use of copper is being increasingly debated: above a certain dose, it may be toxic for plants, aquatic fauna, mammals, soil life and users themselves in case of chronic exposure. In 2015, the European Commission included it on the list of candidate active substances for substitution and the maximum permitted dose was gradually reduced. As of November 2018, it is four kilograms per hectare per year. At the same time, the government's Ecophyto II+ plan aims to reduce the use of plant protection products by half by 2025.


Natural substances to fight against cryptogamic diseases

Developing efficient and more environmentally friendly alternatives is therefore more necessary than ever. One of the avenues being considered is biocontrol, i.e. the use of substances or agents capable of fighting pathogens by using natural mechanisms. This is the purpose of project DIONYSOS, which started in 2021 and is led by Pierre Picot of the NIMBE's Interdisciplinary Laboratory on Nanoscale and Supramolecular Organization (LIONS). The project aims to develop a biocontrol solution for the preventive control of grapevine downy mildew that can also be used in organic farming. The initial idea is based on the use of stabilised hydrogen peroxide (H2O2). Known for its antifungal efficiency, and a stimulant of natural defences, hydrogen peroxide is however unusable as is on a cultivated plot because the molecule is unstable: under the effect of the ultraviolet rays of the sunlight, the H2O2 molecule quickly decomposes into water (H2O) and dioxygen (O2) molecules.

During the test phase, the team discovered that hydrogen peroxide was not necessary and that the substance used to stabilise it had intrinsic fungicidal qualities. Project DIONYSOS then became engaged in the development of this substance, which is naturally present in the environment. As the potential spectrum of action is broad, application to other crops and fungi is also envisaged. Accompanied and financially supported by SATT Paris-Saclay, DIONYSOS is currently in the maturation phase. 


A good start

It was by a combination of various different circumstances that Pierre Picot, a specialist in nanotubes and their reactivity, became interested in cryptogamic diseases. A winegrowers' cooperative in Bordeaux was getting in touch with several different start-ups and research organisations in 2018. The cooperative was looking for alternative solutions to the use of copper against downy mildew in grapevines, and got in touch with the CEA (French Alternative Energies and Atomic Energy Commission). "We could hardly have imagined that our technology would have an application in crop protection", recalls Pierre Picot, who is keeping quiet about the details of the technology. DIONYSOS started out with the SATT Paris-Saclay's young doctors programme, which financed the pre-maturation.

Pierre Picot almost immediately started collaborating with research and development teams to carry out efficiency trials of the substance against mildew on vines in the laboratory and under controlled conditions. The tests were positive and were followed by greenhouse trials with the same results.


Getting back to agronomic basics

The first tests carried out with scientific and technical players in the field did not reproduce these initial results. From then on, it was a question of validating the hypotheses on the modes of action and identifying the conditions of use of the substance. "We decided to go back a little further upstream, to understand how the active substance works and where its effectiveness comes from," says Pierre Picot. This is why, in late 2022, exchanges started with a scientific team, with the aim of building up a partnership that would consolidate the expertise of the project. In particular, an opportunity opened up to explore other pathosystems and to observe more closely how this substance acts on fungi and plants.

Pierre Picot intends to use this new knowledge to determine which types of crops or diseases and which crop/disease combinations are most suitable for testing. "Grapevine mildew may not be the easiest disease to test for, as it parasitises the leaves. Other cryptogamic diseases are more serious, such as botrytis and grey rot, caused by the Botrytis cinerea fungus. Moreover, the vine is a perennial crop: vines, once planted, last for several decades. Other crops, which are planted every year, such as wheat, tomatoes and potatoes, are, in contrast, easier to test," says Pierre Picot.


Optimising product formulation

For this year, the team plans to consolidate the functioning of its active substance. Efforts will focus on product formulation, "in other words, identifying and adding complementary components to maintain the product's full potential when used in the field," explains Pierre Picot. To help him do this, he plans to form partnerships with companies specialising in the field. He will be focusing on greenhouse trials to test the different options, as they can be done all year round, before returning to the field by 2024. "Another advantage is that it is possible to test extreme conditions there, which are known to be prone to high pressure diseases, to see if they invalidate the product or not."


Anticipating the final steps

Once the right formulation is found, the regulatory part will have to be addressed. "This involves following a regulatory path and performing a number of tests, including toxicity and ecotoxicity assessment. To succeed at this stage, we are relying on the expertise of a consulting firm in phytosanitary regulatory affairs."

Finally, the time will come to think about the form that the project will take. "If we choose to move toward by creating a start-up, it will require funding for the next phases, including mass production of the substance. Another possibility would be to consider a technology transfer to an established industrial company capable of producing the active substance," says Pierre Picot. At this stage of the project, all the alternatives are still open.