Development of a chitosan-based biocontrol product against plant diseases (powdery & downy mildews) – ChitoProtect

Six different CHTs, from very low to relatively high degree of polymerization (DP), were obtained and characterized in depth. These CHTs with different DPs have been tested for their fungicidal, eliciting and protective effects on the vine against downy and powdery mildews (in greenhouses and in the vineyard). The formulation of a CHT-based biocontrol product is under development.

The different CHTs have shown a protective effect against downy mildew in greenhouse at a low dose and an eliciting effect on grapevine immune responses. Their effectiveness was then evaluated in the vineyard. The results of these experiments made it possible to demonstrate the effectiveness of a particular CHT against mildew whatever the conditions (meteorological, greenhouse / vineyard), while the others turned out to be very variable and inefficient. However, the level of protection effectiveness of the selected CHT in vineyard is not sufficient and much lower than that observed in a greenhouse. Different hypotheses have been suggested to understand this loss of efficiency in order to solve this problem.

These results led the industrial partner to review the formulation of chitosan-based products to improve their effectiveness and adapt to the actual regulations. These new formulations will be tested in greenhouses in early 2022 and then in the vineyard during 2022.

- 1 International single-partner review
- 1 Single-partner popularization article
- 2 popularization conferences

The project aims to develop a biocontrol product against crop diseases. We chose grapevine as the first target for its economic importance and its dependence on fungicides. Indeed, these are essential to control downy and powdery mildews, two diseases that can have devastating effects. To combat these diseases, winemakers Organic Farming are forced to use significant amounts of copper and sulfur that negatively impact soil microbial biodiversity and groundwater quality. It is therefore necessary to find alternative solutions to reduce the use of these products.
Chitosan (CHT) has anti-microbial properties and elicits plant defense responses. It is therefore a good candidate for the development of a biocontrol product because its source is abundant, cheap, non-toxic and biodegradable. Indeed, CHT is obtained by deacetylation of chitin (polymer of N-acetyl-D-glucosamine), the second biopolymer produced on earth and main constituent of the wall of crustaceans and fungi.
During a previous ANR project (Plant-KBBE PATRIC), UMR Agroecology and Elicityl (polysaccharide producer) found that CHT gave excellent results in the protection of grapevine against downy mildew (> 90 %) in greenhouse trials (TRL4). However, the efficacy in the vineyard was not always reproducible and globally lower. This was later confirmed in field trials conducted in 2018 by Phyteurop, a manufacturer of plant protection products in France. Some achievements of the UMR Agroecology give solid leads to provide a probable explanation of the gap between the greenhouse and the vineyard.
The aim of this project is to confirm our hypothesis and find CHT formulations (CHT plus adjuvants) that can increase its effectiveness in the vineyard. This formulation should reduce the doses of anti-downy and -powdery mildew fungicides in viticulture since CHT is active against these two diseases.
Elicityl will produce a range of very low to high degree of polymerization (DP) CHTs. They will be then assessed against downy mildew in protection experiments in the greenhouse and in small-scale experiments in the vineyard. During these experiments, analyzes will confirm the reasons for the inefficacy gap of CHT in the vineyard and deduce formulation guidelines.
The laboratory of organic polymers chemistry (LCPO) of the University of Bordeaux, using a model system, will seek the appropriate formulations by playing on the modification of various physico-chemical parameters using formulants.
After validation in greenhouse protection trials, the best formulations will be tested against downy and powdery mildews in the vineyard. For this, Elicityl will supply sufficient amount of CHT that Phyteurop will formulate, in collaboration with LCPO, and apply in the outdoor experiments.
If the CHT does not provide complete efficacy, the user should be able to associate it with fungicides used at low dose, especially copper or sulfur. Phyteurop will be in charge of CHT-fungicide compatibility studies and adaptations that would be necessary to obtain a marketable product. The chosen formulation will be tested against other plant diseases. At the end of the project, we expect to reach the TRL7, even 8, with the demonstration of a prototype of CHT with i/ the appropriate formulation in conditions of real applications on vineyard and other crops, and ii/ a scalable process of production with a life cycle projection study.